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The Oxford Handbook of Archaeological Ceramic Analysis (Oxford Handbooks) [1 ed.]
 0199681538, 9780199681532

Table of contents :
CONTENTS
1. Introduction to the Oxford Handbook of Archaeological
Ceramic Analysis
2. History of Scientific Research
3· Designing Rigorous Research: Integrating Science and Archaeology
4· Evaluating Data: Uncertainty in Ceramic Analysis
5
. Statistical Modeling for Ceramic Analysis
6. Recycling Data: Working with Published and Unpublished
Ceramic Compositional Data
7· Ceramic Raw Materials
8. Ceramic Manufacture: The chaine operatoire Approach
9. The Organization of Pottery Production:
Toward a Relational Approach
10. Provenance Studies: Productions and Compositional Groups
11. Mineralogical and Chemical Alteration
12. Formal Analysis and Typological Classification in the Study
of Ancient Pottery
13. Fabric Description of Archaeological Ceramics
14. Analytical Drawing
15. Petrography: Optical Microscopy
16. Ceramic Micropalaeontology
17
. Electron Microprobe Analysis (EMPA)
18. Isotope Analysis
19. X-Ray Powder Diffraction (XRPD)
20. X-Ray Fluorescence-Energy Dispersive (ED-XRF) and Wavelength
Dispersive (WD-XRF) Spectrometry
21. Handheld Portable Energy-Dispersive X- Ray Fluorescence
Spectrometry (pXRF)
22. Particle Induced X-ray Emission (PIXE) and Its Applications
for Ceramic Analysis
23. Inductively Coupled Plasma-Mass Spectrometry (ICP-MS)
and Laser Ablation Inductively Coupled Plasma-Mass
Spectrometry (LA-ICP-MS)
24. Instrumental Neutron Activation Analysis (INAA) in the Study of Archaeological Ceramics
25. Synchrotron Radiation
26. Ethnography
27. Experimental Firing and Re-firing
28. Fourier Transform Infrared Spectroscopy (FT-IR) in Archaeological
Ceramic Analysis
29. Raman Spectroscopy and the Study of Ceramic Manufacture:
Possibilities, Results, and Challenges
30. X-Radiography of Archaeological Ceramics
31. Organic Inclusions
32. Formal Typology oflberian Ceramic Vessels by Morphometric
Analysis
33· Mechanical and Thermal Properties
34· Assessing Vessel Function by Organic Residue Analysis
35· Typology and Classification
36. Direct Dating Methods
Index

Citation preview

THE OXFORD HANDBOOK OF

ARCHAEOLOGICAL CERAMIC ANALYSIS Edited by

ALICE M. W. HUNT

OXFORD UNIVERSITY l?RBSS

OXFORD UNIVERSITY PRESS

Great Clarendon Street, Oxford, ox2 6Dl', United Kingdom Oxford University Press is a department of the University of Oxford. It furthers the University's objective of exceUence in research, scholarship, and education by publishing worldwide. Oxford is a registered trade mark of Oxford Universiry Press in the UK and in certain other countries © Oxford University Press 2017

The moral rights of the authors have been asserted

Impression: 1 All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, without the prior permission in writing of Oxford University Press, or as expressly permitted by law, by licence or under terms agreed with the appropriate reprographics rights organization. Enquiries concerning reproduction outside the scope of the above should be sent to the Rights Department, Oxford University Press, at the address above You must not circulate this work in any other form and you must impose this same condition on any acquirer Published in the United States of America by Oxford University Press 198 Madison Avenue, New York, NY 10016, United States of America British Library Cataloguing in Publication Data Data available Library of Congress Control Number; 2016944779 ISBN 978-0-19-968153-2 Printed and bound by CPI Group (UK) Ltd, Croydon, CRO 4YY Links to third parry websites are provided by Oxford in good faith and for information only. Oxford disclaims any responsibility for the materials contained in any third party website referenced in this work

AcKNOWLEDGMENTS 'CJ

"" 0:) ~

~

---,_

{

THIS Handbook would not have been possible without the hard work and expertise of its contributors. I also owe a debt of gratitude to Hilary O'Shea, Charlotte Loveridge, Annie Rose, Michael De Ia Cruz, and the rest of the OUP team for helping to bring this volume to

fruition with minimum stress and maximum enjoyment. Special thanks to Jeff Speakman

and the Center for Applied Isotope Studies, University of Georgia, for a publication subven· tion that allowed us to include the colored plates. Many of the individual contributors wish to thank various colleagues and asso·dates for reading and commenting upon their contributions, and sharing unpublished materials; space limitations preclude acknowledging each individual by name, and so consider this a heartfelt, if general, round of thanks and appreciation to all involved behind the scenes.

CONTENTS

List ofFigures List of Tables List ofPlates List ofAbbreviations List of Contributors

xi xix

xxi xxiii XXV

PART I INTRODUCTION 1.

2.

Introduction to the Oxford Handbook of Archaeological Ceramic Analysis ALICE M. W HUNT

3

History of Scientific Research

7

MICHAELS. TITE

PART II RESEARCH DESIGN AND DATA ANALYSIS 3· Designing Rigorous Research: Integrating Science and Archaeology

19

]AUME BUXEDA I GARRIGOS AND MARISOL MADRID I FERNANDEZ

4· Evaluating Data: Uncertainty in Ceramic Analysis RoBERTo I-IAZENFRATZ- MARKS

s.

Statistical Modeling for Ceramic Analysis

ss

GULSEBNEM BISHOP

6. Recycling Data: Working with Published and Unpublished Ceramic Compositional Data MATTHEW

T. BoULANGER

PART III FOUNDATIONAL CONCEPTS 7· Ceramic Raw Materials GIUSEPPE MoNTANA

73

viti

CO:S:TENTS

8. Ceramic Manufacture: The chaine operatoire Approach

101

VALENTINEROUX

9. The Organization of Pottery Production: Toward a Relational Approach

114

KIM Du!STERMAAT 10.

Provenance Studies: Productions and Compositional Groups

148

YONA WAKSMAN 11.

Mineralogical and Chemical Alteration

162

GERWULF SCHNEIDER 12.

Formal Analysis and Typological Classification in the Study of Ancient Pottery DANIEL ALBERO SANTACREU, MANUEL CALVO TRIAS, AND JAIME GARciA ROSSELLO

13. Fabric Description of Archaeological Ceramics IAN K. WHITBREAD 14.

Analytical Drawing

200

217

PRABODH SH!RVALKAR

PART IV EVALUATING CERAMIC PROVENANCE 15. Petrography: Optical Microscopy

233

DENNIS BRAEKMANS AND PATRICK DEGRYSE 16.

Ceramic Micropalaeontology IAN

266

P. WILKINSON, PATRICK S. QUINN, MARK WILLIAMS,

}EREMY TAYLOR, AND IA:-1

K. WHITBREAD

q. Electron Microprobe Analysis (EMPA)

288

CORJNA lO:-iESCU A:-ID VOLKER HOECK

18. Isotope Analysis BETTINA A. WIEGAND

19. X-Ray Powder Diffraction (XRPD) ROBERT B. HEIMANN

305

CONTENTS

20.

X-Ray Fluorescence-Energy Dispersive (ED-XRF) and Wavelength Dispersive (WD-XRF) Spectrometry MARK

21.

iX

342

E. HALL

Handheld Portable Energy-Dispersive X- Ray Fluorescence Spectrometry (pXRF) ELISABETH HOLMQVIST

22. Particle Induced X-ray Emission (PIXE) and Its Applications

for Ceramic Analysis

382

MARCIA A. RIZZUTTO AND MANFREDO H. TABACNIKS

23. Inductively Coupled Plasma-Mass Spectrometry (ICP-MS)

and Laser Ablation Inductively Coupled Plasma-Mass Spectrometry (LA-ICP-MS)

399

MARK GOLITKO AND LAU!tE DUSSUBIEUX

24. Instrumental Neutron Activation Analysis (INAA) in the Study

of Archaeological Ceramics

424

LEAH D. MINC AND )OHANNES H. STERBA

25. Synchrotron Radiation ALAN

447

F. GREENE

PART V INVESTIGATING CERAMIC MANUFACTURE 26. Ethnography KENT D. FowLER

27. Experimental Firing and Re-firing MALGORZATA DASZKIEW!CZ AND LARA MARITAN

28. Fourier Transform Infrared Spectroscopy (FT-IR) in Archaeological

Ceramic Analysis

509

SHLOMO SHOVAL

29. Raman Spectroscopy and the Study of Ceramic Manufacture:

Possibilities, Results, and Challenges

531

)OLIEN VAN PEVENAGE AND PETER VANDENABEELE

30. X-Radiography of Archaeological Ceramics INA BERG AND )ANET AMBERS

544

X

CONTENTS

31. Organic Inclusions MARTA MARIOTTI LIPPI AND PASQUINO PALLECCHI

PART VI ASSESSING VESSEL FUNCTION 32. Formal Typology oflberian Ceramic Vessels by Morphometric

Analysis

585

ANA LUISA MARTINEZ-CARILLO AND ]VAN ANTONIO BARCELO

33· Mechanical and Thermal Properties NOEMI S. MULLER

34· Assessing Vessel Function by Organic Residue Analysis HANS BARNARD AND ]ELMER W. EERKENS

PART VII DATING CERAMIC ASSEMBLAGES 35· Typology and Classification EuGENIO BoRTOLINI

36. Direct Dating Methods SOPHIE BLAIN AND CHRISTOPHER HALL

Index

603

LIST OF FIGURES

Diagram flow of the states of ceramics from manufacture to the archaeological record.

20

Bar chart of Hispanic Terra Sigillata from Tritium Magallum recovered at Baetulo, Tarraco, and Ilerda, classified according the range of estimated equivalent firing temperatures.

28

3-3

Bar chart of Hispanic Terra Sigi!latafrom (a) context LL85b context and (b) context TV83, and (c) a bivariate diagram of integrity (H,) vs fragmentation (FI).

37

3-4

Scatter plots of evenness for Hispanic Terra Sigillata from (a) context LL85b and (b) context TV83, and (c) evenness of the rarefaction experiment. A bar chart of the richness after the rarefaction experiment is presented in (d).

40

3.5

Binomial probabilities for n = 15 and p = 0.1.

41

5.1

Bar charts describing the (a) distribution and (b) relative frequency of vessel types in an assemblage.

61

5.2

Pie charts describing the relative distribution of vessel types in funerary assemblages from Athens and Sparta.

61

3.1

3.2

5·3

Histogram of amphora capacity measurements from a hypothetical shipwreck.

63

5-4

Common shapes of data distribution.

63

5·5

Bimodal distribution of mineral inclusions in a ceramic fabric.

64

5.6

Stem-and-leaf plot (worked example) of vessel weights.

65

5-7

Back-to-back stem-and-leaf plot comparing cooking pot volumes from two sites. 65

6.1

Timeline of a selection of former and current nuclear archaeometry laboratories, and estimates of the total numbers of archaeological specimens analyzed. Data compiled primarily from val. 49(2) of Archaeometry.

77

7.1

"Integrated approach'' for characterizing and sourcing ceramic raw materials.

89

7.2

Examples of primary and secondary clays: (a) kaolinite deposits in the crater of Mount Gibele at the volcanic island of Pantelleria (Italy); (b) outcrop of Upper Miocene marine clays in southern Sicily.

91

Brick and roof tile makers in western Sicily traditionally using NaCl as deflocculating agent.

97

7·3 8.1

Classification chart of roughing out and preforming techniques.

105

8.2

Diagnostic features taken into account for reconstructing an Early Bronze Age chaine operatoire from the site of Tell Arqa (Lebanon).

106

xii

I,..IST OF FIGURES

Example of technostylistic trees obtained after dassifying ceramic assemblages according to the concept of chaine optratoire.

108

9.1

Entanglements of the materials used to make a carinated bowL

127

9.2

Chaine operatoire for a Middle Assyrian carinated bowL

130

9.3

Entanglement of the life-history of carinated bowls, from production until deposit in the archaeological record

132

10.1

Local reference samples, late Byzantine workshops, 'Thessaloniki, Greece,

151

10.2

Beirut medieval wares: main compositional groups as determined by hierarchical clustering analysis, and corresponding wares.

155

Beirut medieval wares: binaryplotiron-silicon (top) and histogram of Mahalanobis distances (bottom).

157

Correlation of barium and phosphorus in Roman and Germanic pottery from two sites in Germany.

170

Leaching of calc.ium in two samples of calcareous pottery.

173

Sunomary of the different le~els to approach pottery form and typological analyses discussed in the text.

182

Isomorphic relation between the decorative motifs recorded on Late Iron Age pottery and bronze discs in Ma!lorca (Spain).

187

Format translation related to hybridization phenomena between Punic wheel-thrown vessels and hand-made indigenous pottery in the Late Iron Age in MaUorca (Spain).

194

14.1

Art-historical period pottery illustrations.

218

14.2

Steps of traditional pottery illustration (partr).

220

14.3

Steps of traditional pottery illustration (part 2).

221

14.4

Various aspects of pottery illustration.

222

8.3

10.3 11.1

n.2 12.1

12.2

12.3

14.5

Steps of new pottery illustration (part 1).

225

14.6

Steps of new pottery illustration (part 2).

226

14.7

Steps of new pottery illustration (part 3).

22.8

15.1

A standard polarizing light microscope with rotating sample stage. The camera and imaging software are essential tools for data output

235

15-2

High relief and cleavage of a pyroxene mineraL

238

15.3

Photomicrograph of a Late Roman, quartz-tempered cooking vessel from Carthage (Tunisia).

258

16.1

The earliest known image of a microfossiL

267

16.2

Examples of the main microfossil groups that may be found in ceramics.

268

16.3

Examples of microfossils in ceramic matrices that can be applied in provenance studies.

273

16.4

Degradation of microfossils during firing.

274

LIST OF FIGURES

17.1

xiii

(a) Origin ofBSE, SE, and characteristic X-rays emitted by the interaction between the fOcused electron beam and sample. (b) BSE image of a ceramic

sample from Ibida (Roman- Byzantine period). (c) SE image of the same.

290

17.2

BSE images of various compounds of a ceramic body.

294

17-3

X-ray maps ofCucuteni ceramics (Copper Age).

295

86

18.1

Distribution of 87 Sr/ Sr ratios in ceramic samples from archaeological sites of different regions.

315

18.2

Distribution of 87Sr/ 86 Sr and eNd values in ceramic samples from Turkey, Greece, Bulgaria, and China.

316

18.3

Pb isotope data oflead-based glazes from New Mexico, USA, China, and various European locations.

19.1

319

(a) Permitted electron transitions to generate X-rays of the K series. (b) Interpretation ofX-ray diffraction as the result of simple reflection. (c) Seemann- Bohlin focusing geometry for Debye-Scherrer and Straumanis methods. (d) Bragg-Brentano focusing configuration for scintillation counter

19.2

19-3

(powder diffractometer) method.

329

X-ray diffraction charts of an archaeological calcareous illitic clay from Otter bach, Palatinate, Germany.

335

X~ray diffraction charts of archaeological ceramics buried under arid and

humid conditions.

337

X-ray diffraction chart (CuKa) of stoneware from Sawankhalok, Thailand (14th-15th centuries AD).

338

SEM- ESE micrographs of heterogeneous ceramic matrices showing sand~ temper.

364

21.2

Correlation of pXRF net peak area values to quantitative NAA data.

366

21.3

PCA biplots of the variance-covariance matrix of the pottery samples

19-4 21.1

measured by pXRF and INAA.

370

PCA biplots with density ellipses for clusters indicated by low-dimensional pXRF data and high-dimensional ICP-OES and NAA datasets.

371

22.1

Parameters and coordinates of the experimental PIXE geometry.

384

22.2

Typical thin film yield curve of the Sao Paulo PIXEsystem with a Si(Li) X-ray detector and a 55 ~m thick beryllium X-ray filter.

386

21.4

22.J

General view of LAMPI with the ion sources on the right and the 5SDH accelerator tank in the center.

22-4

22.5

387

The external beam setup at the LAMPI with the different detectors assembled. The lower part of the figure shows in detail the assembly of the coupled detectors.

388

Chimu ceramics at the Museum of Archaeology and Ethnology of the University of Siio Paulo (MAE- USP) collection.

390

XiV

LIST OF FIGURFS

22.6

(a) PIXE spectra of two ceramic vessels (3635 and 3601) of the Chimu culture; (b) comparison of the concentrations values obtained by FIXE at different points, analyzed in the two ceramic pieces.

391

(a) Graph of the correlation between At Si, K, Ti and Fe elements giving rise to 4large groups; (b) graph of the correlation between AI, Si, K and Ti elements, suggesting the origin of three major groups.

392

22.8

Sun ray plots of the elements Al, Si, K, and Ti showing the correlations in the groups and the respectively vessels in each group.

393

23.1

An ICP- MS laboratory, with both laser ablation and liquid sampling equipment visible.

401

23.2

Schematic diagram of plasma~ion source and common mass spectrometer types.

402

23.3

Examples of calibration lines for Fe, Rb, and Pr using NIST610, 612, and 679 as SRMs.

407

23.4

Surface geology of the Sepik coast of Papua New Guinea, with ceramic and clay sampling locations indicated.

416

23.5

Backscatter SEM-EDS image of a sherd cross-section from Worn (Papua New Guinea) analyzed by LA-ICP- MS.

417

23.6

Discriminant function plot summarizing the results ofLA-ICP-MS analysis of all ceramic and clay pastes analyzed from the Sepik coast of Papua New Guinea. 418

24.1

Schematic overview of neutron activation and subsequent decay.

426

24.2

TI1e core of a research reactor provides a high-intensity source of neutrons to activate samples.

428

24.3

The build-up and decay of radioactivity in an isotope according to its half-life and decay constant A.

431

24-4

Complex gamma-ray spectrum resulting from the irradiation of an earthenware vessel from Oaxaca, Mexico.

432

24.5

Ceramic composition groups defined for the central Valley of Oaxaca, Mexico, for the Late~Terminal Formative period.

440

24.6

(a) The industrial potteries and bottle kilns ofNorth Staffordshire, England, c. 1900 (from an historic postcard labeled "Fresh Air from the Potteries"). (b) Each pottery manufacturer developed one or more paste recipes, with a distinctive trace-element composition.

443

Schematic of the Australian Synchrotron's small- and wide-angle X-ray scattering beamline by David Cookson and Jonathan de Booy.

448

One potential schematic of an experimental setup for SR pottery analysis, here micro-X-ray fluorescence, showing the positioning of the SR beam, sample, and solid-state detector.

450

Reflected light micrograph, SEM micrograph, and~- XR diffractogram of the yellow-glazed area of a sherd from Mission San Luis (Florida, USA) collected during the analysis of American majolica by SR.

452

22.7

25.1 25.2

25.3

LIST OF FIGURES

XV

·····~~··~··--~

25.4

'Ihe three microregions of interest on a "black gloss" or "red ftguren potsherd, as investigated by Walton and colleagues with a diverse set ofSR methods.

25.5

An example of a high-temperature XRD pattern collected during "live" time-

resolved temperature experimentation.

458

26.1

The domains of ethnographic and archaeological inquiry into pottery manufacturing practices and the two principle areas of contribution ethnographic observations and explanations may lead to the understanding of past ceramic production systems.

470

The distances travelled to ceramic resources (day and temper} by potters from 117 communities.

475

26.3

Range of firing temperatures and soaking times for firings in West Africa.

479

26.4

Models of the technical and social influences on ceramic manufacturing based upon African case studies,

481

27.1

Examples of open firing and of a traditional updraft kiln.

491

27.2

Sketch of a typical firing diagram used when programming an experimental firing in a laboratory with a furnace.

492

Bar charts showing the changes in the mineral composition as a function of the firing temperature.

494

Determination of the original firing temperature using the K-H method (Teq900-10oooC).

soo

27.5

Two samples made oft he same marly clay re-fired at 1200,C.

501

28.1

Curve-fitted FT-IR spectra of the ceramic material of representative Iron Age pottery from Levan tine sites.

513

FT-IR spectra and second-derivatives of the spectra of the ceramic material of representative Bronze Age pottery from Canaanite sites,

514

28.3

FT-IR spectra and second-derivatives of reference standards of firing silicates.

516

28.4

FT-IR spectra and second-derivatives of reference standards of carbonate and silica minerals.

517

FT-1R spectra and second· derivatives of reference standards of minerals typicaily found in initial or unfired raw materials.

518

28.6

FT-IR spectra and second~derivatives of reformed minerals in pottery.

521

28.7

FT-!Rspectra of paints and pigments.

524

26.2

27.3 27.4

28.2

28.5

456

29.1

Energy-level diagram explaining the different types of scattering.

532

29.2

Raman spectrum of calcite (CaCOJ

533

29.3

Formation and decomposition of calcite (CaC03).

537

29.4

Plot of the polymerization index as a function of the main Si-0 stretching component wavenumber,

539

30.1

Characteristic X-ray features of the main pottery forming techniques.

548

30.2

Inclusion alignment in a clay coil.

548

xvi

L!ST Of FIGURES

30,3

Xeroradiographs of two stirn.1p jars showing both the blue color and edge enhancement inherent to the technique.

551

Examples of types of radiographic equipment available. (a) Portable medical Sirio uolwo CR system; (b) Faxitron single-cabinet X·ray unit

552

30.4

30.5 30.6 30.7

Radiographs of a Middle Minoan amphora (BM registration number G&R1906,1112.90) from the British Museum.

554

Radiographs of a bell-shaped handled cup (Middle Minoan I) from Knossos (BM registration no G&R195o,no6.16).

557

Radiographs of a Mycenaean krater (BM registration number G&Rt898,!20J.H2) taken from the side (a) and above (b).

s6o

31.1

Fan-shaped phytolith from modern rice (1 mm).

567

31.2

Thin section of rice-tempered ceramic from Sumhuram, Sultanate of Oman.

568

31.3

Shell-tempered ceramic from Sumhuram, Sultanate of Oman.

570

31.4

Fracture surface of a potsherd from Surnhuram, Sultanate of Oman.

571

31.5

Renaissance ceramic tefnpered with wool (polarized 1 mm).

572

31.6

Rice-tempered ceramic from Sumhuram, Sultanate of Oman: epidermis of the rice husk with evident silicized tubercles (SEM).

574

31.7

Karnataka rice winnowing in South India.

577

32.1

Map of the study area.

592

32.2

Profiles of the eleven classes of vessels determined by preliminary descriptive analysis.

593

Erosion, dilation, opening and dosing characteristic curves of a profile of the database, using an isotropic (circular) structural element, normalized by the area of the profile.

595

32.4

Segmentation of a profile into rim, hody, and base.

595

32.5

A given ceramic and the ten most similar shapes, with the measure of the distance.

598

Typical load-displacement curves for di!Terent types of fracture observed in archaeological ceramics: (a) unstable; (b) semi-stable; (c) stable.

614

Schematic overview of different organic residues in archaeological ceramics, and techniques frequently employed to investigate these (34.1).

626

Schematic flow diagram showing the position of organic residue analysis in anthropological and archaeological studies.

628

The general principles of"microscopic (a)" and "molecular (b)" methods for organic residue analysis.

629

Schematic of the chromatography arrays used on mass spectrometers to separate the sample into its components and convert them into a form fit to enter the ion source.

631

Schematic representation of the antibody-antigen reaction.

633

32.3

33.1 34.1

34.2 34-3

34·4

34·5

LIST OF FIGURES

35.1

XVii

Two graphical representations of Petrie's chronological ordination of archaeological types.

654

35.2

An example of frequency seriation.

656

35.3

'!be original diagram by which Krieger explained in detail the procedure for a correct application of his typological method.

658

35-4

Some quantifiable formal dimensions in pottery.

662

35.5

An example of categorical classification of pottery surface decoration from a Central European Neolithic context.

664

Schematic of the archaeological clock and radiation doses used in luminescence dating.

673

TL glow curve on quartz grains with the various characteristic peaks and a total OSL decay curve, made of its different components. The surface under the peaks or signal is function of the number of traps occupied before the stimulation.

674

TL glow curve on quartz grains with the various characteristic peaks and a total OSL decay curve, made of its different components.

674

36-4

Luminescence reader.

677

36.5

Microbalance data obtained on a Werra earthenware specimen excavated at Enkhuizen (1979).

685

36.1 36.2

36.3

LIST OF TABLES

1.1

Analytical methods included in this Handbook, and which of the four primary research questions they contribute toward answering.

4-1

Uncertainty values calculated for a ceramic chemical group from the Central Amazon.

54

j.1

Frequency distribution table describing a small assemblage of Greek pottery.

6o

j.2

Random number table (excerpt).

67

7-1

Chemical composition of the "average terrigenous marine clay" (after Clarke, 1924) and of some representative Italian and Greek clays.

94

5

Chemical alteration of Roman sigillata from Arezzo, Lyon, and La Graufesenque found at Velsen and Nijmegen in the Netherlands.

169

Mineral identification table derived from the integrated information of various geological handbooks. They represent a concise list of characteristics in thin section.

242

17.1

Mean atomic number for common minerals in ceramics.

292

17.2

Selected electron microprobe analyses (in mass%) and calculated structural formulae for illite (illitic matrix), albite (Ab ), plagioclase (excluding albite), alkali-feldspar, K-feldspar, and muscovite.

297

19.1

Chemical composition of calcareous illitic clay from Otterbach, jockgrim, Palatinate, Germany.

334

19.2

List of measured diffraction angles 0 28 of mullite and quartz, d values calculated according to the Bragg equation.

334

23.1

Comparison of measurements on NIST679 (brick clay) by LA-ICP-MS, MD-ICP-MS, and other bulk techniques.

411

23.2

Comparison of measurements on New Ohio Red Clay (NORC) by LA-ICP-MS, MD-ICP-MS, and other bulk techniques.

413

24.1

The sensitivity of INAA in the analysis of ceramics varies by element, from percent level to parts-per-trillion.

425

27.1

Basic atmospheric conditions during firing in antiquity.

489

29.1

Based on the lp ratio, the processing temperature of glass structures can be estimated.

538

30.1

Exposure times and kV for clay objects using a Faxitron cabinet X-ray machine with a 0.5 mm focal spot, 6o em focus-to-film distance, 3 rnA, and Agfa Structrex D4 Film.

ss6

11.1

15.1

XX

LIST Of TABLES-

32.1

Vesseis in the study by context

591

3.2.2

Classification rates obtained by the method with one, three, and five suggestions and one, three, and five neighbors.

597

~ormalized confusion matrix resulting from the application of the method to the database, using two subprofiles: rim and the combination ofbody with base.

597

Normalized confusion matrix resulting !rom the application of the method to the database, using the rim and body subprofiles.

598

33.1

Examples of material requirements placed on different ceramic products.

6o6

34.1

Schematic overview of the characteristics of selected techniques to investigate organic residues in archaeological ceramics.

627

32..3

32-4

LIST OF PLATES

Experimental firings of different day raw materials (Sicily, Italy). 2

Photomicrographs of thin sections of medium-high fired sherds with calcite (incompletely crossed polarized light, width of field 0.7 mm).

3

Late Bronze Age pottery sample 133 in (a) hand specimen and (band c) thin-section photomicrograph in plane polarized light.

4

Photomicrographs of thin sections with a basalt-andesitic volcanic rock fragment under plane polarized light (a) and crossed polarized light (b).

5

Photomicrographs illustrating microstructural changes with increasing ceramic firing temperature. (For explanations see text in Chapter27.)

6

MGR~analysis of six ceramic sherds, carrJed out to determine original firlng temperatures. Sample 1 represents a briqueue cut from a model ceramic sample; samples 2.-6 represents archeological samples. (For explanations see text in Chapter 27; photographs were taken with a macro lens by M. Baranowski.)

7

Structural MGR-analysisoftwo ceramic samples {Photographs taken under a reflected light microscope). A~ pottery fragment originally fired at Teq < 70d'C; B""' pottery waste) fragment over-fired at uoo-1150°C. (For explanations see tex:t in Chapter 27; photographs were taken with a macro lens by M. Baranowski.)

8

MGR-analysis {8oo"C, 9oo"C, 120o'C) of five samples belonging to two MGR-groups-a fact which only becomes apparent after re-firing at uoo'C. (For explanations see text in Chapter 27; photographs were taken with a macro lens by M. Baranowski.)

9

Examples of matrix types (samples re-fired at uoo'C) of non-calcareous sherds (iron-rich red-firing or iron-poor whitish-firing) and of calcareous pottery (yellowish-greenish firing). (For explanations see text in Chapter q; photographs were taken with a macro lens by M. Baranowski.)

LIST OF ABBREVIATIONS

AAS BSE EDS EMPA ICP INAA LA MGR MS OES OM OSL PIXE ppb PPL ppm RHX SE SEM SR TL WD XPL XRD XRF 8

Atomic Absorption Spectroscopy Backscattered Electrons Energy Dispersive Spectrometry Electron Microprobe Analysis Inductively Coupled Plasma Instrumental Neutron Activation Analysis Laser Ablation Matrix Groups by Re-firing Mass Spectrometry Optical Emission Spectrometry Optical Microscopy Optically Stimulated Luminescence Particle Induced X- Ray Emission parts per billion (10-9) Plane Polarized Light parts per million (10-6) Rehydroxylation Secondary Electron Scanning Electron Microscopy Synchrotron Radiation Thermoluminescence Wavelength Dispersive Crossed Polarized Light X- Ray Diffraction X-Ray Fluorescence stable isotope ratio expressed relative to a standard measure of isotopic composition relative to a mantle reservoir

LisT oF CoNTRIBUTORS

Daniel Albero Santacreu is Assistant Lecturer in Prehistory and Archaeology at the University of the Balearic Islands (Spain). He has developed archaeometrical and technological analysis of hand-made prehistoric pottery vessels from the Balearic Islands, Sardinia, Andalusia, and Ghana. His current research concerns the role of technology in the inter~ pretation of ceramics and the application of concepts such as agency, habitus, technological choices, and identity in the study of ancient societies. His most recent publication is Materiality, Techniques and Society in the Pottery Production (De Gruyter Open). Janet Ambers is a scientist in the Department of Conservation and Scientific Research at the British Museum. She currently works mostly on the imaging of museum-related materials, with a specific interest in radiography, and on the analysis of museum objects using various techniques but with an emphasis on Raman spectroscopy. Her particular interests include pigment analysis with particular emphasis on the palettes of Ancient Egypt and the Middle East, the identification of gemstones, jades, and geological materials by Raman spectroscopy, and the radiography of ceramics and other similar materials. She also has a professional interest in all forms of archaeological dating and analyses of human remains. Juan Antonio BarcelO is an Associate Professor of Prehistory at the Universitat Auto noma de Barcelona (Spain). He carries out specialized research in archaeological techniques and theory, developing computer applications in archaeology, notably in the domains of spatial analysis, statistics, artificial intelligence, modeling, and computer-aided visualization. He is the director of the Quantitative Archaeology Laboratory ( ). He has directed and participated in archaeological projects in Spain, Portugal, Italy, Syria, Nicaragua, Ecuador, and Argentina. Hans Barnard is Adjunct Assistant Professor at the Department of Near Eastern Languages and Cultures and Assistant Researcher at the Cotsen Institute of Archaeology, both at UCLA. He has worked on sites in Armenia, Chile, Egypt, Iceland, Panama, Peru, Sudan, Syria, Tunisia, and Yemen as archaeological surveyor, photographer, and ceramic analyst. Currently he is involved in research projects investigating the interaction between the Tiwanaku and Wari polities in the Vitor Valley (near Arequipa, Peru), and between the Phoenician and Roman empires in Zita (near Zarzis, Tunisia). Ina Berg is Senior Lecturer in Archaeology at the University of Manchester, UK Her main areas of research are ceramic studies, the archaeology of Bronze Age Greece, the Cyclades in particular, and island studies. While interested in all aspects of ceramics, her current research focus is predominantly on the application ofX-radiography to pottery to explore forming techniques as a means to understanding past potting traditions, workshop organization, learning networks, and knowledge transfer.

XXVi

LIST OF CONTRIBUTORS

Gulsebnem Bishop is a full-time CS!T faculty member and a program leader for the Doctoral Program in Information Technology at Stratford University, VA. She holds a doctorate degree in Computer Science and Information Systems from Pace University, NY, where she was able to combine her two passions: computing and archaeology. Her interests are data analysis and interpretation, database development, and administration, as well as future of data analysis. She has worked at a number of not-for-profit organizations such as the American Museum of Natural History, the Human Rights Campaign, and the National Cathedral in New York City and Washington, D.C., specializing in database systems development, administration, and management. Sophie Blain was a FNRS researcher at the University of Liege, Belgium. Her researches focused on medieval building archaeology and more particularly on dating methods applied to building materials, such as dendrochronology on wood beams and luminescence (TL! OSL) dating methods on ceramic building materials and mortar. She worked on a number of medieval churches in south-eastern England, northern France, Belgium, and northern Italy. Eugenio Bartolini is currently a member of CaSEs Research Group (Complexity and Socio-Ecological Dynamics) as Research Fellow at the Department of Archaeology and Anthropology, IMF-CSIC (Spanish National Research Council, Barcelona, Spain) and Visiting Research Fellow at the Department of Humanities, Universitat Pompeu Fabra (Barcelona, Spain). His main research interests and topics include the adoption and transmission of cultural variants, the coevolution of culture and genes (Dual Inheritance Theory), the development and application of quantitative methods in archaeology, archaeological theory, and the prehistory of the Arabian Peninsula. Matthew T. Boulanger is a Lecturer in the Department of Anthropology at Southern Methodist University and a Research Associate at the Archaeometry Laboratory at the University of Missouri Research Reactor. He has published in Antiquity, American Antiquity, Journal ofArchaeological Science, and Archaeometry. His research interests include compositional analysis of archaeological materials, digital data management and preservation, evolutionary archaeology, experimental archaeology, and Paleoindian lithic technology. Dennis Braekmans is Assistant Professor at the Faculty of Archaeology, Leiden University, and Department of Materials Science, Delft University ofTechnology. He runs the laboratory for ceramic studies, where mineralogical and geochemical laboratory analysis is linked with production studies, mechanical research, and ethnoarchaeological observation. The current research focus is geared to ancient ceramics from North Africa, the Eastern Mediterranean, and the Near East. Teaching activities include materials science, archaeometry, and experimental archaeology. Jaume Buxeda i Garrig6s is Lecturer in Archaeology and Director of the Cultura Material i Arqueometria UB (ARQUB) research unit at the Universitat de Barcelona. His recent work is mainly related to research projects in historical archaeology (ARCHSYMB and TECNOLONIAL) designed to deepen our knowledge in aspects related to the interaction, influence, and cultural change during the colonization process, through the archaeological and archaeometric study of technical/technological impact, and issues of technical/technological traditions and change. Other research interests are classical archaeology, the effect of weathering, and the role and treatment of compositional data in archaeological research.

LIST OF CONTRIBUTORS

xxvii

Manuel Calvo Trias is Lecturer in Prehistory and Archaeology at the University of the Balearic Islands (Spain). He is head of the ArqueoUIB Research Group and PI of a research project focused on the Balearic Islands Prehistory, as well as the project Archaeology in the Upper White Volta basin (north-east of Ghana). His research is centered on the analysis of material culture and technology. He is co-author of 'l\cci6n tecnica, interacci6n social y pr and the Gutai Mountains, Eastern Carpathians (Romania): A Complex Magma Genesis" (2014, Mineralogy and Petrology). Elisabeth Holmqvist works as an Academy of Finland Postdoctoral Fellow at the Department of Philosophy, History, Culture and Art Studies, University of Helsinki. Her research interests deal with ancient technologies and exchange systems, and geochemical provenancing of archaeological materials by ED-XRF, SEM-EDS, PIXE, ICP-MS, and INAA. Holmqvist has worked on archaeological ceramics from the Near East, Europe, and Latin America. In her PhD (UCL Institute of Archaeology, 2010), Holmqvist concentrated on Byzantine-Islamic pottery manufacture and trade in the Near East, while her current research focuses on Scandinavian and Baltic potting traditions and inter-regional ceramic exchange from the Neolithic into medieval times. Alice M. W. Hunt is a Assistant Research Scientist at the Center for Applied Isotope Studies, University of Georgia. Her PhD in archaeological materials analysis developed cathodoluminescence spectrometry of quartz as a method for differentiating raw material sources in fine-grained ceramics. Currently, her research focuses on developing analytical calibrations and protocols for bulk chemical characterization of cultural materials (ceramics, anthropogenic sediments, copper alloys, and obsidian) by portable XRF. Recent publications include

, XXX

LIST OF CONTRlBUTORS

"Portable XRF analysis of archaeological sediments and ceramics" (Journal ofArchaeological Science, 2015) and a monograph Palace Ware across the Neo-Assyrian Imperial Landscape: Social Value and Semiotic Meaning (E.). Brill). Carina Ionescu is Professor at Geology Department at Babe.-Bolyai University of ClujNapoca, Romania, and Associate Professor at Kazan (Volga Region) Federal University,

Tartarstan, Russia. Her research interests focus on archaeoceramics and ophiolite petrology and geochemistry. Her recent publications include "Burnishing versus Smoothing in Ceramic Surface Finishing: A SEM Study" (2015, Archaeometry); "Insights into the Raw Materials and Technology Used to Produce Copper Age Ceramics in the Southern Carpathians (Romania)" (2016, Archaeological and Anthropological Sciences). Marisol Madrid i Fernandez is a Researcher at the Cultura Material i Arqueometria UB (ARQUB) research unit at the Universitat de Barcelona. Her work focuses on the application of analytical techniques to the study of archaeological materials, especially ceramics. She has participated in more than forty research projects highlighting the current TECNOLONIAL project on historical archaeology and archaeometry. She is author/co-author of more than fifty publications and has been co-organizer of two scientific international conferences. She has had longlasting activity in the field of classical archaeology in several excavations, especially in the research project at the Roman town of Cosa, Italy, leading the study of Roman pottery and its archaeometric characterization. Marta Mariotti Lippi focuses on archaeobotany, palynology, and reproductive biology. She has carried out archaeobotanical investigations at sites in Italy (Pompeii and Vesuvian area, Paestum, Tuscany) and abroad (Russia, Czech Republic, jordan, Lybia). Since 2001 she has cooperated in research projects in the "Land of Frankincense" UNESCO site ofSumhuram/ Khor Rori, and at Salut, Sultanate of Oman. Lara Maritan was, between 1999 and 2005, a visiting scholar at the University of Glasgow (UK) and the University of Cardiff (UK), funded by scholarships from the Gini Foundation, the Italian Society of Mineralogy and Petrology (SIMP), and the Accademia Nazionale dei Lincei/Royal Society. From 2003 she was a postdoctoral research assistant at the University ofPadova before joining the faculty in the Department of Geosciences as an assistant professor in georesources and minero-petrographic applications for the environment and cultural heritage (GEO/o9) in 2007.

Ana LuisaMartinez-Carillo is a researcher at the Research Institute oflberian Archaeology, University ofJaen. She is a specialist in the application of new technologies in archaeological analysis, in particular in ceramic studies, and has also participated in several regional, national, and European research projects focused on three-dimensional modeling, integration of datasets, and on-line dissemination of the cultural heritage. Leah D. Mine is an Associate Professor in the College of Liberal Arts at Oregon State University, and INAA Research Coordinator at the Oregon State University Archaeometry Laboratory. Giuseppe Montana has been Associate Professor at the University of Palermo since 2005. His re!earch activity covers topics in the field of mineralogy and petrography applied to cultural heritage (archaeological ceramics, natural and artificial stones). Significant recent

LIST OF CONTRIBUTORS

XXXi

publications include "Characterization of Clayey Raw Materials for Ceramic Manufacture in Ancient SicilY:' Applied Clay Science, 53 (2011): 476-488; 'An Original Experimental Approach to Study the Alteration and/or Contamination of Archaeological Ceramics Originated by Seawater Burial;' Periodico di Mineralogia, 83 (2014): 89-120; "Different Methods for Soluble Salt Removal Tested on Late-Roman Cooking Ware from a Submarine Excavation at the Island ofPantelleria (Sicily, Italy);' Journal of Cultural Heritage, 15(2014): 403-413.

Noemi S. Miiller is Scientific Research Officer at the Fitch Laboratory of the British School at Athens. She has held postdoctoral positions at NCSR Demokritos, where her research focused on mechanical and thermal properties of archaeological ceramics, as well as in Nicosia, Cyprus, and Barcelona, Spain. She is interested in applying analytical methods to investigate inorganic archaeological artifacts and materials, focusing on the study of provenance and technology and with a special interest in archaeological ceramics. Her research also examines the affordance of utilitarian ceramics, focusing on cooking vessels, using material testing to explore the influence of technological choices in manufacture on material properties. Pasquino Pallecchi is Adjunct Professor at the University of Florence and Head of the Laboratory of Archaeological Heritage in Tuscany, Italy. Patrick S. Quinn is an archaeological materials scientist working on ceramics and related artifacts from a range of different periods and regions including prehistoric and later Britain, pre-contact California, and the prehistoric Aegean. His early research focused on the occurrence of microfossils within ancient ceramic pastes and their research potential in terms of pottery provenance and technology on Minoan Crete. He subsequently worked on the palaeontology and ecology of microfossil-producing organisms before rejoining the University of Sbeffield, then the Institute of Archaeology, University College London, as a permanent member of the research staff, undertaking research, teaching, and Consultancy on archaeological ceramic analysis.

Marcia A. Rizzutto has been a Professor at the Physics Institute of the University of Sao Paulo since 2001. She is also the coordinator of the Research Center of Applied Physics to the Study of Artistic and Historical Cultural Heritage of the University of Sao Paulo. Since 2003 she has been devoted to the use of applied physics to the study of cultural heritage objects connected with different areas such as archaeology, history, art history, paleontology, chemistry, conservation, and restoration. As coordinator of the research group she has a wider investigation program using non~destructive physics analyses in different museum collections of the University of Sao Paulo, in partnership with teachers/researchers from the museum's institutions. Valentine Roux is Director of Research at the CNRS, Nanterre, France. Her work combines methodological research on technical skills and an anthropological approach to ceramic assemblages, archaeological research on the history of technology and people in the Southern Levant, and ethnoarchaeological research in India on specialization and diffusion of potting techniques. Selected recent publications include a handbook, in collaboration with M.-A. Courty, entitled Des ceramiques et des hommes: Decoder les assemblages archeologiques (2016); an edited issue of Journal of Archaeological Method and Theory (2013,

XXXii

LIST OF CONTRIBUTORS

20/2), with Courty, entitled "Discontinuities and Continuities: Theories, Methods and Proxies for an Historical and Sociological Approach to Evolution of Past Societies"; and an edited issue of Paleorient (2013, 39!1) with Braun, entitled "The Transition from Late Chalcolithic to Early Bronze in the Southern Levant: Continuity and/or Discontinuity?':

GerwulfSchneider has since 1975 been involved in archaeornetric research and the teaching of archaeometry, from 1980 to 2003 at the Institute of Inorganic and Analytical Chemistry (Arbeitsgruppe Archaeometrie), and currently as a research associate at the Cluster of Excellence Topoi at the Free University of Berlin. His main focus is on chemical and mineralogical analysis of archaeological ceramics and the interpretation of data in archaeological terms. His research interests encompass Roman pottery in Germany, Hellenistic to Late Antique pottery in the Mediterranean region, and various projects on Neolithic to medieval pottery in Europe, Mesopotamia, and Sudan (he has created a joint databank of qo,ooo WD-XRF pottery analyses with M. Daszkiewicz).

Prabodh Shirvalkar is currently working as an associate professor in the department of Archaeology, Deccan College Post Graduate and Research Institute, Pune, India. His research interest focuses on the Harappan Civilization, particularly in regards to ceramic technology, provenance, and trade networks. At present, he is working on creating a model for the rural economy of Harappans. In addition, he has expertise in field archaeology and the application of processualism. Shlomo Shoval is Professor of Earth Sciences at the Open University of Israel. He is also Guest Professor at the Institute of Earth Sciences of the Hebrew University of jerusalem and Visiting Scientist at the Institut Lumiere Matiere ofUniversite Claude Bernard Lyon-1, France. He is an expert in the analysis of archaeological ceramics, ceramic raw materials, and clay minerals by infrared spectroscopy (FT-IR) and other scientific methods (LA-lCP-MS, XRF). Among his current research projects are studies of the technologies used in manufacture and in paint decoration of Levantine Bronze and Iron Age ceramics. Johannes H. Sterba has been working in neutron activation analysis for more than a decade, starting with geological samples and soon moving to archaeologically relevant materials such as pumice, obsidian, and later ceramics. He is interested in the statistical analysis of the gathered data and in the intercomparability of different analytical methods. Recent publications include "NAA and XRF analyses and magnetic susceptibility measurement of Mesopotamian cuneiform tablets" (Scienze dell'Antiquita, 2011); "Raising the temper-fl· spot analysis of temper inclusions in experimental ceramics" (Journal ofRadioanalytical and Nuclear Chemistry, 2011); and "Volcanic glass under fire-a comparison of three complementary analytical methods" (X-RaySpectrometry, 2013).

Manfredo H. Tabacniks is a full professor at the Physics Institute of the University of Sao Paulo. In 1994 he served as a postdoctoral researcher for two years at the IBM Almaden Research Center, San jose, California, on the application of ion beam methods (PIXE and RBS) for tbe analysis of thin films. Since 1996 he has been head of the Ion Beam Analysis facility of the Institute of Physics at USP. His main research interests deal with ion beam methods for advanced material analysis and for the modification of materials. jeremy Taylor took up a Leverhulme Research Fellowship at the School of Archaeology, University of Leicester, in 1999, before being appointed a Lecturer in Archaeology in 2001.

LIST OF CONTRIBUTORS

xxxiii

He is currently a director of the major field project at Burrough Hill, Leicestershire. His research interests center on social change in Iron Age Britain and the Western Roman provinces through study of their rural landscapes, and on interrelationships between theory and method in survey-based archaeological research, such as geophysics, geochemistry, and aerial survey. MichaelS. Tite was, before retiring, the Edward Hall Professor of Archaeological Science and Director of the Research Laboratory for Archaeology and the History of Art at the University of Oxford, where he is now Professor Emeritus and Fellow of Linacre College. Formerly he served as Keeper of the Research Laboratory at the British Museum, and has been a Fellow of the Society of Antiquaries since 1977- The underlining theme of his research during the past thirty years has been the study of the technology involved in the production of (1) faience and related early vitreous materials from Egypt and the Near East, and (2) glazed pottery from the Bronze Age through the Roman period in the Near East, Europe, the Islamic world, and China. Jolien Van Pevenage is currently a PhD candidate in the Raman Spectroscopy Research Group. She is interested in the application of Raman spectroscopy to the study of ceramic artifacts for their identification and classification in order to define, for example, the origin or the composition of the materials and production techniques. Her research combines the use of Raman spectroscopy with X-ray fluorescence spectroscopy and advanced data processing methods. Her work is presented at international conferences and is published in leading scientific journals. Peter Vandenabeele was appointed as research professor in the Department of Archaeology at Ghent University, where he applies his analytical skills to the study of archaeological and artistic objects. His research focuses mainly on the application of Raman spectroscopy in art analysis. He has authored more than a hundred research papers on Raman spectroscopy and its application in archaeometry, along with several book chapters and conference presentations. Recently, he has published, together with Howell Edwards, Selected Topics in AnalyticalArchaeometry (RSC Publishing, 2012). Yona Waksman is a Senior Researcher at the French National Research Center (CNRS) in Lyon. She specializes in archaeometric approaches to medieval ceramics in the Eastern Mediterranean and the Black Sea, through provenance and technological studies. Her publications include major sites such as Constantinople/Istanbul, and lay new foundations for the investigation of economic, cultural, and social phenomena in the Byzantine world and the medieval Middle East. Ian K. Whitbread read Archaeology and Geology at the University of Bristol before undertaking a research fellowship at the Fitch Laboratory, British School at Athens, Greece. Formerly he was a Principal Research Scientist at the Center for Materials Research in Archaeology and Ethnology, Massachusetts Institute of Technology, USA, and then Director of the Fitch Laboratory. He joined the School of Archaeology and Ancient History, University of Leicester, in 2001. His current research interests lie in the analysis of ancient ceramic materials with respect to issues of trade/exchange and the socially embedded nature of technology. Bettina A. Wiegand has long-term experience in isotope geochemistry at the University of Goettingen, Germany, and Stanford University, USA. Application of isotope methods

xxxiv

:UST OF CONTRIBUTORS

to various research fields include ceramic provenance studies, human migration studies, and hydrogeological and environmental research. Related publications include "Strontium Isotopic Evidence for Prehistoric Transport of Gray-Ware Ceramic Materials in the Eastern Grand Canyon Region, USA;' Geoarchaeology 26 (2011): 189-218; and "Reconstructing Middle Horizon Mobility Patterns on the Coast of Peru through Strontium Isotope Analysis;' (Journal ofArchaeological Science 26 (2009): 157-165). Ian P. Wilkinson was a principal scientist with the British Geological Survey before retiring, and is now an Honorary Research Associate at both the BGS and the University of Leicester. He is a specialist in Mesozoic and Cenozoic-Recent ostracods and foraminifera, working on mapping, hydrocarbons, geohazards, and palaeoenvironmental and archaeological projects. Although focusing principally on the UK, he also has experience in, for example, Ecuador, USA, Antarctica, Hong Kong, the Persian Gulf, Papua New Guinea, Armenia, and Russia. Mark Williams is Professor of Geology at the University of Leicester, where he researches climate and environmental change reflected in the fossil record. He has worked at the Universities of Frankfurt, Lyon, and Portsmouth, and for the British Geological Survey and the British Antarctic Survey. He has a strong interest in the geology of the Arabian Peninsula and has consulted for Saudi Aramco.

!ill

!r

PART

I

·································································································

INTRODUCTION .................................................................................................

CHAPTER 1

INTRODUCTION TO THE OXFORD HANDBOOK OF ARCHAEOLOGICAL CERAMIC ANALYSIS ALICE M. W. HUNT

is one of the most complex and ubiquitous archaeomaterials, occurring around the world at prehistoric through industrial sites and used to fashion everything from residences and technological installations to utilitarian wares and decorative/votive figurines. It is not simply the range of cultures and functions that ceramics serve but the diversity in materials and manufacture technology that makes archaeological ceramic analysis as challenging as it is essentiaL In this volume we address the sociocultural, geochemical, and mineralogical complexity inherent in archaeological ceramic analysis and provide insight into the uncertainties by providing concrete guidelines for designing rigorous research strategies and developing sophisticated and answerable anthropological research questions. Part II is dedicated to issues related to designing ceramic research and evaluating the varied types of data this research generates. jaume Buxeda i Garrig6s and Marisol Madrid i Fernandez (Chapter 3) outline the two essential types of research for archaeological ceramic analysis, advancing the discipline and answering archaeological questions, and provide tools and guidelines for approaching each. In Chapter 4, Roberto Hazenfratz Marks discusses how to identify and report the uncertainty inherent in ceramic analysis with particular emphasis on interpreting geochemical data. In Chapter s, Gulsebnem Bishop discusses the types of data generated in archaeological ceramic analysis, the strengths and weaknesses of each, and the appropriate model/statistical tools for describing and analyzing this data. Many of the most interesting and important anthropological questions involve comparing ceramic datasets, often from different excavations or laboratories and separated by decades. In Chapter 6, Matthew Boulanger offers insight into working with these datasets and how to preserve data for future analysis. Part Ill, Foundational Concepts, provides a detailed discussion of, and recommends best practices for, the definition, description, and illustration of archaeological ceramics. In Chapter 7, Giuseppe Montana defines ceramic raw materials and describes their CERAMIC

4

AUCF.M.\V.HUNT

compositional and physical properties, such as plasticity and swelling, and how these properties are manipulated by human behavior. Chapters 8 and 9 both investigate the social and economic organization of ceramic manufacture: Valentine Raux (Chapter 8) evaluates ceramic manufacture using the chaine operatoire approach, while Kim Duistermaat (Chapter 9) offers a relational approach to ceramic manufacture based on network analysis models. Both approaches discuss how to locate the technical behaviors associated with ceramic manufacture within the socioeconomic and cultural constraints in operation. Yona Waksman tackles ceramic provenance in Chapter 10, providing unambiguous definitions and practical guidelines for forming production and/or compositional groups within a ceramic assemblage. In Chapter 11, Gerwulf Schneider details the geochemical and mineralogical uncertainty created by alteration of archaeological ceramics during their use-life and as a result of post-depositional processes, and discusses methods for identifying these changes during analysis. 1be last three chapters in Part III provide practical skills, definitions, and guidelines for the description and illustration of archaeological ceramic artifacts. Daniel Albero Santacreu, Manuel Calvo Trias, and jaime Garcia Rossell6 (Chapter 12) discuss formal classification and analysis of ceramics, offering universal definitions and insight for the interpretation of formal data, while remaining sensitive to the practical and cultural factors influencing vessel shape and size. Ian Whit bread (Chapter 13) similarly establishes guidelines for best practice in describing ceramic fabrics both in hand specimen (macroscopic analysis) and thin section (microscopic analysis), along with methodologies for preparation of samples and reporting/ publishing fabric descriptions. In Chapter 14, Prabodh Shirvalkar provides a primer for constructing accurate and informative analytical illustration of archaeological ceramics. The remainder of the volume is dedicated to the analytical techniques used in archaeological ceramic analysis and is organized broadly by anthropological questions. There are many ways in which these techniques could be categorized (see Chapter 35 on Typology and Classification), especially since each technique or method provides data relevant to more than one line of inquiry and most anthropological questions require more than one type of data (see Table 1.1). However, for reasons both practical and functional we present each analytical technique according to the fundamental anthropological question to which it most often or significantly contributes. These four fundamental research areas are Provenance (Part IV), Manufacture (Part V), Function (Part VI), and Date (Part VII). Each technique- or method-specific chapter includes its scientific and/or theoretical background, discussion of practical issues, such as cost and sample preparation, and case studies emphasizing the utility of the technique in addressing anthropological questions of provenance. When possible, guidelines for best practice of collecting and interpreting the data are provided. Ceramic provenance is typically evaluated using compositional data. In Part IV, bulk chemical, phase, and mineralogical analysis, as well as micropalaeontological analysis, are discussed. Chemical methods include chapters on isotope analysis by Bettina Wiegand (Chapter 18), X-ray fluorescence by Robert Heimann (Chapter 19) and Mark Hall (Chapter 20), handheld portable energy-dispersive X-ray fluorescence spectrometry by Elisabeth Holmqvist (Chapter 21), particle induced X-ray emission spectrometry by Marcia RiZ2utto and Manfredo Tabacniks (Chapter 22), inductively coupled plasma-mass spectrometry by Mark Golitko and Laure Dussubieux (Chapter 23), neutron activation analysis by Leah Mine and johannes Sterba (Chapter 24), and synchrotron radiation by Alan Greene

5

INTRODUCTION

Table 1.1 Analytical methods included in this Handbook, and which of the four primary research questions they contribute toward answering Provenance

Manufacture Technology

Function

EPMA

X

X

X

Ethnography

X

X

X

Experimental Firing/Re-firing

X

FT-IR

X

ICP-MS/LA-ICP-MS

X

INAA

X

!so tope Analysis

X

X

Mechanical Properties

X X

Micropalaeontology

X

Morphometric Analysis

X

X

X

Organic Inclusions

X

X

X

X

X X

Organic Residue

Date

-------

Petrography

X

X

PIXE

X

X

pXRF

X X

Raman Spectroscopy

RHX Dating

X

Tl Dating

X

Typology

X

X-Ray Radiography

X

X

XRD

X

X

XRF-EDS/WDS

X

X

X

X

(Chapter 25). Mineralogical and phase analysis methods include chapters on petrography by Dennis Braekmans and Patrick Degryse (Chapter 15), electron probe microanalysis by Carina Ionescu and Volker Hoeck (Chapter 17), and X-ray diffraction by Robert Heimann (Chapter 19). Micropalaeontology (Chapter 16) is written by Ian Wilkinson, Patrick Quinn, Mark Williams, jeremy Taylor, and Ian Whitbread. In Part V, methods and techniques on ceramic manufacture include chapters on ethnography (Chapter 26) by Kent Fowler, experimental firing and re-firing (Chapter 27) by

6

ALICE M. W. HUNT

Malgorzata Daszkiewicz and Lara Maritan, X-ray radiography (Chapter 30) by Ian Berg and janet Ambers, and organic inclusions by Marta Mariotti Lippi and Pasquino Pallecchi (Chapter 31). Chapters on Fourier transform infrared spectroscopy (Chapter 28) by Shlomo Shoval, and Raman spectroscopy (Chapter 29) by )alien Van Pevenage and Peter Vandenabeele, are also included in Part V because they can provide valuable information about mineralogical alteration in ceramic fabrics and surface treatments. Vessel function can be assessed from the formal attributes and performance characteristics of a vessel or artifact, as well as any organic residues preserved on their surfaces. Therefore, Part VI includes discussion of morphometries (Chapter 32) by Ana MartinezCarillo and juan Antonio Barcelo, mechanical properties (Chapter 33) by Noemi Suzanne Muller, and residue analysis (Chapter 34) by Hans Barnard and )elmer W Eerkens. Part VII investigates the direct and indirect or relative dating of ceramics, and includes chapters on typology and classification (Chapter 35) by Eugenio Bertolini, and direct dating techniques of luminescence and rehydroxylation dating in a chapter by Sophie Blain and Christopher Hall (Chapter 36).

CHAPTER 2

HISTORY OF SCIENTIFIC RESEARCH MICHAELS. TITE

AIMS THE primary aim of scientific research into archaeological ceramics is the investigation of the overalllife~cycle of surviving ceramics starting with their production and continuing through their distribution to their use, reuse, and ultimate discard (Tite, 1999, 2008). The first step involves reconstruction of the production, distribution, and use of ceramics. The second step then involves interpretation of this reconstructed life-cycle in order to obtain a better understanding of the behavior of the people who produced, distributed, and used these ceramics. Reconstruction of the production technology of archaeological ceramics involves the investigation of raw materials, tools, energy sources, and techniques used in the procurement and preparation of the clay, forming of the pot, and its surface treatment, decoration, and firing. Such information can be inferred from the observed macrostructure, microstructure, and chemical and mineral/phase compositions of the ceramics. The reconstruction of distribution (i.e. provenance studies) involves trying to establish, on the basis of thin-section petrography and/or chemical composition, whether ceramics were locally produced or imported, and if the latter, to identify the production center and/or source of the raw materiaL The determination of the use to which ceramic vessels were put involves their examination for surface wear and the presence o.f soot deposits, the analysis of surviving organic residues, and the investigation of their physical properties. In the interpretation of the reconstructed production technology of archaeological ceramics, the primary questions that need to be considered are why ceramics were first adopted for use in different parts of the world, and why, when adopted, a particular production technology was chosen. The interpretation of the reconstructed distribution of ceramics is concerned both with trying to determine patterns of trade or exchange away from any identified production center or source of raw material, and the underlying sociocultural reasons for that pattern.

8

MICHAELS. TITE

OVERVIEW OF HISTORY Leaving aside isolated examples of scientific research into ancient ceramics in the nineteenth and first half of the twentieth centuries, a coherent and continuing program of such research really only began in the 1950s. This occurred as part of the emergence of the overall field of archaeological science which, at that time, included the application of geophysical prospection and scientific dating methods to archaeology as well as the scientific study of the full range of archaeological artifacts (Aitken, 1961). It is generally considered that the starting point for present-day scientific research into archaeological ceramics was the groundbreaking volume by Anna Shepard (1956) entitled Ceramics for the Archaeologist. However, two further crucial, and more or less contemporary, developments were the founding in 1955 of the Research Laboratory for Archaeology and the History of Art at the University of Oxford with E. T. (Teddy) Hall as its first Director, and the beginning of instrumental neutron activation analysis (INAA) of ceramics at the Brookhaven National Laboratory (Long Island, New York) under the direction of(Ed) Sayre (Sayre and Dodson, 1957). The Oxford Research Laboratory, which was founded through the combined efforts of a physicist (Lord Cherwell) and an archaeologist (Professor Christopher Hawkes), went on to become a focus for archaeological science, or archaeometry as it was termed in Oxford, both in the United Kingdom (UK) and internationally, 1hus, the publication Archaeometry, which was started in 1958 as the Bulletin of the Research Laboratory for Archaeology and the History of Art, went on to become an international research journal. Similarly, the training course in 1962, and subsequent annual reunions, organized for archaeologists who had purchased proton gradiometers from the Laboratory, went on to become the International Symposium for Archaeometry, initially held annually, but now held biennially, of which the 40th Symposium was held in Los Angeles in 2014. The continuing development of archaeological science, including scientific research into archaeological ceramics, has depended, first, on the provision of funding for research specifically into aspects of this new discipline, and second, on the inclusion of the teaching of archaeological science in university archaeology degree courses. Although such crucial developments bave now occurred, to a varying extent, throughout the world, the UK has always been at the forefront in this respect. Thus, in 1976, the UK Science and Engineering Research Council established a Science-based Archaeology Committee which was provided with funds to support the development of new scientific techniques and approaches to the study of archaeological material, and such research funding has continued in the UK in one form or another up to the present day. Furthermore, during the 1970s, the University of Bradford introduced one-year MA and three-year BTech courses in archaeological science, and now, few students in the UK can emerge from an undergraduate archaeology course without some knowledge of archaeological science, and many can be classed as true archaeological scientists. As discussed in detail in the next section in this chapter, progress in the reconstruction of the life-cycle of archaeological ceramics has depended mainly on the development and availability of new methods of scientific investigation.ln contrast, progress in the interpretation of the life-cycle of archaeological ceramics has been, in large part, the result ofimproved communication and collaboration between the scientists involved in the reconstruction,

HISTORY OF SCIENTIFIC RESEARCH

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and archaeologists from across the discipline, including field archaeologists, theoretical archaeologists, and ethnoarchaeologists.

RECONSTRUCTION OF THE CERAMIC LIFE-CYCLE In her book Ceramics for the Archaeologist, Shepard (1956) provided a description of the raw materials and processes involved in the production of archaeological ceramics, together with a summary of their physical properties. She then went on to describe how the raw materials used might be identified and production processes revealed. The analytical methods available to Shepard were essentially limited to binocular microscopy, petrographic microscopy, and optical emission spectroscopy (OES). As evident from the contents of the current volume, the range of analytical tools available for the study of archaeological ceramics has increased dramatically during the subsequent fifty or so years (Pollard et al., 2007). Of these, scanning electron microscopy (SEM), a range of methods for the determination of chemical composition, and organic residue analysis, using gas chromatography in combination with mass spectrometry (GC-MS), have had wide-ranging applications. In addition, there are a number of new analytical techniques which, by their nature, have had a more limited application for the study of archaeological ceramics.

Scanning Electron Microscopy Examination of polished sections using SEM has provided extremely valuable information on the production technology of archaeological ceramics, supplementary to that provided by optical microscopy (Tite, 1992). This is, in part, because the SEM provides a higher magnification (typically used in the range xwo to xsoo). However, more importantly, either an analytical SEM with attached X-ray spectrometer or an electron microprobe (EMP) can determine quantitatively the chemical composition of the different phases or components present. For example, the extent of vitrification in earthenware bodies can provide an estimate of the firing temperature, and the composition of the high temperature phases observed in porcelain bodies can provide information about the raw materials used in their production. Additionally, in cross-section, it has been possible to determine, for the first time, the composition of a slip or glaze entirely separately from that of the underlying ceramic body. It has ·thus been possible to distinguish between alkalilime, high lead, and lead-alkali glazes (Tile et al., 1998), and identify the different opacifiers and colorants used. During the 1980s, the application of SEM analysis to archaeological ceramics facilitated research into a wide range of ceramics (earthenwares, stonewares, porcelains, and quartzpaste bodies), which resulted in significant advances in our understanding of their production technologies. Pioneers in this research include Kingery and Vandiver (1986) at Massachusetts Institute of Technology, and Tite and colleagues (Tile, 1992) at the British Museum.

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MICHAELS. TIT£

Determination of Chemical Composition Initially, OES, INAA and X-ray fluorescence spectrometry (XRF) were the primary analytical techniques used in the study of archaeological ceramics. Of these techniques, INAA and XRF have continued in use until the present day, but OES was replaced first by atomic absorption spectroscopy (AAS) in the 198os, then by inductively coupled plasma spectrometry with OES (ICP-OES) in the 1990s, and finally, by ICP with mass spectrometry (ICPMS) at the beginning of the current millennium. In comparison with INAA, ICP-MS has similar detection limits but can analyze for a much wider range of elements. In addition, ICP-MS does not require access to nuclear reactors, which are becoming less widely available. However, INAA, in using a powder sample rather than the acid dissolution required with ICP- MS, retains significant advari.tages in terms of easy interlaboratory comparisons and rapid sample preparation. The primary role of these techniques has been the determination of the chemical compositions of ceramics for provenance studies with the aim of establishing where the ceramics were produced. Initially, chemical analysis was regarded as an alternative to thin-section petrography, especially in the case of fine-grained ceramics or when only the more ubiquitous non-plastic inclusions, such as quartz and shell, were present. However, Shepard, in the Preface written for the fifth printing (1965) of Ceramics for the Archaeologist, was highly critical of the use of chemical analysis in isolation. As a result, a more fully integrated approach to provenance studies has been progressively developed (Heidke and Miksa, 2000). A crucial first step in any such study should now be to group the entire assemblage from a site into pottery types on the basis of observed style (e.g. shape, surface decoration) and temper type, as determined by examination with a low-power binocular microscope. Second, the local geology should be assessed, and fieldwork undertaken to identify and collect samples oflocally available clays and sands. Only then should both thin-section petrography and chemical analysis be undertaken on representative sherds of each pottery type.

Organic Residue Analysis From the 1990s onwards, GC-MS has been extensively used for the analysis of the organic residues surviving in archaeological ceramics (Heron and Evershed, 1993). Lipids, present as fats, oils, waxes, and resins, are the most useful surviving organic compounds for residue analysis, and can be used to establish whether animal, vegetable, or fish products were the original contents of pottery vessels. As well as contributing to the investigation of past human diets, organic residue analysis is particularly valuable in helping to understand the reasons for adoption of the first ceramics (Craig et al., 2013). In addition, the distribution of the bulk quantities oflipids over the interior of vessels has provided information on how different cooking pots were actually used (Charters eta!., 1993).

Analytical Techniques with More Limited Application In the context of microscopy, the very high magnification possible with transmission electron microscopy (TEM) has played a crucial role in understanding the complex processes

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involved in the production oflustre decoration on glazed Islamic ceramics (Perez-Arantegui et al., 2001). In the context of the determination of chemical composition, handheld XRF systems are being increasingly used in the analysis of ceramic glazes. Although these instruments only provide semi-quantitative data and do not analyze for the lighter elements, the particular importance of this technique is that it is entirely non-destructive, and the instrument can be brought to and used on archaeological sites and in museums where the ceramics are located. In the context of phase analysis, the well-established method of X-ray diffraction (XRD), which identifies both mineral phases surviving from the raw materials and those formed during firing the body, has continued to be used to provide information about the raw materials and firing temperatures employed in ceramic production (Heimann and Maggetti, 2014: 73). More recently, Raman spectroscopy, which is again non -destructive, has been increasingly employed to identify the pigments used to decorate ceramics, as well as the colorants and opacifiers used in ceramic glazes (Smith and Clark, 2004).

INTERPRETATION OF THE CERAMIC LIFE-CYCLE In order to achieve satisfactory interpretation of the reconstructed life-cycle of archaeological ceramics, it is essential that collaboration between the scientist involved in the reconstruction and the archaeologist who provided the ceramics is successful. Unfortunately, there were some tensions between scientists and archaeologists when such research first began in the 1950s (Preface to fifth printing of Shepard, 1965), and by the early 1990s there was considerable criticism of archaeological science by archaeologists and curators, particularly in the context of artifact studies (Dunnell, 1993). However, by the end of the 1990s these tensions had significantly reduced, in large part as a result of a more sustained dialogue between archaeological scientists and archaeologists. Thus, a high proportion of university archaeology departments, and particularly those in the UK, now include archaeological scientists on their staff, and a significant number of PhD students are jointly supervised by an archaeological scientist and archaeologist. In addi· tion, there are an increasing number of research excavations, such as Batao Grande in Peru (Shimada and Craig, 2013), and there seems to be less interest in studying organization. 1bis is perhaps because in practice the chaine opera~ loire approach as applied in archaeological pottery studies is mostly limited to the study of the producers and the production stage of ceramics: the preparation of raw materials, and the shaping, decoration, and firing stages, including the used tools, firing installations, and spaces (Sillar, 2ooo; Skibo and Schiffer, 2008; Hodder, 2012a). However, the organization of pottery production is influenced not only by decisions made during the production of pots, but also by considerations related to their distribution and use. After production, pots become tools (Braun, 1983), components of other techniques such as storage, food preparation, transport, and burial, and therefore pots become part of the technological choices

F i

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of users in their activities. Since all techniques can be studied with the chaine opiratoire approach, the method may be applied to the study of the whole life-cycle of a pot or an assemblage, from raw material selection, production, distribution, use, breakage, repair, and reuse, to discard, and to identify the social groups involved in these processes (Lemonnier, 1993, 2012; Naji and Douny, 2009; Knappett, 2012).

Behavioral Archaeology One of the more vocal advocates of the need to focus on the interaction between people and things is behavioral archaeology. Developed since the 1970s by Michael Schiffer and colleagues, behavioral archaeology claims that it is impossible to directly observe "social processes:' such as organization, since these are theoretical constructs. We can only study behavior, since behavior is composed of people-object interactions which leave traces (Schiffer et al., 2001; Schiffer, 2007, 2011; Skibo and Schiffer, 2008; LaMotta, 2012). Behavioral approaches try to achieve a full understanding of a particular technology by studying, in minute detail, several core aspects. Well known is the focus on cultural deposition processes and site formation processes, a topic much neglected in other approaches to pottery production. Other core components of the approach are the behavioral chain and the life history (of objects or of technologies; Hollenback and Schiffer, 2010 ); activities and interactions; technical choices; and performance characteristics and compromises (Skibo and Schiffer, 2008; Hollenback and Schiffer, 2010). Behavioral approaches promote an integrated study of the complete life history of a technology or artifact, from procurement, production, use, reuse, and repair, to discard and deposition. Each link in this behavioral chain is an activity, an interaction between people and things. Behavioral chain analysis specifies all components of these interactions, such as the location, frequency, other artifacts, external influences, techno-communities, and cadena. The concept of cadena is used to indicate all social groups interacting with the artifact during its behavioral chain. A cadena can be homogeneous, when all members appreciate the same performance characteristics of an object, or heterogeneous, including many different (and sometimes conflicting) demands on performance characteristics. The cadena and all activities in a behavioral chain provide input to the technical choices an artisan will make during production, as an artisan weighs the effects of his choices on the various performance characteristics and demands (Walker and Schiffer, 2oo6; Schiffer, 2007; Skibo and Schiffer, 2008). The concept of cadena is comparable to the "relevant social groups" in the SCOT approach, but later publications suggest that a cadena not only includes people but may also contain objects and materials, treating people and things as socially equivalent or symmetrical (Walker and Schiffer, 2006; Schiffer, 2007; Skibo and Schiffer, 2008; Hollenback and Schiffer, 2010; a cadena also resembles the "entanglements" of Hodder, 2012a; see also below). Behavioral approaches see technical choice as a (conscious or unconscious) decision based on the (utilitarian, symbolic, ritual, etc.) use of the pot, while the technological choice of the cultural technology approach concerns the (conscious or unconscious) adoption of a practice based on the experiences and background of the potter (such as social identity, community of practice, and learning patterns). Technical and technological choice are thus two complementary sides of the process of making things, which both may offer useful insights in the organization of production. For Schiffer's views on the differences and similarities

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between concepts of behavioral archaeology and cultural technology, such as behavioral chain vs. chaine operatoire, technical choices vs. technological choices, and techno-communities vs. communities of practice, see Schiffer (zoo7) and Skibo and Schiffer (zooS). One of behavioral archaeology's main attractions for the study of the organization of pottery production is the focus on the people involved in all stages in the life of an artifact, which all may influence production, production decisions, and social relations during production. Behavioral archaeology moreover offers a practical methodology to study these processes. It actively advocates an integrated use of archaeology, ethnoarchaeology, experimental archaeology, and archaeometry. Behavioral approaches have been said to be overly utilitarian and functionalist (Gosselain, 1998) or materially determinist (Hodder, 2012a: z29), emphasizing fhings over people (Webmoor, 2007). Although in principle they claim not to favor utilitarian, materialbased, or functional perspectives over "non-utilitarian" social or ritual explanations (Skibo and Schiffer, 2008: 25; Hollenback and Schiffer, zow: 318-319; Schiffer, 2011), in practice the approach is often understood as such. This is not in the least owing to the insistence that we have to identify utilitarian performance characteristics first, before thinking about possible non-utilitarian characteristics (as advocated in Skibo and Schiffer, zooS: 26; contra Dobres, zooo, 2010). Olsen et al. (zo1z: 186) furthermore object to the fact that behavioral archaeology puts the relational properties of things (performance characteristics) second to their "intrinsic" properties. Others point out that behavioral approaches do not pay enough attention to the deep history of the involvements of people and things (Webmoor, 2007; Hodder, 2o12a), and portray artisans as "engineers'' doing tests and solving technical problems (David and Kramer, zoo>: 141). An additional problem, in my view, is behavioral archaeology's focus and reliance on predefined universal or nomothetic principles and assumptions about the relations between material traces and social processes. For behavioral archaeology they are not only the ultimate aim of our efforts but also an indispensable tool needed to bridge the gap between the archaeological record and our interpretation of it (as, e.g., in Schiffer eta!., zoo1; Walker and Schiffer, zoo6; Schiffer, zo11). However, these principles and laws are obscuring our view of the actual associations between people and things (Gosselain, 1998; see also below).

Holistic Approaches to the Organization of Craft Production An approach specifically developed to study the organization of craft production, and combining methods and insights from ceramic ecology, behavioral archaeology, chaine operaloire, and constructivist perspectives, is the "holistic" approach developed by Izumi Shimada (Shimada and Wagner, 2007; Shimada and Craig, 2013). This ambitious approach explicitly looks at the whole craft production process, from raw material acquisition to product use and recycling, including both the material-technological and the social-ideological components of a craft production system, while trying to avoid modern preconceptions and analytical distinctions (Shimada and Wagner, 2007). It has four major components: (1) a regional, multi-site, and diachronic scope to clarify the environmental, historical, and social contexts of craft production and the distribution and use of its products; (z) the study of production sites, aimed at understanding the complete production process; (3) close interdisciplinary cooperation between complementary specialists; and (4) the integration of

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archaeometry, experimentation, and ethnoarchaeology (Shimada and Wagner, 2007). The focus in the holistic approach is very much on the detailed study of direct evidence for production, although in principle this approach can be applied as well to assemblages that lack such evidence. Recent studies adopting an holistic approach to pottery production organization (including study of the environment, production, production locations, distribution, function, and use), whether or not explicitly following Shimadas framework, are Day et al. (zoo6, 2010), Duistermaat (zooS), Gagne (2012) and Greene (2013). Such holistic studies have been successful in bringing out the nuances and complexities of the (organizational) relations between all actors involved in craft production. They also clearly show that the study of craft production is far from an easy matter, and ideally involves a long-term commitment of an interdisciplinary team.

The Ontological Turn Understanding the relationship between the social and the material, and developing theory and method to bridge the gap and understand the one by studying the other, has been a long-standing issue in archaeology (Olsen, 2003, 2010; Hicks, 2010 ); many would perhaps say that this is what archaeology is all about. A major transdisciplinary ontological turn that has been taking shape since the 1980s promotes a radically different perspective: the dualism between social and material, between humans and things, is not a given, but a construct of modernist thinking that we should let go of (Olsen, 2003; Walker and Schiffer, 2oo6; Witmore, 2007; Hicks, 2010; Watts, 2013). This perspective is strongly influenced by actor-network theory (ANT), a sociological approach originating in STS studies and developed since the 1980s (Law, 1992; Latour, zoos). In archaeology, approaches influenced by ANT that are relevant for my argument here include symmetrical archaeology (Shanks, 1998; Olsen, 2003, 2007, 2012, 2013; Webmoor, 2007: Olsen et al., 2012) and entanglement (Hodder, zon, 2012a). Symmetrical concepts and ideas are also influencing behavioral archaeology (Walker and Schiffer, zoo6; Schiffer, 2007; Skibo and Schiffer, 2008; Hollenback and Schiffer, 2010 ). ANT -inspired approaches share an understanding of the social not as a category separate from the material, as a larger context or framework behind the material world. The "social" or "society" is not something written in or embodied by things; rather, things are an inseparable part of its constitution (Shanks, 1998; Olsen, 2010 ). "1be social" is an interactive effect, emerging during the mutual interaction between humans, nature, things, animals, and so on. People, society, technology, and material culture are continuously coproducing each other, rather than one being embedded in the larger context or framework of the other. In order to see the effect we call "organizing:' we have to reassemble the associations and inter~ actions between all these actants, while treating people and things symmetrically, without any a priori ontological or analytical distinction between the two. In this perspective there is no gap to bridge between the social and the material (Webmoor, 2007: 572); rather, the "materials of past (and present) societies are not seen as an epiphenomenal outcome ofhistorical and social processes [... ] but actually as constituenteven explanatory-parts of these very processes" (Olsen, 2010). The lack of living people as a source of information in archaeology, as opposed to ethnography, is not seen as hindering

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or complicating the study of "the social" through material remains: "We uphold a materialist outlook-you do not have to talk to people to find out how they conceive of the world, because something of the way people operate, work, and do is wrapped up in their achievements. People are so involved with the world of material goods that we can put to one side the old split between mind and matter, beliefs and the material world that may leave traces for the archaeologist to work upon" (Olsen et al., 2012: 167). This is not only relevant for archaeology: students of contemporary organizations increasingly turn to study materials and technology, irrespective of the fact that they can directly observe and interview organizational members (Orlikowski and Scott, zooS; Orlikowski, 2010; Leonardi et al., zo1z; Carlile et al., 2013; Humphries and Smith, 2014). In this respect, organizational research is now starting to look at "things" using concepts and methods that have been used and developed in archaeology for decades. Bruno Latour proposes that "reassembling the social" is best done by looking at situations of innovation, at the places where things are made (such as an artisan's workshop), at situations of breakdown and failure, and through looking at the history of technology (Latour, zoos). This, and the focus of ANT on technology, power, and organization, makes this approach especially interesting for those studying the organization of pottery production. However, there are as yet few pottery studies adopting ANT-inspired or symmetrical approaches (examples are Watts, zooS (cited in Watts, 2013); Jervis, 2011, 2013; Stockhammer, 2012; Van Oyen, 2013).

TOWARDS A RELATIONAL VIEW OF THE ORGANIZATION OF POTTERY PRODUCTION The approaches mentioned in the previous paragraph relate to, and differ from, each other in complex ways (Coupaye and Douny, 2009; Hicks, 2010; Hodder, zoua; Ingold, 2012). A discussion of their compatibility or comparability falls beyond the scope of this chapter. In this section I propose these approaches may be combined to study pottery production organization. Examples of other strategies combining elements of these approaches are Hilditch (zooS) and Jeffra (zona).

Tracing Entanglements As Latour (zoos) suggested, "the social" (such as organizational practices) can be reassembled by empirically following, tracing, the numerous interactions between all human and non-human "actants:· Similar strategies are employed by symmetrical archaeology using the term "rearticulation" (Olsen et al., 2012: 176) or entanglement (Hodder, zo12a). Interactions between these actants lead to the formation of actor-networks (Law, 1992; Latour, zoos), assemblages (Shanks, 199S; Alberti et al., 2013; Fowler, 2013), or entanglements (Hodder, 2012a; see Fowler, 2013, for a more elaborate discussion of the differences and similarities between these concepts). Organization should be understood as a process, as emerging from such entanglements. There exist no such entities as "household production" or "attached

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production" which are out there and can be discovered, or which can be used to explain archaeological data. Rather, we have to explain how organization becomes, how it is a continuously emerging effect of the entangled and enmeshed relations and interactions of heterogeneous actants, including people, objects, tools, materials, spaces, and forces (Law, 199z; Hernes, zooS; jervis, zon; Humphries and Smith, zo14). In the case of pottery production, the actants are many, and may include anorganic materials (day, water, rocks, metal), plants (as fuel, organic temper, resins, rope and textiles, wood), people (potters, users, authorities, children, middlemen; including their skills, needs, demands, and identities), animals (transport animals, cattle and sheep providing dung for fuel and temper, bone tools, and hair as tools and temper), technologies (clay extraction, paste preparation, shaping, decorating, firing, transporting, cooking, storage, distribution, burial), architecture, places, and spaces (fields, mountains, the workshop and its location and layout, roads, places where pots are used), concepts, interests, feelings, and opinions (efficiency, aesthetics, magic, value, gender, norms), forces, energies, processes, and reactions (gravity, pressure, speed, oxidation, weight, temperature, time, decomposition). Each of these actants can, in their turn, be seen as entanglements, networks of relations. For example, a "potter" is a complex meshwork of interactions and associations between a human being, day, tools, technology, knowledge, skills, other people's opinions about "potters;' the community, and more. Recurrent interactions between all these may lead to a stable state that presents itself in daily life as a single entity, recognized as a "potter" (Law, 199z; Hernes, zooS; Michelaki, zooS; Orlikowski and Scott, zooS; Budden and Sofaer, zoo9; jervis, zon; Fowler, zo13). One of the more challenging aspects of a research project is to determine which entanglements we decide to see-for analytical purposes-as such a black-boxed entity, and which entanglements we aim to "untangle" by following the interactions between all the actants involved (Latour, zoos; Hernes, zooS: 7-8). This depends on our research questions. Research questions should avoid a top-down approach, avoid trying to fit archaeological evidence in (and searching for evidence of) a priori existing analytical distinctions (Shimada and Wagner, zoo7), meta-narratives, frameworks, concepts, and models, such as "the emergence of complex societies;' "craft specialization;' or "modes of production'' (Olsen et al., 201z: 175-176, 190). This does not mean that larger-scale questions are irrelevant. I am also not claiming that variables that are thought to influence craft organization, such as task divisions, specialization, or intensity of production (cf. Costin, 2005; Van der Leeuw, zoo8: figures 1z.z-1z.8) are irrelevant. Rather, I suggest that we should not let these constructs lead our way, determining from the start which associations are worth tracing. I propose that it is important to question, rather than assume, the existence and specific nature of these variables and the relations between them in each particular case, and to also actively search for any associations that do not fit these a priori frameworks. We have to adopt a bottom-up approach (Fahlander, z013; Mimisson and Magnusson, 2014), focusing on practice and process, and systematically following the "networks of empirical, statistical, metaphorical, narrative, conceptual, causal and systemic association'' in our data (Olsen et al., zo12: 176), while using our creativity and trying to think beyond our usual assumptions. Such a relational approach will also enable us to see how organization and complexity is apparent on any scale, and how we can approach larger-scale issues through the detailed study of materials on the micro-level (Day et al., zoo6; Kohring, 2on, 201zb; Mimisson and MagnUsson, 2014).

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I propose four interlinked and overlapping strategies to study the organization of pottery production (Hodder, zorza: 204-227; Humphries and Smith, 2014). First, it is important to attend to the material properties of the actants involved in pottery production, and to what they do: how they constrain, afford, or influence (organizational) practices. Secondly, using the chafne ophatoire approach> we can map the sequences, activities, and entanglements of pottery production and its organization, identifying all actants and establishing what they do. Thirdly, the chaine operatoire approach may be used to follow the biography or life-history of our material. Last, we can trace the spatial aspects of these entanglements, including the location of materials and production> users and use activities, and the distribution and circulation of pottery. We can also trace the various temporal dimensions of the entanglements at various timescales (Hodder, 201za). These approaches may be combined to bring the relevant social groups or cadena into view. All strategies are interlinked) and have no particular order or sequence (and most probably will be performed simultaneously). They provide different lenses one can use to look at the same material, to bring different aspects of it into focus. Together, they can be used to map entanglements and situate them in space and time. I will briefly describe these strategies in more detail below, each time using a Middle Assyrian "carinated bowl" from Tell Sabi Abyad, Syria (c.1zoo BC), as an example of an actant under study (all information is based on Duistermaat, zooS).' I chose this particular shape because it has become almost iconic for the supposedly standardized, centralized, state-controlled mass production of pottery in the Middle Assyrian period, a view which I find overly simplifying and unhelpful for understanding Middle Assyrian craft production. Moreover, my choice for a vessel instead of a find from the pottery workshop we also excavated at Sabi Abyad, will hopefully show that many useful insights can be gained in the absence of direct evidence for production. I chose to draw "tanglegrams" (Hodder, zmza) as a visual support of my point, but this actually may not be the most practical solution. Of course, tracing entanglements should not be limited to one bowl, but should include the whole ceramic assemblage (Roux, zon; Van Oyen, 2013). It should also include tools, spaces, materials, texts, images, and any other actants involved in the organization of pottery production, as much as are available.

First Strategy: Tracing Material Properties A first step in tracing entanglements involves tracing materials, and studying how the physical properties of materials affect the organization of production (Jones, 2004), what these materials do, and what happens to them during their life (Ingold, 2012). We can look at materials from at least three perspectives. The first perspective concerns the physical nature and properties of the materials involved in the actant under study, and their interrelations or entanglements with other materials and actants both within the object itself and outside it (Figure 9.1). Our bowl was made of calcareous clays with vegetal inclusions. Possibly, animal dung was used as temper material. If we focus on tracing the entanglements of dung, this opens up a range of connections to other actants and processes, such as animals, the plants they ate, agriculture, procurement of amounts of dung, drying times and places for dung cakes, seasonal activities, and the use of dung in other activities (e.g. as fuel, or as a component of plaster; cf. Sillar, 2000; Goldstein and Shimada, 2013). Of course, detailed

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potting cooking

\ II

fields

I

seas~

smithing

hearths, kilns

dung as fuel

plan\

building / dung in plaster - - architecture

excrements smell fertility

~-~

smell

sheep

sheep herding

increase workability decrease plasticity reduce weight increase porosity rough vessel surface

/ brackish water?

farming

fields wadi

~-~···-··0"-Salt supply?

pits and bins \

~soils -r--'----..;~ ~

/calcareou\ay

river

~ houses

dust

building writing not very plastic high shrinkage risk of lime spa !ling

FIGURE 9.1

dust and dirt soil, land fertility

Entanglements of the materials used to make a carinated bowl.

understandings of materials will also provide information on the spatial dimensions of entanglements, for example when establishing the geographical source of materials. Secondly, we can study what materials do: how they interact together and how their interaction results in constraints and a:ffordances for action of other actants, affecting the material engagement between material and potter (Malafouris, 2008), the chaine operatoire, and the organization of work. Materials do not have intrinsic properties that are waiting to be brought out by people; rather, these properties and affordances are the result of the interaction between actants in specific situations (Knappett, 2004; Hodder, 2012a; Jones and Alberti, 2013: 24) and have functional as well as representational aspects (Gosselain, 2011). In our case of dung temper, these interactions may result in specific technologies for mixing clay and dung, the smell of the clay body, effects of the dung temper on increased workability of the otherwise rather

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short clay body, effects of vegetal inclusions on coping with shrinking problems, and the behavior of the clay body during firing and its relation to kiln technology and firing skill. A third perspective focuses on what happens to materials during activities after their production: how they perform and affect use, but also how they change, decay, and disintegrate during their life-history. In our case most of the dung will have burnt out during the firing stage. However, the dung-containing fabric of the bowl will have particular qualities including fabric porosity and vessel weight. Together with size and shape, this fabric will have effects on, for example, tensile strength and mechanical shock resistance of the bowl, breakage patterns and frequency, or the resistance to hot contents. This particular fabric will also change during its lifetime; for example, as a result of its interaction with acid contents. Apart from the functional consequences of material properties, these properties also constrain or afford social practices (Jones, 2004). In our case (although this has not been studied yet), we may, for example, wonder whether any material properties of dung, such as its smell, may relate to cultural connotations of dung (Sillar, 2000 ): if these were negative, perhaps we can link them to the choice of dung-free fabrics for drinking goblets, the preference of the high elite for glass and metal drinking vessels, or the low social status of the potters and their profession. The entanglements of the calcareous clay and other components of the fabric can be traced in similar ways. A second aspect of material properties is form; the specific size and shape of our vessel. Again, form is a bundle of connections among processes, uses, techniques, and performances (Olsen et al., 2012: 191). We are dealing with a small bowl with a flat base, a simple rounded rim, and a flaring, lightly carinated wall. The bowl is somewhat slanted to one side and the base is cracked. The surface is left untreated and undecorated. Comparisons with similar bowls show that ours belongs to the middle one of three loosely defined size groups. Form and material affect interactions between actants in specific situations, resulting in particular constraints and affordances (Knappett, 2004; Gosden, 2005; Hodder, 2012a). For example, our bowl affords the holding and taking out of food, drink, and other materials, it fits in a hand, the carinalion and surface prevent slipping and facilitate grip, it can easily tip over, it can be stacked (but the irregular slant prevents a high stack), it is lightweight, it is not very watertight, it fits the mouth oflarge jars as a lid, it can hold c.o.3liters, it is not particularly beautiful, and it is very recognizable (and regarded as an archaeological "type-fossil" for the Middle Assyrian period). This specific form is closely tied to the way in which it was made, and to the ways it was expected to perform during use. It is also closely related to bowls made in the same shape, but from bronze. Bronze bowls were expensive and rare. Still, these bowls shared the shape of our everyday pottery bowl, which was found in huge quantities in a large variety of contexts. This suggests that the carinated shape is not only recognizable for us archaeologists but carried meaning for its users as well. Meaning and value may also be accessed through its quick and rather careless shaping and finishing, and through their relative uniformity.

Second Strategy: Tracing chaines operatoires Using the second lens to look at our bowl, the aim is to study in detail its chaine operatoire and forming techniques, using a variety of low-tech and high-tech methods of analysis

1

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(e.g. Smogorzewska, 2007; Bouzakis et al., 2011; Berg, 2013), in order to trace the entangle~ ments of the production process. A close mapping of all sequences and activities related to the making of our bowl will enable us to identify the actants related to each step ofproduction (such as the potter, assistants, the clay and other ingredients, tools and firing installations, and spaces). We can study how materials and their properties affect the chaine operatoire, and what happens to them during the work Questions are provoked about the kind and size of spaces and tools needed, and about access to materials and spaces. A thorough study of the chaine opiratoire and traces on the vessels (such as fingerprints, mistakes and correc~ tions, or differences in skill levels) provides information on the probable number of people at work, on task segmentation, repetition and serial work, and on the possible involvement of children or trainees (Crown, 2007; joy, 2009; Sofaer and Budden, 2012). Moreover, through this approach, we can come closer to gestures, kuowledge, and skills. These are important aspects when addressing questions about the intensity of production or the output per potter, the relative skill level of the potter, or the amount of time spent on production (Roux, 2003a, 2003b; Crown, 2007). We can focus on the potter's social identity and status, and on communities of practice. The chaine opiratoire approach also helps to assess time, including issues such as seasonality and the involvement of people in other activities, time-flow of the work, and the minimum amount of time needed to complete the work. This is crucial information if we want to estimate the intensity and output of production. The chaine operata ire opens up possibilities for comparisons with other crafts and activities using similar technologies, gestures, tools, spaces, or materials, producing similar products, or dealing with similar user groups (Sofaer, 2006; Brysbaert and Vetters, 2010 ). Regarding our interest in the organization of production, we may want to pay special attention to those parts of the chaine operatoire that involve communication between people involved in production, and communication and cooperation with other human actors (such as neighbors, users, suppliers of materials, or authorities). We should also consider how techniques, tools, infrastructure, and spaces afford organizational practices. Figure 9.2 presents a basic chaine operatoire for our carinated bowl. In order to keep the image readable, I have listed the various materials, places, and activities that are part of the entanglement in separate boxes rather than in a tanglegram. Also, in order to focus on organizational practices, I have marked those steps that are likely to have involved task divisions or the help of assistants, as well as those steps that likely involved communication and cooperation with people outside the workshop (see also Sofaer and Budden, 2012). It appears that our bowl was made by a skilled potter and at least one assistant, who were able to throw vessels from the cone using the rather short local clay, and fire them with modest firing losses. Communication and cooperation with others was mostly needed for the acquisition of raw materials and tools, and perhaps for kiln building. Despite skill levels, or perhaps we should say enabled by them, our potter was focusing on output and speed, and less on quality and aesthetics. Among the interesting and unexpected entanglements of our bowl in production are the frequent links to scribes. In one phase of the site, the pottery production takes place in the courtyard of a scribe's house (identified by texts found there). Furthermore, cuneiform writing and seal impressions occur sporadically on our type of bowls, and unfired waste fragments from pottery production are found in recurrent association with unfired cuneiform tablets and clay sealing fragments. These entanglements show that the cooperation and social relations between potters and scribes may have gone beyond the sharing of raw materials.

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MATERIALS day water dung digging tools baskets water skins or jars grinding tools stick to stir liquid clay lubricant potter's wheel stik to spain the whet! bowl of water thread kiln fuel gypsum bitumen basalt thread reeds wind direction wood sunshime rainfall temprature seasons ACTIVITIES potting assisting kiln building sheep herding

(clay digging

(

(

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( collecting sheep drug ~

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take out large particles

I

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FIGURE 9.2 Chaine operatoire for a Middle Assyrian carinated bowl with a flat base. Gray circles indicate likely situations where communication with "outsiders" is necessary. Open circles indicate likely moments of task division and the presence of assistants.

Third Strategy: Tracing Biographies The "biography" approach has enjoyed some popularity in the past decades (Hicks, 2010). Some studies focus on the meaning or significance of objects to people (as in Kopytoff, 1986; Gosden and Marshall, 1999), some on the technical and functional changes of objects during their use-life (as in behavioral chain analysis, see above; see also Pefia, 2007). Others call for more attention to the literary techniques of biography writing (Burstrom, 2014), discuss the long-term life-history or evolution of a particular technology (Roux, 2010, 2013; Laneri, 2011), or investigate the extension of an object's life-history into the present (Shanks, 1998; Holtorf, 2002). I do not intend to sketch a linear or chronological life-course for our bowl, starting with production, through use, maintenance, and reuse, and ending with discard. Of course, all these stages in the "life" of our bowl are important to consider, but the sequential aspect (was it first used during meals, and later as a lid, or the other way around?) is

M$A

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often hard to reconstruct. My focus is mostly on the relations between objects and people during the post-production part of the bowl's life-cycle: these relations determine the use, value, and meaning of our vessels and directly influence production (Clark, 2007a). We will follow the bowl as it gathers entanglements of heterogeneous actors (Shanks, 1998). 1be purpose is to consider "the range of interactions between people and objects and [to explore] how multiple forms of agency emerge through them" (Jervis, 2013: 219). Recurrent associations with other pottery vessels, with other objects and materials, with places, and with people create durability in the social assemblages in which our bowl was a participant (Jervis, 2011, 2013; Zedei\o, 2013). Therefore, I will adopt a "relational" perspective and attempt to map the heterogeneous events and actions that our bowl (and similar bowls) was participating in (Joy, 2009), in order to understand the variety of activities and actants. These different activities, interactions, and resulting social assemblages (or cadenas) may have affected the organization of pottery production in different ways (Walker and Schiffer, 2006). The mapping ofinteractions is based on traces of use and repair and residues of contents (Skibo, 2013), specific find contexts, and the appearance of this particular shape in other materials, contemporary images, and texts. The same approach should, of course, also be applied to any available direct evidence for production, including spaces (e.g. Papadopoulos and Sakellarakis, 2013, using computer simulation to study the affordances of a room identified as a pottery workshop), architectural features, and tools (studying tool manufacture, acquisition, and style, e.g. Gosselain, 2010; Ramon and Bell, 2013), use-wear on potter's tools (e.g. Torchy and Gassin, 2010; Van Gijn and Lammers-Keijsers, 2010), and tool provenance (e.g. Murphy and Poblome, 2012; Fiaccavento, 2013: 85). It is crucial to link these studies to the chaine operatoire studies of the pottery assemblage. The resulting tanglegram (Hodder, 2012a) in Figure 9-3 presents several instances of our bowl's "cumulative" biography. Our bowl has now become a tool in other technologies, such as cooking, food preparation, storage, and burial. The entanglements of each of these technologies can be traced again by using the chaine operatoire approach, following the courses of action resulting from these associations (Sillar, 2000; Jervis, 2013); Figure 9-3 shows only the very start of such entanglements (cf. also figure 3-5 in Hodder, 2012a). As Figure 9-3 shows, our bowl was a multipurpose bowl mainly used for the presentation and consumption of food and drink. As such, the bowl played a role in re-enacting and maintaining social relations, traditions, and feelings of "home;' through specific ways of sharing meals. Perhaps these ways were similar to the modern Middle Eastern "mezzeh;' where multiple small bowls containing different kinds of food are placed in the middle of a group of people, rather than each person having their individual plate. The connections with "brewing" raise questions about connections between potting and brewing, especially in the light of a contemporary text from the site suggesting that the brewer was on occasion in a position to order the potter to produce vessels (Wiggermann, 2008). Perhaps this lead can be followed further by attempting a better identification of the vegetal fibers in the pottery fabric. Did the potters indeed use animal dung as temper, or did they use the waste of the brewing process, so that the brewer was not only a user but also a supplier to the potter? Our bowl had additional roles in craft production, storage, and ritual activities such as burial. Comparisons of this tanglegram with that of other types of small bowls reveals that other small bowls were never used in burials, nor as lamps or jar lids, although they do afford such uses. This, combined with the rather rare occurrence of maintenance and repair of carinated bowls, raises

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KIM DUISTERMAAT

cooking /

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FIGURE 9·3 Entanglement of the life-history of carinated bowls, from production

until deposit in the archaeological record. The size of the circles indicates the relative importance of this use. Gray circles indicate secondary uses after fragmentation beyond repair.

questions about the values and meanings our bowl had for the community living at the site. The use of specific vessels in burials and during shared meals touches on the creation of identity and community, issues that were of special importance in a settlement that was founded by Assyrians in "hostile" territory, as part of a hegemonic strategy to incorporate the region into the Assyrian empire. The variety of our bowl's biography also illustrates its multiplicity, and this opens up ways to investigate the composition of the various "relevant social groups" interacting with our bowL As these groups are directly contingent on decisions concerning design and technology, they are of interest for the study of the organization of pottery production.

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Fourth Strategy: Locating Entanglements in Space and Time Tracing the spatial dimensions of the entanglements of materials, production, and biography will enable us to access issues of source, distribution, circulation, and deposition of materials and objects (Hodder, 2012a; Jervis, 2013). We can look at source areas of materials and tools, helping to plot the location of production regionally, and bringing peoplelandscape interactions into focus (Druc, 2013; Michelaki et al., 2015). At different scales, we can study the spatial dimensions of the chaine operatoire, the specific layout of the workshop, and the location of production in relation to the site (Stissi, 2012). Also important is the distribution of vessels after production: were they exchanged locally or further away, through which mechanisms, and which actants are involved? Each use also has its own spatial dimensions. At our site, we were fortunate to find the production locations where our pottery was made, including workshop areas, drying areas, and kilns. We were able to study the spatial organization of production activities in detail, both in the workshop as well as in relation to the rest of the site. But even if that is not the case, careful plotting of spatial dimensions may yield interesting understandings on the movement of materials, tools, products, and people. Again, we should study these processes through the whole life-cycle of the actants involved in production. One example of the spatial dimensions of our bowl is its regional distribution. Sabi Abyad was a fortified estate founded in order to incorporate the region into the Assyrian empire, and to exploit its agricultural resources. Texts suggest that there were numerous settlements in the close surroundings of our site, housing local non-Assyrian inhabitants who were dependent on the Assyrian administration. However, our typical carinated bowl was only sporadically found at such sites. This raises questions on how dependent the local population really was, and on the apparent lack of active attempts to ''Assyrianize" the local population by encouraging the use of''Assyrian" vessels. Moreover, if pottery was not distributed among dependents, this informs us about the relatively small size of the user group for whom our potter produced, putting doubts on the idea that production was a full-time affair (Duistermaat, 2015). Locating entanglements in time can also be done on several scales (Gosden, 2005; Hodder, 2012a). On one scale, there is "operational" time: the time and sequence that builds up each activity that is part of making or using our pottery vessels. There is often a specific order for doing things, and there are constraints and demands on time in each sequence. One can think of drying time needed before firing a vessel, or of the need to finish an operation before the wheel loses momentum. Moreover, certain cooking or storage techniques require vessels to be in use for considerable durations of time, while other uses result in quick fragmentation. The temporal perspective also brings in concerns of seasonality, and the simultaneous involvements in other tasks and crafts. On a second scale, we can consider the life-history of artifacts. This does not only concern the various uses an artifact had, but also the recycling, inheriting, or purposeful destruction or deposition of artifacts. Assemblages are never homogeneous in age: some pots will be brand new, while others will have been used and reused for decades. This is not only relevant for chronological purposes, but also directly impinges on production organization, affecting aspects such as replacement needs and rates, and output volumes. On a third scale, we can look at the historical developments and changes of techniques and organization. The very important and currently much studied concept of innovation and technological change is crucial in this respect. Historical

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patterns-in the form of knowledge and experience-may constrain the adoption of new practices. For example, the use of a certain technique or production organization can com~ plicate the adoption of a new one (Arnold et al., 2007; Vander Leeuw, zoo8; )effra, zona), or a certain layout of a building may dictate future locations of walls (Hodder, zo12a).

Analyzing Entanglements and Reassembling Organization Despite the hard work of tracing the innumerable entanglements of all possible actants we have at our disposal, one could argue (as do jones and Alberti, 2013: 27) that this does not immediately bring forth an understanding of organizational practice. Nevertheless, in the process of doing so, we have gained an amazingly detailed understanding of our pottery, its production, and related materials and people. In itself, this is already much more than we ever could have learned from classifying our case based on a limited number of predefined criteria, as in typological approaches. We have now identified the relevant actants (including people and non-humans) and traced their relations. But the relations between the actants should not simply be lines. It is more productive to view these relations as actions expressed with verbs, such as "use;' "produce;' "depend on:' To understand organizational practices, we should look at what these actants do: what are the actions they perform together and on each other, and how do they affect organizational practices? Which actants are "mediators:' influencing and consolidating roles, relationships, communication, control mechanisms, decisions, and power, and how do they do so (Latour, zoos: 37-42)? We should also look for patterns, recurrent actions, and routines (Olsen et al., 2012). Partly, these questions can be tackled through archaeometry or experimental archaeology. For Latour, the clue to reassembling the social lies in the process of writing (Latour, 2005: 121-140; see also BurstrOm, 2014). He sees the writing process as crucial, because the social will appear only through a well-written account. He defines a good account as a narrative in which every participant is a mediator, is doing something. The quality of an account is measured according to the number of actors the scholar is able to treat as mediators, without taking the shortcuts provided by concepts such as, for example, "efficiency:· I think it is also interesting to see if we can approach the relations between actants in a more formal way. Any tracing of actants will quickly result in a large and varied collection of heterogeneous connections between heterogeneous actants, which need to be analyzed for significant relational patterns. Would it be possible to approach these entanglements with techniques from the quickly growing field of network analysis and computer applications in archaeology (Knappett, zon; Hodder and Mol, 2015)? Organization studies adopt such a formal approach with the concept of"narrative network" (Pentland and Feldman, 2007) or "action network'' (Pentland et al., 2010 ), in order to visualize and analyze these patterns and routines to understand organizational practices. In a narrative network, each action between actants is a "narrative fragment" (e.g. "the potter forms a vessel on the wheel"). Fragments are linked together in coherent sequences (narratives), much like a chaine operatoire (e.g. "potter waits for assistant to place clay on wheel-potter forms vessel on the wheel-potter cuts vessel from wheel head and puts it aside"). A narrative is different from the perspective of each of the multiple actants (humans and non-humans alike). All narratives together, and the links between them, form the narrative network which characterizes that particular

p

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organizational routine (e.g. "throwing a vessel on the wheel"). 'The narrative network can be visualized in a graphical image. Analysis of the network, and comparisons with networks for similar situations elsewhere in place or time, can yield information on which actants and actions affect organizational change the most (Pentland and Feldman, 2007; Hayes et aL, 2011; Pentland et al., 2012). Narrative networks and organizational routines can also be analyzed and compared through a variety of statistics for network analysis (Pentland et al., 2010), and through agent-based simulation (Gao et al., 2014). Of course, this approach cannot be transferred from organizational studies to archaeology as is, but I think it is worthwhile to explore the possibilities it offers for the analysis of archaeological material. As yet, archaeological applications of computer techniques in the study of craft production organization are rare: Brysbaert et al. (2012) discuss how process mining techniques can be used to analyze chaines operatoires, and perhaps ontological datasets will be key in exploiting the strength of computers to search for meaningful patterns in our entanglements (Hong et al., 2013). An example of the application of agent-based simulation to the organization of salt mining in Hallstatt can be found in Kowarik et al. (2012); while Rouse and Weeks (2011) use agent-based modeling to study production specialization in Bronze Age Arabia. This is not the place to present a full discussion of network approaches and related computer techniques, nor of their compatibility with the approaches discussed in this chapter. Useful introductions are published elsewhere: for discussions of formal network analysis in archaeology, see Brughmans (2010, 2013, 2014), Knappett (2011, 2013), Ostborn and Gerding (2014), Peeples and Roberts (2013); for introductions to complexity theory and modeling, see Bentley and Maschner (2007), Kohler (2012), Kohler and Vander Leeuw (2007); for introductions to simulation and agent-based modeling, see Barton (2014) and Lake (2013).

CoNcLusioNs In this chapter I have discussed two major traditions in the study of pottery production organization: ceramic ecology and typological approaches. Despite their major contributions to our understanding of pottery production, there are two important shortcomings. First of all, there is an analytical gap between pottery production and the larger social or economic "context:' It is often not clear how a certain type of production is linked to these larger-scale concepts. The nature of the relations between organizational practices, power, and social inequality should be the subject of our inquiries, not part of the typological label used as explanation. Secondly, typologies link variables such as output, intensity, economic dependence, or labor divisions, while these links should be questioned in each particular case. These issues, as well as the more recent development of approaches focusing on technology and people-thing relations, suggest that the time has come to develop new strategies to study the organization of pottery production. I suggest that such strategies can be built from elements offered by SCOT, cultural technology, behavioral archaeology, holistic approaches, symmetrical archaeology, and entanglement perspectives. I provided brief summaries of each of these different approaches. An approach to the organization of pottery production should view organization as a process, emerging from the specific interactions between peOple, materials, objects, animals, and so on. It should study organizational processes first on their own merits, rather

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KIM DUISTERMAAT

than as a proxy for the larger sociopolitical or economic context or complexity. We should follow the evidence: organization should be explained from the relations emerging from our data, not used as a label to explain our data. We should adopt an empirical, bottomup perspective, focusing on relations and actions. We should incorporate the multitude of factors influencing organizational processes in an holistic perspective, and allow for active roles of people, materials, and things in a symmetrical manner. This will result in an acknowledgment of the unique historical quality of each case, and in an appreciation of variation in organizational practices rather than a search for universal principles. The approach should ideally also cover the study of relations with related crafts and containers in other media, breaking down traditional boundaries between material categories in field projects. As a limited illustration of these points, I proposed to study the organization of pottery production applying the concept of entanglement through four related strategies, focusing on materials, chaines opiratoires, biographies, and placements in space and time. These strategies can be used to trace the entanglements of all vessels, tools, materials, spaces, and so on, relevant to the organization of pottery production, while keeping an open view on relations that do not fit our traditional concepts. They will also yield information on the relevant social groups or cadenas involved, and how they relate to production decisions. A careful analysis of this multitude of relations will allow us to "reassemble" organizational practices. I used the example of a small bowl to illustrate each strategy. The analysis of these entanglements can take the form of carefully written narratives. I also suggested that it would be worth exploring the possibilities offered by formal network analysis and computing technology. All this will only be possible by fully integrating archaeology, experimental archaeology, and archaeometry, and by enlisting the expertise of different specialists, something that is increasingly done (Pollard and Bray, zoo7). Tracing entanglements and analyzing their patterns will be a laborious, time-consuming project, but I am positive that our analytical methods and techniques are capable of making such a project both feasible and worthwhile. A new strategy does not need to discard all previous insights, but can build on them. Through mapping entanglements of materials, chaine operatoires, and life-histories, and by placing them in space and time> many of the variables important for understanding organizational practices (e.g. those listed by Costin, zoos) will come into view. However, by carefully tracing entanglements, we can approach each variable independently, without any preconceived typologies, predefined links between variables, or a priori assumptions on organization. Tracing entanglements is a way to systematically and consciously explore relalions and associations in our data, without following only those paths prescribed by models. This may yield new and unexpected understandings and avenues for research. The results of such a study will not yield a cover-alllabel to characterize production organization, but rather a detailed and animated narrative. This will not render cross-cultural comparisons impossible, only more laborious. In any case, I think it is an illusion to think that specific cases grouped under the typological label of, for example, "individual workshop organization" or "attached production" have more in common or are better comparable than cases described in detailed narratives. In conclusion, the time is right to develop new approaches to the study of pottery production organization. A broad variety of theoretical perspectives and practical methods are being developed, including those that promote a radically new perspective on people, things, technology, and their mutual relations. Analytical techniques and methods, both in

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archaeometry and in computer science, have reached unprecedented levels of precision and strength, and have opened up a wide range of possibilities for studying pottery. I am confident that these developments will contribute to exciting new approaches and discoveries in the field of craft organization.

NoTES r. I do not use the phrase "craft specialization" here. The use of the word "specialization''

2.

where actually"organization'' is meant, even in basic textbooks (Orton and Hughes, 2013), has caused a lot of confusion and discussion and should be avoided (Clark, 2007a, 2007b vs. Costin, 2007; Hendon, 2007; Smith, 2004: 82-83). Organization and specialization are different processes with different causes and dynamics (Neupert, 2007). I used a typology based on vessel shape. However, for the approach proposed here a typology based on forming techniques and fabric, rather than shape, would have been more useful (Jeffra, 2onb; Roux, 2011). For more reading on categories and typologies, see Fowler (2013), jervis (2011), Lucas (2012), Shanks (1998), Van Oyen (2013), and Zedeiio (2013).

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Method and Theory 21: 306-324. Baysal, E. (2013). "Will the Real Specialist Please Stand Up? Characterising Early Craft Specialisation, a Comparative Approach for Neolithic Anatolia:' Documenta Praehistorica 40:233-246.

Bentley, R. A. and Maschner, H. D. G. (2007). "Complexity Theory:' In: Bentley, R. A., Maschner, H. D. G., and Chippendale, C. (eds), Handbook of Archaeological Theories (Lanham, MD: AltaMira Press), 245-270. Berg, I. (2004). "The Meanings of Standardisation: Conical Cups in the Late Bronze Age Aegean:' Antiquity78(299): 74-85.

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Schiffer, M. B. (2011). Behavioral Archaeology. Principles and Practice (London and New York: Routledge). Schiffer, M. B., Skibo, ). M., Griffitts, ). L., Hollenback, K. L., and Longacre, W. A. (2001). "Behavioral Archaeology and the Study of Technology:' American Antiquity66(4): 729-737. Schortman, E. M. and Urban, P. A. (2004). "Modeling the Roles of Craft Production in Ancient Political Economies:' Journal ofArchaeological Research 12(2): 185-226. Shanks, M. (1998). "The Life of an Artifact in an Interpretive ArchaeologY:' Fennoscandia

archaeologica 15: 15-30. Shimada, I. and Craig, A. K. (2013). "The Style, Technology and Organization ofSican Mining and Metallurgy, Northern Peru: Insights from Holistic StudY:' Revista de Antropologia Chilena 45 (1): 3-31. Shimada, I. and Wagner, U. (2007). ''A Holistic Approach to Pre-Hispanic Craft Production:' In: Skibo, ). M., Graves, M. W., and Stark, M.T. (eds), Archaeological Anthropology. Perspectives on Method and Theory (Tuscan: University of Arizona Press), 163-197. Sillar, B. (2ooo). "Dung by Preference: The Choice of Fuel as an Example of How Andean Pottery Production Is Embedded within Wider Technical, Social, and Economic Practices:' Archaeometry 42(1): 43-60. Sillar, B. and Tile, M. S. (2ooo). "The Challenge of 'Technological Choices' for Materials Science Approaches in Archaeology:' Archaeometry 42(1): 2-20. Sinopoli, C. M. (1998). "Identity and Social Action among South Indian Craft Producers of the Vijayanagara Period:' Archeological Papers of the American Anthropological Association 8:161-172.

Sinopoli, C. M. (2003). 7he Political Economy of Craft Production: Crafting Empire in South India, c. 1350-r6so (New York: Cambridge University Press). Skibo,). M. (2013). Understanding Pottery Function (New York: Springer). Skibo,). M. and Schiffer, M. B. (2008). People and Things. A Behavioral Approach to Material Culture (New York: Springer). Smith, M. E. (2004). "The Archaeology of Ancient State Economies:' Annual Review of Anthropology 33:73-102. Smogorzewska, A. (2007). "Technological Marks on Pottery Vessels. Evidence from Tell Arbid, Tell Rad Shaqrah and Tell )assa el-Gharbi (Northeastern Syria):' Polish Archaeology in the Mediterranean 19: 555-564. Sofaer, ). (2oo6). "Pots, Houses and Metal: Technological Relations at the Bronze Age Tell at Szazhalombatta, Hungary:' Oxford Journal ofArchaeology25(2): 127-147. Sofaer, ). and Budden, S. (2012). "Many Hands Make Light Work: Potting and Embodied Knowledge at the Bronze Age tell at Szazhalombatta, Hungary." In: Stig S0rensen, M. L. and Rebay-Salisbury, K. (eds), Embodied Knowledge: Historical Perspectives on Belief and Technology (Oxford: Oxbow Books), 117-127. Stissi, V V (2012). "Giving the kerameikos a Context: Ancient Greek Potters' Quarters as Part of the polis Space, Economy and Society:' In: Esposito, A. and Sanidas, G. M. (eds), "Quartiers" artisanaux en Grece ancienne. Une perspective Miditerranienne (Villeneuve d'Ascq: Presses Universitaires du Septentrion), 201-230. Stockhammer, P. W. (2012). "Performing the Practice Turn in ArchaeologY:' Transcultural Studies 1: 7-42. Tite, M. S. (2008). "Ceramic Production, Provenance and Use-a Review~' Archaeometry 50(2): 216-231.

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Production, Ceramic Sequence and Vessel Function at Late Bronze Age Tell Sabi Abyad, Syria (PALMA 4) (Turnhout: Brepols), 559-564. Witmore, C. L. (2007). "Symmetrical Archaeology: Excerpts of a Manifesto:' World Archaeology 39(4): 546-562. Zedei\o, M. N. (2013). "Methodological and Analytical Challenges in Relational Archaeologies: A View from the Hunting Ground:' In: Watts, C. (ed), Relational Archaeologies. Humans, Animals, Things (London and New York: Routledge), 132-153.

CHAPTERlO

PROVENANCE STUDIES Productions and Compositional Groups

YONA WAKSMAN IN MEMORIAM MAURICE PICON

INITIAL DEFINITIONS AND PRINCIPLES "PROVENANCE studies" is the common expression used by archaeological scientists to designate analytical investigations, that aim at identifying the place of manufacture of archaeological artifacts, or the location of the raw materials sources used to manufacture them. Such investigations are not new as, according to Harbottle (1976), they were introduced by Fouque (1879), who studied ceramics found in Santorin petrographically in order to distinguish local artifacts from imports. They have been carried out by many researchers since (e.g. Catling et aL, 1963; Shepard, 1963; Perlman and Asaro, 1969; )ones, 1986; Peacock and Williams, 1986; Picon, 1993; Mannoni, 1994; Schneider, 2ooo; Speakman and Glascock, 2007; see also Tite, Chapter 2, this volume, for further history of research). In spite of its widespread use and general acceptance, the term "provenance studies" may be ambiguous, if not misleading (Hunt, 2012). Therefore, we would like to begin by defining our terminology before addressing some of the issues related to "provenance studies:'' This chapter mainly deals with ceramics considered representative for a given production, which is part of the output of a workshop or group of related workshops.' A production may include different types of wares and last for variable periods of time, but it always corresponds to similar clayey material or ceramic paste. The characteristics of the paste are those of the final product; they integrate both those of the raw materials and their potential changes due to processing by the potters, subsequent changes being considered independently. A single pottery workshop may manufacture several different productions corresponding, for instance, to different functional categories, such as table and cooking wares, the latter having technical constraints requiring a more careful selection of raw materials (Picon, 1995; Tite et aL, 2001). Conversely, it may be difficult to distinguish within an "area of uncertainty" the output of several workshops working in the same technical tradition, exploiting raw materials within the same geological formation presenting similar geochemical and mineralogical features, sometimes over long distances (Picon, 1993). The place of manufacture of an artifact is defined as its origin, and the location where it was recovered archaeologically as its provenance. Provenance studies, as defined here,

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designate the procedures and reasoning that aim at attributing archaeological ceramics to their origin, and by extension to a predefined production, based on petrographic or chemical analysis.' Provenance studies rely on the postulate that, within a given production, ceramics share similar features that differentiate them from ceramics belonging to other productions. Chemical and petrographic analyses of a representative sample for a production enable us to define it analytically as a compositional group, and to separate it from others, provided that they are not included in the same area of uncertainty. The comparison of the analytical features of ceramics of unknown origin with those of predefined productions enables us to test hypotheses of attribution, and to identify origins when these productions are localized. Localized productions stricto sensu correspond to workshops attested archaeologically, if not by their structures (e.g. pottery kilns), at least by evidence related to the production process, which often include reference samples of undoubted local origin (e.g. pottery wasters). 4 Whenever such evidence is absent, field prospecting, geological maps and reports, and textual documents concerning craftsmanship may give indications about possible locations of the raw materials' sources. In general, provenance studies require appropriate comparative data, usually organized in databases, in order to test hypotheses of origin based on archaeological criteria.

IMPLEMENTATION

Contexts of Use and Related Issues Study of a Site The most common case is one of an archaeological site where no pottery workshops were found, and where ceramics were initially classified according to typology and fabric-' Laboratories may be requested to test this field classification by defining productions according to analytical criteria, to determine which ceramic categories belong to the same production, and to evaluate the choice in raw materials. Whenever appropriate comparative data are available, issues concerning the local status of productions, the consumption of imported ceramics at the site, and its location within exchange and commercial networks can be addressed. These latter questions require reference groups stricto sensu to attribute ceramics to their origin, and more generally comparative compositional groups to attribute artifacts to predefined productions, and to determine whether the site is included in their respective area of diffusion. Compatibility with a local origin or, on the other hand, imported status might be inferred from local geological features illustrated on geological maps, especially when using petrographic analysis. However, local attribution usually requires either a thorough field survey of the area,6 to investigate available raw materials and their specificity (see, e.g., Gauss and Kiriatzi, zon), or evidence oflocal production, which brings us to the next point.

Study of a Workshop Whenever evidence of pottery production is found, the corresponding reference group(s) may be defined, and the following issues addressed: which ceramic categories

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and types belong to the local repertoire? to the same local production? choice of specific raw materials and reasons for this choice (technical? cultural? etc.), chronological evolution in raw materials procurement or processing, specialization of production, and so on. Reference groups may also enable the identification of local wares which are not attested archaeologically (e.g. wares pre- or post-dating the available evidence of production, see for example below, Fatimid wares in "A Case Study: The Medieval Productions of

Beirut"), provided that they correspond to similar choices in raw material procurement and processing. Investigations of the diffusion of pottery from a particular workshop require analysis of sherds from consumption sites and open another area of inquiry: which part of the production is exported? what is the area of diffusion of the workshop? is it concurrent with other workshops manufacturing similar wares? what is its part in the market, and how does it evolve? and so on.

Study of a Ceramic Type Another approach in provenance studies consists in investigating a specific ceramic type: was it manufactured in several workshops? can we distinguish the different productions? did some of the workshops dominate the market? what is their respective contribution to the procurement of a given site? are there geographical or chronological trends? was this type manufactured in specialized workshops, or in workshops manufacturing other types as well? was it diffused as byproduct of another ware? and so on. These different approaches in provenance studies are complementary but, in practice, are rarely addressed simultaneously. Most studies correspond to, or may be broken down into, one of these cases, which conditions the sampling strategy and the interpretation of data.

Sampling Sampling is an important part of the process in provenance studies, and determines, to a large extent, what may be expected from the results of analysis. The selection of samples for analysis is closely connected to the archaeological data (context and questions, see previous paragraph), the archaeometric data (especially availability of comparative analyses), and, obviously, the available material.' We detail below the initial steps of sample selection leading to the analytical definition of productions; further discussion about sampling for chemical analysis is also provided.

Defining Unlocalized Production When defining productions with unknown geographic locations, we are generally evaluating whether or not one or more ceramic types with similar fabric belong to a single production. 1be samples, which may come from different sites, should be selected from among the most common examples of the ceramic types. A frequent mistake is selecting atypical samples whose attribution on the basis of macroscopic criteria is difficult. In practice, the "core" of the production has to be defined before variants and marginals can be considered.

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FIGURE 10.1 Local reference samples, late Byzantine workshops, Thessaloniki, Greece. They include kiln furniture-tripod stilts, some still attached to ceramic bases (left), overfired wasters, unfinished biscuit-fired wasters (right).

Samples should also be selected among well-documented ceramics, in terms of archaeological context, drawing, and photographs. Sherds should have enough form and decoration to be representative of an identified typological category. Our ability to extrapolate the results obtained from a batch of samples to an entire ceramic production critically depends upon these factors.

Defining Localized Production When analyzing ceramics from a site where evidence of pottery production is available, it is essential to sample reference materials of undoubtedly local origin: pottery wasters rejected at various stages of the manufacturing process, such as unfinished or overtired wares; 8 kiln furniture made with the same material as pottery, such as saggars, tripod stilts, kiln bars (Figure 10.1).' Evidence of production may be difficult to discern in the archaeological record, especially in contexts that do not include structures related to pottery manufacture, such as kilns. In these cases, it is critical to carefully check the status of potential wasters, especially overfired sherds which may come from hearths or burned destruction layers and not from workshops. In order to complete the definition of a production, samples representative of the typological repertoire of finished products, whether shown by similar wasters to be local or still

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awaiting confirmation of their local status, should also be selected, using the same criteria as in the case of non-localized production. Common assumptions may sometimes be misleading, as shown by the examples of sherds found in the filling of a kiln representing a later depositional event and not corresponding to its output; and of imported ceramics present in workshop contexts, possibly coming from nearby warehouses. Additionally, finished products are not always present in workshop contexts in large quantities, requiring a second step in tbe sampling process. Pottery from consumption sites will be sampled both to study the diffusion of the production and to complement its definition. Consumption contexts may significantly contribute to our knowledge of its repertoire and dating, and to the building up of its typo-chronology (see the the section "A Case Study: The Medieval Productions of Beirut"). In instances where several productions were manufactured in the same workshop (different functional categories, evolution of clay procurement or processing in time, etc.), each production has to be defined independently..It is often necessary in these cases to supplement the initial sampling in order to obtain statistically significant compositional groups for each production. ' The number of samples required to define a production may vary according to the homogeneity of the raw materials, the degree of standardization of its processing, the coarseness of the fabric, and so on. An empirical rule of thumb for chemical analysis is to take a first sample of about zo individuals and then determine if further sampling is requested. An iterative procedure should be carried out as much as possible: initial sampling, analyses, examination of the results, and further sampling whenever necessary. The latter may be needed, for instance, when too many marginals were present in the initial sampling, or in the case of heterogeneous material or poorly standardized processing, or to strengthen less well-defined groups in case of multiple productions. Correlation between the initial criteria (typology, fabric) and members of compositional groups should guide supplementary sampling. 1be attribution of ceramics to predefined productions is less demanding in terms of number of samples, as we are comparing them to a well-defined group to which they will add (or not), However, we usually consider a group of sherds rather than a single example, as the latter might present chance similarities or dissimilarities.

Productions and Compositional Groups Classifications and Attributions Depending upon the type of analysis, the initial analytical results typically consist of tables of quantitative data (chemical analysis) or descriptions based on mostly qualitative data (petrographic analysis).w The next steps are generally carried out in two phases: classification and attribution. In the case of chemical analysis, the large number of variables requests the use of multivariate statistical tools such as cluster and discriminant analysis. In the classification phase, samples are clustered, according to analytical criteria, into groups considered homogeneous and distinct enough to correspond to different productions. The evaluation of the latter point is part of data interpretation, an important part of the work of archaeological scientists, as opposed to analysts. In the classification phase are determined: how many groups are present; what are their boundaries; should marginal

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samples be considered part of a group or excluded; and, mostly, are the similarities and differences observed significant in terms of production. This interpretation is based on a number of factors, discussed in some detail in the section "Classifying and Defining Productions, Using Chemical Analysis", most of which cannot be taken into account by statistical tools. Attribution supposes that the productions to which the samples under study potentially belong have been defmed previously using archaeometric analysis. The attribution phase involves comparison of analytical characteristics, between samples to be attributed and predefined productions. Both cluster and discriminant analysis may be used with quantitative data, although the latter is theoretically better suited to studies in which there is a choice among a finite number ofhypotheses. The combination of petrographic and chemical approaches may be useful, because these two approaches access different types of information (e.g. Day eta!. 1999; Schneider, zooo )." Petrographic data are more closely connected to fabrics and technological features on the one hand and to geological features on the other than chemical data. Petrographic data may indicate potential raw materials origin even when a priori hypotheses and reference groups are lacking. On the other hand, mineralogical associations and petrographic features may be too common to be indicative. Chemical analyses are usually more discriminating, and generate quantitative data which are better adapted to statistical analysis.

Classifying and Defining Productions, Using Chemical Analysis Chemical analysis is considered here as a mean to characterize ceramic productions by determining the bulk composition of ceramic pastes. Given that ceramic pastes are composite and heterogeneous by nature (see, e.g., Montana, Chapter 7, this volume), the sample taken from a sherd for analysis, and more precisely the volume analyzed, should be large enough to be representative of the material. In addition, because statistical analyses are generally used to compare the chemical data from the current investigation and previous chemical data stored in the laboratory database, it is essential that the analytical method used provides reproducible results. Homogenized samples (analyzed as powders, pellets, or beads) and stable experimental conditions are critical in this respect. A production is defined chemically by the distribution of elemental concentrations in ceramic pastes within a batch of representative samples. The assumption that distributions are normal, or log-normal, is often implicit in multivariate statistical treatments. This assumption is not always verified, especially for small batches of samples, or for productions corresponding to ellipsoidal rather than spherical distributions (see, e.g., "A Case Study: The Medieval Productions of Beirut")." A distribution is often summarized by its mean value (m) and standard deviation (o), which characterizes the dispersion of values around m. Variable dispersions may be observed within a single production, depending on the element, the mineralogical features of the components, the geological context from which they derive, and so on. For example, the CaO content in calcareous pastes may vary by more than 10% in absolute weight percent; Ti concentrations above 1% Ti0 2 in kaoliniterich pastes may be fairly variable too; in clayey materials related to ultrabasic contexts, concentrations of Cr and Ni may also vary widely from sample to sample within a range of high to very high values. For the same element, a large dispersion may be considered "normal" in one geochemical context and "abnormal" in another, in the latter case indicative for

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instance of more than one production or of a pollution. As a result, compositional groups may be defined at different levels of aggregation within the same hierarchical clustering analysis. Each chemical element, or group of related elements in Mendeleiev's periodic table, may have a different behavior and be affected differently by a variety of factors. As far as we know, there is no general rule for these behaviors. Instead, from raw materials to statistical treatment of the data, there are combinations of geochemical, technological, and analytical parameters which archaeological scientists have gradually come to recognize and integrate in their interpretative schema. Lines of interpretation include, but are not necessarily limited to, the following (see also Maggetti, 1982): geological features of the initial environment, whenever the latter is known, and generally speaking, the nature of the material as a geological material, which will condition its mineralogical and geochemical features • technological aspects: raw material processing (tempering, refining, mixing), shaping, decoration, firing, and so on. alterations due to the use of the object post-depositional alterations analytical precision and biases related to instrumental or analytical aspects biases introduced by statistical analysis last but not least, archaeological data. In our opinion, the latter should be taken into account while interpreting analytical data, which does not mean that the archaeological scientist is influenced by possible expectations about the results. Although a limited number of parameters may be formalized and integrated in statistical analysis (e.g. Beier and Mommsen, 1994), a large part is left for the archaeological scientists to determine connections between the patterns observed in the data and their possible causes. In our opinion, which follows Picon's, multivariate statistics should be considered as a guide to interpretation, and not a substitute for it. Statistical analyses are very useful for highlighting the structure of the data and provide convenient outputs for the graphical presentation of results, but it is always necessary to come back to the initial individual chemical compositions of the samples for interpretation.

A

CASE STUDY: THE MEDIEVAL PRODUCTIONS OF BEIRUT

Large-scale excavations were carried out in Beirut after the civil war, prior to the reconstruction of its city center. Remains of pottery workshops from the Roman and Crusader periods were unearthed (Fran~ois et al., 2003; Reynolds et al., 2oo8-2009), providing us with the opportunity to analytically define the corresponding productions. Research on medieval wares, carried out at the Laboratoire de ceramologie in Lyon, 13 are summarized below as an illustration of different aspects of provenance studies.

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Beirut red-paste wares

e wasters and kiln furniture ceramics from kiln contexts

···1ffi11 Beirut buff-paste wares FIGURE 10.2 Beirut medieval wares: main compositional groups as determined by hierarchical clustering analysis, and corresponding wares. Local productions, identified thanks to reference samples stricto sensu (black dots), complemented with sherds coming from pottery workshop contexts (gray dots), correspond to different compositional groups and sub-groups. Two very different clayey materials were used: low to moderately calcareous for red-paste cooking and table wares (part of the classification shown at the top and bottom left), and highly calcareous for table wares of a different technical tradition (bottom right) (after Waksman 2011).

Definition of Reference Groups The first step in provenance studies in workshop contexts is sample selection for the definition of local reference groups. Beirut workshop contexts provided local reference samples, chosen among pottery wasters (biscuit-fired unfinished wares, over-fired wares) and kiln furniture (kiln bars). Additional sampling of the medieval ceramic corpus was conducted to include representatives of most pottery types present in large quantities in these workshop contexts. The classification according to chemical compositions of the samples distinguished two main groups; one containing several loosely defined subgroups (Figure 10.2). Local reference samples are spread among all the different groups and subgroups, confirming the local status of the whole sampling considered, with some noticeable exceptions such as a Cypriotimport found in a workshop context (not included in the classification Figure 10.2). Two very different raw materials were used by the potters. One group is composed of low to moderately calcareous pastes, of variable chemical compositions but sharing a number of common features, such as low alkali and fairly high to high iron and titanium contents. In this specific case, compositions are too variable to be well represented by a single mean and standard deviation. The classification tends to split the samples in a large number of

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subgroups, but all these subgroups follow roughly two main geochemical behaviors, indi~ cated by inter~element correlations and associated with their calcium contents (Figure 10.3, low CaO and mid CaO groups). Mahalanobis distances, which are able to take such correlations into account, may be preferred to Euclidean distances in this case. The clayey materials corresponding to Beirut red-paste group (Figure 10.2) were used to manufacture glazed cooking wares, for the less calcareous ones, and slipped and glazed table wares presenting with various decoration techniques (plain glazed, reserved-slip, slip-painted, and sgraffito wares). The other main chemical group corresponds to a production of buff-paste table wares following a completely different technical tradition, which is based on the association of highly calcareous pastes (around 30% CaO) and alkali or lead-alkali glazes (making possible the turquoise color). This technical tradition is more specifically related to the Islamic world. The first part of the study enabled us to constitute reference groups, and suggests that the choice of raw materials corresponds either to technical criteria (use of low~calcareous clays for cooking wares and of high-calcareous clays to favor bonding of the alkali and lead-alkali glaze) or to cultural ones (symbolic value of turquoise). It also demonstrated that the traditional typological categories (plain glazed, reserved-slip, slip-painted, and sgraffito wares), usually considered separately in archaeological publications, are in fact part of the same production, which represents a significant change in perspective when studying commercial fluxes.

Diffusion of Beirut Wares and Complements of Definition Beirut red wares were already known archaeologically, and partially defined analytically, before the Beirut workshops were unearthed (Stern and Waksman, 2003; Waksman et al., zoo8). In these early studies,' 4 compositional groups corresponding to the, as yet unlocated, productions were defined using a sample from consumption contexts, and especially from Crusader Acre. They helped approaching the diffusion of Beirut wares, widespread in the Eastern Mediterranean and occasional in the Western Mediterranean and the Black Sea regions. Petrographic analysis carried out by Porat identified lower Cretaceous formations, extending through Lebanon, Israel, and jordan, as the likely source of the clayey material used to manufacture these productions (Waksman et al., 2oo8). The discovery of the workshops, and subsequent inclusion of Beirut reference samples into the compositional groups defined by the early studies, set their exact location to Beirut (Waksman, 2002). Consumption sites also provided valuable information about the Beirut productions: precise chronological data; variability of the typological repertoire; evidence on which types from the production were preferentially exported; quantities of Beirut wares found in consumption contexts, and thus the relative part that Beirut played in the sites' procurement; identification of other productions associated in the same trade networks; and so on. These "complements of definition" are, for instance, well illustrated by the contribution of Stern's studies of the pottery of Crusader Acre to our knowledge of Beirut wares (Stern and Waksman, 2003; Stern, 2012). Stern established their typochronology during the Crusader period, and, through quantification of pottery finds, pointed out their massive presence in the region. Contrary to still common prejudices, cooking wares constitute the part of Beirut productions which experienced the largest diffusion.

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FIGURE 10.3 Beirut medieval wares: binary plot iron-silicon (top) and histogram of Mahalanobis distances (bottom). The low-calcareous pastes show large variations in absolute concentrations values, but also strong inter-elements correlations, related to a same geochemical behavior and interpreted as a same production (top). Fatimid cooking wares coming from terrestrial contexts (in black) may be attributed to Beirut using discriminant analysis, as they fit the low-calcareous Beirut reference group (in gray), whereas the attribution of sample LEV548, coming from the Sen;e Limam shipwreck and altered by sea water, requests to come back to the initial chemical data (bottom).

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Attribution to Beirut of Other Types Pottery production also existed in Beirut at periods which lack the corresponding archaeological evidence, such as workshops and kilns. 1be reference groups defined for the Crusader productions may be used to identify other local products, provided that their manufacture involved similar raw materials and processing. For example, Beirut Fatimid wares, which just precede the Crusader ones, can be positively identified as locally manufactured in Beirut by their chemical similarity with the Crusader reference groups (Waksman, 2011). Figure 10.3 presents the histogram of Mahalanobis distances between a sampling of Fatimid cooking wares and the Crusader low-calcareous reference group. Cooking wares from terrestrial excavations are well integrated in the reference group on the histogram, unlike examples of similar typology coming from the Sen;e Limam shipwreck (Bass and van Dorninck, 1978), one of which (LEV548) is shown in Figure 10.3. On closer examination, the shipwreck samples can be attributed to Beirut as well, provided that the chemical alterations associated with marine environment are taken into account (Pradell et al., 1996; Waksman, 2011). This is an obvious example of why coming back to the unprocessed chemical data is criticaL The Sen;e Limam shipwreck, well dated thanks to glass stamps and coins, is an important chronological reference point for the Fatimid period. In the present case, it helped identify the Beirut Fatimid repertoire, including a type of sgraffito ware previously attributed to Egypt, Palestine, or North Africa (Jenkins, 1992; Mason, 2004). The results also suggested a Levantine origin for the main cargo of the shipwreck, consisting of glass cullets. Laboratory investigations of Beirut medieval productions provide a concrete example of the following aspects of ceramic provenance studies: definition oflocal productions (in this case, multiple productions) and establishment of chemical reference groups, based on the analysis of pottery wasters and kiln furniture together with finished products. It is notable that these productions could be defined before the discovery of the workshops, which established their location, and that petrographic analysis indicated potential areas of origin the diffusion study contributed to the typo-chronological definition of the productions and provided information about trade networks and fluxes " reference groups were also used to attribute to Beirut Fatimid wares whose local status was not attested archaeologically

CONCLUDING REMARKS Provenance studies of ceramics may appear a well~established res·earch area. However, instrumental developments, in portable equipment (e.g. portable X-ray fluorescence devices), and in large research infrastructures (synchrotron), have stimulated new field and laboratory practices. The latter may provide some interesting results (e.g. Molera et al., 2013), but also urge us to remember fundamental constructs, such as the complex nature of

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ceramic material and the range of parameters involved in the interpretation of analytical results, sampling procedures, and archaeological issues. Engagement with the latter is fruitful in provenance studies of ceramics owing to the need to build up the corpus of geochemical and petrographic data adapted to specific archaeological questions. Furthermore, unlike other materials, we cannot only reason in terms oflocalization of raw materials. The ubiquity of clays, their processing by potters, and the composite nature of ceramic pastes imply that we should rather think in terms of the final output; that is, the productions, defined by both their archaeological and archaeometric features. The development of provenance and technological studies of ceramics has generated large chemical and petrographic databases in different laboratories. An important issue currently facing the discipline concerns the status of archaeometric data and good practices for its sensible use, depending on the level of archaeological information recorded in archaeometry databases. This issue involves both the safeguarding of"historical" databases and the interconnection of ceramics databases containing complementary information. 15 The building up of such networks, using IT and statistical tools of complex data modeling, sharing, and handling,' 6 may open new perspectives in the field.

NOTES 1.

2.

3. 4· s. 6.

J.

8. 9. 10.

n. 12.

13.

An extended version may be found in Waksman (2014). The term "workshop" does not suppose here a specific level of organization of the production unit (Peacock, 1982). The concept of"production;' however, implies a certain degree of standardization in raw material selection and processing. We use here "chemical" analysis in the sense of"elemental" analysis. Compositional groups including reference samples become reference groups. i.e. the features of the paste as observed with the naked eye, using a hand lens, or under the binocular microscope; see, for example, Tomber and Dore (1998). In most cases clay materials are expected to come from the close surroundings of a production site (Arnold, 1985), although some rare examples of clay transport over long distances are known (Ballet and Picon, 1987). In practice, it often comes as a limitation when trying to define productions using material from a single site. Overfired wasters are more likely to be chemically altered during burial (Picon, 1987), so that other reference samples should be preferred whenever possible. Fragments of kiln walls were shown to be inadequate in the cases we examined, as different raw materials had to be selected for them. Quantitative approaches to petrographic data are seldom used (Whitbread, 1991). Other analytical methods, such as heavy mineral analysis and X-ray diffraction, may be useful as welL In ann-dimension hyperspace, n being the number of elements analyzed. Analysis is carried out by wavelength-dispersive X-ray fluorescence. TwentyMfour elements are determined, seventeen of which, including major and minor elements (MgO, Al 2 0y SiO:P K2 0, CaO, Ti0 2 , MnO, Fe2 0 3 ) and trace elements having various geochemical behavior (V, Cr, Ni, Zn, Rb, Sr, Zr, Ba, Ce), are used on a routine basis in clustering and discriminant analyses. Classifications are carried out by hierarchical clustering analysis on standardized data, using Euclidean distances and average linkage.

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14. A first report appeared in 1999: Waksman, S. Y., Segal, !., Porat, N., Stern, E. )., and Yellin,). (1999). ''An Analytical Study of Ceramics Found in Crusader Acre: Levantine Productions and Imports from the Byzantine World" (Jerusalem, Geological Survey of Israel Internal Reports GSI/8/99 ). 15. See a selection of online resources in References. 16. Ongoing doctoral research is carried out on this subject by A. bztiirk at the University of Lyon.

REFERENCES Arnold, D. E. (1985). Ceramic Theory and Cultural Process (Cambridge: Cambridge University Press). Ballet, P. and Picon, M. (1987). «Recherches preliminaires sur les origines de Ia ceramique des Kellia (Egypte). Importations et productions egyptienneS:' Cahiers de Ia ceramique egypti-

enne 1: 17-48. Bass, G. F. and van Doorninck, F. H. (1978). ''An nth Century Shipwreck at Ser~e Liman, TurkeY:' International Journal of Nautical Archaeology 7: 119-132. Beier, Th. and Mommsen, H. (1994). "Modified Mahalanobis Filters for Grouping Pottery by Chemical Composition:' Archaeometry36(2): 287-306. Calling, H. W., Richards, E. E., and Blin-Stoyle, A. E. (1963). "Correlations between Composition and Provenance of Mycenaean and Minoan PotterY:' Annual of the British School at Athens 58:94-115. Day, P.M., Kiriatzi, E., Tsolakidou, A., and Kilikoglou, V. (1999). "Group Therapy in Crete: A Comparison between Analyses by NAA and Thin Section Petrography of Early Minoan Pottery:' Journal ofArchaeological Science 26: 1025-1036. Fouque, F. (1879 ). Santorin et ses eruptions (Paris: Masson). Fran~ois, V., Nicolaides, A., Vallauri, L., and Waksman, Y. (2003). "Premiers elements pour

une caracterisation des productions de Beyrouth entre domination franque et mamelouke:' In: Actes du VIle Congres International sur la Ciramique Midil~vale en Miditerranie (Athens: Caisse des Recettes Archeologiques), 325-340. Gauss, G. and Kiriatzi, E. (2011). Pottery Production and Supply at Bronze Age Kolonna,

Aegina: An Integrated Archaeological and Scientific Study of a Ceramic Landscape (Vienna: Verlag der Osterreichischen Akademie der Wissenschaften). Harbottle, G. (1976). 'i\ctivation Analysis in Archaeology." Radiochemistrn: 33-72. Hunt, A. (2012). "On the Origin of Ceramics: Moving towards a Common Understanding of 'Provenance':' Archaeological Review from Cambridge 27(1): 85-97. jenkins, M. (1992). "Early Medieval Islamic Pottery: The Eleventh Century Reconsidered:' Muqarnas 9: 56-66. jones, R. E. (1986). Greek and Cypriot Pottery. A Review of Scientific Studies. Fitch Laboratory Occasional Papers, 1 (Athens: British School at Athens). Maggetti, M. (1982). "Phase Analysis and Its Significance for Technology and Origin:' In: Archaeological Ceramics (Washington D.C.: Smithsonian Institution), 121-133. Mannoni, T. (1994). 25 Anni di archeologia globale, vol. 5: Archaeometria geoarcheologia dei manufatti (Genoa: Escum). Mason, R. B. (2004). Shine Like the Sun: Lustre-Painted and Associated Pottery from the Medieval Middle East (Costa Mesa, CA: Mazda Publishers, and Toronto: Royal Ontario Museum).

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Peacock, D. P. S. (1982). Pottery in the Roman World: An Etlmoarchaeologica/ Approach (London: Longman). Peacock, D.P. S. and Williams, D. F. (1986).Amphoraeand the Roman Economy. An Introductory Guide (London: Longman). Perlman, I. and Asaro, F. (1969). "Pottery Analysis By Neutron Activation Analysis:'

Archaeometry n: 21-52. Picon, M. (1987). "La fixation du baryum et du strontium par les ceramiques:' Revue

d'Archiomitrie n: 41-48. Picon, M. (1993). "!:analyse chimique des ceramiques: bilan et perspectives:' In: Archeometria

della Ceramica. Problemi di Metoda, Atti 8° Simposio Internazionale della Ceramica (Bologna: Int. Centro Ceramico ), 3-26. Picon, M. (1995). "Grises et grises: quelques retlexions sur les ceramiques cuites en mode B." In: Aetas das ws fornadas de Ceramica Medieval e Pas-Medieval (Porto, Maio: Camara Municipal de Tondela), 283-292. Pradell, T., Vendrell-Saz, M., Krumbein, W.-E., and Picon, M. (1996). "Alterations de ceramiques en milieu marin: les amphores de repave romaine de la Madrague de Giens (Var):' Revue d'Archeometrie 20:47-56. Reynolds, P., Waksman, S. Y., Lemaltre, S., Curvers, H., Roumie, M., and Nsouli, B. (20082009). 'An Early Imperial Roman Pottery Production Site in Beirut (BEY 015): Chemical Analyses and a Ceramic Typology:' Berytus 51-52:71-115. Schneider, G. (2ooo). "Chemical and Mineralogical Studies of Late Hellenistic to Byzantine Pottery Production in the Eastern Mediterranean:' In: RCRF Acta 36 (Abingdon), 525-536. Shepard, A. 0. (1963). Ceramics for theArchaeologist(Washington D.C.: Carnegie Institution). Speakman, R. j. and Glascock, M.D. (eds).Archaeometry 49(2). Stern, E. j. (2012). 'Akko I, The 1991-1998 Excavations. The Crusader-Period Pottery. 2 vols.IAA Reports 51 (Jerusalem: Israel Antiquities Authorities). Stern, E. j. and Waksman, S. Y. (2003). "Pottery from Recent Excavations in Crusader Acre: Typological and Analytical Study:' In: Actes du VIle Congres International sur Ia Ceramique Medievale en Mediterranee (Athens: Caisse des Recettes Archeologiques), 167-18o. Tite, M. S., Kilikoglou, V., and Vekinis, G. (2001). "Review Article: Strength, Toughness and Thermal Shock Resistance of Ancient Ceramics, and Their Influence on Technological Choice:' Archaeometry 43(3): 301-324. Tomber, R. and Dore, j. (1998). The National Reference Roman Fabric Reference Collection. A Handbook (London: Museum of London Archaeological Service). Waksman, S. Y. (2002). "Ceramiques levantines de l'epoque des Croisades: le cas des productions apate rouge des ateliers de Beyrouth:' Revue d'Archeometrie 26: 67-77. Waksman, S. Y. (2011). "Ceramics of the 'Sen;e Limam type' and Fatimid pottery production in Beirut:' Levant 43(2): 201-212. Waksman, S. Y. (2014). "Etude de provenances de ceramiques:' In: Circulation des matiriaux et des objets dans les sociitis anciennes (Paris: Archives Contemporaines), 195-215. Waksman, S. Y., Stern, E. j., Segal,!., Porat,N., and Yellin, j. (2oo8). "Some Local and Imported Ceramics from Crusader Acre Investigated by Elemental and Petrographic Analysis:' 'Atiqot 59:157-190.

Whitbread, I. K. (1991). "Image and Data Processing in Ceramic Petrology:' In: Recent Developments in Ceramic Petrology. British Museum Occasional Papers, 81 (London: British Museum),369-391.

CHAPTER 11

MINERALOGICAL AND CHEMICAL ALTERATION GERWULF SCHNEIDER

INTRODUCTION PoTTERY is a very stable material compared to wood, metal, and glass. In consequence, sherds of archaeological ceramics have survived for up to 10,ooo years while buried in the ground. This, in addition to its occurrence on nearly every archaeological site, is one of the reasons why pottery is important as a carrier of information about ancient cultures. Many ancient cultures are even named after their typical pottery type. On the other hand, archaeological sherds buried in the ground are part of the surrounding soil and will behave accordingly. The study of ancient pottery in the archaeo~ceramologicallaboratory is aimed at reconstructing the technology used in its manufacture and determining the date and place of its manufacture. The interpretation of analyses is based on the assumption that the potsherds have not been altered during deposition in the ground. That this possibility exists, however, was already mentioned by Sayre et al. (1957) when they used neutron activation analysis (INAA) to determine the provenance of archaeological potsherds from the Mediterranean region. The many analyses of archaeological ceramics done thereafter using NAA, optical emission spectrometry (OES), AAS (atomic absorption spectroscopy) and WD-XRF (wavelength dispersive X-ray fluorescence), and later also inductively coupled plasma emission or mass spectrometry (ICP-OES and ICP-MS), yielded a large body of evidence relating to possible post-depositional chemical and mineralogical changes in ceramic materials. Nearly everybody working on analysis of ancient ceramics has at least once been faced with the problem of alteration, and there are many published papers on this issue, which has also been discussed at various archaeometric meetings. Suggestions for further reading may be found in the articles referred to herein. Three approaches have been used to study the possible alteration of ceramic material during deposition in its burial environment (Schwed! et a!., 2004). The most common approach is that of comparative studies. Products made by a single workshop within a fixed period should have the same composition given that material changes due to technical reasons can be excluded,

"I i'v!INERALOGICAL AND CHEMICAL ALTERATION

163

such as, for example, changing the recipe for pottery designed to serve a special purpose. The differing chemical composition of sherds buried in different environments can, thus, be interpreted in terms of chemical alteration (Freeth, 1967). A special case is presented when material from an excavated kiln can be analyzed (Buxeda i Garrig6s et al., 2001). The advantage of this approach is that the effects of the depositional environment on many sherds of differing ceramic quality are considered. As another approach, profile studies can be employed in order to avoid the assumption that the examined sherds originally had the same composition. In this approach, different layers of a large sherd cut parallel to its surface are analyzed. Because the surface of the sherd is most vulnerable to environmental influences, it will show a different composition to that of the sherd's core (e.g. Picon, 1976; Thierrin-Michael, 1992, Schwedt eta!., 2004). The third approach is the experimental simulation of burial conditions to study possible changes (e.g. Segebade and Lutz, 1976, 1980; Franldin and Vitali, 1985; Bearat eta!., 1992). However, the interpretation of the results here is limited by the question of whether short-term experiments on a few selected samples can really be compared with the post-depositional alteration of sherds varying in composition and ceramic quality and buried in very different depositional environments for thousands of years. Thus, experiments can only highlight some possible tendencies. It is very difficult to define general rules on how post-depositional alteration can be recognized and how severe its effects on a ceramic object can be. This is due to the large chemical and structural variability of ceramics and of the post-depositional environments encountered in different climates (e.g. humidity, temperature, pH, and redox conditions). Therefore, any generalization of results is limited. The original clay composition, preparation of the body, forming, and firing have a big influence on the size and number of dosed and open pores within the ceramic body, and thus on the accessibility for soil solutions. Non -calcareous and calcareous ceramics behave very differently. The application of a slip or a glaze, as well as many other factors, must also be taken into consideration. Another aspect is the part played by the degree of vitrification of the sherd. A lot also depends on body composition and on temperature, atmosphere, and time of firing. Furthermore, post-depositional chemical changes are very much bound to the corrosion of glass as discussed, for example, by Freestone (2001). Products with the same composition and made at the same pottery workshop can differ significantly depending on frring in their resilience to weathering, because of the varying amount of glass in the sherds. When comparing results from different studies, another factor which must also be considered is how the samples were taken and prepared for analysis. It is common practice to remove a surface layer before drilling, or before powdering a fragment in a mill, for chemical analysis. In these instances, the issue of whether the post-depositional alteration effects on the chemical data are significant or negligible depends on the thickness of the removed surface layer. This may explain some contradictory experiences. In our laboratory we clean fragments before analysis by removing all surface layers of about 1 mm or more> if possible. Maybe therefore, among our 30,ooo or so chemical analyses of archaeo~ logical ceramics by WD-XRF only a minority are seriously affected by post-depositional alteration effects. Non -destructive chemical analysis of the surfaces or old breaks of a sherd using a portable energy-dispersive XRF-analyzer will, however, be far more greatly affected by such alteration.

164

GERWUI..F SCHNEIDER -----~~----

MINERALOGICAL ALTERATION

Rehydration and Rehydroxylation During firing, clay loses water in several stages. Below soo'C mainly physically adsorbed water is lost (dehydration). Between about soo'C and 90o'C the clay minerals more or less lose their structural water (dehydroxylation) forming new badly crystallized or amorphous phases. During burial and exposure to environmental humidity these mineral and amorphous phases can take up water again (Grim and Bradley, 1948). This results in an expansion and in an increase in weight of the ceramic. Incompletely destroyed clay minerals will be rehydrated and rehydroxylated in a humid surrounding. If the newly formed crystals are large enough, reflexes of clay minerals appear again in X-ray diffraction diagrams and may then be detected in pottery fired between soo'C and woo'C. The most important implication of rehydration and rehydroxylation is that the abundance of clay minerals in ceramics does not exclude high firing temperatures. It must be mentioned, however, that the basal peak of the clay mineral illite may be seen in diffractograms of pottery fired to about woo'C. In non-calcareous high-fired illitic clays, illite thus may appear together with mullite (Maggetti, 1982). An example of rehydration in low-fired non-calcareous Neolithic sherds from Switzerland was given by Maggetti (1982). The X-ray diffractograms frequently showed a large peak indieating the presence of very fine-grained clay particles of a mixed layer type that disappeared after re-firing above 30o'C, which was well below the original firing temperatures. The disappearance, therefore, is an indication that these minerals were formed during burial. Rehydroxylation of clay minerals caused by environmental humidity was observed long ago (Grim and Bradley, 1948; Hill, 1953; Kingery, 1974: Hamilton and Hall, 2012). This uptake of water is very slow. It was, therefore, proposed that determining the quantity of water required for rehydroxylation be used as a means of dating fired ceramics (Zaun, 1982; Wilson et al., 2009). The problem is that even sherds made from the same clay behave differently depending on their original firing temperature and on environmental conditions. This may be partly overcome when each sample is refired at soo'C or 6so'C (Bowen et al., 2011) to determine its original water content, and then the experimental gain of mass in a humid environment is detected for every individual sample (individual kinetic constant). The age of this sample can then be determined through extrapolation. There are many assumptions: the temperature of re-firing must be sufficient for a total dehydration and dehydroxylation without decomposing eventual carbonates; eventual contributions to the loss of weight by oxidation of carbon or organic contents must be excluded; the influence of the environmental temperature and of other possibly varying burial conditions over a long time span must be corrected. It is, therefore, still an open question as to how reliable such data are and how much they depend on the assumptions made.

Formation of Gehlenite and Calcite Mineralogical changes occur in calcareous pottery fired above about 8so'C. Calcium from the decay of calcite reacts with the new phases after decomposition of the clay

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minerals to calcium silicates and calcium-aluminum silicates. In experiments, gehlenite, diopside, wollastonite, and anorthite are then observed as new phases by X-ray diffraction. The gehlenite problem, however, was that this mineral was not found in the Roman pottery which was supposed to have been made from the clay used in the experiments and fired at similar temperatures. This was explained by the breakdown of gehlenite as a metastable mineral to calcite during burial in humid climates (Maggetti, 1981). The decomposition of gehlenite to calcite was confirmed in experiments by Heimann and Maggetti (1981). In thin sections of medium-fired calcareous pottery (between about 85o'C and 95o'C) where all primary calcite is decomposed secondary calcite derived from gehlenite appears finely distributed within the matrix (Plate 2a). It explains the presence of calcite in calcareous pottery fired above 85o'C. At lower firing temperatures, between 6oo°C and 8oo°C, secondary calcite is formed by recarbonatization of calcium oxides and hydroxides after the decomposition of primary calcite. In thin sections it can mostly be distinguished from primary calcite which survives in very low-fired pottery (below about 7oo'C depending on grain sizes and time). In high-fired calcareous pottery (above c.10oo'C) in thin sections only precipitated calcite appears in open pores of a vitrified matrix. X-ray diffraction will detect calcite in all these sherds but only primary calcite proves a low firing temperature below 7oo'C or 750'C, depending on firing atmosphere and time.

Formation of Zeolites In experiments, zeolites are formed together with rehydroxylation (Hill, 1953) or with the breakdown of gehlenite (Heimann and Maggetti, 1981). The formation of small amounts of zeolites is common in altered sherds of high-fired calcareous pottery (e.g. Picon, 1991). This process has also been observed in experiments (Heimann and Maggetti, 1981). Analcime (or wairakite) derives from the decomposition of gehlenite and from the alteration of the glassy phase. This has been shown by X-ray diffraction of samples from sites in Switzerl possible post-depositional alterations must be taken into account Rehydration and rehydroxylation only change the water content However, of the elements determined by WDXRF or NAA, it seems that significant absorption effects exist for a series of chemical elements, such as Ca, Sr, P, Ba, Fe, Mn, Na (and Cs), including possible post-depositional contamination by Cu, Zn, and Pb, Many of these effects depend on the high cation exchange capacity of ceramics, which may be of the same order as it is in clay (Hedges and McLellan, 1976). To remove possible contamination by soluble salts, the fragments to be prepared for analysis should be washed with distilled water in an ultrasonic device. Some of the mineralogical alterations change the bulk chemical composition of a sherd. This is the case, for example, when calcite is precipitated within the sherd or if zeolites are formed in high-fired calcareous pottery. Other post-depositional changes, such as, for example, recarbonatization, do not change the elemental chemical composition which is used to determine the provenance of sherds. The post-depositional alteration effects differ for non-calcareous and calcareous pottery and depend very much on firing temperatures. Therefore, the effects of absorption, as well as those ofleaching, in overfired calcareous pottery may be very different from those in the lower-fired parts of the same sherd (Picon, 1991),

Water Rehydration and rehydroxylation result in a gain of weight because of the absorbed water. This may be easily determined as loss on ignition, for example, at 950° C. However, this is only a measure for the water content if there is no organic matter, no sulfur, and no carbonates in the ceramic matrix. In chemical analyses, the water content acts as a dilution agent and can be treated as such. 1 For varying water contents, chemical data can easily be accounted for by comparing analyses on a water-free (ignited) basis, as is done in many laboratories,

Calcium The formation of calcium silicates and calcium-aluminum silicates, such as gehlenite, and recarbonatization does not change the initial calcium content. An example of homogeneously distributed secondary calcite from recarbonatization after gehlenite in

II I!

I

i

I

I

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a calcareous sherd of Arretine sigillata is shown in Plate 2a. The calcite within another calcareous sherd of Eastern sigillata A (Plate 2b) very probably also originates from recarbonatization. During burial it was leached at the surface where environmental acid solutions had access as for example on the upper right hand site where the protective gloss is missing. The secondary calcite does not change the original calcium content of the samples (if not leached). On the other hand, calcite or gypsum crystallized within cracks and open pores of a sherd derived from precipitation by invading calcium bicarbonate-containing solutions will change the composition significantly. In Plate 2c of a high-fired sherd of non -calcareous North- Mesopotamian metallic ware the precipitated calcite appears as a fine scale in the matrix and in open pores. 'Ihe precipitation here caused an increase to about 6 wt.% CaO in. the core of this non-calcareous sherd which previously had less than 1 wt.% CaO detected from comparison to sherds of the same compositional group without secondary calcite. A special case of post-depositional alterations is illustrated by a sherd of Tripolitanian sigillata shown in Plate zd. Here a thin scaly layer between body and gloss makes the sherd macroscopically appear to have a white engobe below the red gloss. For chemical analysis this layer, however, would be removed. All four examples of calcite are connected with medium- to high-fired sherds (c.8oo-rooo'C). The presence of calcite in diffractograms therefore cannot be attributed to low firing temperatures. Gypsum in ceramics may be recognized by analyzing sulfur. In thin sections, the possible original gypsum content of the clay can be distinguished from secondary infiltrated gypsum by the "swallow-tailed" pores left by the original gypsum crystals. After firing, these characteristic pores are filled with very fine-grained secondary gypsum. Gypsum derived from precipitation will fill cracks and open pores with irregular shapes. In studies of Mesopotamian pottery these effects play an important role and certainly must also be taken into account in studies of pottery from other areas with similar environments. Besides the increase of calcium by infiltrated calcite or gypsum, the values of strontium and its relation to calcium may also be changed dramatically. Analyzing profiles of four sherds using an electron microprobe, Freestone et al. (1985) found an enrichment of calcium in the outer layers which was not connected to precipitation of calcite. This could be excluded because only the fine matrix was analyzed and thin sections were studied. Thus, the U -shaped profiles as found for calcium, phosphorus, and iron are clear indications of absorption within the matrix.

Phosphorus Another very common effect of contamination is the absorption of phosphorus. In archaeological sherds, P,0 5 concentration is nearly always higher than in the clay from which the sherds have been made. Phosphorus contents above about 0.5 wt.% P ,0 5 generally indicate altered sherds, even if macroscopically they look intact. The fixation of phosphorus certainly represents the largest of the alteration effects. Phosphorus originates from the soil in which the sherds are buried. It can be particularly high in pottery in humid climates and in acid soils containing bones and organic waste, as is the case with many archaeological finds. In some cases, for example in weathered sherds of Roman Terra Sigillata, phosphorus can rise up to more than 10 wt.% P ,0 5 in the bulk analysis

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of the body, and it would be even higher in the surface layers normally removed before analysis. In rare instances some of the phosphorus may also derive from former organic contents in the vessels (Duma, 1972; Dunnell and Hunt, 1990; Bearat and Dufournier, 1994). Phosphorus from temper containing crushed bones can easily be detected in thin sections, and it normally yields much higher contents of P,0 5 which then are correlated to calcium contents. As phosphorus is not determined by NAA, this effect is only observed when other techniques, such as WD-XRF, are used for chemical analysis (Schneider, 1978; Rottlander, 1981-1983; Lemoine and Picon, 1982; Freestone et al., 1985; Picon, 1987; Walter and Besnus, 1989). The absorbed phosphorus is homogeneously distributed within the sherds and is not correlated to calcium or iron. Discrete grains or crystalline phosphate phases are not detected. Phosphorus, thus, must be bound to amorphous and organic phases (Collomb and Maggetti, 1996). Calcareous pottery seems to be more involved and the alteration is certainly connected to the ceramic quality of the sherds, particularly to their porosity and to their level of vitrification. The phosphorus absorption as a rule is connected with other chemical alterations and thus can be used as a marker for alteration. Elevated phosphorus in most instances is correlated with higher ignition losses (rehydroxylation), with higher barium contents, and, sometimes, with leaching of other elements.

Example: Roman Pottery at Different Sites Finds of Roman sigillata produced at three production centers: Arezzo, Lyon, and La Graufesenque, found in Velsen and Nijmegen in the Netherlands, were examined in terms of alteration. The samples represent medium- to high-fired calcareous pottery (c. 8oo-1,ooo"C), the three production centers represent sigillata of different quality and the different find spots represent different burial conditions. For each site the element concentrations for each of the three centers are averaged in spite of their large variation and are compared to the values of the respective reference groups. Arezzo is represented by forty-seven finds in Arezzo; for Lyon and for La Graufesenque data from Schneider (1978) have been used. In Table 11.1 the values are shown for loss on ignition (l.o.i.) and for the chemical elements associated with alteration effects. Compared to the reference groups the absorption of water (l.o.i.), phosphorus, strontium, and barium of the finds in Velsen may be regarded as negligible, but in the samples found in Nijmegen the increases are obvious. The effects are least pronounced in sigillata from La Graufesenque, known for its high quality. Analyses of pottery from the Roman legionary camp of Dangstetten (Schneider and Daszkiewicz, zoo6) offer a similar example. Nearly all samples from this site showed elevated phosphorus contents. The effects on products from Lyon and from Arezzo again differ significantly. In sherds of sigillata from Lyon the average phosphorus content was 3-9 wt.% P,0 5 (n ~ 19) and all samples had more than 1.3 wt.% P,0 5. In sherds ofsigillata from Arezzo the average was 1.3 wt.% P,0 5 (n ~ 148). Here 121 of 148 samples (82%) had more than 0.5 wt.% P,0 5. This may be compared to analyses of sherds of Arretine sigillata found in Arezzo where only six of 96 samples (6%) had more than 0.5 wt.% P,0 5• The elevated phosphorus contents noted at Dangstetten, Nijmegen, and Velsen, as well as in Arezzo,

r '

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Table 11.1 Chemical alteration of Roman sigillata from Arezzo, Lyon, and La Graufesenque found at Velsen and Nijmegen in the Netherlands. The values for absorption are as analyzed. For leaching, the analyses results have been normalized without phosphorus to a constant sum of 100% Production site

find spot

l.o.i(wt%)

P20 5 (wt

------>

jLevel 3 j

I level 4

Interpretative

Interpretative

~

j

Fractality/Homology

tools

(Extrinsic parameters)

{e.g. form-based

analysis)

fN;~=~cti_ve

I

Q"''"'""

{e.g. geometric, topological)

II

Quantitative

Intuitive/Objective

(e.g. metricalmathematical)

Theorie:al/Practica I

Variability symmetry/Shape/Size lsomorphism/Skeuomorphism

Teclmological Approach (multidimensional)

.......

Paradigmatic/Taxonomic

Agency

I

Chrono-cultural Approach

---Fossil Index Seriation

Ceramic Homology

Polythetic/Monothetic

Habitus Hydridization

Class Type Variety

Etc:.

Functionalist Approach

---Symbolic Approach

Product Specialization

-------Identity

Style

Summary of the different levels to approach pottery form and typological analyses diScussed in the text. It includes the main concepts and tools in each level. FIGURE 12.1

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grouping (\Vhittaker et al., 1998; Read, 2007), frequently considering the application of such methodology as the aim of the study (Dunnell, 1986; Read, 1989). This was the case for more systematized form analyses (e.g. form-based analysis) and their combination with mathematical and statistical protocols (e.g. discriminant analysis, principal component analysis, cluster analysis, curve analysis; Sheppard, 1971; Whallon and Brown, 1982; Read, 1989, 2007; Hendrix et al., 1996; Gilboa et al., 2004), which gave rise to the so-called electronic paradigm (Adams and Adams, 1991). Nevertheless, there has always been a minor interest in moving from the application of the different methods used to describe and classify pottery to the interpretative meaning of the typologies proposed (Sheppard, 1971; Read, 1989). Due to their growing marginalization, pottery typological and form studies are currently suffering in favor of archaeometric analyses, a revision and revalorization of the role played by the former is needed in order to restore them as potentially relevant tools to approach both technology and people in past societies. Furthermore, morphological analysis is considered to facilitate the generation of multidimensional and holistic interpretations of materiality. Consequently, it is assumed that vessel form is related to certain phenomena which are not evident in the technological studies that focus on vessel fabrics and forming. This chapter introduces a summarized revision of some of the theoretical-methodological aspects key to typology so as to comprehensively understand the main interpretative proposals which use this research tool, evaluating their particular aims, proceedings, and concepts. Finally, a revision of the use of pottery form analysis is proposed, as well as its incorporation into the theoretical and interpretative framework that is provided by the social theory of technology to elaborate explanations for the active role of vessel form and to develop typologies which include a new explanatory dimension.

FORM DESCRIPTION AND CLASSIFICATION STRATEGIES

Most of the classification efforts in the last decades have been devoted to the definition of strategies aimed at delving into the problems postulated by the first two analytical levels. A comprehensive revision of such research is far from the possibilities and aims of this chapter; instead, a short and general outline of the most important trends currently in use is provided. The first strategies for the study and description of pottery form and decoration were characterized by their limited, systematized, highly intuitive, eclectic, and subjective nature, supported by aesthetic assessments coming from the personal experience or perspective of the analysts. As a result, imprecise terminology usually based on morphofunctional criteria was used (Hendrix et al., 1996). Since the 1950s, however, these guidelines have been complemented by other methodological strategies-such as the form-based analysis (e.g. Sheppard, 1971; Ericson and Stickel, 1973; Hendrix et al., 1996), which was aimed at bringing greater objectivity to the description of pottery following a strict and systematized analysis of the form on the basis of geometrical models. Since then, morphometric quantitative analyses have been incorporated into morphological studies, significantly increasing the number of

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attributes recorded in a pottery piece, as well as defining its form through the use of ratios, indexes, and mathematical models. Regarding the second level, the focus has been centered on defining typological classifications for pottery. Classifications in archaeology usually tend to organize the record into categories which share some internal coherence, depending on the similarities and differences present in the artifacts' attributes. On the one hand, it implies the definition of categories and, on the other, the assignation of the individual pieces to such categories (Sheppard, 1971; Rice, 1987; Read, 1989). In pragmatic terms, both descriptions and classifications of pottery have to be systematic and coherent in order to promote the use of a standardized terminology and a typology devoid of subjective interpretations, so as to favor understanding amongst researchers (Whittaker et aL, 1998). At this second level, typological classifications have originated either from proposals based on the intuitive researchers' perceptions of the differences and similarities existing between ceramics (e.g. Krieger, 1944; Gifford, 1960; Rouse, 1960), or alternatively, on allegedly more objective methodologies which used mathematical and statistical tools for grouping. They are intended to inductively create replicated descriptions and classifications of the vessels which can simultaneously compare a broader number of attributes with better definition of both the data and the variables being analyzed. This kind of tool creates groups with a strong internal coherence and provides a less arbitrary boundary between categories (Whallon and Brown, 1982; Read, 2007). However, these grouping strategies are not devoid of problems, since the analysis frequently incorporates variables or attributes of the vessels which are not relevant for archaeological questions. Nevertheless, some authors such as Read (1989, 2007) considered that intuitive classifications could be even more informative and useful than some of the more objective ones. Typological groupings may also vary depending on the way the attributes are considered: they can either be paradigmatic (Whallon, 1972) or taxonomic (Read, 1989, 2007 ). In the former, the most frequent in multivariant statistical analyses, no hierarchy is postulated for the variables used in the classification, so all the attributes recorded for a vessel can be treated both simultaneously and independently. In the latter, the several attributes of a vessel are considered to have a different validity for determining pottery types; thus they have to be used in a sequential and hierarchical order according to many different criteria. Furthermore, pottery classifications migbt also depend on different ontologies. In this sense, a heated debate has been generated about the ernie or etic nature of the typologies archaeologists create. Hence, it is possible to discriminate between theoretical (e.g. Krieger, 1944; Spaulding, 1953; Gifford, 1960; Rouse, 1960) and practical typologies (e.g. Hill and Evans, 1972; Adams, 1988; Adams and Adams, 1991; Kampe! and Sablatnig, 2007). The former can be encompassed as ernie classifications, closely related to so-called folk classifications or ethnotaxonomies (Kempton, 1981; Rice, 1987; Fowler, 2006), where both potters and other members of their community (i.e. consumers and non-consumers) are assumed to base their classifica~ lions on tangible aspects related to certain physical parameters of the materials (e.g. appearance, form, and size) as well as on intangible or cultural phenomena. In this context, many scholars understand the pottery classification process as proceeding from an inductive or theoretical nature which allows the discovery and/or replication of the natural types present in the artisan's mind; a classification which underlies the data recorded. In this sense, the ceramic types defined are considered to carry an important cultural and historical meaning, and, consequently, to mirror the ideas and values of the people who made and used the artifacts.

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As a counterpart to ernie typologies, the classifications drawn by analysts from etic perspectives, also referred to as devised classifications, have dominated research since the 196os, coinciding with the boom of processualist and positivist views in the typological study of archaeological pottery. Although these perspectives consider that the pottery found in archaeological sites was originally related to the rationality scheme of the potters and their communities, as well as to the functional, socioeconomic, and symbolic-ideological contexts which characterized the life-cycle of the vessels, it must be accepted that archaeological typologies designed in the present have little to do with folk classifications. The many complex terminological and classificatory shades used by the members of a certain culture to arrange a pottery assemblage in their minds maybe impossible to perceive or replicate by foreigners. In this sense, a number of papers have proved (Weigand, 1969; Birmingham, 1975) that many of the classificatory elements frequently used by archaeologists (e.g. base, rim, lip form) have a weak connection with those used by ancient societies. Moreover, it should be considered that several of the elements people use to classify their surrounding material culture are difficult to see in the archaeological record. Practical perspectives argue that rypologies imply an interpretative process, an analytical and creative operation, that originated in the ideational and conceptual realm. Similarly to the other attributes of pottery (e.g. fabric), they suppose an action which goes beyond the empirical world and is deeply influenced by the theoretical approach of the researcher. However, it triggers a certain degree of artificiality and arbitrariness in the classificatory process as, for instance, the researcher has to decide which attributes, of the seemingly endless possibilities, should be measured and selected for formal comparison. In short, morphometric and typological analyses of pottery are considered to be born from the rational schemes of the scholars and to be aimed at structuring a specific ceramic universe. This idea invited some authors (Hayden, 1984; Rice, 1987; Whittaker et al., 1998) to make a conceptual distinction between classification and typology. The former is considered as an empirical grouping of objects based on their differences and similarities. Typology, on the other hand, implies a classification with a clear theoretical background as well as explicit and well-agreed norms or proceedings to solve specific problems. According to Rice (1987), although devised classifications and folk classifications originate from different and often opposed concepts and objectives, both can provide feedback and interesting incentives for pottery classification. Currently, the general option is an intermediate position, where typologies are accepted to be subjective but are also potentially suitable for going beyond the mere description or organization of the record and being used in an interpretative discourse. That is, the differences perceived at the etic level can be reflected at the ernie level (Read, 2007). In any case, each and every different typological proposal defines its own concepts to organize the factual universe depending on its interpretative and instrumental objectives and the kind of record it works with. This is the case particularly for concepts such as mode (Rouse, 1960 ), type-variety (Gifford, 1960 ), and type (Dunnell, 1986), among many others. This diversity is a consequence of each typological classification strategy (i.e. the attributes selected and the grouping strategies used) being drawn, either consciously or unconsciously, for specific research objectives which vary depending on their intention of creating descriptive, comparative, or analytical typologies or, rather, dealing with chronological, cultural, functional or technological aspects by using such typology (Adams and Adams, 1991). Furthermore, as already noted by these authors, the aim of typology determines the kind of record to be selected (for instance, if it considers only complete pieces or also includes sherds).

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TYPOLOGICAL-INTERPRETATIVE TOOLS The third analytical level comprises a series of interpretative tools which transcend the typological classifications and morphological analyses described above. TI1ese tools, which are understood and used differently by each perspective, allow the researcher to go beyond the data and build coherent discourses about past societies. A large number of interpretative tools can be included at this level, some of which are the following: (a) Morphotypological variability. The morphological variability of the record can be accessed by organizing the pottery assemblage into different categories and observing the pieces' differences and similarities in different chronological and spatial segments. This variability is informative of the routines and the repetition of actions followed in the production process. Thus, some of its aims are facilitating a formal comparison of pottery and identifying the existence of either variations or continuities in the record (Adams and Adams, 1991). As will be explained in the section "Pottery Typologies and Main Interpretative Proposals;' the variability present in any record has been interpreted in a myriad ways which are also related to different analytical scales (Ericson and Stickel, 1973; Dobres, 1999) and objectives. In most interpretations, such as culture historical and processualist typologies, macroscalar analyses are dominant as they consider extensive regional spaces and temporal segments (e.g. Hendrix eta!., 1996), although microscalar analyses of variability can be also applied (Dobres, 1999). (b) Symmetry, size, and form as evidence of the potter's expertise. The analysis of symmetry, form, and size of the individual pieces is fundamental for pottery studies. As well as descriptors of the vessels, the symmetry, the kind of forms modeled, or the size of the objects have been proposed as an indication, together with a number of attributes such as the fabric, surface treatment, or wall thickness, or the potters' level of technical skill (Sheppard, !971; Budden and Sofaer, 2009; Vidal, 2011). (c) Translation of the form (isomorphism and skeuomorphism). 1be concept of isomorphism implies the repetition of a given form in several objects, thus providing them with the same meaning. In these cases, any potential variation does not trigger changes in the behavior or relationship between the elements constituting the object; thus its structural relation remains constant (Samaniego, 2013). Isomorphism cases in pottery may be numerous and varied. The most common is the preservation of the form and the metrical proportions of the vessels when their size is modified. Another example may be the repetition of decorative patterns on different media (Figure 12.2). Skeuomorphism, a variant of isomorphism which has been also reinterpreted by the different schools of thought (see Frieman, 20 I 0), refers to the translation of the form and other perceptive aspects of the ceramic universe to other technologies and vice versa. Well-known examples of skeuomorphism in pottery are the reproduction of forms and decorative patterns copying basketry, carpentry, or leather-work (Manby, 1995; Hurcombe, 2008), as well as the imitation of some types of metallic containers such as occurs in Etruscan bucchero pottery. The analysis of both isomorphism and skeuomorphism has a large interpretative potential when its identification is followed by an evaluation of the influence of these phenomena over society. Hence, it is

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FIGURE 12.2 Isomorphic relation between the decorative motifs recorded on Late Iron Age pottery and bronze discs in Mallo rca (Spain).

important to record whether the translation of the form is restricted to certain types or affects a wide variety of forms, which is the direction of the translation, whether the loan is limited to two technologies or affects more spheres, whether the replicated form shares the same contextual relationship in the many materials or is significantly different, and so on.

POTTERY TYPOLOGIES AND MAIN INTERPRETATIVE PROPOSALS Both pottery typologies and interpretative tools are drawn, conceived, and used in a certain way depending on their ultimate aims. Interpretative strategies in archaeology have played a key role in the classificatory systems which structured and organized the real world. After briefly describing the use of form analysis and typologies by the different interpretative position, a projection of the future of morphotypological analyses and their inclusion in more technological-social interpretations will be discussed.

Typologies and Chronological Frameworks Typological seriation strategies can be considered, together with stratigraphic principles, the first methodological tools promoting modern archaeology, because one of the first objectives of typological seriation was to organize and chronologically place the myriad of archaeological objects already recovered, which in the early nineteenth century were considered exclusively from a collector's and antiquarian's point of view (Trigger, 1989; Orton et al., 1993). The first modern typological proposals are therefore found at the very beginnings

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of the discipline, in the development of seriation strategies according to raw material and stylistic criteria. Archaeological objects were not only classified and organized into types, but were also relocated in concrete chronological and stratigraphic sequences: this was the birth of relative chronology, the essential and only dating method available before the discovery of absolute dating. Thus, the late nineteenth century produced paradigmatic examples of pottery seriation (see Chapter 37, this volume) such as Smitl1s study of terra sigillata (1854), Pottier's Normand pottery (1867), or Plique's research (1887), as well as Petrie's work in Lachish, Palestine (1891), and Egypt (1890), where the ceramic types were identified in the stratigraphic sequence (Sinopoli, 1991; Orton eta!., 1993; Hendrix eta!., 1996). Originally, the association between typology, seriation, and stratigraphy rested on considering the ceramic type as the chronological reference for a culture, based on the principles which allowed the paleontological identification of fossils with geological strata (Adams and Adams, 1991; Orton et a!., 1993). The definition of ceramic types from different sites provided cross-datings which were grouped into regional chronological sequences, the similarities between types representing temporal proximity (Trigger, 1989). This twofold nature of pottery typology (i.e. as stylistic-formal organization and chronological reference) was present as one of the main analytical strategies in most archaeological discourses until well into the twentieth century, and is still in use despite the conceptual redefinition of typology. Currently, multiple archaeological discourses still find this relationship, based on the concept of relative chronology and cross-dating, essential in many typological classifications. 1bis association is clear, for instance, in the analysis of wheel-made seriated pottery, such as amphorae, thin-walled Roman ceramics, and Terra Sigillata.

Typologies and Cultural Frameworks Far from denying the chronological use of typology, culture history provided it with a new meaning. A century ago, the evident relationship between certain findings and concrete geographical areas was proposed, and the definition of cultural areas as being home to different human groups followed (Trigger, 1989). This threefold association among recurring objects, geographical areas, and cultural groups signaled an important qualitative and conceptual leap. Since then, types have not only provided a concrete chronology but also a regional and cultural perspective, and even an ethnic affiliation by studying the objects recovered (Childe, 1929). Culture history defined a new concept of culture, which was eventually integrated into archaeology as the archaeological culture and fossil directeur, which implied the relationship among the archaeological materials found in a particular place, their chronology, and a specific ethnic group or people (Childe, 1925, 1929; Kossina, 1926). This new perspective promoted typology to another dimension, as it fulfilled one of the objectives of the culture historical paradigm: the interpretation of the archaeological record as a mirror of nameless prehistoric peoples identified by the characterization of their archaeological cultures rather than as developmental evidence of their culture. Furthermore, diffusionism as an interpretative tool was used to explain cultural change, using materiality to define the origin, movement, and interaction of those peoples. In these interpretations, pottery gained protagonism owing to its identification with cultures and ethnic groups. Many typological strategies used for pottery analysis had an impact

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on its cultural dimension (e.g. Krieger, 1944; Gifford, 1960; Rouse, 1960). Until the 1950s pottery typologies and the concept of fossil directeur were prevalent for the archaeological identification of ethnocultural groups. Such was the case of the debate on the integration of the Prague ceramic type into Slavic ethnicity, the association of Linearbandkeramik with the first Neolithic communities in Central Europe (Childe, 1929; Klopfleisch, in Hibben, 1958), and the first research on the ethnic group responsible for the Bell Beaker pottery (Castillo, 1928; Bosch Gimpera, 1940 ). Aiming at defining chronocultural typological entities, their analysis of pottery variability was focused on macroscales covering regional territories and large time periods. Furthermore, in order to determine the scope and distribution of cultural entities, diffusion~ ism understood isomorphic phenomena as the imitation and subsequent copy of forms or other specific elements owing to the dominance or influence of one culture over another by means of trading (e.g. colonial), political, military, or other relations.

Typology and Functionality The New Archaeology, closely related to a functionalist view of society, considered pottery a product (Sackett, 1977; Binford, 1989) or tool (Braun, 1983) whose manufacture responded to known and preconceived needs. 'Ihus, one aspect which characterized pottery life for them was its function regarding one or more ends (Rice, 1990 ); hence, pottery was designed following functional criteria (Sheppard, 1971; Smith, 1985; Rice, 1987; Orton eta!., 1993). Its function determined or restricted pottery forms, so innovative forms may have responded to new needs, making them representative ofhuman behavior. The definition of morphofunctional relationships demanded more systematic and (presumed) objective criteria, such as ethnographic analogy, to address vessel functionality: differentiating between the description of the form and the analysis of functionality (Birmingham, 1975; Henrickson and McDonald, 1985; Rice, 1987). This close relationship between form and function, supplemented by absolute dating which overcame the definition of chronocultural entities as the main interest of typologies, favored the development of new classificatory and interpretative strategies. This was the theoretical context at the peak of functional classifications characterized by organizing materiality from the presumed function of the artifacts, usually considering the morphological attributes inherent to the objects (Adams and Adams, 1991). Here, pottery classifications depended primarily on vessel form to establish functional categories. In such classifications, numerous parameters of the form (e.g. mouth width) were considered broad indications of its function, the kind of contents (i.e. liquid vs. solid), and their manipulation inside the container (Sheppard, 1971; Henrickson and McDonald, 1985; Rice, 1987; Sinopoli, 1991). Similarly) varieties of the form were also related to the use of certain culinary techniques (Rice, 1987). The link between the function and effectiveness of a form and the physical properties of the vessels was also addressed. In this sense, some morphological elements, such as the curved profile in a pot, were proved to maximize thermal shock resistance in cooking pottery (Woods, 1986) as well as impact resistance (Schiffer and Skibo, 1987), caloric efficiency, or thermal conductivity (Hally, 1986; Schiffer and Skibo, 1987).

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In short, this functionalist interest pretended to understand the socioeconomic view of a society. For processualism, isomorphism did not necessarily imply the direct derivation or influence of one style on another; it may have responded to an autochthonous adaptation to a specific environment and economy (e.g. agriculture) together with the use of peculiar culinary practices (Sheppard, 1971), with the subsequent functional specialization of the whole materiality. Similarly, processualist typologies considered a limited variability in any specific form as the evidence for both specialization and a reduced number of potters. Actually, this school has always been interested in defining the degree of specialization and its links with more evolved behaviors, where potters produced better quality and technically more efficient products. This question was addressed using form and surface analyses, considering asymmetrical profiles the production of scarcely specialized potters regarding their mastering of technical gestures. Vessel size was also considered indicative of experience (Longacre, 1999; Broda et al., 2009).

Typology, Textual Metaphor, and Identity The first post-processual paradigms stressed the active role of pottery forms and decorations as the material medium of a communicative event which was expressed with the symbols inherent to the objects. In this context, Hodder's seminal work (1982) shook up archaeology in general and pottery studies in particular by highlighting the symbolic and ideological aspects of material culture. According to his views, material culture and, consequently, pottery features were significantly constructed and should be considered an active element in the definition of societies. He also reinforced the idea that material culture was neither innate nor did it passively mirror society; on the contrary, it was created by people's actions (Hodder, 1998). 1hese ideas originated the textual metaphors held by interpretative archaeology (Hodder, 1991; Tilley, 1999). Under the influence of semiotics and hermeneutics, it understood the analysis of material culture and its interpretation as a communicational event full of signifier and signified elements. People acted in accordance with the social symbolic system and each individual in turn played an active role in his/her society. Thus, pottery forms and attributes were not just a neutral product but the embodiment of the symbolic connotations of a community in a certain place and time. Pottery, as a social product, reproduced the symbolic system of the society it was inserted in, and the similarities and differences embodied in the stylistic tendencies of formal analysis expressed a common rationality and emphasized the identity of a particular style against the rest (Prieto, 1999 ). This new association with symbolic and identitarian constituents explains the new uses of typology. In this view, the study of pottery style made visible identities related to status, cast, ethnicity, and genre, among others. Mahias (1993), for instance, documented the link between technological and stylistic variations and the caste-based social structure in India. Regarding ethnic identity, a number of papers integrated typological and technological analyses of pottery (Dietler and Herbich, 1989; Gallay and Huysecom, 1991; Hardin and Mills, 2000). The work of Gosselain (2ooo) exemplified the distribution and expansion of styles regarding local languages. Alternatively, Bowser (2000) observed that Achuar and Quechua women in Ecuador use pottery as a descriptor of political identity.

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Typology and Technology: New Perspectives and Interpretative Possibilities of Social Dynamics In the last few decades, there has been a rise in the incipient application of typological strategies to technological analyses born from a clear integration with the social dynamics of the groups studied. This social perspective of technology has mainly been developed from anthropological views and focused its interest in the study of the materials and techniques associated with pottery-making. However, in addition to these issues, typological analyses are also a useful strategy for a social approach to technology. This analytical strategy has gained popularity since the 1980s, with the active participation of two schools from different academic backgrounds: the anthropology of techniques (e.g. Lemonnier, 1986) and the analysis of technology of the social agency theory (e.g. Dobres, 2ooo). The inclusion of this proposal in archaeological questions implies that the study of the objects-that is, elements made, used, exchanged, maintained, and abandoned in a social space, usually during daily activities-can lead to the complex social practice of the technological process and its connection with rationality schemes, social praxis, power relations, economic bases, material reality, and so on; all of them interpreted as parts of a whole and unable to be understood separately because they are mutually constructed. The technological process, similarly to other social activities, would originate in the daily and contingent praxis through habitus dynamics (Bourdieu, 1977) and agency (Barrett, 1994), in a web of relations between objects and people (Latour, 2008). It implies the incorporation of patterns culturally chosen through constant practice. These attitudes, elections, and perceptions of technical alternatives, embedded in social relations and configured by the habitus, may be perceived as natural and absolutely logical, besides any consideration of the efficiency of techniques and materials. Even if technological practice and tradition can be seen as predetermined and static, they imply relational and dynamic phenomena. 1bey are an historical product which is active in the present, for technological practice is materialized in a series of learnt and interiorized dispositions which allow the reproduction of social structures and, at the same time, explain their changes through agency. Hence, tech~ nology becomes a complex cultural phenomenon, incorporated in historically contingent worldviews, interiorized social actions, and agency. Consequently, the study of technological processes has to transcend the analysis of the simple physical medium as it is intimately connected with social phenomena. Typological strategies and their interpretative contributions can be incorporated into this discourse as the analysis of pottery form, as far as it implies a collective technological choice in a specific social context, makes possible the identification of the conscious and uncon~ scious schemes, and praxis of the technological process. Hence, typological strategies are understood as a valuable tool for the interpretation of technological-social dynamics. This implies considering pottery form and the typologies developed from it as an active element relevant for interpretation and thus different from passive views and typological mechanicist interpretations. In this interpretative context, vessels' morphometry and typology, accepting pottery as a social rather than individual formalization, could be considered a priori as indirect evidence of certain technological praxis embodied with sociocultural connotations. However, such

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evidence does not need to be defined by the structure of the classifications devised; that is, by the types, categories, or groups created, nor by the grouping strategies used (e.g. paradigmatic/taxonomic, intuitive/objective). So, from this perspective, typological analyses are mainly focused in taking advantage of the interpretative potential of third-level tools. Some examples may clarify their current use.

(a) Analysis ofMicro scale Knowledge Transfer and Agency This perspective considers the analysis of morphotypological variability at a microscale so as to deepen the dynamics behind two specific questions: knowledge transfer and agency. In clear opposition to processualist typologies, social technology considers that the variability present in the pottery forms produced by a community depends upon people's interaction (either conscious or unconscious) with multiple and varied elements and values typical of their society. The presence of variability is frequently considered as evidence of a break with traditional learning patterns and the disintegration of the potters' technological-formal schemes (Garda Rossell6, 2010). A second interpretative position in the analysis of variability is focused on the role played by individuals and their agency capacity. The idea of the individual has traditionally been uncomfortable for the main interpretative paradigms; clearly seen in the many typological grouping strategies which tended to establish highly standardized typologies insisting on the importance of making them consistent and homogeneous (Whittaker et al., 1998). In the search for consistent standardizations> "anomalous" cases were considered outliers-that is, unconnected with the norm determining the perceptive difference noted by the researchers-thus they were difficult to classify, understand, and explain. Since the active role of the individuals and their agency capacity has been made clear, the analysis of marginal forms or types validated in typological classifications has offered more interpretative flexibility to address different kinds of phenomena while explaining the complexity observed in material culture with more coherent discourses (Dobres, 1999 ). Regarding agency, it should be remembered that vessel form, as well as other highly visual attributes such as decorative motifs, is frequently a collectively perceived aspect. These more visible dimensions of pottery are precisely those favored by individuals to communicate messages to the rest of the community and define their social space (Herbich, 1987: Gosselain, 2oo8). It explains the higher degree of innovation in vessel form and decoration than in any other dimension of pottery, such as paste preparation or modeling techniques, as the latter are less visible to the rest of the community. A useful strategy to study the concept of variability and its interpretative potential in knowledge transfer dynamics, agency, and technological tradition could be their articulation in the type-variety system (Gifford, 1960). Although this system was developed as a mere taxonomic tool, some scholars (Rice, 1987; Sinopoli, 1991; Read, 2007) suggest its use to interpret cultural aspects and observe record variability. Ihis typological system presents the advantage of simultaneously recording the cultural patterns shared and accepted by the whole society which originated the traditions materialized in the recurring material attributes (types), while also reflecting the variations in the artifacts as a consequence of an individual's or small social groups' actions (varieties). In short, this kind of conceptual tool becomes useful when materiality gains an active role in the configuration of society.

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(b) Potter's Expertise and Social Context of Production A second variable used by this school is the analysis offormal and perceptive aspects of pottery such as symmetry, size, or form complexity as representative of the potter's profile. Far from considering the potter in evolutionary terms such as specialization and technical complexity, morphology is used to identify apprentices and consider questions such as learning, knowledge transfer, and the social interaction of pottery production. The identification of the potter's expertise using these variables demonstrates the existence of processes made of repeated actions which produce certain standardization and technological knowledge transfer (Budden and Sofaer, 2009). Because pottery features, which result from the specific way-of-doing of each person> respond to social determinants and evidence the strategies of the technological habitus used by a potter to manufacture a product in a concrete social situation, their analysis would evidence the potter's profile. His/her technical skill and its embodiment in certain morphological attributes of the pottery should be considered contingent. Thus, tbey can be evaluated only in the concrete contexts for pottery making. In this view, technical skill is not studied as the mere evidence of the potter's technical knowledge per se or the existence or a specialized production, but rather as the response to a specific social context; and, consequently, it constitutes a key element to enlarge on the dynamics of

a society. (c) Isomorphism and Hybridization Social technology understands that the ultimate interpretation of isomorphism and skeuomorphism is determined, not by simple imitation, but by the integration of praxis into a contextual and social framework as well as into the technological and symbolic relationship between the different kinds of materials and objects participating in any society. Thus, their interpretation should consider that the loan of a form does not necessarily imply a functional or symbolic translation: it cannot be automatically inferred by the sole formal similarity of two objects, as only contextual analyses can determine the coincidence between function and meaning. Postcolonial perspectives, used in the analysis of material culture (Gosden, 2004; Van Dommelen, zoo6), understand the translation of the form derived from the contact between different cultures as hybridization. This idea is based on the premise that intercultural con~ tacts are never neutral and that the parts involved cannot be considered passive entities, but rather active agents. The complex phenomena of hybridization occurs where the material outcome of cultural contact is noticeably different from the original material culture of each culture because both groups have actively modified, reinterpreted, and hybridized practices, objects, and dynamics, giving rise to new contexts and meanings. In the case of the typological analysis of pottery, the translation of the form, even if it retains some reminiscence of the original, goes hand in hand with variations and reinterpretations which constitute a rupture in the structural relationship between the parts which have originally made the object. Hybridizations in pottery form are quite common in the Western Mediterranean during the Iron Age, particularly along the French coast (Dietler, 1997) and the Balearic Islands (Albero, 2011), resulting from the intensification of contact between indigenous and Greek or Punic communities. Although formal references can still be identified, these new hybrid types present their own peculiarities and characteristics which affect many aspects related to pottery, from the manufacture system (hand-made

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FIGURE 12.3 Format translation related to hybridization phenomena between Punic wheel-thrown vessels and hand-made indigenous pottery in the Late Iron Age in Mallorca (Spain).

pottery continues) to structural or metric elements. The result is a hybridized and reinter~ preted form, typologically different from the original schemes of both indigenous and foreign communities (Figure 12.3).

(d) Homology and Fractality Conceiving ideas and matter as a group of connected webs and nodes rather than separate elements (Latour, 2008) leads to Lemonnier's concept of representation (1993). Hence, any technological action is related to a series of mental operations which are often unconsciously internalized by a habitus which has to be interpreted in the global technological scheme of the group and facilitates technological transfers and loans among crafts sharing the same scheme. Furthermore, the concept of representation, the mental models of the sequence and order of the action, is not exclusively related to a concrete technological action, but incorporates coutent and information of an ideological, social, and/or symbolic kind which function in a network of supra-technological meaning affecting the totality of the signification and semiotic schemes and models of the community. The idea of the transversal direction of the signification schemes and technological processes in a community suggested by Lemonnier (1993) leads to a fractal and homological approach to society. This approach is related to the formal view of the object analyzed from typological strategies. In this sense, the ultimate analysis of third-level tools is understood to be inserted in an holistic interpretative framework. Thus, the study of typological identities and correspondences which have been analyzed from third-level variables has to follow four analytical levels: (a) an intrinsic level, restricted to pottery form; (b) a second intrinsic level from a multidimensional view of pottery technology; (c) an extrinsic analysis covering the diverse technological fields; and (d) a further extrinsic analysis between technology and the remaining social spheres considering different scales, as they represent the many manifestations of the same phenomena.

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1his integral analysis is possible thanks to two strategies: the study of homology relations among different fields and the analysis of the presence of fractal patterns. The concept of homology, taken from Bourdieu's perspective (1977), reveals structural similarities between different fields beyond their own peculiarities and dynamics. Applied to the social interpretation of technology and, specifically, to typological strategies, this concept of homology would refer to the similarities in the praxis and dynamics of the diverse technological fields of the society. As an interpretative strategy, homology aims at analyzing whether the behavior of each of the third-level tools used is restricted to the typological dimension of pottery or whether structural homologies are observed in other dimensions of the ceramic universe regarding the rest of the steps in the chaine opiratoire, such as raw material management, paste preparation, or forming activities. This analysis provides a mul~ tidimensional picture of pottery and identifies whether the same phenomena are materialized throughout the pottery-making process. Later on, based on the logics of the homology of fields, it is possible to evaluate if the dynamics identified in the pottery are present in other technologies (e.g. metallurgy, building, glass-making, basketry). The documentation of the same dynamics in other stages of pottery technology, as well as their identification in the rest of the technological manifestations, furthers the analysis of the typological differentiation, transcending the mere formal identification level to be inserted in the dynamics of the global technological scheme of the community. This holistic view would provide information regarding knowledge transfer dynamics, the social structures related to the learning process, technical skill, the social value of objects, and so on. The second tool which the comparison and signification aspects of third-level variables allow is the application of fractal strategies which try to record the existence of recurrent patterns or structures at several scales. Fractal patterns facilitate comparison between microscalar and macroscalar processes, for they are understood as manifestations of the same dynamics (Brown et al., 2005). A fractal interpretative framework constitutes an effective tool to integrate the typological data into another manifestation of scalar models which are expressed in the same way at upper levels, such as the technology or the social and ideological relations of the group analyzed. This strategy aims at confirming whether the typological patterns of pottery variability, appearance, and perception, as well as isomorphism and hybridization, now integrated into the technological praxis of the group and thus with ideological, social, or symbolic contents and information, are also present in other dimensions of the society. Documenting the patterns detected at these different scales helps us evaluate the significance level of the typological proposal and articulate more complex and coherent interpretative discourses beyond the classification strategy. It thus demands integrating the typological strategy first into technological questions and then expanding it to upper-level social and ideological discourses.

CONCLUSIONS

This chapter has examined the wide variety of systems used by archaeology to analyze pottery form and decoration depending on the different philosophy, methodology, and interpretative option favored, originating quite diverse typologies which respond to similarly differing objectives. Nevertheless, the several interpretative proposals should not be

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considered exclusive but rather complementary: each proposal is important in the study of the form. For instance, without the chronological determination it would have been hard to deal with other aspects related to the use of ancient vessels. Nevertheless, once these temporal and cultural parameters have been established, it should be considered whether it is worth devoting so much effort to the description of pottery form and typological study. Taking this view, some scholars have stated that form analysis and typology development has turned into a "rite of passage" archaeologists have to go through. However, the descrip· tion of vessel form and the typological classification of pottery should not nowadays be an end in itself in archaeological research. A thorough critical reflection is needed to evaluate the potential role and use of these kind of analyses in the study of pottery, both in historical and anthropological terms. This question is particularly critical in the case of prehistoric pottery, where a lack of systematization and large formal variability within a single assemblage could impair the development and application of reliable typologies able to achieve accurate seriations and chronological determinations.

NOTE L

Although typological classifications of pottery may include technical aspects (e.g. fabric or forming technique), this chapter deals with the classical concept of typology; that is, the analysis and classifications focused on vessel form, size, and decoration.

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CHAPTER 13

FABRIC DESCRIPTION OF ARCHAEOLOGICAL CERAMICS IAN K. WHITBREAD

INTRODUCTION found in the archaeological record were produced to serve many functions ranging from the transportation and storage of goods, food preparation, cooking, and consumption (Orton and Hughes, 2013: 247) to supporting activities involving heat, such as hearths and crucibles, representative art, such as figurines and sculptures, and building materials (Mills, 2013). The diversity of these functions and the wide geographical distribution of ceramic production are reflected in the materials of which ceramics are made-their fabrics. CERAMICS

Ceramic fabrics can be described in terms of their compositional and structural properties; more specifically, the arrangement, size, shape, frequency, and composition of the material constituents of the ceramic (Whitbread, 1995: 368). The term "fabric" is also used in reference to groups of ceramics that are characterized by having specific material properties in common (Tomber and Dare, 1998). Ceramic fabric descriptions aim to record, so far as possible, not only significant geological properties of the raw materials but also the potters' technological choices and actions (the chaine operatoire; Sillar and Tite, zooo; Whitbread, 2001), such as preparation of the clay body, vessel construction, and firing. Ceramic fabrics are synthetic in origin (Rice, 1987: 3). Their constituents reflect the geological characteristics of the regions from which the raw materials were obtained. However, selection and processing of these raw materials are dictated by the agency of potters with the aim of preparing clay bodies possessing physical properties appropriate for the production methods and intended functions of specific end products. Preparing a clay body may have required only the simple combination of water with a natural clay, but potters often mixed different clays and matrix materials, removed inclusions by sieving or sedimentation, that is settling in water, or added inclusions through the process of tempering to optimize the physicomechanical properties of the vessel. There are many reasons why a potter might make such adjustments. Often raw materials are unsuitable for ceramic production in their original state (Nicklin, 1979). Furthermore,

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particular physical properties can enhance the forming and drying process, or the functional performance of the resultant ceramic. For example, thick-walled vessels dry more quickly and evenly prior to firing if inclusions are present that "open" the clay (Gibson and Woods, 1990: 206). Ceramics that are repeatedly heated during use, such as cooking pots, benefit from the presence of inclusions to increase mechanical toughness and thermal shock resistance (Tite eta!., 2001). However, clay body preparation also depends on the ways in which potters learn to engage with their materials and, in part, may reflect personal or cultural preferences (Gosselain, 2000). Construction methods such as pinching, coiling, slab construction, hammer and anvil, molding, and wheel throwing, used individually or in combination, may leave their imprint in the micromorphology of ceramic fabrics (Rye, 1981; Woods, 1985; Courty and Raux, 1995; Whitbread, 1996; Raux and Courty, 1998). The most distinctive fabric characteristics, however, are produced by firing. The temperatures, oxidizing and reducing atmospheres, and duration of firing affect the appearance and physicomechanical characteristics of ceramic vessels. In most archaeological examples, the matrix component was converted to terracotta or earthenware ceramic by firing it in temperatures up to 900-1000°C using a bonfire or kiln (Gosselain, 1992). Under these conditions the crystalline structure of clay minerals breaks down, as a result of the loss of structural water, and is converted to ceramic by the sintering and vitrification that subsequently develops (Shepard, 1956: 19-31, 49-94; Cardew, 1969: 61-68; Rhodes, 1973' 64-71; Rye, 1981: 29-40, 96-no; Rice, 1987: 93-94; Gibson and Woods, 1990: 24-56).

DESCRIPTION OF CERAMIC fABRICS

Fabric descriptions need, so far as possible, to record the critical properties of ceramic materials that fulfil the requirements of three fundamental and related areas of archaeological interpretation (Whitbread, 1995: 366-378): characterization, technology, and provenance determination. Characterization is the process of defining groups or classes of similar ceramic fabrics that, in combination with additional evidence such as shape, decoration, function, or find context, can be used to examine patterns of ceramic production, distribution, and use. Technological studies investigate potting practices specific to one or more social groups, which may reflect sociocultural identities, boundaries, and the transmission of technical knowledge ( Gosselain, 2000 ). Finally, composition of the raw materials can be used to study exchange and trade networks by determining the likely geological provenance ' of ceramics that have passed into areas of different regional geology (e.g. Fitzpatrick et a!., 2003). At the most basic level of description archaeological ceramics are frequently divided into two broad types of fabric, coarse and fine. There is no universally recognized distinction between these types. In some situations "coarse ware" may simply refer to undecorated utilitarian ceramics in contrast to "fine ware;' which is often decorated, used for serving and display. From a materials perspective, however, coarse and fine fabrics are normally distinguished by whether they contain inclusions visible to the naked eye (coarse fabrics) or not (fine fabrics). Both coarse and fine fabrics can be described in hand specimen or thin section using polarizing microscopy. Sometimes more advanced analytical methods are

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required to address questions of characterization, technology, and provenance, and ceramic fabric description is used in combination with these methods (Day et al., 1999: Stoltman and Main fort, 2ooz). Generally speaking, however, thin-section petrography is better suited for analyzing coarse fabrics and their inclusions and bulk chemical analysis is usually more effective for fine fabrics. A fabric description is the analyst's record of observations. So far as possible, it needs to be kept independent of interpretations concerning technology and provenance. This approach allows alternative interpretations to be proposed, tested, and amended without affecting data from the original fabric analysis. The process of interpretation draws upon evidence from fabric descriptions and characterization, but also additional sources such as regional geology, production methods, and geochemistry. This wider analytical process of description and interpretation constitutes ceramic petrology (Whitbread, 1995: 28-29). As fabric descriptions using polarizing microscopy are usually necessary to achieve adequate resolution for such interpretations, ceramic petrology commonly refers to such studies. The greatest challenge in describing ceramic fabrics lies in recording complex visual and physical information in ways that are meaningful and reproducible for archaeologists unfamiliar with the fabrics in question. A second major challenge is in defining recognizable, coherent, and sustainable fabric groups across different ceramic assemblages. Such assemblages may contain overlapping ranges of material variation and are commonly studied by pottery specialists with diverse research interests. Macro- and microphotographs are invaluable aids to fabric description but they also illustrate the difficulties outlined above. They are severely limited in value without appropriate interpretation. Their restricted field of view rarely conveys the full range of fabric variation encountered within a single sample, and one photograph cannot illustrate the variation within a group of samples. Finally, they are no substitute for the physical and optical tests carried out in hand specimen study or under a polarizing microscope. For this reason, comprehensive written records are essential. Training in mineralogy and petrology is also necessary to gain proficiency in polarizing microscopy and in determining the optical properties of minerals and rocks in thin section (Stoltman, 1989: 147: Nesse, 1991). Descriptions based on optical examination by hand specimen or polarizing microscopy both rely heavily on the observational skills of the analyst. As such they incorporate significant elements of interpretation and inevitably reflect the analyst's range of experience in studying geological materials and archaeological ceramics.

HAND SPECIMEN STUDIES Ceramics break with a brittle fracture to leave a fresh surface that can be readily studied in hand specimen. This analytical method lacks the accuracy and precision oflaboratory-based techniques, such as chemical analysis or thin-section microscopy. However, it is not constrained by the limitations of physical damage and costs that accompany laboratory sample preparation. For this reason, hand specimen examination continues to be the most effective method for characterizing fabrics across ceramic assemblages from excavations and surveys (Moody et al., 2003; Garcia-Hera, 2000; Pentedeka et al., 2010). It is often the first step in selecting samples for more advanced analytical methods. More importantly, where fabric

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groups defined by thin section or chemical analysis possess characteristic features in hand specimen then it can be used to extend laboratory characterization from a set of samples to the ceramic assemblage as a whole (Gauss and Kiriatzi, 2011).

Surface Preparation Occasionally sherds of broken pottery display suitable breaks, but where tbese do not occur it is necessary to create a fresh break. The most effective tool is a pair of spring-loaded pliers that open wide enough to accommodate the thickness of the vessel walL These can produce a clean break with little waste and minimal damage to the sherd. Pincers are effective with very soft fabrics, but can crush or crumble harder sherds. A small hammer and chisel is best used for producing fresh breaks on large objects such as brick, tile, or thick-walled storage jars. Using these methods to remove samples for thin section or chemical analysis has the advantage of leaving a fresh break for hand specimen examination.

Hand Specimen Description There are many methods of describing ceramic fabrics in hand specimen, reflecting the different aims and experience of pottery specialists and the materials they study. One widely used method was proposed by Peacock (1977), based on the study of Roman ceramics at Carthage in North Africa. It describes the key components of ceramic fabrics in hand specimen, but aims to be simple enough for rapid sorting oflarge ceramic assemblages (Tomber and Dore, 1998: 5-9). The method also forms the basis of fabric descriptions proposed by the UK Prehistoric Ceramics Research Group (2010 ). Color is a particularly distinctive property of ceramic materials in hand specimen. lt does not feature in the definition of fabric given above because different firing conditions can produce a wide range of colors within and between ceramic objects composed of the same materials (Shepard 1956: 102-107; Beck, 2006). For example, there may be a different colored core visible in a fresh break, or the external surface of a vessel may have a different color from its interior (Velde and Druc, 1999: 122-126). The most frequent color is normally noted, along with the range of variation observed on several sherds. Where variation appears to be systematic it may reflect consistencies in the firing process and be a useful guide to the technological control maintained by potters (Frankel, 1994), but relatively minor or erratic variations should not be over-emphasized. The most widely used method of describing color is based on comparisons with colored chips in the Munsell' Soil-Color Chart (Munsell, 2009; Shepard, 1956: 107-113; Rice, 1987: 339-343). Each coded color chip provides a common reference for other researchers to consult and interpret in their own terms. The value of these charts lies in aiding precision (repeatability) rather than accuracy (closeness to the "true" color); however, both can be compromised as color perception varies between people and lighting conditions (Frankel, 1980; Gerharz et al., 1988). Groups of tablets are referred to by a color name which provides a structured reference with wider tolerance than individual chip codes. For this reason, Munsell' color names should be used rather than substituted with seemingly more "accurate" personal color descriptions.

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The hardness of a ceramic fabric depends upon its composition and degree of vitrification and/or firing temperature. The Peacock system provides a rapid hardness assessment in terms of soft (scratched with a fingernail), hard (scratched with a steel knife), and very hard (not scratched with a steel knife). These divisions are simple and quick to apply, and can be equated to Mobs' scale of mineral hardness. This is composed of ten minerals, from talc (1) to diamond (10), each harder than the next. Hardness points based on Mobs' mineral scale can also be used to test pottery, but caution is necessary when interpreting results from any scratch tests as they may reflect bonding of the material rather than its hardness (Shepard, 1956: 113-117; Rice, 1987: 355-356). Mobs' scale is an ordinal scale. Its numerical values should therefore be treated as labels of rank and not used in mathematical calculations (Curewitz, 2004). Handling ceramics is a tactile process and, while subjective assessments may not be reliably reproduced, the system recognizes variation in the "feel" (harsh, rough, smooth, soapy, or powdery) of ceramic fabrics, which can be a distinctive property when processing large quantities of material. The surface appearance of a fresh break is described by its fracture, ranging from conchoidal to smooth, hacldy (angular facets), or laminated; although Shepard (1956: 137) noted that this property catches the eye but tends only to be significant across broad categories of fine and coarse fabrics. Peacock described the frequency of inclusions as: sparse, moderate, common, or abundant. These terms are subjective in the absence of independent reference points to maintain consistency in their application, such as the percentage boundaries outlined below for thinsection analysis. The mode (most frequent size visible) and the maximum grain diameter are usually adequate measures of inclusion size. Equally significant is the degree of grain-size sorting (well or ill) and rounding/angularity as assessed using comparator charts derived from sedimentary petrography (Boggs, 2009: figures 2.3 and 2.12). Peacock (1977: table 3) provides an inclusion identification table. With experience it is possible to identify some inclusions accurately in hand specimen but it is also very easy to make mistakes. Difficulties arise from the small size of most grains and their abraded surfaces. Inclusion color can also be misleading. For example, both quartzite and limestone can be white, requiring use of a steel knife (which scratches limestone but not quartz) or dilute hydrochloric acid (which fizzes if the material is calcareous) (Moody et al., 2003) to discriminate between them. If in doubt, it is more reliable to describe the appearance of inclusions first and then suggest possible compositions. Inclusion compositions can be verified by thinsection microscopy.

Hand Specimen Description Example This section illustrates the hand specimen fabric description for the Early Bronze Age sherd described in thin section below (for illustration of the sherd in hand specimen see Plate 3). Hand specimen fabric: Red, well sorted fine sand Number of samples: 1 Sample number: 133 Color: 2.5YR 5/8 red. Hardness: soft.

FABRIC DESCRIPTION OF ARCHAEOLOGICAL CERAMICS

205

Feel: rough. Fracture: hackly Inclusion Frequency: c.20%. Sorting: well sorted. Maximum size: c.l mm. Average size: c.0.5 mm. Rounding: Subrounded-subangular. Inclusion composition: predominant: pale yellowish gray rock fragments, rarely with foliation, phyllite(?); very few: white limestone (softer than steel knife blade), very dark gray quartz/feldspar(?) (harder than steel knife blade); rare: vughs

THIN-SECTION STUDIES Analyzing thin sections of ceramic fabrics under the polarizing microscope provides greater resolution than hand specimen study. Microstructures and the compositions of inclusions can, for the most part, be more accurately identified down to a grain size of 0.03 mm, which is the standard thickness of a thin section (Reedy, zoo8: 109-231; Quinn, 2013: 39-68). Thin sections are studied by observing the optical properties of minerals, rock fragments, and fired clay with respect to the path of polarized light which is transmitted through the sample. Two types of polarized light are employed in combination. Plane polarized light (PPL) uses one polarizing filter, located below the microscope stage, and crossed polars (XPL) is applied when a second polarizing filter is inserted into the light path, above the sample, at 90° to the lower polarizer. In this latter case, all light from the lower polarizer is blocked by the upper polarizer and the image appears to be black if materials in the light path have no crystalline structure (e.g. glass) or where minerals are optically isotropic, having the same optical properties in all directions. However, most minerals are optically anisotropic, having different optical properties in different directions, and refract the polarized light passing through them such that they display a range of interference colors (Nesse, 1991).

Sample Preparation Samples need to be removed as chips that are large enough to be ground to a flat surface between 1 x 2 em and 2 x 5 em in area, depending on the dimensions of the ceramic objects and the size of the microscope slides. A larger surface area is more representative of a fabric, especially if it contains large or sparse inclusions, and leads to a more reliable analysis. 1hin sections are usually prepared as vertical cross-sections through the wall of a ceramic vessel (Whitbread, 1996). Friable fabrics need to be impregnated with epoxy resin before grinding (Quinn, 2013: 23-33). Once mounted on microscope slides the samples are ground to a thickness of 0.03 mm, at which point most rock-forming minerals are translucent. Considerable skill is required to prepare thin sections that are evenly ground to the correct thickness. A sample should be large enough to allow at least two thin sections to be produced in the event that there are problems in sample preparation.

206

IAN K. WHIT BREAD

Qualitative Thin Section Description As fired sedimentary material, ceramic fabrics have been likened to metamorphosed sedimentary rocks (Peacock, 1977), but there are significant differences. Sedimentary petrography is most effective when studying materials dominated by sand-sized (o.o6zs-z mm) and coarser grains, whereas ceramics are mainly composed of fired day-size particles or matrix, often comprising 70% or more of the sample. While petrographic methods inherited from geology are essential for describing igneous, metamorphic, and sedimentary rock and mineral inclusions (Williams et al., 1982), additional methods are required to address features arising from the technological processes of ceramic production. For example, micromorphology of the matrix material can provide important technological information on preferred orien~ations arising from vessel-forming techniques and on the degree of firing used to produce the ceramic. Ceramic fabrics can also contain anthropogenic inclusions not normally encountered in sedimentary deposits, such as grog (grains of pottery found within the ceramic, cf. Whitbread,1986; Cuomo DiCaprio and Vaughan, 1993), industrial waste such as slag from metal processing (Knowles and Quinlan, 1995), and agricultural waste such as chaff(Quinn, 2013: 161). Quantitative methods can be used to characterize ceramic fabrics (see below), but thinsection descriptions are usually qualitative, focusing on the observation of compositional and structural properties with supporting measurements, such as inclusion frequencies and grain-size ranges. Early studies often focused on inclusion compositions owing to their critical role in provenance determination and often incorporated interpretation within descriptions, which meant that technological assumptions were not always tested. For example, inclusions might be referred to as "temper" without an explicit justification for their being intentionally added by the potter. In contrast, the presence of crushed schist temper in Hohokam buff wares was argued to be temper by Miksa (2001) based on a range of explicit properties comprising grain size distribution, rock homogeneity, angularity, fractured grains, finely disseminated micas from the crushed schist, and occasional grains of volcanic rock and quartzite from implements used to do the crushing. Greater sensitivity to recording technological properties has been introduced by applying a more comprehensive and systematic method of description that allows analysts to record all features observed in a ceramic thin section. By enabling the characteristics and properties of ceramic fabrics to be isolated and recorded, their significance, in terms of technological and provenance determination, can be more effectively established rather than merely assumed. To this end, elements of sedimentary petrography and soil micromorphology, using the system proposed by Kemp (1985: 15ff.; derived from Bullock et al., 1985), are combined and modified for ceramic fabrics (Whitbread, 1995: 379ff.; see also Josephs, zoos). This approach adopts existing terminologies where appropriate but remains open to adaptation to accommodate new developments in ceramic petrology. It is most efficient to sort samples of ceramic fabrics into groups and/or classes with similar properties before describing them (Quinn, 2013: 73-79), rather than combining the descriptions of individual samples as a basis for constructing a classification. Groups may be based on broad geological characteristics, such as major rock or mineral components, while classes may constitute subdivisions based on secondary compositions or technological variation, such as grain size, sorting, or frequency. The classification is tested by attempting to reassign samples to alternative or new groups and classes based on further examination

FABRIC DESCRIPTION OF ARCHAEOLOGICAL CERAMICS

207

of their compositional and micromorphological properties. The procedure ends when the classification achieves its greatest stability, and reassigning samples no longer improves the definition of groups or classes within the dataset. Fabric descriptions therefore usually refer to collections of samples rather than individual pieces. Various degrees of diversity are often observed between the fabric characteristics of individual samples within a fabric class. This is an important property, expressed in terms of the homogeneity of the class, which can arise from a number of factors. It may reflect materials variation inherent within the production of certain ceramics or possibly limitations in the sampling program for fabric analysis. Acknowledging this variation by defining the boundaries of class membership is an effective way to establish the properties that must be met for attributing future samples to a group or class, rather than relying on the description of a "typical" sample without any indication as to the range of variation that may be present between related fabrics. The frequencies of different components within a fabric can be estimated using pointcounting or digital image analysis (see below). More commonly, however, estimates made using comparator charts are favored as a more rapid method of evaluating proportions based on illustrations of different percentage areas of the field of view (Matthew et aL, 1991). These estimates have limited accuracy and precision, with a general tendency towards the over estimation of proportions, especially where fabric properties vary widely across the thin section or where inclusions are poorly sorted. One way of reducing such inherent errors is to allow a degree of tolerance by referring to frequencies in ranges. Frequency ranges derived from soil micromorphology are: predominant (>70%), dominant (70-50%), frequent (5030%), common (30-15%), few (15-5%), very few (5-2%), rare (2-0.5%), and very rare ( are simple monochrome artworks: drawings are rendered in black, and variations are shown using different patterns of shading to give an idea of depth, motifs, and curvatures. These drawings basically illustrate the shape of the pot, its cross-section, and its decorative motif(if any). The remaining attributes of the vessel, such as. the actual color of the pot and its decorations, are usually explained in the text or presented in a separate section of colored plates or photographs.

PRA RODH SHIRVALKAf which is a common problem with images taken using a wide-angle, telephoto, or zoom lens. Photographs should be taken using natural light, filtered with a thin white doth. Bright sunlight might change the original color of the ceramics, and filtering in

224

PRABODH SHIRVALKAR

this way helps to capture true colors. In certain cases, white thermocol (polystyrene) sheets can be used to reflect or bounce the light, which helps to record the original or true colors of the pottery fragment and its motifs. While photographing the sherd, it is crucial to keep the rim flat or on a horizontal plane, otherwise the curvature of the rim creates problems in the next stage. At the same time, owing to the curvature of the body, the painted motifs also gain a curvature, which needs to be avoided in order to allow their correct orientation. Owing to the natural curvature of the rim, it is not possible simply to overlap or "digitally paste'' the photograph within the line drawing. To overcome this methodological problem, table photography should be used instead of traditional dimensional photography for archaeological specimens. In table photography or flat photography, the photographs are taken from 180' or vertically, also known as a bird's-eye view, thus eliminating other attributes of the pot such as thickness and curvature (Figure 14.5a). For decorative motifs located on the top of the rim, the photograph should have proper dimension and perspective to record the precise curvature of the rim and motif. In this case the curvature of the rim portion has to be maintained with its original curvature (Figure 14.5b ). This photograph can then be matched with the boundary of the line drawing and with the diameter of the pot just as with traditional line drawings, photographic documentation requires the use of a scale: pottery fragments must be photographed using a scale in order to match them with the scale of the line drawing. It is also important that the two scale bars, in the drawing and photograph, be identical in size and scale (i.e. both 2 em bars with each o.s em demarcated). The line drawings of the sherds, made using the traditional techniques, should then be scanned. It is important to take care that during the scanning, the drawing sheet is flat in the scanner bed. Generally, it is thought that the highest resolution is the better one, but in reality it depends upon the quality of paper. If the paper quality is not good then in high resolution scanning the paper pixels are also visible. To avoid such problems, it is essential to use 300 dot per inch (dpi) resolution for scanning. The digital photographs are individually opened in Adobe Photoshop software (or a similar program) to combine or merge the line drawings with the color photographs. Using the "lasso tool;' the required sections of the photograph can be selected and unwanted parts of the image discarded (Figure 14.5c). Both the photograph and line drawings are imported to the same page (Figure 14.5d). The scales of both the line drawings and photographs are matched without changing their morphological features. The transparency tool can be used so that the scales can be matched perfectly (Figure '+se). This setting makes the line drawing and photograph visible at the same time and helps in lining them up exactly. After matching the scales of the line drawing and photograph, the photograph is placed within the left or right compartment, as per the motif painted on the pottery fragment. The photograph is slightly overimposed on the line drawing of the left or right side (Figure 1+6a), and then, using Photoshop's "lasso tool" again, the photograph is digitally "cut" (Figure 14.6b ). This stage is essential because the sherds often have irregular or uneven sides. By digitally "cutting" the potsherd, it is possible to obtain the exact profile of the pot and gain a more natural or realistic view (Figure 14.6c). This digital cutting is optional, because some researchers might prefer to show the breakage pattern of the ceramics. Special care must be taken when dealing with decoration on the top of the rim. Photographs of these decorations are placed on top of the line drawing, aligning them to

ANALYTICAL DRAWING

225

(a)

(e)

(d)

)

\I

.adetailed, but by no means complete, table of identification of various minerals is provided at the end of this chapter (Table 15.1). In general, minerals can be classified as primary (e.g. quartz), secondary (formed after firing, during burial, e.g. precipitated calcite) and formed during firing (e.g. diopside) (Maggetti, 1982). Rock fragments are described according to their genesis and texture and classified according to the three basic rock types: igneous, metamorphic, or sedimentary. A short overview of frequently encountered rocks is provided here: Igneous rocks: Plutonic rocks comprise all magmatic rock fragments of plutonic origin and are typically recognized by the large grain size of the crystals or phenocrysts. If the type of plutonic rock can be determined based on its mineralogy (i.e. basic, intermediate, acidic; gabbro, diorite, granite), this is included in the petrographic description. Volcanic rocks refer to all magmatic rock fragments of volcanic origin and are characterized by a finer texture than plutonic rocks; small crystal grain size to glassy amorphous texture. Owing to the often small size of the grains, an accurate identification of volcanic rock type can be problematic. Often volcanic rocks can only be broadly classified according to their general composition (i.e. basic, intermediate, or acidic). Volcanics may recrystallize, mostly by silicification, which may result in a less exact identification of these rock fragments (MacKenzie and Adams, 1994). Metamorphic rocks: Metamorphic rocks are the result of, in most cases, a high temperature and high-pressure recrystallization of rocks. The original rock type can be any igneous, sedimentary, or metamorphic rock. A polyquartz fragment, for instance, refers to all types of quartzites of metamorphic and igneous origin composed of more than two quartz crystals. A straight extinction of the quartz grains suggests an igneous classification, while stretched grains and an undulatory extinction suggests a metamorphic origin (GOtze and Zimmerle, 2000). Mica schist, for example, is a metamorphic rock with more than so% of mica content (mostly muscovite); common accessory minerals in mica schists are quartz and garnet. Phyllite is a fine-grained, foliated, low-grade metamorphic rock which is typically composed of quartz, mica (sericite), and albite. Sedimentary rocks: Sedimentary rocks are formed through the weathering of preexisting rocks, as well as once living organisms. Some of these rocks have a detectable layering as a result of the accumulation of fragments and debris on the Earth's surface. Carbonate rocks, such as limestone or dolomite, are one of the most common groups encountered in archaeological thin sections. Limestone is composed of calcite and aragonite minerals and is easily identified by its texture and interference colors. Chert, another common sedimentary rock

Table 15.1 Mineral identification table derived from the integrated information of various geological handbooks. They represent a concise list of characteristics in thin section 10

Occurrence

Composition

Relief (PP)

Appearance Twinning and habit

n/a

tabs,

Cleavage

Color (PP)

Interference Extinction

Colors (XP)

Angle

pleochroic, varieties of

Interference colors may

brown, yellow,

range up to

Birds-eye or pebbly extinction or

red or green.

2nd order red

wavey

Similar Minerals

Remarks

n/a

Often contains

--····~--

Biotite

(a-Clinopyroxene: Augite

igneous and metamorphic rocks; immature sedimentary rocks

mafic to intermediate igneous rocks and their metamorphic equivalents.

Annite KFe 3AlSi 30 10(0Hh - phlogopite

KMg 3A!Si 3 0w(OHh

(Ca,Mg,Fe,Na) (Mg,Fe,AI) (Si,AI)z0 6 ; augite [Ca,Mg,Fe)_;;Si 206

n]a

elongated

dependent on grain orientation,

flakes which may be bent

moderate to four or eight high relief sided crystals, prisms or anhedral crystals

excellent,

possible twinning and exsolution visible; exsolved orthopyroxene may form fine lamellae in clinopyroxene, simple or polysynthetic twins.

pleochroic halos around small included zircons.

rarely

Biotite with

pattern of

Often alters to

hexagonal crystals

low Fe-content

interference

chlorite.

(ph!ogopite), coloration is more subtle (clear, light browns)

colors, especially when looking down on flat side of flakes. Extinction angle is 0 to a few degrees from cleavage

basal sections show cleavage angle near 90~, longitudinal sections show one cleavage

light green; varieties of light brown or yellow

2nd order yellow to pink interference colours in XP, up to high 2nd order

inclined extinction

Orthopyroxene, pigeonite, sodic pyroxenes, amphiboles, olivine

distinguishing different pyroxenes and olivine can sometimes be difficult

·~

,

,

I

Calcite- Dolomite

primary minerals in a wide variety of sedimentary and metamorphic rocks

CaC0 3 "' calcite; CaMg{C03h"" dolomite

high relief

euhedral and hexagonal, more typically anhedral in

common, one

rhombohedral cleavage

colorless or vague pastel

extreme

n/a

colouring

variable relief in PP

birefringence,

required to

while rotating

parallel

one of two sets

twinning

of poiysynthetic twins PP and

distinguish dolomite from calcite

or two sets of

aggregates

I

XP. Chemical staining as

differentiating tool. Very high interference

colors, often appearing nearly white Chlorite

Chlorite is variable common as a secondary chemistry mineral, forming after mafic minerals, in rocks of many types. ltmayalsobea primary mineral in low- to medium-grade metamorphic rocks.

n/a

Chloritoid

low- to medium- grade metasedimentary rocks

high relief

n/a

Clinopyroxene endmember: Oiopside

Ca-Mg clinopyroxene CaMgSi 20 6 ; (Na,Ca} is found mostly in (Mg,Fe 3 +,AI)Si2 0 6 marbles. Fe-free. Mafic (Na-clinopyroxene) and ultramafic rocks, and metamorphic equivalents. Associated with garnet

High Relief

short prismatic incipient crystal, or twinning well equant cross-sections

(Fe,Mg,Mn) AI 2Si05 (0Hb

PRIMARY'

n/a

single

similar to muscovite or biotite;

pleochroic, colorless to pale to medium/dark green. Rare other colours

SECONDARY' flake-like crystal (mostly anhedral), replacement "patch" of biotite along cleavage traces simple or parallel twins

anomalous green gray interference colors (lower first order) ; anomalous bleu, purple, brown

n/a

n/a

II I

often ovelooked greenish minerai because it is secondary and thus not develop large crystals.

single

greenish and pleochroic, color zonation with "appearance"

low-order (yellow) or anomalous

n/a

n/a

n/a

90"

clear to light green

mid to upper second order

large

n/a

n/a

(continued)

Table 15.1 Continued ID

Occurrence

Composition

Relief (PP)

Appearance Twinning and habit

Cleavage

Color (PP)

Colors (XP)

Interference Extinction

Angle

Similar Minerals

Remarks

·-··~~-

Clinopyroxene endmember: Hedenbergite)

Fe-rich

CaFeSi 20 6

high relief

n/a

n/a

n/a

green; more dark coloured and weak pleochroism

n/a

n/a

n/a

n/a

Clinozoisite

common in igneous rods and low- to medium-grade methamorphic rocks.

Ca 2Al 3Si3

high relief

n/a

n/a

n/a

colorless

first order, anomalous

parallell in n/a elongate grains

nla

O,(OH)

yellow green, anomalous blue-green

Alteration product in rocks of many sorts

Cordierite

metamorphic,

{Mg.Feh

high-grade pelitic

AI4Si 50l 8

n{a

metamorphic rocks

generally

common,

blocky and

polysynthetic-

n/a

clear

first order grays n}a and whites

plagioclase, quartz

included minerals, f.e. zircons, burn marks due to radiation damage

anhedral, pseudohexagonal appearance

Epidote

common in igneous rocks and low- to medium-grade metamorphic rocks. Alteration product in rocks of many sorts

Caz[AI,Fe-3+) 3Si 30 12

Garnet

wide variety of solid solution of metamorphic rocks and end members: some igneous rocks almandine(Fe3AI:J, pyrope (Mg 3AI 2), spessatine [Mn 3A!~, grossular (Ca 3AI 2Si 3 0n), andradite (Cale 2)

high relief

n/a

lamellar, not common

single cleavage

yellowish green (weakly pleochroic)

upper second parallel in to third order, elongate multiple colors, grains sometimes in concentric rings, sometime anomalous colors

biotite and other micas ; green amphibole

typical anomalous green yellow color or clear; pastels interference within individual grains

n/a

euhedral: 6-8 sided, more common subhedral or anhedral

n/a

n/a

generally colorless, slight pinkish or gra image

n/a

spinel, perovskite

inclusions of quartz and other minerals are common

n/a

..J

l HornblendeActinolite

common mineral in igneous and

mi:tamorphic rocks

Actinolite: Ca 2 (Mg.Fe) 5Sis0n; Hornblende more variable (K,Na) 0 • 1

n{a

(Ca, Na, Fe,Mgh

concentric or

n/a

pleochroic, in shades of

max middle

patchy zonation. Form: sub

brown and

to anhedral

green, less common yellow or

but may be masked by the

(Mg,Fe.AI)5

but maybe prismatic

(Si,AI) 6022 (0Hh

crystals forming

60°-120.

views may show diamondshaped

AI 2Si05

high relief

n/a

widespread and common in a wide variety of igneous and metarr:orphic rocks, to a lesser extent in some immawre sedimentary rocks {low temperature). SiHdc to intermediate plutonic rocks (not volcanics)+ metamorphic rocks

Anorthite: CaAI 2 Si 20 8 ; Albite: NaA!Si:,08 ; Orthoclase

n/a

Anhedral

color of the mineral

(green) from (Fe-poor) to dark green (Fe-rlch)

n/a

n/a

schists and gneisses

Microcline

n}a

light green

cross-sections. high-pressure mica

n/a

redbrown; Actinolite

lathes. End

Kyanite

n/a

second order

cross-hatched twinning

n/a

colorless, pale rarely higher

orthopyroxene, n/a

blue, slightly pleochroic

dinozoisite

colorless

30° from than upper first cleavage order (yellow), direction, rarely second obHque order red)

low birefringence; white to gray

n/a

n/a

in gneiss, also wavy pattern ; exsolved ->lamellae of a!bite(strlpes in XP)

KAJSi 30s

(continued)

_j

Table15.1 Continued ID

Occurrence

Composition

Relief (PP)

Appearance Twinning

low to moderate,

tabs or long skinny flakes which maybe

widespread and common in a wide variety of igneous and metamorphic rocks (+some immature sedimentary rocks)

KAI 2AISi 301o(OHh

white

n/a

excellent, depending

on grain

transparent bent

orientation. Hexagonal tabular crystals are rare

mineral

Interference Extinction

Similar

Colors (XP)

Angle

Minerals

upper second order interference colours (up to second order red), birds~ eye or pebbly extinction, wavy pattern of interference colors

Otoafew

n/a

Remarks

--~--·-

~·····--·--

Muscovite

Color (PP)

Cleavage

and habit colorless, less commonly pale green and slightly pleochroic

commonest white mica, distinguishing from other whi~e

degrees from

cleavage

micas and brit!e micas in thin section can be difficult or impossible. Therefore 'white mica'. Sericite is a fine grained variety of muscovite; destroyed around 600-700"

Na- Amphibole (glaucophane)

typically found in high- Na 2tv'1g 3Al 2 pressure metamorphic (Si 80,)[0H), rocks.

n/a

plates or long slender crystals, less common are diamondshaped cross-sections

Na-Ciinopyroxene; jadeite

high-pressure metamorphic rocks, blueschists

moderate to low

also granular, may form fibrous aggregates.

NaAlSi206

n/a

n/a

pleochroic in upper first order, n/a various shades, but modified by blue or violet the color of the based on minerals composition

simple or lamellar

n/a

colourless but may be very pale green or yellow

First or anomalous; often anomalous blue interference colours

n/a

Kaersutite (Na,Titroumaline, sodic pyroxenes rich igneous amphibole); has very strong red-brown pleochroism

n/a

n/a

'1 Na*Ciinopyroxene ; high-pressure omphacite metamorphic rocks, eco!ogite

AI exceeds Fe 3+ in

Na-C!inopyroxene; {aegirine-augite)

alkalic igneous rocks

NaFe3..Si 206

Olivine

mafic to ultramafic igeneous rocks and in their metamorphic equivalents

(Mg.FehSi0 4 ; Forsterite (Mg 2Si04) and Fayalite (Fe 2Si04)

(Na,Ca)[Mg,Fe''.AI)

moderate to also granular low

simple or lamellar

o/a

high relief

four- or eight- simple or sided crosslamellar sections with two cleavages nearly perpendicular. Short prisms or plates showing one cleavage are more typicaL

o/a

moderate (forsterlte) to very high (fayalite)

triangular, none easily alters, produces deep red or brown iddingsite, serpentinite e.a. euhedral crystals, also in igneous rockssubhedral grains, sometime aggregated.

very poor colorless or cleavage not very pale visible in thin yellow section, fracture in irregular manner

Si20G

I 'i

nondescript light green, faint pleochroism

low order, upper n/a first or second order maximum

n/a

brown, yellowish brown, shades of green. Darkest when Fe3+ content is high. green varieties are pleochroic. Colour zoning is common

aegerine-augite n/a slightly lower 3rd order birefringence. Color may mask interference colours.

amphiboles, acmite and aug;te epidote, zoisite are distinguishable from other [calcic) pyroxenes by their deeper colour and stronger pleochroism, al~o their extinctior: angle is smali (0-20"), index of refraction and birefringence are larger

up to strong third order

n/a

n/a

I I

n/a

nla

(continued]

""

Table 15.1 Continued

ID Orthoclase

Occurrence

variety of igneous and metamorphic rods, to

Composition

Anorthite:CaAI 2Si 208 ; Albite: NaAISi30 8 ;

Relief (PP)

and habit

n/a

anhedral

Appearance Twinning

Cleavage

Similar

Angle

Minerals

low

n/a

n/a

Remarks

exsolved ~> 1ame1lae of albite(stripes

incipient alteration

white to gray

inXP)

orthopyroxenes Near 90" may show fine cleavage in twinning or basal sections. Longitudinal exsolution sections show one cleavage.

pale green, peochroic to pink

first order Extinction is white to gray, parallel to the low order cleavage interference,· up to first order yellow

andalusite, clinopyroxene

pleochroic halos around zircon inclusions, visible as burn marks in PP

large variety two cleavages possible but but often not also untwinned, well developed XP: diagnostic polysynthetic twins; stripes or simple twinning

colorless, altered giving grainy or grayish appearance in PP" Concentric compositional zoning possible (both visible in PP and/or Xp)

birefrigence is low, only white to gray low order interference colours, occasionally first order yellow

quartz, K-feldspar, Cordierite

lntergrowth of Na-rich feldspar with K-feldspar (microcline or orthoclase)= perthite. Alteration to a fine grained micaceous material, partly or entirely.

n/a

show straight extinction

rocks. Often in many

Interference Extinction

Colors (XP) birefringence;

simple twins;

Carlsbad twinst or contact, both

a lesser extent in some immature sedimentary Orthoclase KA!Si 30 8

Color (PP)

colorless, frequently

silicic plutonic rocks, less commonly in volc:anic rocks. Also in metamorphic and some sedimentary rocks

Orthopyroxene (hypersthene)

Plagioclase

common in mafic igneous rocks, commonly associated with plagioc:\ase and clinopyroxene. Also found in high-grade metamorphic rocks

widespread and common in a wide variety of igneous and metamorphic rocks, to a lesser extent in some immature sedimentary rocks

(Mg,fe,Ca)[Mg,fe,AI) (Si,AI}.z0 6. Natural compositions are dominated by two major end member components: enstatite: Mg 2Si 20r;and ferrosillte fe 2Si 20 6

moderate to well developed, sometimes fairly high visible as blocky four~ or eightsided crystals. Frequently stubby prisms, rectangular lathes, anhedral crystals and masses

low to Anorthite: moderate CaAI 2Si 20s; Albite: NaAISip8 ; Orthoclase KAISi 308

subhedral to anhedral, maybe euhedral in volcanics. Plates and lathes common in igneous rocks. Compositional zoning in XP.

n/a

'l Quartz

common mineral in sedimentary, metamorphic: and igneous rocks

Si0 2

low relief

anhedral, rarely n/a euhedral.

never c:!eavage, possible

colorless

f1rst order white wavy extinction Plagioclase, to gray, rare first {undulatory) order yellow

fractures

Alkali feldspar, apatite, cordierite,

beryl& scapolite

subgrains by low grade

methamorohism. Coesite as high pressure polyrr•orph of quartz. Ouartz

does not alter

Rutile

common accessory

Ti0 2

very high

possibly

n/a

n/a

associated with biotite

mineral in intermediate to mafic igneous rocks and in many

widespread and common in a wide variety of volcanic, igneous, and metamorphic rocks, to a lesser extent in some immature sedimentary rocks (high temperature).

Anorthite: CaAI 2Si 208 ; Albite: NaAISi3 08 ; Orthoclase

n/a

euhedral

yellowish

extreme birefringence, Interference

brown.

colors may not

possibly pleochroic. yellowish to reddish brown

show due to the strong color of the mineral. When present, they are pastels of very high order

red~brown,

metamorphic rocks

Sanidine

usually red,

simple twins

n/a

low colorless, generally dear birefringence; white to gray

n/a

Hematite has

n/a

a deeper red color and a more irregular, platey, habit.

n/a

n/a

exsolved ->lamellae of albite (stripes inXP)

KAISi 30 8

(continued)

Table 15.1 Continued

ID Serpentine

Occurrence

altered ultrabasicrocks, especially from ophiolites

Composition

Mg::~Si 2 0 5 (0H)4

Relief (PP)

Appearance Twinning

low to

irregular

Cleavage

Color (PP)

Interference Extinction

Colors (XP)

and habit

----occasional

moderate

yes; chrysotile fibrous, others

one perfect

Angle

·~-··-~~~-·~"- --~

lower birefringence than micas, chlorite higher Rl

n/a

n/a

n/a

birefringence parallel! colourless to low, mostly first pale green, often order whites oxidizes to red in and grays

needle-like, fibrous, or bladed habit

n/a

very high relief

wedge, diamond, or distorted hexagonal shape, euhedral crystals

n/a

n/a

nearly colorless, sometimes brownish or gray due to high refractive index

very high birefringence-; interference· colors

n/a

n/a

n/a

combination of endmembers: spinel (MgAI 204), hercynite (FeAI 204 ); gahnite (ZnAI 204); galaxite (MnAI:P4)

n/a

n/a

n/a

commonly anhedral

highly variable

isotropic

n/a

n/a

n/a

metamorphic mineral, common in mediumgrade micaceous schists and gneisses

Fe 2AisSi 4 023 (0H)

n/a

often also comains many quartz inclusions

common twins

n/a

yellow,

up to 1st order red but often masked by the strong colour of the mineral

n/a

tourmaline, epidote

n/a

marbles or as an alteration product of mafic and ultra-mafic rocks

n/a

high birifrigence, 3rd order interference

n/a

Difficult to nfa distinguish from muscovite and white micas

metamorphic mineral AI 2SiO.s found in high-grade aluminous schists and gneisses. Polymorph of and-alusite and kyanite

high relief

Titanite

accessory mineral CaTiSi05 in igneous and metamorphic rocks, less commonly found in sedimentary rocks

Spinel

common isotropic minerals in aluminous Si-poor, metapelitic rocks

Staurolite

Talc

n/a

Remarks

fibrous amphiboles; patchy and mixed with other minerals

pleochroic;

pottery Sillimanite

Similar Minerals

n/a

clear

upper second

order

similar to white n/a micas

pleoc~roic

single

clear

l Tourmaline

granites, higher grade Na(Mg,Fe,Mn,Li,AI} metamorphic rocks, and 3AI6!Si601s](B03) often as detrital grains 3(0H,F),

moderate

n/a

rare

very poor

Fe-rlch blue to yellow, Mg-rich yellow-pale yellow, Li-rich

n/a

n/a

n/a

n/a

upper 1st to

n/a

n/a

n/a

n/a

Ca-Mg Silicates n/a

colourlessother

Tremo!ite

marbles, talc, and

Ca 2 Mg 5Si 802z[OHh;

forsterite

some Fe may substitute for Mg, forming solid solutions

n]a

bladed, columnar, needle-like crystals

n/a

towards actinolite

one cleavage longitudinal and two when

dear to pale

viewed in end section

green, slightly 2nd lower order pleochroic interference more colours pronounced

{60"-i20")

with greater

n/a

colorless

Fe content Wollastonite

high-grade marbles, associated with diopside and garnet

CaSi03

moderate to elongate and high relief

bladed

n]a

low, 1st order yellow

252

DENNIS BRAEKMANS AND PATRICK DEGRYSE

found in archaeological ceramics, is mainly composed of fine-grained ( COJ and produce a reddish-orange fabric color, resulting from the oxidation of iron and iron-rich minerals (Fe,03). Black and gray fabrics, on the other hand, often indicate a reducing atmosphere (0, poor/ CO rich). A reducing atmosphere allows both the reduction of iron oxides as well as the deposition of carbonaceous material and thus yields an intensification of dark and black colors. In reducing conditions, FeO and Fe,0 4 are prevalent phases resulting

PETROGRAPHY

i

I.

259

from1 Fe,03 +CO 7 2FeO +CO, or 3Fe,0 3 +CO 7 2Fe,0 4 +CO. In reality most prehistoric firings are not completely oxidized nor reduced because the atmosphere can fluctuate extensively in time and temperature. Iron compounds can only be fully oxidized after removal of carbonaceous material, in the

form of C0 2 • Therefore, the presence of organic matter in the ceramic fabric is also responsible for dark coloration and zonation. Under oxidizing conditions, all or most of the organic matter is burned out, resulting in an oxidized reddish fabric. Nevertheless, even in an oxidizing environment, if firing is done quickly and vessels are not allowed a sufficient "soak time;' a dark core may be produced by the incomplete oxidation of iron in the fabric and/ or the incomplete burning of organic material. The presence or absence of different firing cores or layering effects is influenced by the type of firing, length of firing, type of fuel, placement of vessels in the kiln, and amount of air flow (Velde and Druc, 1999). Open- or pit-fired pottery, for example, is rarely fully oxidized as a result of direct contact with fuel (e.g. wood and ash) and, typically, insufficient firing time for complete oxidation. Dark patches and surfaces are in this case no result of reduction) but rather a deposition of carbon on and directly below the surface. Kiln firing, on the other hand, involves the separation of fuel and pottery and typically longer (controlled) firing times and higher temperatures producing oxidized ceramics-or fully reduced ceramics (Tite, 1995, Maritan et al., 2006). A combination of fabric color and birefringence of the matrix can be used to provide information about the atmosphere and extent of firing (Buxeda I Garrigos et al., 2001). Owing to the oxidation of iron-rich phases within the matrix, a birefringent, evenly colored yellow to red matrix indicates complete oxidation, which could result from high firing temperatures, a gradual heating rate, prolonged firing, and/or an oxidizing atmosphere. Reducing atmospheres, low temperatures, and quick firing times produce a dark optically inactive matrix in thin section. Intermediate or imperfect conditions, such as rapid firing to high temperatures and quick cooling, lack of uniform atmosphere, and poor air circulation, result in a partial or incomplete oxidation and will produce both optical active (exterior) and dark non-active (interior) features in thin section (Amadori et al., 2002). Firing features are easily visible macroscopically, but can be described more systematically with thin sections, incorporating void texture and ground mass features as described in the section "Identification of Porosity in Thin Section': However, the color of a ceramic vessel is more related to mineralogical composition in combination with firing techniques than to exact firing regimes (Martin-Socas et al., 1989). Identifying the firing temperature in thin section is based on the relationship between firing temperature and chemical and structural changes that occur in the mineralogy and microstructure of the vessel. Multiple factors, in addition to temperature, influence these transformations, including the mineral composition of the raw materials, rate of cooling, the maximum temperature attained, soak time, total duration of firing, the grain size of the nonplastic inclusions, CaC0 3 content in the matrix or use of calcareous clays, and firing atmosphere, making it very difficult to estimate firing temperature accurately. Estimating these maximum temperatures precisely is usually not possible because of the wide range of ternperature variations found within a single kiln or pit, whether open or closed. Tite (1995) prefers the use of"equivalent firing temperature:' defined as the temperature at which ceramics, allowed to soak for one hour, would exhibit the observed mineralogy or microstructure. Changes in mineralogy, microstructure, and texture result from the combination of firing temperature and soak time or the overall heat input during firing. The benefit of thinking

260

DENNIS BRAEKMANS AND PATRICK DEGRYSE

about tiring temperature estimates as "equivalent firing temperature" is that it accounts for both time and temperature. Equivalent firing temperatures for open firings generally range between 550-75o'C and 750-95o'C for kiln firings. Firing temperatures up to woo'C are relatively easy to achieve in a kiln environment, although achieving temperature between noo-1150'C requires signif1cantly more technological sophistication (e.g. thermal insulation of the kiln and throughput of hot gasses) (Tile, 1995). Thermal decomposition of mineral phases is highly variable and dependent upon the chemical composition, crystal structure, and grain size of the phases involved. Most firing temperature studies are conducted using X-ray diffraction (XRD), scanning electron microscopy (SEM), electron probe microanalysis (EPMA), or physical testing procedures, such as experimental re-firing. However, some of these features are also identifiable in thin sections. Mineralogically, quartz is stable until approximately 1150'C, although a modification from alpha to beta quartz takes place at approximately 570'C. When fired for a long enough period at high temperatures, quartz will recrystallize into the higher temperature silica forms, such as tridymite (867'C) and cristobalite (nso'C) (Freestone and Hughes, 1989; Henderson, 2ooo). Both K-feldspars and plagioclase minerals are also stable up to woo-wso°C. At higher temperatures, plagioclase feldspars can experienCe separation along cleavage planes. Orthoclase feldspar, however, is only stable at

3p

Ml

2

>

329

D

3s

llll 3

l

""

2p

ll

2' v

c v

~

2

4

K

2s

Ka2

Ka1

K~'·'

1s

(d)

(c)

d

d

'

~,c

,'

FIGURE 19.1 (a) Permitted electron transitions to generate X-rays of the K series. (b) Interpretation of X-ray diffraction as the result of simple reflection (8 angle of incident radiation, d distance among crystal lattice planes). (c) Seemann-Bohlin focusing geometry for Debye-Scherrer and Straumanis methods. (d) Bragg-Brentano focusing configuration for scintillation counter (powder diffractometer) method. E entrance slit of X-ray radiation, C position of scintillation counter) D diffracted beam position.

and Kp, 1.39217 A. For an iron anode these values are FeKa, 1.93597 A, FeKa, 1.93991 A, and FeKp, 1.75653 A. The characteristic X- ray radiation consisting of Ka and KP lines is always superposed on the continuous radiation (bremsstrahlung). However, for exact measurements monochromatic X-ray radiation is required. Near monochromatic radiation can be obtained by inserting thin metal foils as filters in the X-ray beam that absorb the bremsstrahlung and considerably weaken the KP contribution. This is based on the fact that the adsorption edge of the metal (Ni for Cu radiation, Mn for Fe radiation) is situated between the Ka and Kp lines of the X-ray radiation used. However, these filters are not able to separate the Ka, from the Ka, interferences. 1his can only be achieved by a focusing concave single-crystal monochromator employed in the Guinier method (Guinier, 1956), for very accurate measuring oflattice constants.

fUNDAMENTAL PHYSICS OF X-RAY DIFFRACTION

The diffraction technique is based on the fact that if a thin beam of electromagnetic radiation of an appropriately small wavelength (X-rays, electrons, y-rays) is incident to a crystal

330

ROBERT B. HEIMANN

lattice, the beam is scattered or "diffracted" in specific directions and angles depending on the distances of atoms in the crystal lattice, thus forming a "diffraction pattern." Consider, for example, a one-dimensional lattice in which the atoms are replaced by pointlike scattering centers; each point acts like the origin of a secondary wave that spreads out spherically (Huygens' Principle). According to a simplified set of assumptions, the relationship between the directions of the incident (primary) and the diffracted (secondary) rays, scattered at a linear lattice of points with distances or "translations" (a0 ), can be expressed by the geometrical relationship shown in Figure 19.1b. The figure shows three parallel lattice planes of distance d. A parallel bundle of X-rays is incident to these planes at a "glancing" angle 8. The interference condition between the rays reflected from points A0 and B, and travelling along the same trajectory, requires that the path difference BA0 -BM is a whole number. The path difference is the distance by which the ray reflected from fhe second lattice plane is displaced backwards relative to the ray reflected from the first lattice plane at point A0 • Since BA0 = BA, the path difference isBA,.- BM = MA, = A0 A,-cos(90°-8) = A0 A,-sin8 =2d·sin8. An interference maximum (''constructive interference") will be observed when:

n•A = 2d•sin6

Equation 19.1

whereby n, the order of interference, is a whole number, Ais the wavelength of the X-rays in

A, dis the lattice plane spacing, and eis the glancing angle.

Equation 19.1 is the fundamental Bragg equation that governs the vast field of X-ray crystallography and, in particular, provides the condition for constructive interference for X-rays scattering from atomic planes of a crystal. It also provides the important link between the measured angle and a characteristic lattice dimension d, that is, the spacing of lattice planes parallel to a crystal face with the Miller index (hkf), also called interplanar spacing. This index triple describes the position of a crystal plane in an appropriate coordinate system commensurate with the symmetry of the crystal. Since the plane intercepts the coordinate system (a,a,a3) at the three points a,/h, a,jk, and a,/f, or some multiple thereof, the Miller indices are proportional to the inverses of the intercepts of the plane. If one of the indices is zero, it means that the plane is parallel to an axis, that is, the intercept is at infinity. For further details referto textbooks of geometric crystallography, such as Vainshtein (2003).

e

POWDER METHODS To an analyst seeking to determine the phase composition of ancient ceramics, basically two methods are available, the Hull-Debye-Scherrer photographic method and the scintillation counter-method using a powder diffractometer. The choice between these methods is largely determined by the amount of sample material available and the accuracy of the results desired. Useful hints for sampling strategy and requirements can be obtained from Kingery and Vandiver (1986). X-rays diffracted by a single crystal are collected in a discrete spot pattern using photographic techniques such as the Laue, Weissenberg, de jong-Bouman, or precession (Buerger) methods (Klug and Alexander, 1974). In contrast to this, X-rays diffracted by a fine powder, in which every possible crystalline orientation is equally represented, yield smooth diffraction rings or arcs when recorded on a circularly bent film (Debye-Scherrer method).

X-RAY POWDER DIFFRACTION (XRPD)

331

Hull-Debye-Scherrer Method In many cases the ceramic object under investigation is unique, and thus, highly valuable so that the amount of sample removed from the sherd must be rigorously minimized, for example extraction of the material using a dentist's drill from a location hidden when the object is on display. The total amount of material may be only in the micro- or low-milligram range as frequently found in forensic samples (Kugler, 2003).

Sample Preparation The grain size of the powdered sample should be below 10 ~m; larger particles will cause a spotty appearance of the diffraction rings. Usually, the powder is confined to a commercially available narrow tube called a Mark capillary (internal diameter 0.3 or 0.5 mm, wall thickness o.o1 mm) made from special glasses, including vitreous silica that absorb X-ray radiation only weakly. These fragile capillaries must be handled with extreme care. Very minute amounts of a powdery material, won for example by rubbing a ceramic sherd against emery paper, can be fixed to the outside of a glass fiber coated with glue. Even smaller microgram amounts of material can be collected under the microscope using a small drop of resin glued to the tip of a glass fiber. By using these sample preparation techniques, XRD becomes virtually a non -destructive analytical method.

Equipment The sample is mounted in the center of a sealed flat metal cylinder called a Debye-Scherrer

camera of either 180 or 360 mm internal circumference (diameter 57.3 and 114.6 mm, respectively). These dimensions ensure an exact conversion of the distances of the recorded interference rings (in mm) into angular degrees (in "8 and 0 28, respectively). A strip of photographic film is pressed against the inner wall of the cylinder in such a way that, through two holes punched in the strip, the conical entrance and exit apertures of the X-ray beam can be threaded: the Straumanis configuration (Straumanis and Jevins, 1940). The entrance aperture, diameters of 0.3 to 1.5 mm, is designed to collimate the beam to yield sharper reflections; the exit aperture serves as a beam stop and is equipped with a fluorescent screen to control the alignment of the sample in the center of the camera. A motorized rotatable axis allows the mounted sample to be located exactly in the center of the camera cylinder, and turn during exposure. 1be loaded Debye-Scherrer camera is attached to an X-ray machine in such a way that an X- ray bundle, collimated by the circular exit window of the X-ray tube, shines exactly through the center of the entrance aperture of the camera.

Seemann-Bohlin Configuration The intensity and sharpness ofthe diffracted X- ray beam can be considerably improved by focusing. The Seemann-Bohlin technique (Seemann, 1919; Bohlin, 1920) uses the fact that entrance aperture E and sample are positioned on one common focusing circle (Figure 19.1C). The focusing principle is based on the geometric rule that if the incident X-rays diverge from a point and are reflected-that is, refracted to pass through another point D-these two points are required to lie on the same circle as the (surface) of the powder spectmen as well as the slit of the entrance aperture E.

332

ROBERT B. HEIMAN :-.I

Evaluation of Measurements The best method for evaluating the film is to place the developed film on a light box and measure the diameters of the corresponding interference rings with a transparent ruler (o.s mm divisions). In the Straumanis configuration (see above), the centers of the two holes punched in the film are 90 mm apart for a small camera with 57.3 mm diameter and 180 mm for a large camera with 114.6 mm diameter, each corresponding to 180 °28. Any deviation from this distance, caused for example by shrinkage of the photographic film during wet processing, can be accounted for by calculating a correction factor with which the measured distances of the interference rings must be multiplied. For a small camera, with radius r = 57-3 mm, the distances x between two symmetrically arranged rings measured in mm correspond directly to the diffraction angles according to 8 = (18o/zm)•X. From the angles 8 the d-values can be calculated by the Bragg equation for a given X-ray wavelength A(Equation 19.1).

e

Powder Diffractometer Powder diffraction data are usually presented as a diffractogram that records the diffracted X-ray intensity I as a function of the scattering or "glancing" angle 0 28 (Figures 19.2-19.4). The advent of electron synchrotron sources (Courant eta!., 1952) has increased the number of available wavelengths considerably. The intensity of an X-ray beam diffracted by the crystallites in the powdered sample is recorded by a CKf (cathode ray tube) instead of a photographic film. Using an automated goniometer, step-by-step scattered intensities may be measured, and stored digitally and processed by very detailed software. The advantage of this method over the Debye-Scherrer technique is fourfold: the intensities of the interferences can be determined directly with high precision; the method is fast and highly reliable, since frequently only a few selected reflections need to be considered; no darkroom work is required; and equipment is easily available at virtually every university department of chemistry, materials science, and geology/mineralogy as well as numerous industrial and governmental research facilities. On the downside, the technique requires expensive apparatus caused by the much higher demand in terms of constancy of the direct current source for the X-ray tube, as well as the more complex recording and control devices.

Sample Preparation Grain size of the powdered samples should be around 10-30 ~m to obtain maximum and reproducible intensities of the diffracted X-ray beam. The specimens will be fiXed to a sample holder made from aluminum or a polymeric material that carries a machined, shallow square or circular hollow into which the powder will be pressed to achieve a smooth and planar surface. If the powder is fine enough, it will stick to the holder without any additional binder. Care must be taken to avoid texture effects caused by the preferential orientation of the powder particles relative to the specimen surface. This frequently happens because platy particles, such as clay minerals, orient themselvesparallel to the sample surface when too much pressure is applied during sample preparation. As a result the lattice planes parallel to the surface of the platelets show highly exaggerated intensities, whereas the intensities oflattice planes perpendicular to the surface will be suppressed. Several techniques exist to reduce

X-RAY POWDER DIFFRACTION (XRPD)

333

these texture effects including mixing the sample with X-ray inert spherical particles-for example, cork or lycopodium powders-to which the platelets may stick and thus present their surfaces in the desired random orientation. Alternatively, the powder can be dusted onto thin foils of poly( ethylenterephthalate) (PET; Hostaphan~, Mylar'"") or polypropylene.

Equipment The measuring principle of a powder diffractometer is shown in Figure 19.1d. The sample surface is positioned in the center of the measurement circle (solid circle). By slowly tilting the sample at a constant rate, its angle towards the incident X-ray beam is varied, and consequently the diffracted beam also moves. The focus of the beam inside the X -ray tube, the entrance aperture E, the sample surface, as well as the counter Care located at the circumference of a virtual circle, the focusing circle (dashed circle in Figure 19.1d). This is the BraggBrentano configuration (Bragg, 1921; Brentano, 1923). During recording, the scintillation counter C moves along the measurement circle with an angular velocity that is twice that of the sample. The resolution of the diffractogram, and hence, the precision of the measurement, depends upon various parameters including selection of filters, apertures, goniometer speed, maximum signal range of the recorder, time constant, type ofX-raytube, voltage, and proper alignment of the focusing condition.

Evaluation of Powder Diffractograms Since the X-ray diffractograms already present the peak positions recorded as intensity versus diffraction angle plots, the angle 0 26 can be directly read from the chart and converted to d-values by the Bragg equation (Equation 19.1). Modern X-ray diffractometers are computer controlled, and with appropriate software the diffractogram can be evaluated directly on a computer screen. Since the pattern of diffracted X-rays is unique for a particular structure type it can be used as a "fingerprint" to identify individual minerals in a ceramic material. The PDF database of the International Centre for Diffraction Data allows searching for unknown compounds by comparing the d-values of the lines with the highest intensities (peak height) with those of the database in which the substances are ordered after the d-values of the strongest peaks, the so-called Hanawalt groups (Hanawalt et al., 1938). A calculated example is shown in Table 19.2.

APPLICATION OF

XRD

TO ARCHAEOLOGICAL CERAMICS

Investigation of an Archaeological Clay: Provincial Roman Terra Sigillata The clay under investigation is calcareous illitic clay sampled from the banks of the Otterbach creek, a small tributary to the Rhine River, near jockgrim, Palatinate, Germany. This clay has reportedly been used to manufacture provincial Roman Terra Sigillata ware in the East

334

l

ROBERT B, HEIMANN

Table 19.1 Chemical composition of calcareous illitic clay from Otterbach, Jockgrim, Palatinate, Germany (Heimann et al., 1980) Oxide

Si0 2

Al 20 3

Ti0 2

Fe20 3

CaO

MgO

Na 20

K20

P20 5

massOfo

61.7

19.3

0.8

5.5

7.0

2.7

0.8

3.5

0.1

Table 19.2 List of measured diffraction angles 0 28, d values calculated according to the Bragg equation (Equation 19.1), referenced values and intensities of mullite (first numbers refer to 3:1 mullite, numbers in brackets to 2:1 mullite) obtained for comparison from the Powder Diffraction File (# 79-1275 for 2:1 mullite; # 82-0037 for 3:1 mullite), and assignment of Miller indices (hkt). The d v~lues for quartz were calculated from the lattice constants a0 = 4.9133 A, c0 = 5.4053 A. X-ray wavelength A= 1.5418 A(CuKo) line#

'28 (meas.)

d (calc.)

d (PDF)

Intensity (PDF)

(hkl)

Assignment

1

16.50

5.372

5.386 (5.400)

530 (800)

110

3:2-mullite

2

21.00

4.230

4.255

100

quartz

3

26.50

3.363

3.386 (3.402)

210

3:2-mullite

4

26.75

3.332

3.344

101

quartz

5

30.75

2.907

2.884 (2.889)

170 (200)

001

2:1-mullite

1000 (1000)

6

33.00

2.714

2.693 (2.700)

370 (450)

220

2:1-mullite

7

35.25

2.546

2.542 (2.548)

480 (490)

111

2:1-mullite

8

36.50

2.462

2.456

120

quartz

9

39.40

2.429

2.427 (2.428)

160(150) 175 (560)

130

2:1-mullite

201

3:2-mullite

10

39.50

2.281

2.291 (2.298)

11

41.00

2.201

2.206 (2.202)

550 (340)

211

2:1-mullite

50 (60)

400

3:2-mullite

380 (230)

331

2:1-mullite

12

48.50

1.887

1.886 (1.897)

13

60.75

1.524

1.525 (1524)

Gaulish settlement Tabernae Rhenanae (today's Rheinzabern) between the second and third centuries AD. 1his is indeed one of few fortuitous cases in which the original clay source still exists so that through experimental firings the ancient technology can be ascertained and reconstructed with confidence. Table 19.1 shows the chemical composition of the as-mined clay obtained by XRF spectrometry. The left panel of Figure 19.2 shows X-ray diffraction charts of several clay size fractions from this raw material source, separated using an Atterberg cylinder. ~Ihe coarse

i

---·---·--···-----------------------X-RAY POWDER DIFFRACTION (XRPD)

il

I

chi

I I chi rljJ,.

c

b

I(

ml ( \jchl I

'V

I \

ch~; lep i\)rl m~ 1 j V,} ~~chi .._,.., il

,.../ ~~ pi 'lch I

~I

chi

i

;z J\ 1\) J --.,.j·\·1/\ qz '-.)W \.,..N ,, p!

a

Ji

I; ch 1

qz

,Iii il

chi

20

g

f

e

il

J~)li~v;~~'I#~W~'( 30

335

10

d 30

20

19.2 Left panel: X-ray diffraction charts of an archaeological calcareous illitic clay from Otterbach, Palatinate, Germany: (a) as-mined non-separated clay, fine sand fraction (-420+74 ~m); (b) silt fraction (-74+5~m grain size); (c) clay fraction (-5+1 11m). Right panel: as-mined clay fired at different temperatures and atmospheres; (d) 6oo°C in air; (e) 8zo°C in reducing atmosphere (jO, > 10- 4 atm); (f) 1010°C in reducing atmosphere (jO, > 10- 4 atm); (g) 1010°C in air (Heimann et al. 1980). Labelling of the peaks is as follows: cc calcite, chl chlorite, di diopside, he haematitie, il illite, ml mixed layer mineral, pl plagioclase, qz quartz, sa sanidine, sp spinel, tr tridymite.

FIGURE

granular non-clay constituents quartz, plagioclase, and calcite appear in the as-mined clay (Figure 19.2a), whereas in the silt (-74+5 11m) (Figure 19.2b) and clay fractions (-5+111m) (Figure 19.2c) the clay minerals illite (il), mixed layer (ml) mineral(s), and iron-rich chlorite (chl) dominate. The finest fraction contains lepidocrocite (lep, y-FeOOH) as an important carrier of iron. This high-illite fraction was used by the Roman potters as a slip, applied to the leather-hard green body prior to firing. The results of experimental firing of the clay are reported in Figure 19.2, right panel (Heimann et al., 1980). Firing using an oxidizing environment at 6oo°C (Figure 19.2d) reveals that the original phase content of the clay is still maintained even though chlorite (chl) has already disappeared from the XRD record. In particular, calcite (cc) and illite (il)

appear unchanged. In contrast to this, firing using an oxidizing environment at

1010°C

(Figure 19.2g) shows neoformation of diopside (di), calcium-rich plagioclase (pl), traces of sanidine (sa), and hematite (he), but no mullite. Diopside is a fingerprint mineral of calcareous ceramics fired above about 950°C under oxidizing conditions. The iron oxide present as the minerallepidocrocite (lep) as well as released from the illite or chlorite lattices crystallizes under oxidizing conditions as hematite (a-Fe,0 3), producing the telltale rich coral red color of air-fired Terra Sigillata pottery. Firing under mildly reducing conditions (/0 , >10- 4 atm; Mn,O/Mnp 4 redox buffer) at 8zo°C (Figure 19.2e) reveals that decomposition of illite has already started, manifested by the disappearance of the (ozo!t1o) and ( 003) interplanar spacings at around 21.0 and 25.3 °28, respectively. Calcite (cc) still occurs in the phase assembly since its decomposition starts at

336

ROBERT B. HhiMANN

temperatures higher than 85o0 C. A firing temperature of 1010°C under mildly reducing conditions (Figure 19.2f) produces a phase assembly consisting of calcic plagioclase (pl), tridymite (tr), and spinel (magnetite). The occurrence of magnetite is responsible for the gray to black color of the fired ceramics.

Low-Fired Earthenware Produced from Calcareous Clays: The Gehlenite Problem Most ancient low-fired earthenwares were produced from red-firing clays and shales, the main clay mineral content of which is illite. The presence of feldspars and, in particular, calcite provides fluxing agents that considerably lower the sintering temperature. Consequently, it is not surprising that ancient pottery was predominantly produced from calcareous illitic clays that, on firing to temperatures well below 1000°C, yielded a reasonably dense and rather impervious body. Corinthian and Attic ware, Roman Terra Sigillata, and many medieva! earthenware products were produced from calcareous illitic clays .. However, such clays have non-refractory properties and thus possess a rather narrow softening interval so that great care had to be taken not to "overfire" the vessels and thus create undesirable largescale melting of the clay, leading to warping, bloating, and ultimately failure (for example, Maniatis and Tite, 1975). Evidence of such failure exists in the archaeological record; almost all ancient pottery production sites contain copious numbers of deformed and otherwise misfired wasters. With increasing control over the complex physicochemical parameters existing in a pottery kiln and a judicious choice of appropriate clays, a shift to less calcareous clay, and, as a result, an increase in quality occurred. This is evident, for example, in the change from highly calcareous Neolithic pottery of Crete to much less calcareous clays during the Middle and Late Minoan Kamares periods, achieved presumably by blending clays from different sources with high (northern coast of Crete, Knossos) and low (southern coast, Phaistos) lime contents to yield a consistent product (Noll, 1982; Heimann,1989). A similar blending of clays from different sources has been deduced from compositions of Italian maiolica (Caiger-Smith, 1973; Baldi, 2003) and French faience (Maggetti, 2012). Higher amounts of CaO in the clay result in ceramics with considerable amounts of gehlenite, Ca,Al1v[A!Si0 7 ) when fired to 8so-woo0 C. Gehlenite persists metastably in the ceramic and reacts at higher temperatures (>wso°C) with silica released during decomposition of meta-kaolinite or illite to anorthite+ wollastonite (or in the presence ofMgO to diopside, CaMgSi,06 ) according to:

J

Ca 2 Al[ AlSiO, + 2 Si0 2 ---> CaAl 2 Si 2 0 8 + CaSiO,

Equation 19.2

The formation of gehlenite outside its field of thermodynamic stability, and its occurrence in and disappearance from calcareous illitic clays has long been considered an analytical challenge as a thermodynamic problem. However, the solution to this problem has been found in the realm of reaction kinetics. Well-processed clays utilized to make fine Roman Terra Sigillata, with a narrow and small grain size distribution and, in particular, absence oflarger calcite grains, do not show gehlenite, whereas coarse and low-fired utilitarian ware (Terra Helvetica) made from identical clays contain significant amounts of gehlenite (Maggetti and

X-RAY POWDER DIFFRACTION (XRPD)

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KUpfer, 1978; see Figure 19.3, right panel). Evidently, the reaction rate of gehlenite formation is a function of grain size which, in turn, is influenced by the degree of processing of the clay; a dear measure of the technological skill of the potter. Since ancient earthenware ceramics were almost always fired below I000°C, gehlenite should indeed have been formed during oxidizing firing. However, this phase is rarely detected in such ceramics with some notable exceptions; for example, when the ceramics were buried under strongly arid conditions (Figure 19.3a-b). In contrast to this, in contact with soil solutions, gehlenite transforms to zeolitic minerals. Depending on the composition of soil solutions there are several reaction paths; confirmed experimentally by Heimann and Maggetti (1981) using XRD (see also Rathossi et al., 2010). Gehlenite reacts with diluted inorganic (HCl) and organic (acetic, oxalic, citric, aspartic, tartaric) acids to hydrogrossularite (hibschite, Ca3Al,[(Si,H)O 4 ],), under moderate humid conditions in the presence of CO, to wairakite (Ca[AlSi,0 6 ],·zH,O), garronite (NaCa,. 5 [Al3Si 50, 6 ],·14 H,O) (Figure 19.3c-d), scawtite (Ca7 [(CO,JSi 6 0, 8 ].2H,O), and montmorillonite, and, under very humid conditions, in the presence of humic acids and C0 2 , to calcium carbonate modifications (aragonite, vaterite) with different stabilities with respect to the calcite that finally remains as the thermodynamically stable phase, together with smectites. In high-fired (>wso°C) calcareous ceramics, gehlenite reacts with silica to form anorthite that, during burial under humid conditions and pH-values >8, very slowly decomposes to calcite and a smectitic phase. These experiments clearly show how the sensitivity of some minerals in low~fired ceramics to aggressive solutions. Here is a lesson to be learned: extensive cleaning of excavated shards with acids (pH [ 2Al 2 0

3 •

SiO, J + 2Si0,

3[2Al 2 0 3 ·Si0 2 ]+Si0 2 ->2[3Al 2 0 3 ·2SiO,J

Equation 19.3 Equation 19-4

qz

mu

10

15

'29

FIGURE 19.4 XRD chart (CuKa) of stoneware from Sawankhalok, Thailand (14th-15th centuries AD), formed by firing of a refractory kaolinitic clay beyond 125o'C, showing (residual) quartz (qz) and mullite solid solution (mu) phases. The inset shows an SEM image of the (etched) ceramic microstructure with primary platy mullite (Mu I; 2Al,03 SiO,), secondary needle-shaped mullite (Mu II; 3Al,0 3 zSiO,), and a quartz grain dissolving in glass (Heimann 1989).

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The XRD chart (Figure 19-4) shows the main peaks of mullite as well as those of residual quartz (Table 19.2). In addition, the elevated background (mottled area) centered at 22 °26 suggests the presence of a high-silica glass. If such a glass could be crystallized by long-term tempering at sufficiently high temperature, the centroid position would narrow to the (m) spacing of il-cristobalite at 21.93 '28 (d, = 4.128 A). Frequently, peaks overlap so that both their angular positions and intensities cannot clearly be resolved. The XRD chart of Sawankhalok stoneware reveals a substantial overlap of the strongest quartz interference at d = 3-332 A with the strongest mullite interference at d = 3.363 A between 26.50 and 26.75 °28. To deal with such problems, the Rietveld method (Rietveld, 1969, 2010) was introduced. This method uses a least squares approach to refine a theoretical line profile until it matches the measured profile. Subtracting the theoretical and measured line profiles yields information on the quality of structural refinement. As mentioned above, not only crystalline but also non-crystalline (amorphous or glassy) phases occur in archaeological ceramics formed by quenching of high-siliceous melts from high firing temperatures. During cooling in these highly viscous melts, nucleation required for crystallization is suppressed, so that the non-crystalline state is maintained down to room temperature. In glass formed in this way, the atomic arrangement is non-periodic and, consequently, lacks well-defined symmetry. This leads to a distorted network of silica tetrahedra that does not produce a sharp diffraction pattern but a diffuse pattern instead, resulting in broad shadowy rings on the De bye-Scherrer film or an elevated background in the diffractometer record (Figure 19.4, mottled area, 15-30 °28). Hence, normal XRD techniques are not suitable for investigating amorphous materials. However, the rich structural information contained in diffusely scattered patterns can be retrieved by high-resolution wide-angle X-ray scattering (WAXS) using synchrotron radiation. This technique comprises determination of the so-called complex scattering vector S(Q), the deconvolution of which yields information on repetitive structural units such as SiO 412 tetrahedra of differing degree of condensation, topology, and conformation, and thus will allow determining quantitatively the chemical composition of a glass (Pietsch et aL, 2004; Pentinghaus et al., 2004; Heimann et al., 2007).

REFERENCES -----------·-------·······---~---

Baldi, G. (2003). "Indagine archeometrica sulle ceramiche di Montelupo:' In: Berti, F. (ed), Storia della ceramica di Montelupo, (Montelupo Fiorentino: Aedo), vol. 5, 87-114. Bohlin, H. (1920). "Eine neue Anordnung fUr rontgenkristallographische Untersuchungen von Kristallpulver:' Annalen der Physik (Leipzig) 61: 421-439. Bragg, W. H. (1921). ''Application of the Ionisation Spectrometer to the determination of the Structure of Minute Crystals:' Proceedings of the Physical Society (London), 33: 222-224. Brentano, ). C. M. (1923). ''A New Method of Crystal Powder Analysis by X-rays:' Nature (London), 112(2818): 652-653. Caiger-Smith, A. (1973). Tin-Glaze Pottery in Europe and the Islamic World (Faber & Faber: London). Courant, E. D., Livingston, M.S., and Snyder, H. S. (1952). "The Strong-focusing SynchrotronA New High Energy Accelerator:' Physical Review 88(5): 1190-1196.

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Embs, ]. P., Juranyi, F., and Hempelmann, R. (2010). "Introduction to Quasieleastic Neutron Scattering:' Zeitschrift Fur Physikalische Chemie 224: 5-32. Feldman, L. C. and Mayer,). W. (1986). "Glancing Angle X-ray Diffraction." In: Fundamentals ofSurface and 1l1in Film Analysis (New York, Amsterdam, and London: North- Holland). Guinier, A. (1956). Theorie et Technique de Ia Radiocristallographie Second Edition (Paris: Dunod). Hanawalt, J. D., Rinn, H., and Frevel, L. K. (1938). "Chemical analysis by X-ray diffraction. Classification and use of X-ray diffraction patterns:' Industrial Engineering Chemistry and Analytical Edition 10: 457-512. Heimann, R. B. (1989). ''Assessing the Technology of Ancient Pottery. The Use of the Ceramic Phase Diagrams:' Archeomaterials 3(2): 123-148. Heimann, R. B. and Franklin, U. M. (1979). ''Archeothermometry: The Assessment of Firing Temperatures of Ancient Ceramics." journal of the International Institute for ConservationCanadian Group 4(2): 23-45. Heimann, R. B. and Maggetti, M. (1981). "Experiments on Simulated Burial of Calcareous Terra Sigillata (Mineralogical Changes):' British Museum Occasional Paperr9: 163-177Heimann, R. B., Maggetti, M., and Einfalt, H. C. (1980 ). "Zum Verhalten des Eisens beim Brennen eines kalkreichen illitischen Tons unter reduzierenden Bedingungen:' Berichte der Deutschen Keramischen Gesellschaft57(6/8): 145-152. Heimann, R. B. and Maggetti, M. (2014). Ancient and Historical Ceramics (Stuttgart: SchweizerbartScience Publishers). Heimann, R. B., Pentinghaus, H.)., and Wirth, R. (2007). "Plasma-sprayed 2:1-mullite coatings deposited on aluminium substrates:' European Journal of Mineralogy 19: 281-291. lsphording, W. C. (1974). "Combined Thermal and X-ray Diffraction Technique for Identification of Ceramic-ware Temper and Paste Minerals." American Antiquity 39: 477-483. jenkins, R. and Snyder, R. (2012). Introduction to X-ray Powder Diffractometry (Hoboken, N): John Wiley & Sons). Kilb, L. (1979). "Gefiigeanalytische Untersuchungen historischer steinzeugartiger Werkstoffe zur Behandlung archfiometrischer Fragestellungen:' PhD dissertation, Technical University Clausthal, Germany. Kingery, W. D. and Vandiver, P. B. (1986). Ceramic Masterpieces. Art, Structure, and Technology. The Free Press: New York. Klug, H. P. and Alexander, L. E. (1974). "X-ray Diffraction Analysis in the Forensic Science: The Last Resort in Many Criminal Cases:' In: X-ray Diffraction Procedures for Polycrystalline and Amorphous Materials. Second Edition (New York: John Wiley & Sons). Kugler, W. (2003). "X-rayDiffraction Analysis in the Forensic Science: The Last Resort in many Criminal Cases:' Advances in X-Ray Analysis 46:1-16. Maggetti, M. (2012). "Technology and Provenancing of French Faience:' In: Herrero,). M. and Vendrell, M. (eds), Seminarios de Ia SociedadEspanola de Mineralogia, vol. 9, 41-64. Maggetti, M. and Kiipfer, T. (1978). "Composition of the Terra Sigillata from La Peniche (Vidy, Lausanne, Switzerland):' Archaeometry2o(z): 183-188. Maggetti, M. and Rossmanith, M. (1981). ''Archaeothermometry of Kaolinitic Clays:' Revue d'Archeometrie, Supplement no. 5:185-194Maggetti, M., Rosen, J., Neururer, C., and Serneels. V. (2010). "Paul-Louis Cyffle's (1724-1806) Terre de Lorraine: A Technological Study:' Archaeometry 52(5): 707-732.

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Maniatis, Y. and Tite, M. S. (1975). ''A Scanning Electron Microscope Examination of the Bloating of Fired Clay:' Trans. Brit. Ceram. Soc. 74:229-232. Noll, W. (1982). "Mineralogy and Technique of the Ceramics of Ancient Crete:' Neues ]ahrbuch fur Mineralogy (Abhandlungen) 143(2): 150-199. Pawloski, G. A. (1985). "Quantitative Determination of Mineral Content of Geological Samples by X-ray Diffraction:' American Mineralogist 70: 663-667. Pentinghaus, H. j., Precht, U., and Gottlicher, j. (2004). "Fundamental Material Constants of Silicate Glasses and their Melts from High-resolution WAXS Applying Synchrotron Radiation:' Proceedings of!CG Kyoto (Kyoto: Ceramic SocietyofJapan). Pietsch, U., Baumbach, T., and Holy, V (2004). High-Resolution X-ray Scattering from Thin Films and Lateral Nanostructures (New York: Springer). Rathossi, C., Pontikes, Y., and Tsolis-Katagas; P. (2010). "Mineralogical Differences between Ancient Sherds and Experimental Ceramics: Indices for Firing Conditions and Post~burial Alteration:' Bull. Geol. Soc. Greece, LXJII(2): 856-865. Rietveld, H. M. (1969). ''A Profile Refinement Method for Nuclear and Magnetic Structures:' Journal ofApplied Crystallography 2(2): 65-71. Rietveld, H. M. (2010 ). "The Rietveld Method: A Retrospection:' Zeitschrift Fur Kristallographie 225: 545-547· Schwartz, A. )., Kumar, M., and Adams, B. L. (2ooo). Electron Backscatter Diffraction in Materials Science (New York: Kluwer Academic/Plenum Publishers). Seemann, H. (1919). "Eine fokussierende r6ntgenspektroskopische Anordnung filr Kristallpulver:' Annalen der Physik (Leipzig) 59:455-464. Stojakovic, D. (2012). "Electron Backscatter Diffraction in Materials Characterization." Processing and Application of Ceramics 6(1): 1-13. Straumanis, M. and Jevins, A. (1940 ). Die Priizisionsbestimmung von Gitterkonstanten nach der asymmetrischen Methode (Berlin:). Springer). Vainshtein, B. K. (2003). Modern Crystallography 1: Fundamentals ofCrystals (Berlin: Springer).

CHAPTER 20

X-RAY FLUORESCENCEENERGY DISPERSIVE (ED-XRF) AND WAVELENGTH DISPERSIVE (WD-XRF) SPECTROMETRY MARK E. HALL

ENERGY dispersive X-ray fluorescence (ED-XRF) spectrometry and wavelength dispersive X-ray fluorescence (WD-XRF) spectrometry are two analytical techniques that use X-rays to generate compositional data. Although not as popular for ceramics as neutron activation analysis (NAA, INAA) or inductively coupled plasma-mass spectrometry (ICP-MS), X-ray fluorescence (XRF) spectrometry can provide a low cost and fairly rapid way of determining the chemical composition of ceramic materials. In the case ofED-XRF spectrometry, it also can be a non-destructive method for generating quantitative chemical data. The purpose of this chapter, in addition to providing a review of these two analytical techniques, is to illustrate some of the archaeological studies that have utilized one or both of these techniques, and discuss some of the anthropological questions XRF spectrometry can address. I provide a brief technical overview of XRF spectrometry and refer readers to Bacso et al. (1998), Brouwer (2003), jenkins (1999), Janssens (2003), Lachance (1993), Rouessac and Rouessac (2007: 263-281), Shackley (2012), Whiston (1987), and Williams (1987) for more detailed information. Additionally, I do not focus on portable or handheld XRF spectrometry of ceramics in this chapter; instead the reader is referred to Chapter 21 in this volume and papers by Speakman et al. (2011) and Hunt and Spealanan (2015). Whereas the focus in this chapter is X-ray spectrometry, it is emphasized that a single analytical technique is often insufficient for addressing the question(s) at hand. Consequently additional analytical techniques are employed to facilitate a better understanding of the chemistry from both materials science and cultural perspectives. For example, Buxeda i Garrig6s et al. (2001) used not only XRF, but also X-ray diffraction (XRD) and scanning electron microscopy (SEM) to understand chemical patterns observed at the Late Bronze Age kiln at Kommos, Crete. Other examples of ceramic research incorporating XRF and instrument-based analytical techniques include, but are not limited to, Baxter et al. (2008),

X-RAY

ED~XRF

AND

WD~XRF

SPECTROMETRY

343

Day and Kilikoglou (2001), Fortina eta!. (zooS), Hall and Nishida (2oos), Inanez eta!. (2007, 2008), and Knappe! et al. (zoos).

ANTHROPOLOGICAL AND ARCHAEOLOGICAL ASSUMPTIONS AND ISSUES The provenance of ceramics can often be determined by comparing the concentrations and relative amounts of the major, minor, and trace elements contained within them. A pri~ mary assumption behind this approach is that a relationship exists between the chemical composition of the pottery and the clay(s) and temper(s) used to manufacture the pottery (Wilson, 1978: 220, 221; Harbottle and Bishop, 1992: 27; Steponaitis et a!., 1996: sss-s6o; Hein eta!., 2004: 245-246). Furthermore, for prehistoric pottery, the chemistry of the clay and tempers used in the pottery are seen as being a reflection of local geological materials (Bishop eta!., 1982; Bishop and Neff, 1989; Harbottle and Bishop, 1992; Hein eta!., 2004). Although human behavior may alter the chemical signature and prevent sourcing to a specific clay deposit (e.g. the addition of temper(s) and the refining of clay(s)), it does not prevent the analyst from identifying unique, statistically significant compositional groups (Neff et a!., 1988; Arnold et a!., 1991). Distinct compositional groups of ceramics can be viewed as having originated from different "sources:' These "sources" could correspond to specific clay deposits, regional clay deposits, and/or "production workshops" (Arnold eta!., 1991; Costin, 1991). A final corollary, particularly for prehistoric sites lacking evidence for a kiln or other production features, is that the dominant chemical group found at a site is often presumed to represent local production, whereas other chemical groups of ceram* ics found at the site are presumed to represent trade or exchange (Tile, 1999). This principle, often referred to as the criterion of abundance, can be highly problematic especially in areas where there is substantial movement of pottery and/or when sample sizes are small, and/or when there is limited/no knowledge of the chemical signature(s) of pottery from other sites. The conceptual framework described above is only a useful starting point for chemical analyses of ceramics, and not a set of axioms. Research has shown that reality is often more complex. Hein eta!. (2004) have illustrated the variability that can exist in local and regional clay deposits. Even within a single clay deposit, when normality is assumed, individual clay samples from deposits appeared as outliers when compared to the majority of the samples. When human behavior gets added to this chemical variability in the clay, links to the raw material can be further obscured or even non-existent. Buxeda i Garrig6s et al. (2003), in an ethnoarchaeological study of pottery production in a single village in Spain, illustrate how human preparation of the local clays increased the chemical variability, and there was not a single chemical group that could be considered characteristic of the village as a whole. Additionally, it is important to mention that ceramics are also subject to post-depositional alteration (see Chapter 11, this volume). A number of factors, such as the firing temperature of the ceramics, how the ceramic was used (e.g. crucibles, storage of salts, etc.), porosity, burial environment, and the pH of the groundwater, can lead to chemical alteration (Hedges and McLellan, 1976; Buxeda i Garrig6s et al., 2001; Schwed! eta!., 2006). Depending on the

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MARK E. HALL

extent of the alteration, this could alter the bulk chemical composition of the pottery and ultimately affect the ability of the analyst to identify reliable compositional groups. It is with this conceptual framework (and its caveats), combined with archaeological knowledge, that one can begin to use chemical analyses of ceramics to address the cultural aspects of ceramic manufacture and production.

PHYSICS OF X-RAY FLUORESCENCE Although X-rays have long been used to image the skeletal structures, or to examine the contents of bags and packages at security checkpoints, our interest herein is the secondary (or fluoresced) X-rays that occur when an object is subjected to X-ray radiation. Photons from the primary or incident X-ray beam, with an energy between 5 and 100 keV (Rouessac and Rouessac, 2007: 263), displace electrons in the K, L, and M orbitals of atoms forming the surface of the sample. Secondary X-rays are formed when electrons from the higher orbitals release energy to fill voids in the lower orbitals (i.e. L orbital electrons drop to the K orbit, while M orbital electrons drop to the L orbit, etc.). An L orbital electron drops to the K orbit and loses energy; the energy loss is measured as Ka and K~ X-rays. The La and L~ X-rays are produced when an M orbital electron drops down to the. L orbital. As the atomic number (Z) increases, the number of resulting secondary X-rays (such as!(,., K~, La, L,, etc.) and their intensity increases. Not all the incident X-ray photons produce secondary X-rays. Depending on the energy of the incident X-ray, a certain percentage of the photons can end up producing Auger electrons instead of secondary X-rays, and another percentage of them can be coherently and incoherently scattered. Alternatively, if too powerful, incident photons can pass through the sample's atoms and not produce any secondary X-rays or be scattered. Efficient production of secondary X-rays occurs when the incident photons have energy just slightly greater than the binding energy (also known as the absorption edge) of the K orbitals.' For example, Ca, which has a binding energy of 4.03 keV, has a cross-section of 6r6 cm'/gm at 5 keV, but at 30 keV has a cross-section of only 4 cm'/gm.' At 5 keV, Rb has a high cross-section at 386 em'/ gm, but its binding energy is 15.2 keV-thus, an incident photon with an energy of 5 keV would not have enough energy to displace an electron in the K orbital of aRb atom. Despite having a lower cross-section of 20.2 cm2 /g at 30 keV, the incident energy is more than sufficient to produce secondary X-rays. It is for this reason that different tube voltages are commonly used to detect elements of interest and multiple runs are needed. As noted by Janssen (2003: 371): "An element can therefore be determined with high sensitivity by means ofXRF when the exciting radiation has its maximum intensity at an energy just above an absorption edge of that element:' Coherent X-ray scattering is the basis for X-ray diffraction (see van der Veen and Pfeiffer, 2004). Incoherent scattering, also known as Compton scattering, is where the photon strikes an electron in the orbital of the atom, and loses part of its energy and is deflected in a different direction. For non-destructive ED-XRF and WD-XRF, this incoherent scattering is important since it is a function of the size and thickness of the sample. By ratioing the peak heights to the Compton scattering peaks, size and shape effects are accounted for in nondestructive ED-XRF (Shackley, 2012: 23).

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ED-XRfl AND WD-XRF SPECTROMETRY

345

The secondary X-rays emitted by the sample are what the XRF detector measures. EDXRF spectrometry measures the energy and intensity of the secondary X-rays, primarily the K and LX-ray lines. It is best suited for elements with an atomic number (Z) between 20 and 41, though with the proper excitation voltage, filters, and sample preparation, this method can measure elements from about Z ~ 11 through about Z ~ 92 depending on the instrument. WD-XRF spectrometry measures the wavelengths of the secondary X-rays and it can readily measure fluoresced X-rays from the lighter elements (e.g. Na, Ca) given their longer wavelengths (Lachance, 1993: 158). While in principle straightforward, there are complications to account for when it comes to measuring and quantifying the secondary X-rays. First, the generation of secondary X-rays occurs on the order of10-' 6 seconds, and all elements present have the potential of fluorescing. One must have a detection system in place that can record this flood of signals. Second, there are elements that have overlapping X-ray lines; two common examples include the Rb line overlapping with the Y Ka line, and the Pb La line overlapping with the As Ka line. In addition, mass absorption effects, also called inter-element effects, need to be accounted for. Some of the secondary X-rays that are produced can be absorbed by the sample and generate Auger electrons, whereas others can excite other atoms present in the sample and enhance their production of secondary X-rays. Generally speaking, higher Z elements have the potential for enhancing lower Z elements, particularly when the higher Z elements are present in much greater concentrations than the lower Z elements (Wobrauschek eta!., 2010: 4). Inter-element effects and overlapping peaks can generally be dealt with in the calibration software in newer ED-XRF and WD-XRF spectrometers. In terms of absorption, it must be emphasized that although the primary X-ray beam often penetrate deep into the sample, the fluoresced X-rays essentially come from the surface of the sample. Low Z elements produce lower energy X-rays and generally originate from within 10-20 microns of the surface. Higher Z elements, such as Cu, Ag, Au, and Hg, can produce (depending on the sample matrix) higher-energy X-rays from as deep as 100 microns.

K'

SAMPLE SELECTION AND PREPARATION A variety of factors need to be accounted for in the selection of ceramic samples for analysis. Obviously, the samples should potentially provide answers to the research question(s) at hand. Keep in mind, though, that without a prior study to reference to, chemical analyses of ceramics are often exploratory in nature. That is to say that although ceramics are being analyzed, the lack of a reference database makes determining the source of the ceramics inherently challenging. One approach is to measure as many samples of a given ceramic type or style as possible from a single site to see the potential variation in that single type or style. 'The condition of the ceramic samples is also important; samples that are extremely friable or encrusted with salts have the potential of being altered by post-depositional processes (see the end of this section). Given that most researchers use some form of multivariate statistics to identify groups in their chemical data, larger numbers of samples helps prevent singularities from occurring in the calculations. As a general rule of thumb, the number of samples analyzed should be a minimum of two to three times the number of elements being analyzed

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for. Tims, if twenty-seven elements are being measured, ideally more than fifty-four samples should be analyzed. One of the most important steps in preparing the sample for XRF analysis is cleaning the surface of the sample. Soil and other substances (e.g. soluble salts), not originally part of the pottery, need to be removed. As a minimum, pottery should be subjected to repeated washings with distilled/deionized water and scrubbing with a light nylon brush (Habu and Hall, 2001; Hall, zou; Ravisankar et al., 2011). Washing with ethyl alcohol in the final stages is also possible. Ideally, mechanical cleaning of the surface with an abrasive rotary-type tool is necessary to remove pigments> glazes, slips, and any other non-ceramic deposits that occur in and on the outer surface of the sherd. For qualitative analyses, both ED-XRF and WD-XRF require minimal sample preparation after cleaning. The sample can be a solid ceramic surface, a pressed pellet, a fused glass bead, or an unconsolidated powder. Although less desirable, the main requirement for analyzing solid surfaces is that the surface is relatively flat, sufficiently cleaned from soil or other foreign substances (see above), and homogeneous. Pressed pellets can be used for both quantitative ED-XRF and WD-XRF measurement of trace elements. Pellets are made by grinding several grams (2-15g depending on the laboratoryprotocol) of precleaned pottery sample into a fine powder (200-300 mesh).' Care must be used to avoid contamination. Most earthenwares can be ground in an agate or porcelain mortar by hand without too much risk of contamination. For hard ceramics) such as porcelains, it may be necessary to use silicon carbide or a tungsten carbide mill. 4 Alternatively, some laboratories routinely obtain samples by drilling into the ceramic and then collecting the resulting powder. Once the ceramic is powdered, it is typically mixed with a binder, such as polyvinyl alcohol or crystalline cellulose, and pressed into a pellet using a hydraulic press at 10-30 tons/in' (0.15-0.45 gigapascals). Pellets are often encased in a shell of aluminum or boric acid. Major elements with lower Z, such as Na, Mg, P, AI, and Si, are best measured using WDXRF spectrometry on a fused glass disk. As with pressed pellets, the pottery sample is finely powdered and mixed with low melting flux such as lithium tetraborate or lithium metaborate, and heated above 1ooo"C (Bennett and Oliver, 1976). 'The flux melts and the powdered pottery sample is dissolved. Upon cooling the molten mixture, a glassy disk is formed. A key aspect of fused disks is that matrix effects between samples and standards are negated given that everything is converted to a similar glass matrix. Specific procedures for producing fused discs of ceramic and refractory samples are detailed in the American Society for Testing and Materials (ASTM) standard ASTM Cl6o5-04(2009) and International Standards Organization (ISO) standard ISO 12677:2011. These two standards also specify operating conditions for WD-XRF spectrometers.' Fused discs with large dilutions (e.g. flux:sample ratio of 9:1) are not suitable for measuring most trace elements. In some cases, success has been obtained using low dilutions on the order of 2:1 to 5:1 (flux:sample). Eastell and Willis (1990), Hutton and Elliot (1980), johnson eta!. (1999), and Mori and Mashima (2005) have all developed protocols that produce fused discs that can be utilized for measuring both the major, minor, and select trace elements. Recently, De Vleeschouwer et al. (2011) and Ichikawa et al. (2o12b) have published methods for using 100 to 300 mg of unconsolidated powders in WD-XRF studies. However, measurements of unconsolidated powder are not common practice, and experimental protocols

X-RAY ED-XRF AND WD-XRF SPECTROMETRY

347

should be rigorously studied prior to attempting to generate reliable and valid quantitative data. This is especially true for measurements of major elements. Quantitative non-destructive ED-XRF and WD-XRF can also be performed on ceramics.' Once again, it is important that the sample surface be thoroughly cleaned. To minimize shape effects, it is also important that the area to be analyzed is relatively flat. Some researchers compensate tor shape effects by using tightly focused (e.g. collimated) X-ray beams a few millimeters in diameter or smaller to irradiate the sample. Smaller beams are particularly useful when studying paints, glazes, or some other unique feature on a ceramic, but are not ideal for bulk measurements. A larger beam size of 0.5 to 1.0 em in diameter is preferred for ceramic analysis as this permits irradiation of a larger area, thereby reducing variability in the measurement. Smaller diameter X-ray beams have been shown to produce highly variable measurements in ceramics, even in cases where the sample is relatively homogeneous (e.g. Speakman et al., 2011). Since non-destructive quantitative XRF spectrometry is a technique that only analyzes the surfaces of the pottery, post-depositional chemical alteration is a major concern. Studies by Buxeda i Garrig6s et al. (2001), Hedges and McLellan (1976), and Ichikawa (2012a) on post-depositional alteration have demonstrated that the alkali metals Ca, Mn, and P can be altered by a variety of post-depositional processes and skew the results of any analytical method. Several of the elements measured in ED- XRF studies of pottery, such as Ga, Nb, Th, Ti, Y, and Zr are only mobile in extreme metamorphic ;:onditions (Winchester and Floyd, 1977; Bishop et al., 1982), which are not typical of most archaeological sites. A few studies have demonstrated, with proper surface preparation, that non-destructive ED-XRF produces similar results to other analytical methods (Romano et al., 2oo6; Bonizzoni et al., 2010; Barone et aL, 2011).?

ED-XRF As noted above, ED-XRF spectrometry measures the intensity and energy of the fluoresced X-rays. 11re most important elements in an ED-XRF system are: (1) the X-ray source; (z) the detector; and (3) spectrometer geometry (Wobrauschek et al., 2010: 6-ro; Shackley, 2012: 26-33;).

X-Ray Sources X-rays can be generated from either a radioisotope or an X-ray tube. Radioisotopes commonly used for XRF spectrometry include ' 4 'Am, "Co, '"9 Cd, and "Fe, which as part of their radioactive decay emit either gamma rays or other photons. While useful for measuring select elements, radioisotopes have disadvantages as an X-ray source (Whiston, 1987: 3ll; Szal6ki et al., 2001): (1) they have a set energy level; (2) their intensity is often low and decays with time; (3) conventional semiconductor detector efficiencies are often low for the high energy ranges produced by the radioisotopes. Additionally, radioisotope sources are highly regulated. With technological advances in miniaturized X-ray tubes, XRF spectrometers using radioisotope sources have become increasingly scarce over the past ten years.

348

MARK E. HALL

Currently, X-ray tubes are the most common X-ray sources used in laboratory-based EDXRF spectrometers. Two types of X-rays are generated when high-voltage electrons travel from the cathode to the anode of the tube. The bremsstrahlung radiation is produced from the loss of kinetic energy when the electrons strike the anode; it ranges in energy from o keV to just a few ke V over the tube voltage. It defines the background signal. The anode produces X-rays characteristic of its composition. Anodes are typically made of higher melting point metals (e.g. Mo, Pd, Rh, W) that have a high photon flux. The spectrum produced by the X-ray tube can be optimized for elements of interest by varying the operating voltage and current. Further llexibility can be obtained by using primary filters and secondary target. Primary filters are inserted between the X-ray tube and the sample. Filters, when made of metal sheets, can fluoresce and generate Ka and K' X-rays that can enhance the lluorescence of elements in the sample. Filters also help reduce the background near the absorbing edge energy, and increase the detection limits of elements in the background "trough:' For example, Pd filters with a Rh tube can enhance detection of elements with a Z between 37 and 42 (Shackley, 2012: 28), whereas Ag filters with a Rh tube enhance detection of elements with a Z between 38 and 43 (Rose, 1990: table 5b ). In contrast to primary filters, a secondary target is a material that is excited by the primary X-rays. This material then emits secondary X-rays characteristic of the elemental composition of the target. These secondary X-rays are then what irradiate the sample. The use of secondary targets results in lower backgrounds and better excitation than primary filters, but requires a much higher initial X-ray energy. Tbe major advantage of secondary targets, however, is lower detection limits for Na and Mg (elements very challenging to measure by ED-XRF) and better detection limits for many other higher Z elements that occur in the low ppm range.

X-Ray Detectors For ED-XRF units, lifhium drifted silicon (Si(Li)) detectors are commonly used to measure X-rays with energies between 1 and 50 keV Si(Li) detectors can process between 40,000 to roo,ooo counts/second/mm' (cps/mm'), 8 and resolve 120 to 150 eV at 5-9 keV (Janssens, 2003: 386-387). Efficient operation ofSi(Li) detectors is obtained when they operate at temperatures below 250 Kelvin (K); one way to do this is by using liquid nitrogen. Another way of cooling the detectors is by using Peltier elements (i.e. a thermoelectric cooler) attached to fhe detector. Two common Peltier-cooled detectors are Si-PIN (silicon-p-type semiconductorintrinsic semiconductor-n-type semiconductor) diodes and SDD (silicon drift detectors). Si-PJN detectors are photodiodes used to detect X-ray and gamma ray photons. Beginnings in the early 2000s Si-PIN detectors were widely adopted by XRF instrument manufacturers as compact and inexpensive replacements for conventional liquid nitrogen cooled Si(Li) detectors. Si-PIN detectors typically have resolutions of 170-230 eVat 5.9 keV and can process count rates of about 40,000 cps. SDD detectors have typical resolutions of c.125-150 eV at 5·9 keV at and can process in excess of roo,ooo cps. The primary advantage ofSDD is that these sensors are capable of delivering lower electronic noise and higher count rates than their Si-PIN counterparts. 1beir primary drawbacks of SDD detectors are that their detection efficiency is lower than conventional Si(Li) detectors for X-ray energies greater than 10

X--RAY Fm-XRF AND WD-XRF SPECTROMETRY

349

keV (Potts eta!., 2004: 1399; Kenik, 2011: 40) and they typically cost twice as much as their Si-P IN counterparts. Other materials used for X-ray detectors include high purity germanium (HPGe), cadmium zinc telluride (CZT), and mercury iodide (Hgl,). HPGe detectors are suitable for measuring X-ray energies over 30 keV CZT detectors can operate at room temperature with a resolution of 250 eV at 5.9 keV and are also designed to handle high-energy X-rays (Janssens, 2003: 387). 11rese detectors can handle up to 15 x 10 6 cps/mm' (Szeles eta!., 2008). Detectors made from Hgl 2 can also operate at room temperature, deal with energies up to 150 keV, and when operating at 273 K, they have a resolution of2oo eV at 5.9 keV While commercial ED-XRF units have focused on using semiconductor detectors, research is still ongoing on high-resolution cryogenic detectors (Potts eta!., 2004; West eta!., 2010). Most of the research is focusing on superconducting tunnel junction detectors (S)T) which can achieve resolutions of 26-52 eV at 5·9 keV

Spectrometer Geometry '!he layout and arrangement of the X-ray source, sample, and detector dictate the size of an ED-XRF spectrometer and have an influence on the background. The simplest arrangement, known as a direct excitation system, is when theX-rays strike the sample at a 45° angle and the detector is placed at 45" to the sample surface. The sample is excited by both the X-ray tube anode lines and the bremsstrahlung radiation. '!his arrangement takes a minimum amount of space, and collimators and filters can be used to home in on specific areas of the sample and reduce the background. In a secondary excitation system, the primary X-ray beam strikes a secondary target whose X-rays are then reflected onto the sample. The fluoresced X- rays strike the detector at an angle of 45". By using filters, a secondary excitation system can have lower detection limits than a direct excitation system. The final geometry creates a polarized X-ray beam, which strikes the sample. In this configuration, the primary X-rays strike a polarizer at 90", which reflects the X-ray beam to the sample at a 90" angle. The fluoresced X-rays are collimated and directed to the detector at a 90" angle. While requiring more space, the background is decreased and lower elemental concentrations can be measured.

Quantification While there are a variety of computer programs available for the quantification ofED-XRF spectra, they all depend on either a fundamental parameters (FP) algorithm or an influence coefficients method (Janssens, 2003: 401-415; Thomsen, 2007; Brouwer, 2010: 48-56; Markowicz, 2011). FP methods are based on the theoretical X-ray production. For a given current and voltage setting, pure element samples are analyzed. These spectra of fhe pure elements are then used to iteratively calculate the concentration of the sample (run at the same current and voltage setting) .9 FP methods assume that one knows the matrix of the sample and has a good idea of the elements one needs to analyze for. Many FP programs require the chemical composition to be normalized to wo%.

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MARK E. HALL

Influence coefficients methods are based on a regression of elemental concentrations in standards of known concentration. For each element of interest, a calibration curve is created that links the X-ray intensity to a known concentration. This method can account for Compton scattering and inter-element effects. The standards used to create the calibration curves should be of similar composition as the samples; for ceramic studies, clay and sediment standards are available from the US Geological Survey, the US National Institute of Standards and Technology, and elsewhere that cover the relevant major, minor, and trace elements (see Hunt and Speakman, 2015). The calibration curve that is created should be checked against the known standards to determine accuracy. To monitor the calibration of the ED-XRF unit and determine the precision, known standards should be analyzed with each batch of unknown samples. Finally, it needs to be realized that the calibration curve is only valid for a given element between the highest and lowest concentrations in the standards used to create the linear calibration. Extrapolation of the regression line is not valid since inter-element effects at concentrations outside the range can cause the concentration versus intensity line to become non-linear.

WD-XRF As the name implies, WD-XRF spectroscopy measures the wavelengths of the fluoresced X-rays. A typical WD-XRF unit consists of an X-ray tube, a collimator, a diffracting crystal( s ), and an X-ray detector. X-ray tube technology for WD-XRF spectrometers is very similar to that discussed above for ED- XRF spectrometers. Collimators are optional for ED-XRF spectroscopy, but they are necessary in WD-XRF spectrometers. The polychromatic X-rays that are fluoresced from the sample are directed and channeled to the diffracting crystal(s) by the collimator. Collimators can improve the resolution by restricting the angles that the fluoresced X- rays strike the crystal.

Diffracting Crystals The crystals in a WD-XRF spectrometer diffract X-rays with different wavelengths, like a prism. When the Bragg equation is satisfied for a particular wavelength, the crystal reflects the X-rays into a detector instead of diffracting the X-rays. The detector then converts the X-rays of a specific wavelength into intensities for the given element. Individual crystals are used in WD-XRF spectrometers. Lithium fluoride (LiF) is commonly used since it can resolve the K-lines for Ti to U, and the L-lines for the rare earth elements (REEs). Pentaerythritol, also called PET, are used to resolve the K-lines of the elements between AI and K. Layered synthetic multilayers (LSM) are synthetic crystals manufactured using thin films. LSM crystals can be designed to measure the K lines of elements between Be and F.

PLATES

EXPERIMENTAL CLAYTEST -PIECES

state

Color by

(moisture content

Munsell

15-20 weight)

code

code

2.5Y 6/4

10R 5/6

2.5Y 6/3

2.5YR 5/8

5Y 5/2

10R 5/8

5Y 6/4

10R 6/8

2.5Y 5/3

10R 5/8

2.5Y 5/2

10R 5/8

Leather~hard

''

I

After firing 900 °C (oxidizing atmosphere)

Color by Munsell

,I

! 'l 'i

I

i I

Ij

PLATE 1

Experimental firings of different clay raw materials (Sicily, Italy).

(d)

(c)

PLATE 2 Photomicrograph of thin sections of medium-high fired sherds with calcite: (a) homogeneously distributed secondary calcite from recarbonatization after gehlenite in calcareous pottery (sigillata from Arezzo); (b) secondary calcite in calcareous pottery (Eastern Sigilata A) is dissolved at the surface where environmental acid solutions had access, as, for example, on the upper right site where the protective gloss is missing; (c) precipitated calcite in non-calcareous North Mesopotamian metallic ware; (d) calcite scale below the red gloss of a sherd of Tripolitanian sigillata from Carthage. (Photomicrographs by G. Schneider; incompletely crossed polarizers, width of field 0.7 mm.)

1,1

(c)

PLATE 3 (a) Late Bronze Age pottery sample 133, hand specimen of the fabric in fresh break, width of field is 15 mm (photograph I. K. Whitbread); (b) Late Bronze Age pottery sample 133, photomicrograph of the fabric in plane polarized light, width of field is 4.65 mm (photograph I. K. Whitbread); (c) Late Bronze Age pottery sample 133, photomicrograph of the fabric under crossed polars, width of field is 4.65 mm (photograph I. K. Whitbread).

---------------~~--

4 Photomicrographs of thin sections with a basalt-andesitic volcanic rock fragment under plane polarized light (a) and crossed polarized light (b); (c) pale green pleochroic colors of a pyroxene mineral in plane polarized light (field is 1.8mm); (d) moderate (low second order) interference colors of an amphibole (field is 1.2mm); (e) secondary calcite formation in pore space; (f) test-fired ceramic with grog under crossed polarizers. A clear demarcation can be detected between grog and the matrix (field is 1.8mm). PLATE

5 Some microstructural changes with increasing firing temperature involving inclusions, pores, and groundmass. Photomicrographs in polarized transmitted light, parallel polars of: a-d) mollusk shells with still preserved (a) and completely obliterated (b) internal structure, pores with irregular (vughs, c) and spherical (vesicles, d) shape, and optically active (a, c) and inactive (b, d) groundmass, as a consequence of the firing temperature of the same base clay material; e-f) micritic limestone grains with still-preserved crystalline optical behavior (a) and completely obliterated (b) from the firing. Scanning electron microscope back scattered images of an illitic-chloritic clay in which the groundmass is still composed of well-defined grains at 1050°C (g), whereas at uoo°C it is partially melted, forming an amorphous phase, which determines bridging between grains. PLATE

Original sample

Sample after refiring 400 °C

600 oc

700 °C

800 oc

900 oc

PLATE 6 MGR-analysis of six ceramic sherds, carried out to determine original firing temperatures. (For explanations see text in Chapter 27.)

(a)

(b)

7 Structural MGR-analysis of two ceramic samples. A= pottery fragment originally fired at Teq < 70o'C; B =pottery waste, fragment over-fired at 1100-1150'C. (Photographs taken under a reflected light microscope.) PLATE

Sample after refiring Original sample

800 "C

900 oc

1200"C

2

3

4

5

PLATE 8 MGR-analysis (8oo•c, 9oo•C,12oo•C) of five samples belonging to two MGRgroups-a fact which only becomes apparent after re-firing at 12oo•c.

l

8

SN

ovf

ovM

sMLT

MLT

fl

sovM (temper MLT)

9 Examples of matrix types (samples re-fired at 12oo'C) of non-calcareous sherds (iron-rich red-firing or iron-poor whitish-firing) and of calcareous pottery (yellowishgreenish firing). (Photographs by M. Baranowski.)

PLATE

X-RAY ED-XRF AND \VD-XRF SPECTROMETRY

351

WD-XRF Detectors WD-XRF spectrometers can use proportional counters, scintillation detectors, or gas scintillation detectors to measure the intensity of the fluoresced X-rays (of a given wavelength). Proportional counters are essentially a sealed glass tube containing a wire and are filled with an inert gas. 10 The wire leads out of the tube and is connected to a resistor and capacitor in parallel. A high-voltage charge is placed across the wire. When an X-ray strikes the tube, the gas is ionized and the negative ions are drawn towards the wire. The voltage pulse across the capacitor is proportional to the energy of the fluoresced X-ray beam. Proportional counters, depending on the gas/gases they are filled with, can handle over 1 million cps. Their resolution ranges from soo to woo eV. Scintillation detectors are better at measuring X-rays with wavelengths less than 1.5A (jenkins, 1999: 97). These detectors are made of sodium iodide doped with thallium, or caesium iodide doped with thallium or sodium. This material is then connected to a photomultiplier. When X-rays strike the scintillator, light is produced that has intensity proportional to the energy of the X-ray. The photomultiplier converts the light to an electron pulse. The resolution of these detectors is quite poor; they are on the order of 1 ke V Scintillation detectors can also handle over 1 million cps. Gas scintillation detectors combine elements of both the proportional counter and scintillation detector. A gas filled tube holds two wire mesh electrodes, similar to a proportio"nal counter; a photon enters in the tube and ionizes the gas. A charge is placed across the two electrodes. Ultraviolet radiation is emitted when the ions collide with the electrodes. A photomultiplier measures the ultraviolet radiation that is produced. The resolution of these detectors is around 300-500 eV. When the detectors are mounted on a goniometer and they rotate at an angle of 26 degrees as the crystal rotates e degrees, the intensities of the wavelengths are sequentially measured. This classifies the spectrometer as a sequential spectrometer. When there are a series of detectors mounted at fixed angles with a fixed series of crystals, then the intensity of several wavelengths can be measured simultaneously. WD-XRF spectrometers with this arrangement are known as simultaneous spectrometers.

COMPARISONS BETWEEN AND

WD-XRF

ED-XRF

SPECTROMETERS

Both ED-XRF and WD-XRF spectrometers can be used to measure elements of interest for studies of technology and provenance. 1he advantages and disadvantages inherent to both spectrometers may influence the ability to answer the research questions, though. In theory, both types of spectrometers can measure elements with Z >8, but light element measurements are more challenging by ED-XRF. WD-XRF spectrometers measure the light elements with better precision and resolution. WD-XRF spectrometers can also more readily measure some of the REEs (rare earth elements). In terms of detection limits, while there are associated issues of sample preparation, backgrounds, and counting times,

352

MARK E. HALL

WD-XRF spectrometers generally have superior detection limits over ED-XRF spectrometers (Jenkins, 1999: 117-119; Janssen, 2003: 418). With respect to acquisition costs, WD-XRF spectrometers, generally, are expensive (>$zooK) and require dedicated laboratory space. ED-XRF spectrometers have a lower cost ( n).' The detection limits of the PIXE technique are very low, of the order of~g/g (ppm), or ro' 4 at/em', which is of the order of one atomic monolayer. Owing to the high yield of the X-rays in the energy range ofr to 20 keV produced by ion impact (Johansson, 1970 ),'small samples, to the lower limit of approximately 1 ~tg/cm 2 , can still generate enough X-rays, allowing acceptable minute-long measurements. For this reason, PIXE is also known for its speed. Broad beam PIXE analysis is used to measure sample areas of about or lower than o.s cm2 • Nowadays microbeams (with a lower limit of a few nm in diameter) are used to analyze micrometer-sized samples (Legge, 1997; Salamanca, 2001; Mesjasz-Przybylowicz, 2002; Calligaro, 2004; Salomon, 2008). Samples can be analyzed either in vacuum or in atmosphere. Former PIXE analysis took place in-vacuum setups, but with the developmentofhighly resistant and very thin (less than 1 ~m) exit windows, external beam PIXE analysis is becoming more popular. This allows the analysis of samples that cannot be placed in vacuum, either because of size limitations, beam heating sensitivity, or the presence of volatile compounds. In external beam PIXE analysis, the beam is extracted through an exit window, necessary to separate the ultra-high vacuum environment of the accelerator from the outer atmosphere where the sample is placed. Objects of cultural heritage such as paintings, ceramics, bones, and wood samples have been successfully analyzed on external beam PIXE systems (Grassi, 2004; Constantinescu, 2014).

PIXETheory The atomic de-excitation of an atom and the subsequent emission of characteristic X- rays follow a set of quantum mechanical selection rules, resulting in a group of X-ray lines univocally tied to the emitting chemical element. Moreover, the Moseley law found in 1913 (Moseley, 1914) produced a simple mathematical relationship between the energy of a given X-ray line and the atomic number of the emitting atom. This enabled a practical method for the identification of all chemical elements. To quantitatively relate the number of detected X-ray photons of a given line and the corresponding number of atoms in the sample, several experimental parameters have to be taken into account. The quantitative formulation of the PIXE method is usually undertaken with the following steps (Johansson, 1970,1976, 1988, 1995).

384

MARCIA A. RIZZUTTO AND MANFREDO H. TABACNIKS

Taking the geometry and parameters described in the drawings of Figure 22.1, the incidence of n(x,y) ions in a sample will create N X-ray photons of a specific i line, proportional to the number of incident ions and the atomic (or mass) density of the chemical element j present in the sample. The proportionality factor is called X-ray production cross-section, axi· The complete differential PIXE formula is:

Equation 22.1 Q

where -

4n

is the fraction of the solid angle seen by the detector, e is its detection efficiency

(including fllters), Pi is the elemental mass density of atoms of kind j in the sample and supposed to be homogeneously distributed in the sample, T(z) is the transmission efficiency (or attenuation) of the X-ray photons on their path d to the detector, and dxdydz is the elementaryvolume to be integrated over the whole sample. Referring to Figure 22.1, the output path, d, can be written as a function of the x-coordinate along the beam direction:

do cos a= x o cos (accessed January 2014). Legge, G. J. F. (1997). "A History of Ion Microbeams:' Nuclear Instruments and Methods in Physics Research B130: 9-19. Leighton, R. B. (1959). Principles ofModern Physics (New York: McGraw-Hill). Lima, S.C. (2010). "Tecnologia ceramica Chimu: estudo arqueometrico da cole.;ao MAE/USPChimu ceramic technology: archaeometric study of the MAE/USP collection:' Doctoral thesis, MAE/USP. Lima, S.C., Rizzutto, M.A., Added, N., Barbosa, M.D. L., Trindade, G. F., and Fleming, M.l. D. A. (2011). "Pre-Hispanic Ceramics Analyzed Using PIXE and Radiographic Techniques:' Nuclear Instruments and lvfethods in Physics Research B269: 3025-3031.

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PIX£ AND ITS APPLICATIONS FOR CERAMIC ANALYSIS

397

MAE (2014). Museu de Arqueologia e Etnologia da Universidade de Siio Paulo-MAE/ USP: (accessed january 2014). Mesjasz-Przybylowicz, ). and Przybylowicz W ). (zooz). "Micro-PIXE in Plant Sciences: Present Status and Perspectives." Nuclear Instruments and Methods in Physics Research B1S9: 470-4S1. Moseley, H. G.). (1913). '"!he High Frequency Spectra of the Elements:' Philosophical Magazine 26:1024.

Moseley, H. G.). (1914). "The High Frequency Spectra of the Elements:' Philosophical Magazine 27:703. Moseley, M. E. (1990 ). "Structure and History in the Dynastic Lord of Chimer:' In: Moseley, M. E. and Cordy-Collins, A. (eds ), The Northern Dynasties: Kingship and Statecraft in Chimor (Washington, D.C.: Dumbarton Oaks Research Library and Collection). No una, M., Roumie, M., Calligaro, T., Nsouli, B., Brunetto, R., Baklouti, D., L. d'Hendecourt, L., and Della-Negra, S. (2013). "On the Characterization of the 'Paris' Meteorite Using PIXE, RBS and Micro-PIXE:' Nuclear Instruments and Methods in Physics Research B3o6: z61-z64. Papachristodoulou, C., Oikonomou, A., Ioannides, K., and Gravani, K. (zoo6). "A Study of Ancient Pottery by Means of X-Ray Fluorescence Spectroscopy, Multivariate Statistics and Mineralogical Analysis:' Analytical ChimicaActa 573/574:347-353. Pie!, N., Schulte, W H., Berheide, M., Becker, H. W., Borucki, L., Grama, C., Mehrhoff, M., and Rolfs, C. (1996). "Efficient y-Ray Detection in Ion Beam Analysis:' Nuclear Instruments and Methods in Physics Research BnS: 1S6-189. Quaranta; A., Dran, J. C., Salomon, J., Tonezzer, M., Scian, C., Beck, L., Carturan, S., Maggioni, G., and Della Mea, G. (zooS). "Ion Beam Induced Luminescence on White Inorganic Pigments for Paintings." Nuclear Instruments and Methods in Physics Research Bz66: Z301-z305. Rizzutto, M. A., Tabackniks, M. H., Added, N., Barbosa, M. D. L., Curado, ). F., Santos )r., W A., Lima, S.C., Melo, H. G., and Neiva, A. C. (2005). "The External Beam Facility Used to Characterize Corrosion Products in Metallic Statuettes:' Nuclear Instruments and Methods in Physics Research Bz40: 539-553. Rourniea, M., Wicenciak, U., Bakraji, E., and Nsouli, B. (zow ). "PIXE Characterization of Lebanese Excavated Amphorae from jiyeh Archeological Site:' Nuclear Instruments and Methods in Physics Research Bz68: 87-91. doi:10.1016/j.nimb.zoo9.09.061. Ruvalcaba-Sil, ). L., Manzanilla, L., Melgar, E., and Lozano Santa Cruz, R. (zooS). "PIXE and Ionoluminescence for Mesoamerican Jadeite Characterization." X-Ray Spectrometry 37' 96-99· Salamanca, M. A., Ager, F. )., Ynsa, M. D., Gomez Tubio, B. M., Respaldiza, M. A., Garcia Lopez, )., Fernandez-Gomez, F., de la Bandera, M. L., and Grime, G. M. (zoo1). "External Microbeam Set-Up at the CAN (Sevilla) and Its Application to the Study of Tartesic jewellerY:' Nuclear Instruments and Methods in Physics Research B1S1: 664-669. Salomon, )., Dran, ). C., Guillou, T., Moingnard, B., Pichon, P., Walter, P., and Mathis, F. (zooS). "Present and Future Role of Ion Beam Analysis in the Study of Cultural Heritage Materials: The Example of the AGLAE Facility:' Nuclear Instruments and Methods in Physics Research B226: 2273-2278. Swann, C. P., Caspi, S., and Carlson, ). (1999 ). "Six Stirrup Handled Moche Ceramic Vessels from pre-Colombian Peru: A Technical Study Applying PIXE Spectrometry:' Nuclear Instruments and Methods in Physics Research B150: 571-575.

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MARCIA A. RIZZUTTO AND MANFREDO H. TABACNIKS

Tabacniks, M. H. (1983). "Calibra.;ao do sistema PIXE-SP de analise elementar-Calibration of PIXE-SP Elemental Analysis System:' MSc thesis, Institute of Physics, USP, Sao Paulo, Brazil. Tabacniks, M. H. (2005). "Os Elementos na Materia-Elements in Matter:' Thesis, Institute of Physics, USP, Siio Paulo, Brazil. Tesmer, J. R. and Nastasi, M. (1995). Handbook of Modern Ion Beam Materials Analysis. First Edition (Pittsburgh, PA: MRS). Woldseth, R. (1973). X-Ray Energy Spectrometry (Burlingame, CA: Kevex Co.). Yang, C., Malmqvist, K. G., Elfman, M., Kristiansson, P., Pallon, J., Sjijland, A., and Utui, R. ). (1997). "Ionoluminescence and PIXE Study oflnorganic Materials:' Nuclear Instruments and

Methods in Physics Research B130: 746-750. Yap, C. T. and Vijayakumar, V (1990 ). "Principal Component Analysis of Trace Elements from EDXRF Studies:' Applied Spectroscopy 44( 6): 1080-1083. Zhua, J., Shana, J., Qiua, P., Qina, Y., Wanga, C., Heb, D., Sunb, B., Tongb, P., and Wub., S. (2004). "The Multivariate Statistical Analysis and XRD Analysis of Pottery at Xigongqiao Site." Journal ofArchaeological Science 31:1685-1691. Ziegler, J. F., Biersack, J.P., and Littmark, U. (1985). The Stopping and Range of Ions in Solids, val. 1 (New York: Pergamon Press).

CHAPTER 23

INDUCTIVELY COUPLED PLASMA-MASS SPECTROMETRY (ICP-MS) AND LASER ABLATION INDUCTIVELY COUPLED PLASMA-MASS SPECTROMETRY (LA-ICP-MS) MARK GOLITKO AND LAURE DUSSUBIEUX

INTRODUCTION

CERAMIC provenance studies are, in effect, cultural/technological and geological studies. Rarely can the actual geographical boundaries of a "source" be delimited with precision. Instead, pronouncing a sherd "local" or "non-local" is a probabilistic statement reflecting a variety of potential criteria, including: knowledge oflocal geochemistry and mineralogy; the likelihood of observing a similar compositional profile in sherds produced elsewhere; how far from a particular location people are likely to travel to obtain their raw materials (e.g. Arnold's (1985) "primary exploitation threshold"); how frequently represented particular ware types or chemical types are at a given location versus elsewhere (the "criterion of abundance"); cultural-technological choices such as clay preparation and vessel use; and postburial changes that may impact observed sherd composition. Many ceramic provenance studies rely on techniques such as instrumental neutron activation analysis (INAA) or X-ray fluorescence (XRF) to generate bulk compositional data. Inductively coupled plasma-mass spectrometry (ICP-MS) was first used by archaeologists interested in finding a lower cost, more widely available alternative to INAA during the early to mid-1990s (e.g. Burton and Simon, 1993: Tykot and Young, 1996). However, the major contribution of ICP-MS to archaeological ceramic analysis is more recent; the use oflaser ablation (LA) sample introduction to produce spatially resolved chemical information to

400

MARK GOLITKO AND LAURE DUSSUBIEUX

supplement mineralogical or bulk chemical analysis. Elemental "mapping" and phase analysis by LA-ICP- MS facilitates identification of the underlying chemical structure and mineralogy of a ceramic and which geological, cultural, technological, and/or post-depositional processes account for the variation observed in bulk chemical studies. Several other analytical techniques offer spatially resolved imaging and analysis-electron probe microanalysis (EPMA) and scanning electron microscopy with energy dispersive spectrometry (SEMEDS) for example-but these techniques have relatively high detection limits and cannot typically measure elements present at very low concentrations that are often of interest in ceramic compositional studies. LA-ICP-MS has consequently emerged as the preferred technique for targeted analysis of archaeological ceramics owing to the wide range of elements it can measure, low detection limits, and minimal destructiveness. In this chapter, we review the basics ofiCP-MS, liquid and solid sample introduction, mass spectrometer types, and discuss data quantification appropriate for ceramic analysis. Next, we examine applications and advantages of!CP-MS for archaeological ceramic studies, including a critical review of paste characterization by laser sampling, and conclude with a case study from the Sepik coast of Papua New Guinea that highlights some of the potential advantages of the technique. We emphasize that ICP- MS analysis is most valuable as part of a combined study incorporating bulk chemical and mineralogical characterization in concert with targeted analysis by LA-ICP- MS.

BASICS OF INDUCTIVELY COUPLED PLASMA-MASS SPECTROMETRY (ICP-MS) An inductively coupled plasma-mass spectrometer measures ions separated by an arrangement of powerful magnets according to their mass to charge ratio (m/Z) (Thomas, 2013). The ions are generated (i.e. the sample is ionized) by preparing the sample as an aerosol, a colloid suspension in gas, and passing that aerosol through a superheated plasma that strips electrons from the atoms (Figure 23.1). For the purposes of ICP-MS, a plasma can be understood as a super-heated ionized gas consisting of positive ions and free electrons in proportions creating a roughly neutral electrical charge. Plasmas used in spectrochemical analyses should be formed from an elemental gas that has a high ionization energy but is minimally reactive, enabling it to efficiently ionize most other elements while at the same time preventing the formation of oxides or poly atomic species that can interfere with the detection/quantification ofions with identical masses. Argon (15.76 eV) is typically the gas used to create plasmas for ICP-MS, reaching a temperature of about 10,ooo K. Only four elements, H, He, F, and Ne, have higher ionization energies than Ar and, while these cannot be measured using an Ar plasma, some of these elements (Fin particular) are of analyticalutilityin archaeological studies (Ammann, 2007). Ne plasmas have been tested, but their use results in lower sensitivity than when using Ar (Petibon et al., 2002), while He is substantially more expensive than Ar. To create the plasma, Ar gas is introduced into a torch consisting of three concentric quartz tubes, surrounded by an induction coil linked to a radio-frequency (RF) generator that produces an alternating current in the gas. A spark is applied to introduce free electrons,

---------------ICP-MS AND LA-ICP-MS

He canister

401

Nd:YAG laser and focusing

camera

Mass spectrometer laser control software

Liquid

auto-sampler

··~·-· de'.!

FIGURE 23.1 An ICP-MS laboratory, with both laser ablation and liquid sampling equipment visible. (Photograph: Photo by Laure Dussubieux.)

which are rapidly accelerated via the electromagnetic field induced by the RF generator and coiL These electrons collide with Ar atoms, ionizing a small percentage of them to form the plasma (Figure 23.2). When the sample aerosol is introduced into the plasma, it collides with electrons removed from Ar atoms in the plasma and is ionized into positive elemental ions and more free electrons. The resulting ion beam is then passed through a series of cones with narrow apertures that facilitate coupling between the relatively low-vacuum ( -IXw' Pa) high-temperature conditions in the plasma chamber and the very-high-vacuum conditions (~1x10- 4 Pa) in the mass spectrometer. The ion beam then passes through positively charged electrostatic ion lenses

situated just past the cones, which focus the beam and remove photons and electrons that would otherwise generate background noise if they reached the detector. Some instruments also feature collision cells or other optics that remove polyatomic species or other unwanted constituents from the ion beam, reducing background noise, although at the loss of signal strength (Ammann, 2007; Thomas, 2013). After passing through the mass spectrometer (see the section "Mass Spectrometer Types"), ions collide with a detector, usually a Faraday cup, and are measured as electrical current. Plasma-ion sources have existed for decades; however, previous generations of ICP instruments used atomic emission or optical emission spectroscopy, ICP-AES and ICP-OES respectively, to measure the characteristic light emitted by atoms excited by the plasma rather than directly measuring the ions themselves. The benefits of using mass spectrometry over AES and OES instruments, particularly for cultural materials studies, include lower limits of

402

MARK GOUTKO AND LAURE DUSSUBIEUX

(a)

Detector

------·------I (b)

Skimmer and sampler cones

Plasma torch

Plasma

j

-~

·····-u------------------···.······flt'fl. tt

Rf coil

1

(c)

···---~-----.

----~agnets

~~" II!'

Exit slit

Argon Gas

Detectors Detector (d)

Detector

·····t············--·---:c==

Q\=

= =

rn'

\,/

=

\/~ =

FIGURE 23.2 Schematic diagram of plasma-ion source and common mass spectrometer types: (a) quadrupole; (b) single-collector magnetic sector; (c) multicollector magnetic sector; (d) time-of-flight. Dashed lines represent the path of the sample aerosol or ion beam. ( © Mark Golitko.)

detection, a broader range of detectable elements, and perhaps most importantly, the ability to more rapidly generate usable signal measurements. This last characteristic means that ICP- MS instruments can generate data reliably using smaller sample volumes, reducing potential damage to objects while also allowing measurement of very small sample areas. Commercial ICP-MS units were first marketed in 1983 and have become fairly standard instrumentation in geological> chemical, and environmental testing laboratories since then (Ammann, 2007). ICP-MS was first used for archaeological material studies during the 1990s to study elemental concentrations in obsidian (e.g. Tykot and Young, 1996) and archaeological ceramics (e.g. Burton and Simon, 1993).

SAMPLE INTRODUCTION

Samples must be introduced into the ICP- MS in the form of a fine aerosol, ideally with particles less than wo nanometers (Guillong et al., 2003). The two principal methods for creating an aerosol from the sample material are by dissolving it in liquid or by removing a small portion of the sample with a laser to produce fine particulate matter.

ICP-MS AND

LA~ICP-MS

403

Liquid Sample Introduction Liquid sample introduction involves powdering solid samples, dissolving them in an acid, and introducing the resulting solution into the ICP-MS, via a nebulizer, as a constant controlled stream of aerosol. Two of the major advantages ofliquid sample introduction are precise control of input volume and flow, and the ability to produce a truly representative bulk characterization of a sample by powdering a relatively large volume of material. However, liquid sample introduction has a serious disadvantage; the sample must be readily soluble in acids. Ceramics, like most aluminosilicates, are very difficult to put into solution, often requiring the use of caustic and expensive acids to achieve full dissolution. Early attempts at weak acid dissolution of archaeological ceramics using 1-molar hydrochloric acid (HCl) (Burtoh and Simon, 1993; Nieves Zedei\o, 1994) proved problematic because the acid bath differentially extracted elements depending on initial composition, firing temperature, temper type and abundance, and post-depositional mineralogical alteration of the ceramic material. Consequently, it proved difficult to ensure that weak acid extraction of ceramics was consistent and reproducible for a single sample, let alone across an assemblage or between laboratories. As a result, the chemical composition of ceramics determined by weak acid extraction ICP-MS was difficult to interpret and unhelpful with regard to provenance determination (Neff eta!., 1996; Triadan eta!., 1997; cf., Burton and Simon 1996), precluding the establishment of weak acid extraction as a reliable technique for analysis of archaeological ceramics by ICP-MS. More aggressive acid dissolution regimes can consistently extract the elemental composition of archaeological ceramics and have been demonstrated to be effective and reproducible for their bulk chemical characterization (e.g. Clark and Kennett, 2009). Tsolakidou eta!. (2002) evaluate several approaches for archaeological ceramics in their study, such as digestion in open vessels using hydrofluoric and hydrochloric acid, alkali fusion, and microwave digestion. While they achieved good recovery rates for most elements, their experiments indicated low recovery rates for important trace elements, including zircon and most rare earth elements (REEs), which are often contained in acid-resistant mineral phases included in the ceramic fabric. By adding boric acid to the microwave digestion routine described by Tsolakidou eta!., Kennett eta!. (2002) were able to improve recovery rates for many elements including the REEs, and this method has proven effective for bulk chemical characterization of ceramic materials.

Laser Ablation Laser ablation sample introduction was first developed by geologists interested in analyzing mineral phases that were small and difficult to dissolve into solution (Gray, 1985; Fryer et a!., 1995), and is now the most widely used sample introduction method for archaeological studies. In laser ablation ICP-MS, a beam of coherent light is used to remove small particles of sample which are then swept along in a carrier gas, typically He. The beam width can be varied to between about 5-100 microns, and penetration depth can be controlled by ablating for different durations depending upon the composition of the sample or phase of interest. For instance, analysis of surface treatments such as glazes or slips can be achieved by rapidly scanning the laser. LA-ICP-MS is often considered

404

MARK GOT.TTKO AND LAURE DUSSUBIEUX

quasi-non-destructive because, while the sample is being ablated, the damage is invisible to the naked eye. A variety of laser types can be used for LA-ICP-MS, most commonly 266 or 213 nm neodymium doped-yttrium aluminum garnet (Nd:YAG) lasers; although newer argon fluoride (ArF) excimer and solid-state lasers operate at 193 nm wavelength. Shorterwavelength lasers are desirable because they help reduce fractionation, an effect noted during early applications oflaser ablation when longer wavelength lasers (~woo nm) were employed. In ICP-MS, fractionation refers to any process that results in differential efficiency of ablation, transport, and/or detection of elements, usually because of differential elemental volatility during melting, and is principally an effect of aerosol particle size (Chen, 1999; Eggins et aL, 1998). Shorter-wavelength lasers produce smaller, more uniformly sized particles during ablation than longer-wavelength lasers and, as a result, result in lower fractionation (Gonzalez et aL, 2002; Guillong et aL, 2003). Shorter-wavelength lasers are also less affected by differences in sample density and opacity and, therefore, are more consistent in ablation efficiency across different matrix types, which is a critical component of matching standards to archaeological materials for calibration purposes (Gaboardi and Humayun, 2009 ). Commercially available LA-ICP-MS spectrometers used in archaeology are similar to those first developed and reported by jackson et aL (1992), combining a laser for ablation with a magnifying microscope or camera that allows targeted focusing of the laser on areas as small as a few microns. A motorized stage also facilitates precise positioning of the laser, and sampling either creates craters ablated downwards through the material or lines ablated across the surface of a sample. Consequently, laser ablation can be effectively used for either depth-profiling; for instance, by drilling down through a multilayer surface treatment, or to sample only the first few microns of glaze, slip, or paint Although laser ablation can be described as quasi-non-destructive, most ablation units require that the sample fit in a chamber that can be purged of ambient air, which can induce fractionation if present (Kasler et aL, 2002). Consequently, even laser ablation sampling requires that samples be relatively small, on the order of a few em in maximal dimension. For ceramic sherds recovered from active excavations this may not be an issue; however, for analyses of complete vessels and/or sherds in museum collections, for instance, it may be a problem (Giussani et aL, 2009). Large ablation cells have been developed by some laboratories, as well as "open~cell" designs to accommodate the special needs of cultural history and archaeological applications. Open-celllaser units either use a small volume cell that is sealed onto the sample surface, or an annular argon gas flow to remove ambient atmosphere without requiring physical contact with the sample surface. This latter method has been used for archaeological ceramic studies, facilitating analysis of complete vessels; however, sample throughput is typically much slower using an open-cell unit than with conventional closedcell designs (e.g. Wagner and j~dral2on).

MASS SPECTROMETER TYPE§

Several types of mass spectrometers may be used to sort ions according to mass and charge. The most common spectrometer used for archaeological applications is the quadrupole

ICP-MS AND LA-ICP-MS

405

mass spectrometer (Figure 23.2a), which consists of four parallel rods connected to variable currents generating an adjustable magnetic field that allows only one m/Z ratio through to the detector at a time. Quadrupoles sweep through the complete mass/charge range in a matter of seconds in order to measure the widest range of elements in the sample, but consequently, measurements on individual elements do not reflect simultaneous ablation at the sample surface. When very small features are analyzed (which are thus rapidly vaporized by the laser), measurements on loW'~ and high- mass elements may not correspond to the same feature of interest. Quadrupoles also have relatively low mass resolution (ability to resolve small dif!erences in m/Z ratios), and can suffer from mass-spectral interference for isotopes of different elements with similar m/Z ratios and because of the formation of polyatomic ions. For instance, 6 4o Ar' 0 interferes with the detection and quantification of 56Fe, the most abundant isotope of Fe, because of their similar mass (55-9349 u vs. 55-9573 u) (May and Wiedmeyer 1998). However, most quadrupole instruments are able to overcome these weaknesses by generating high signal strengths for elemental isotopes that suffer from less interference (e.g. 57 Fe). Quadrupoles are of great utility for chemical characterization of ceramic pastes, glazes, slips, paints, and individual inclusions/phases because they are able to measure a wide range of elements quickly and efficiently. Another common spectrometer is the magnetic sector field ICP-MS. 1bese instruments use a magnetic field to bend ions through a curved path with a different radius for each m/ Z ratio/ion of interest. One ion at a time is directed toward the appropriately positioned exit slit placed before the detector, determined by the force of the magnetic field. Sector field instruments can be either single collectors for non-simultaneous measurement of ions of different masses (Figure 23.2b) or multicollectors (Figure 23-2c), in which several detectors allow simultaneous measurement of ions of different masses. Magnetic sector ICP- MS (MC-ICP-MS) is also referred to as high-resolution ICP-MS (HR-ICP-MS) because it has superior resolving power compared with quadrupole instruments. The high mass-resolu~ tion achievable with these detectors eliminates many isotopic interferences, making them ideal for isotopic measurements (White et al., 2ooo; Vanhaecke et al., 2009). As a result, MC/HR-ICP-MS has gradually replaced thermal ionization mass spectrometry (TIMS) as the method of choice for isotope measurements in geological and archaeological studies (White et al., zooo). However, MC/HR-ICP-MS instruments are very expensive, particularly multicollectors, compared with TIMS and quadrupole ICP-MS instruments, and are, consequently, less widely available. That said, HR-ICP-MS has been successfully used to study lead isotopes in ceramic glazes for provenance determination by both liquid sampling (e.g. Habicht-Mauche et al., 2002; Cui et al., 2010) and laser ablation (Habicht-Mauche et al., 2002; Ifiaftez et al., 2010 ). The third spectrometer used for archaeological applications is the time-of-flight (TOF) mass spectrometer (Figure 23.2d). Rather than using differential m/Z ratios to sort ions in a magnetic field, as quadrupole and magnetic sector instruments do, TOPs use the time of flight after application of a uniform accelerating voltage to sort ions by mass by forcing ions through a curved path of particular length. TOF spectrometers can measure the entire mass range simultaneously, and integrate that mass range about three times faster than quadrupole instruments. Consequently, TOF spectrometers are of particular utility in applications where short signal integration time is necessary (Leach and Hieftje, 2ooo; Thomas, 2013); for example, the analysis of microfeatures

406

MARK GOLITKO ANO LAURE DUSSUBIEUX

such as pore boundaries, small grain inclusions, and very thin slips or glazes. Although less resolved than I-IC-ICP-MS instruments, TOF spectrometers generally achieve better mass-resolution than quadrupole instruments, and thus in principal represent a relatively cheap means of isotopic analysis. However, TOFs have low sensitivity (ability to detect signal above background), and Dudgeon et al. (2007) were only able to achieve sufficiently high signal counts for low-abundance isotopes by generating several hundred readings per sample, removing "noisy" readings resulting from low concentrations in some areas of the analyzed samples, and averaging the remaining measurements to generate isotopic ratios.

QUANTIFICATION

Quantitative results are obtained by comparing the signal intensity measured for a given element in a sample to the signal intensity for the same element in a standard solution or a certified reference material (CRM), also called an external standard in the literature. ICPMS instruments exhibit cyclical patterns of drift over time, meaning that the relationship between signal strength and sample elemental concentration changes between analyses. Consequently, quantification requires repeated analysis of external standards across the course of analysis to ensure that values are comparable. In addition, an internal standard is required to correct for potential changes in sampling rate-how much material enters the plasma per unit time. For liquid sampling, quantification is relatively straightforward; the internal standard is an element absent in the sample material, and each sample and standard solution is spiked with a known concentration of the element. External standards are typically produced by diluting commercially available elemental solutions with ultra-pure water and nitric acid to produce standards at varying concentration levels (see, for example, Kennett et al., 2002). Generating quantitative results for LA-ICP-MS analysis is more challenging. For solid samples, the internal standard has to be an element already present in the material because it is not possible to add elements/material to the sample. The control element must have a relatively high concentration in each sample and external standard so that its measurement is as accurate as possible (Gratuze et al., 2001). In most archaeological ceramic studies, Si is the internal standard used; however, Al or another major element could, in principle, serve just as well. In order to obtain absolute concentrations for analyzed elements, the concentration of the internal standard has to be known. Some studies measure major element concentrations using an independent method, such as SEM-EDS or EPMA (e.g. jackson et al., 1992). Most archaeological studies use the method employed by Gratuze et al. (2001), in which values for all elements measured by LA-ICP-MS are converted to oxide weights and summed to 100% to recover the concentration of the internal standard. This approach assumes that all elements are present as their most common oxides, that nearly all of the elemental content of the analyzed portion of a sample has been measured, and that any elements missing from the total elemental composition, therefore, represent only an insignificant percentage of the total content. For ceramics, measuring more than fifty elements at a time with LA-ICP-MS

if· ICP-MS AND LA-ICP-MS

407

makes it likely that both assumptions are applicable enough to minimally impact the resulting calibration. Gratuze et a!. (2001) quantified their results by repeated measurements of several standards, averaging these values to calculate a "response coefficient" from which sam~ ple concentrations were derived. Alternatively, these multiple standards can be used to generate a linear regression line for each element, as done by Speakman and Neff (zoos). A number of different standard materials have been used in ceramic analyses to produce calibration slopes, most commonly NIST61x glasses, New Ohio Red Clay (NORC), NIST679 ("brick clay"), Corning synthetic glasses (matching the compositions of ancient glasses), and fused USGS rock standards such as BHV0-1 (Giussani eta!., 2009). It is desirable to use standards that are closely matrix-matched to samples; however, clay standard materials tend to be heterogeneous at the scale sampled by laser ablation (Robertson et al., 2002), producing variability of 20% or more between readings on some elements, while variability in NIST glasses is typically less than 5% between readings. With shorter-wavelength lasers (213 and 193 nm lasers), fractionation and issues oflaser coupling related to differing sample opacity are reduced to the point where a combination of both homogeneous glass standards and matrix-matched clay standards can produce a reliable calibration slope for archaeological ceramics (Figure 23-3).

0.4

r 0.0016

'

0.0012 c 0

z

0.001 u

-~

"0

0.2

0.0008 -~ 0.15

"=

"

11

I

Qi u

0.1

D

~

g

8

E

T

~

0

,,

0

Pr

o Rb

0.05

l3 . 0.0006 'f

0. 0.0004

- - -Linear (Fe) ··~-··Linear (Pr)

0

0.0002

········Linear (Rb)

Si-normalized signal

FIGURE 23.3 Examples of calibration lines (Si-normalized signal versus Si-normalized concentration) for Fe, Rb, and Pr using NIST610, 612, and 679 as SRMs, with NORC (symbols in circles) as a quality assurance standard.(© Mark Golitko.)

408

MARK GOLiTKO AND LAURE DUSSUBIEUX

APPLICATION IN ARCHAEOLOGICAL CERAMIC PROVENANCE STUDIES

Liquid Sample Introduction ICP-MS was first used in archaeological materials studies in an attempt to find a lower-cost and more widely available alternative to INAA (Kennett et al., 2001), particularly given fears that activation reactors would increasingly be shut down because of environmental concerns. Consequently, many early ICP-MS ceramic studies used liquid sampling for bulk chemical characterization. After initial attempts using weak-acid extraction proved problematic, more aggressive acid-digestion routines were applied in studies by Mallory-Greenough et al. (1998), Bentley (2ooo ), and Hall (2002). More recent studies have used microwave digestion of powdered ceramic for bulk characterization. For example, Kennett et al:s studies of Lapita and post-Lapita ware from the western Pacific (Kennettet al., 2004; Clark and Kennett, 2009) and Little et al. (2004), whose work on Mayan ceramics from Belize, demonstrated the comparability ofMD-ICP-MS and INAA for bulk compositional analysis. However, MD-ICP-MS has not supplanted INAA as the "gold standard" ofbulkceramic characterization. In part, this is because INAA reactors, although fewer in number, remain active, and INAA not only achieves excellent precision for most elements of interest for ceramic provenance studies but the huge databases of comparable ceramic data that have been built using the technique facilitate the identification/ determination of fabric groups across large regions. Acid dissolution is time-consuming and requires the use of expensive and caustic acids; acid dissolution in open vessels can take upwards of twenty-four hours, while fusion and microwave digestion take several hours prior to analysis as several evaporation sequences are required to fully digest the sample and remove acids that might be harmful to the instrumentation. The cost associated with purchasing ultra-pure acids for trace element analysis also drive the cost of MD-ICP- MS into the range available for subsidized INAA (Little et al., 2004). However, bulk characterization by acid dissolution ICP-MS can generate quantitative data for more than fifty elements in principle, an advantage over the thirty-two elements typically measured by INAA.

LA-ICP-MS for Spatially Resolved Analysis Laser ablation was first applied to archaeological ceramic analysis during the 1990s as an alternative and less destructive method for characterizing ceramic glazes than SEM-EDS or EMPA (Gratuze et al., 2001). These early studies focused on the unique abilityofl.A-ICP-MS to produce spatially targeted chemical information providing valuable insight into production techniques and raw-material provenance determination of surface treatments, either as a primary means of reconstructing intercommunity and interregional ties or as a complementary line of evidence to supplement bulk paste analysis. For instance, in his study of Plumbate ware from the Pacific coast of Guatemala, Neff (2003) compared slip composition, determined by LA-ICP-MS, to paste composition, previously determined by INAA, and concluded that the same raw-material resources were used for both the vessels themselves and the surface treatments. Oka et al. (2009) analyzed the

ICP-MS AND LA-ICP-MS

409

composition ofblue and white and celadon glazes to differentiate between true Chinese-produced wares and Middle Eastern imitations recovered at archaeological sites in East Africa and Western India. Speakman (zoos) used LA-ICP-MS to map composition of paints on Mesa Verde and Mancos black-on-white pottery from the American southwest. His results established refined characterization subdivisions of styles, previously defined by paint color and design, and demonstrated that interregional connections inferred from style alone can gloss over the finer distinctions revealed by the use of distinctive paint compositions to produce the same designs. These studies all used quadrupole ICP-MS instruments to generate elemental concentrations; however, MC-ICP-MS studies oflead isotopes in ceramic glazes have also been successful in determining raw-material provenance. Habicht-Mauche et al. (2002) were able to match glaze paints on Rio Grande style vessels to lead sources in the American southwest, both by LA-MC-ICP-MS and by acid dissolution MC-ICP-MS. Ii\aiiez et al. (zow) were similarly able to link the lead glazes on colonial period Romita pottery from central Mexico to Mexican ore sources using LA-MC-ICP-MS. In other studies, the spatial resolving power of LA-ICP- MS is used to study mineral inclusions in ceramics for provenance purposes. Cogswell et al. (zoos) used LA-ICP-MS to characterize schist temper in l-Iohokam ceramics from the Gila River area, but it proved difficult to assign sherd inclusions to particular sources because of the large amount of natural variability in the geological sources. In a study of tephra temper in Mesoamerican ceramics by Neff and Sheets (2005), researchers were able to conclusively link tephra grains in ceramic vessels back to particular volcanic ash deposits. Palumbi et al. (2014) studied the composition of obsidian temper in Chalcolithic Caucasian pottery, and were able to combine unequivocal source assignments for obsidian temper grains with data on paste chemistry and suggest possible production locations for pottery from the site of Aratashen, Armenia. '!he latter two studies in particular highlight how LA-ICP-MS analysis of temper can both supplement analyses of ceramic paste and complement mineralogical data determined by petrography, identifying variability within temper types that would likely not be identified using optical microscopy alone. A third research area in which the spatial resolving power of LA-ICP-MS has been used for archaeological ceramic analysis is in the identification of chemical alteration resulting from firing, use, and/or burial. In the aforementioned study of Plumbate ware, Neff (2003) noted systematic evolution of slip composition by depth, which he attributes to firing induced migration of particular constituent elements. Golitko et al. (2012) were able to identify a pattern of barium enrichment in sherds from northern Papua New Guinea, consistent with post-depositional alteration processes, using raster mapping of sherd cross-sections by LA-TOF-ICP-MS. Spatially resolved analysis by LA could also, in principle, be used to map chemical enrichment or depletion along pore boundaries, fractures, and voids, where postburial uptake, leaching, or redeposition may potentially leave characteristic traces.

LA-ICP-MS FOR PASTE ANALYSIS LA-ICP- MS is also increasingly used to generate an averaged composition for the fine paste fraction of archaeological ceramics (e.g. Cochrane and Neff, 2oo6; Golitko and Terrell,

410

MARK GOLITKO AND LAURE DUSSUBIEUX

2012). Compositional analysis of the matrix material has two benefits over bulk compositional studies; the chemical signature of the temper, which might obscure patterns or groups of the matrix material, is eliminated (e.g. Cochrane and Neff, 2006); and, as a result, it is possible to more closely match archaeological ceramics with the composition oflocally available raw material resources/clays (e.g. Sharratt et al., 2009). In some cases these studies build on or are complemented by petrographic analysis (e.g. Fitzpatrick et al., 2006; Golitko and Terrell, 2012), or bulk characterization by INAA (e.g. Vaughn et al., 2011), or acid dissolution ICP- MS (e.g. Cochrane and Neff, zoo6). The effectiveness of a spot analysis technique for characterizing heterogeneous ceramic paste might be questioned; however, comparative studies of both clay standard reference materials and archaeological ceramics suggest that LA-ICP-MS can provide reliable compositional data for many archaeological ceramic pastes, although variability should be assessed on a case-by-case basis. Comparison at two laboratories of averaged compositional analysis by LA-ICP-MS with MD-ICP-MS and INAA for NIST679 (Table 23.1) and New Ohio Red Clay (Table 23.2) suggests that the precision and accuracy achieved by repeated analysis is comparable to that achieved by other techniques for the majority of elements (data from Glascock and Anderson, 1993; Kuleff and Djingova, 1998; Meloni et al., 2000; Grave et a!., 2005; Wallis and Kamenov, 2013). For some elements in each standard, there are discrepancies in measured concentrations relative to bulk characterization, particularly major elements Si and AI, and trace elements Zr, Hf, and some of the REEs. Enrichment and dilution patterns for major elements Si and AI in NORC can be explained by the high percentage of quartz in that standard compared to NIST679. As Si is typically used as an internal standard, the variable ablation of quartz and other Si-rich inclusions is an issue relative to calibration, and likely introduces some error to both standard and sample measurements as a result. It is possible a less variably distributed major element such as K might serve better as an internal standard. Alternatively, Si can be calibrated using signal strengths only for homogeneous glass standards, and a dilution correction factor (e.g. Mommsen and Sjoberg, 2007) then applied to measured samples to constrain error resulting from variable Si content. Zr and Hf, which occur in ceramics primarily as zircon inclusions, and some REEs (Ce, La), which also commonly occur in ceramics as discrete mineral phases, such as monazite-xenotime, exhibit high levels of measurement error when sampled by LA-ICP-MS (Neff, 2003; Wallis and Kamenov, 2012). Precision and accuracy may be impacted, therefore, by how many ablation spots or lines are sampled per ceramic, and whether data are "despiked" to remove anomalous measure~ ments that might result from ablation of a variable numbers of small mineral grains. The data from the Field Museum Elemental Analysis Facility (EAF) reported in Tables 23.1 and 23.2 were generated by measuring ten 100 micron ablation craters, and removing up to three outlier values (for elements with %RSD between measurements of more than 20%) to gen~ erate a final averaged value. In comparison to the values reported by Wallis and Kamenov (2012), for instance, values for Zr, Hf, and most REEs in the EAF measurements are much closer to published consensus values. In their study, Wallis and Kamenov also achieved better accuracy after despiking their data. Stoner and Glascock (2012) also generated multiple measurements per sample and despiked the resulting data, ablating six lines per sample and removing divergent measurements to derive a final averaged value. In their 2012 study, they removed aberrant measures only for specific elements known to be elevated in temper grains. Running multiple ablation lines or spots also facilitates assessment of actual sample

Table 23.1

Comparison of measurements on NIST679 (brick clay) by LA-ICP-MS, MD-ICP-MS, and other bulk techniques. MD-ICP-MS

LA-ICP-MS

INAA

-----------------------certified

Wallis and Kamenov (2013[

FM EAF

mean

1-o

li

82.67

1.75

Be

4.2

0.26

B

95.51

3.31

Na [%)

0.1

0.01

mean

0.14

1-o

001

Kennett et al.

NISTvalues

(2002[

---mean

1-o

mean

1-o

83.20

4.99

71.70

6.20

0.15

0.097

0.13

0.00

Mg [%)

0.64

0.02

0.87

0.03

0.78

0.05

0.76

0.01

AI(%)

12.5

0.44

13.74

0.34

10.60

0.80

11.01

0.34

Si (%)

26.96

0.42

19.37

0.43

24.34

0.30

p (%)

0.86

0.005

0.08

0.01

2.74

0.07

2.57

0.16

2.43

0.05

Ca (%)

0.19

0.02

0.14

0.01

Sc

28.45

1.68

23.7

2.32

published

Glascock andAnderson (1993) mean

1-o

0.123

0.003

10.60

0.30

2.38

0.14

Melloni et al. Grave et al. (1999) (2005)

mean

1-o

s K[O/o)

Ti(%}

2.46

0.21

32.80

3.14

215.4

28.2

- 0.5 MeV) born of the ' 35 U fission which still retain much of their original energy; (2) the intermediate flux (- 1 eV to - 0.5 MeV) comprising neutrons which have been partially slowed down through collisions with surrounding material down to the epithermal range; and (3) the slow or thermal flux consisting oflow-energy neutrons (energies below- o.s eV) that have been slowed to the point that they are in thermal equilibrium with atoms in the reactor's moderator (although it should be noted that these "slow" neutrons still have an average velocity of 2200 m s·'). As we shall see, neutrons in these different energy ranges generate distinctive suites of radioisotopes. Overall, the thermal neutrons are most important for INAA of ceramic mate~ rials. Most research reactors have a well-thermalized neutron spectrum, such that 90-95%

INAA IN THE STUDY OF ARCHAEOLOGICAL CERAMICS

429

of the neutrons available are in the thermal range. Further, thermal neutrons have a much higher probability of being absorbed by a nucleus within the sample because at low neutron energies, the reactions of many nuclides obey the Maxwellian r/V law, which states that the probability of neutron absorption is inversely proportional to the neutron velocity. Higher energy neutrons can, however, play an important role in INAA. Many isotopes experience resonance and a correspondingly high probability of neutron absorption for specific neutron energies in the intermediate region. Finally, while fast neutrons are generally a thousand times less likely to activate a target nucleus than thermal neutrons, they can be important in the analysis of specific isotopes where activation with slower neutrons fails (routinely in the analysis of nickel, for example, or in the determination of oxygen and nitrogen isotopes). Research reactors differ in design, size, and power output, and, hence, in neutron density and neutron energy spectra characteristics. Small university research reactors with 100-200 kW power can generate thermal neutron fluxes on the order of 10 12 n cm- 2 s-\ while larger research reactors of 10-70 MW thermal power provide neutron fluxes up to 1d5 n crn-2 s- 1 . Moreover, most reactors offer multiple locations where sample materials can be loaded for irradiation; irradiation facilities may be placed in the center of the core (in a high flux location) or peripheral to the core fuel assembly (in a generally lower flux location). Each irradiation location is unique: while most reactor facilities quote their peak thermal flux, it is generally more helpful to know the neutron energy spectrum and density for specific irradiation locations utilized for INAA.

Nuclear Reactions When target nuclei are bombarded with neutrons, one of several distinct types of reaction will occur. In general terms, we can denote the processes of reaction as:

a+A-7B+b where: a is the projectile, i.e., a neutron of a specific energy, A is the target nucleus in the isotope being analyzed, B is the product nucleus of the resulting radioisotope, and b is the resulting particle released during activation. Nuclear reactions are usually identified by the abbreviated convention A(a,b)B or simply (a,b). Neutron Capture The most common type of nuclear reaction that occurs when target material is placed within a well-thermalized beam of neutrons is "neutron capture", also known as the (n,y) reaction in which a thermal neutron is gained and a prompt gamma is lost. 1be absorption of a thermal neutron (nth) increases the mass of the nucleus (A) by 1 and creates an unstable compound nucleus which immediately decays through release of a prompt gamma ray (Yp• a high-energy photon):

430

l

LEAH D. MINC AND jOHAN'NES H. STERBA ,,

,,,,,,,,,,

In some cases, the resulting isotope will be stable. More commonly, the nucleus remains unstable, indicated by an asterisk('), and will undergo radioactive decay. In the case of mono-isotopic aluminum, bombardment with thermal neutrons leads to the following reaction: ~n + ~;Al -:? ~!Al' + yP also designated as~;Al(n, y) :!Al'. Note that the (n,y) reaction results in a radioisotope of the same element, having increased the mass number from A to A +1, while Z remains unchanged. Transmutation The absorption of an epithermal or fast neutron, in contrast, creates a highly. unstable compound nucleus which de-excites by releasing a charged particle, usually . 1n + z"X -:? z_''X' + 1P· a proton, d enote d t h e (n,p ) reactwn: 0 1 1 1 Note that in this case, atomic mass (A) remains the same, while the number of protons (Z) decreases to Z-1 as the proton is lost. Other transmutations involve the (n,a), (n,2n), and (n, t) reactions. For aluminum, the (n, p) reaction involving the addition of a neutron and the loss of a proton transmutes aluminum into magnesium; a similar reaction on silicon transforms it into an isotope of aluminum: or It is important to note that, depending on the energy of the neutron, the same radioisotope

can be produced from two different reactions of two different stable isotopes. That is, ~:AI' can be produced from the thermal neutron (n,y) reaction on or a fast neutron (n, p) reaction on~.~ Si. Effective Cross-sections The preceding neutron interactions occur with different frequencies depending on neutron energy and the nuclear properties of the target isotope. The probability of a specific reaction occurring is governed by the isotopic cross-section (cr), which can be envisioned as the size of target that the nucleus presents to a neutron in a given energy range. Effective cross-sections are measured in barns (1 b = 10~ 24 cm 2) and are defined for each type of interaction. Isotopes with large effective cross-sections are said to activate readily, while it may be difficult to build up measurable activity in isotopes with very small cross-sections. In general, for isotope I, the number of activated nuclei (X,) generated per unit time is directly proportional to the number of target nuclei (N;), the neutron flux (700 to ing

"',,,,

"' !11{11

I

"'

"

lii(OO

L

Heml

OJ)l

!SO

Na 20

30.25 067

Ho

M~'

-- ----K20 319

'" 0"

P,O,

Tot

lOI

010 9S29 2518

l

--r;:;;;;:alog indicating that this temperature is higher than the original firing temperature. The example presented here, according to K-H analysis, was originally fired at Teq:::::: 900-I000°C, consistent with the known To. Maximum apparent density for this material occurs at uoo 0 C. Additionally, the apparent density values of a sherd after re-firing at 120o°C can point to differences in ceramic body preparation in those instances where analyzed sherds are made of the same

500

MALGORZATA DASZKIEWICZ AND LARA MARITAN ,,,,_,,,-.,,,,,,,,,,

FIGURE 27.4

Determination of the original firing temperature using the K-.H method (Teq

900-1000°C).

raw material (Daszkiewicz, and Bobryk, 2001), because where the same raw material is concerned any differences noted in its open porosity are linked to differences in the de-.airing of the ceramic body. 11

RAW MATERIAL CLASSIFICATION USING MGR-ANALY§IS

MGR-.analysis can be used for the classification of ceramic sherds according to the compo-. sition of their matrix material because the thermal behavior of plastic components during firing is governed by their chemical and phase composition (Daszkiewicz and Schneider, 2001). Before it became a routine use it was preceded by a control series of comparing chemical analyses using the WD-.XRF technique on several thousand samples, and thin-section studies of several hundred samples. Numerous experiments have shown that the optimal temperature for re-firing in order to identify matrix type is 1200°C. Plate 8 shows five samples of archaeological pottery re-fired at 8oo°C, 900°C, and 12oo°C: note that it is not until the samples were re-fired at 1200°C that differences associated with the sherds' chemical composition became clearly visible (the two samples which fire yellow have the same chemical composition, which differs from that of the three identical reddish-brown firing samples). Classification of ceramic sherds according to the mineralogical and chemical composition of the matrix (MGR-groups) requires only abridged MGR-analysis, i.e. re-firing at three temperatures. Firing conditions are the same as those described in the section on determining Teq. The thermal behavior and appearance (color, shade of color, and texture) of samples

EXPERIMENTAL FIRING AND RE-FIRING

A B

50.2 48.2

0.88 1.45

15.0 13.9

7.54 9.10

5.48 17.9 8.07 16.5

0.50 2.08 0.26 0.49 1.74 0.43

123 157

Cr

Ni

Zn

Rb

Sr

238 288

149 182

102 89

80 218 54 419

501

Zr

Ba

168 189

297 244

FIGURE 27.5 Two samples made of the same marly clay re-fired at noo"C. A ; sample

without intentional temper. B; sample tempered with crushed basalt (temper is meleted at this re-firing temperature). Photographs were taken with a macro lens by M. Baranowski.

re-fired at three different temperatures (noo°C, nsooc and 1200°C) are taken into account when defining individual MGR-groups;" however, definitive classification is based on thermal behavior at 1200°C. Different colors and shades of the re-fired matrix are indicative of different matrix mineralogy and chemistry. Therefore, samples displaying the same color and shade after refiring at 120o°C are manufactured from plastic raw material of the same composition and are considered a single MGR-group. Ceramics from a single MGR-group which also have the same non-plastic inclusions (same non-plastic material group) were manufactured from the same body and have a similar chemical composition. They show the same fabric. However, ceramics from the same MGR-group belonging to different non-plastic material groups, because they were intentionally tempered with different non-plastic components or different quantities of the same components, show different ceramic fabrics and have different chemical compositions. This means that two sherds made from the same clay can belong to two different fabrics and/or chemical groups, but to the same MGRgroup because chemical and fabric groups consider the bulk composition of the sherd, matrix material and temper, whereas MGR-groups consider only the matrix material (Figure 27.5). Therefore, in provenance studies, both MGR and chemical analyses should be conducted. Macroscopic analysis of non-plastic inclusions in ceramic fabrics after re-firing is beneficial because many mineral phases are more clearly visible in samples after re-firing (Plate 6, sample 6). MGR-analysis can be used to classify ceramic sherds according to the composition of their non-plastic components (clastic material groups; CM-groups) and to make an assessment of the recipe, i.e. the ratio of the non-plastic inclusions to the matrix. The results of this classification are more reliable than the macroscopic descriptions of temper seen in fresh fracture widely used by archaeologists.

MGR-ANALYSIS DATA REPORTING The growing use of MGR-analysis in the study of ancient pottery, both as an auxiliary method to bulk chemical and petrographic analysis, as well as for the rapid and inexpensive

502

J\'lALGORZATA DASZKIEWI(;Z AND LARA MARITAN

raw material classification of large quantities of ceramic sherds, has made it necessary to establish a standard formula for writing up results. The principles of classifying re-fired samples in raw material classification are outlined below. Based on the color of samples after re-firing at 12oo'C three fundamental categories of matrix minerals can be identified: non-calcareous, calcareous and mixed matrices. The following criteria are used in matrix classification: (i) Samples are considered to have a non-calcareous matrix if no calcium silicate or calcium aluminum silicate phases form during laboratory re-firing in air at a temperature of 1200'C, which is indicated by the fact that the samples do not take on a greenish tint after re-firing. (ii) Samples are said to have a calcareous matrix if calcium silicate or calcium aluminum silicate phases form during laboratory re-firing in air at a temperature 1200'C, indicated by the fact that these samples do become greenish in color (or have a greenish or greenish-yellowish tint, or grayish-green tint). (iii) Samples are considered to have a mixed matrix if various irregularly distributed patches of greenish color are noted in the fabric after re-firing.

Matrix texture is identified based on the appearance of samples when re-fired at uoo 0 C. Principal matrix textures are as follows (examples are shown in Plate 9 ): sintered (SN): the sherd is well-compacted; it may or may not become smaller in size in comparison to the original sample, whilst its edges remain sharp over-fired (ovF): the sample changes in shape; bloating, however, does not occur nor does the surface of the sample become over-melted slightly over-melted (sovM): over-melting of the sample surface is observed, but there is no change in shape, and edges remain sharp over-melted (ovM): the surface of the sample becomes over-melted and its edges become rounded semi-melted (sMLT): over-melting of the surface occurs, changes in sample shape are observed (not just rounded edges), but no bloating is noted melted (MLT): the sample becomes spherical or almost spherical in shape bloated over-fi~ed (BlovF): the sample expands in volume, but the surface does not become over-melted bloated over-melted (BlovM): the sample expands in volume and its surface is over-melted flowed (Fl): the sample flows into a thin layer The non-plastic phases of the matrix can alter the appearance of samples after re-firing, especially where grains of carbonates are present, as these decompose when fired at temperatures exceeding 6oo-7oo'C (e.g. Plate 6 sample 6). The destruction products expand by taking up water and by subsequent re-carbonatization. The following behaviors can be distinguished: the re-fired fragments crack; the re-fired fragments crumble to a powder.

1

I

EXPERIMENTAL FIRING AND RE-FIRING

503

CoNCLUSION§

Experimental firings are a very powerful method to understand the dynamics of the firing process, all the possible modification that could have been used in the past and presently testified by ethnographic stndies. The analysis of the compositional and structural changes with the temperature, in combination with the firing cycle duration and redHox conditions on fired briquettes obtained by laboratory firings, in which the firing process can be planned ad hoc, can provide precise information of the ancient firing technology of specific types of pottery. It should be strongly emphasized that the results of experimental firing cannot be directly transferred to the results of re-firing. It is necessary always to keep in mind that each ceramic body has its own very specific features and, especially for ancient ceramics, there is no such thing as a typical clay/body or a typical thermal behavior of typical clay/body (how it is unfortunately found in publications). There are only very few instances where the raw material used by ancient potters is currently available for experimental firing (as is the case, for example, with clay used in the manufacture of Terra Sigillata in Rheinzabern) and the ancient technological process is known. This situation may represent a limit when ancient pottery is compared with modern experimental firings, which can cause an over- or underestimation of the ancient firing temperature. Therefore, the advantage of re-firing fragments of ancient sherds instead of firing model briquettes is that the interpretation of the re-firing results is securely based on the same material composition. Re-firing can be used to obtain information about the original firing process: about the temperature of the original firing (also within the range where original phases were already thermally decomposed and new ones did not build), about the firing atmosphere, about the firing cycle duration and the soaking time at maximum temperature, about the number of times glazed pottery was fired in those cases where the hemisphere point of the glaze is known, and about the technological process which led to the creation of a black surface (for a simplified classification of archaeological pottery with a black surface). Re-firing at temperatures higher than the original firing temperature can also be used to classify the raw material used for the manufacture of ceramics, hence to carry out a classification based on the variety of the plastic part of the body and an assessment of the non-plastic part of the body (MGR-analysis). It is a powerful tool for revealing inhomogeneities in sherds and for determining the composition of the matrix independent of any possibly added nonplastic material. Therefore, re-firing is a useful auxiliary method to chemical analysis.

NOTES Although parts of this chapter have been co-authored, Lara Maritan is solely responsible for the sections "Experimental Firing;' "Experimental Archaeology Firings;' "LaboratoryControlled Firing;' and Malgorzata Daszkiewicz is responsible for the sections "Re-firing;' "Reconstructing tbe Original Firing Process by Re-firing;' "Raw Material Classification Using MCR-Analysis;' and "MGR-Analyis Data Reporting:'

504

1.

2.

3.



s.

6.

MALGORZATA DASZKIEW!CZ AND LARA MARITAN

The principles of MGR~analysis were formulated in 1987-1990 by Daszkiewicz whilst working on her PhD thesis on the technology of fourteenth-sixteenth-century pottery from Plock (Daszkiewicz, 1992). MGR-analysis was not intended as a means of evaluating phase composition in qualitative and quantitative terms (other than to provide a general identification of the clay type used by ancient potters), but as a means of quickly classifying samples in terms of their matrix. Since 1987 the author has carried out MGR-analysis on almost 12,000 fragments of ancient ceramics ranging in date from the Mesolithic to the medieval period from Europe, the Near East, Egypt, Sudan, and the New World. Model analyses have also been conducted. MGR-analysis results have always been, and continue to be, correlated with the results of chemical analysis (WD-XRF) and thin-section studies. Experiments have also been carried out on originally black/gray colored ancient ceramics fragments. These samples, after re-firing in air (standard MGR-analysis), were re-fired once again in various conditions that led to their becoming black/gray once more. Moessbauer spectroscopy was used on these samples to gauge what it was that was responsible for their coloration (part of this study is published for gray ware from Plock: Daszkiewicz and Raabe, 1995). Results of model analyses carried out by the author during 1987-1990 on clay from the Plock region, and jointly with Bobryk in 2014 on jockgrim clay (used in the manufacture ofRheinzabern sigillata). The opposite of dynamic methods are static methods, in which specific characteristics of a given sample are analyzed and the results are used to draw conclusions about the original firing temperature (To). Static methods can be used to define these characteristics, for example, the degree of vitrification, or to make an estimate of firing temperature based on the presence/or absence of clay minerals, calcite, gehlenite, and diopside. The occurrence of specific phases and the degree of vitrification are dependent not only on the original temperature but also on the chemical, as well as mineralogical and petrographic, composition of the ceramic body, grain sizes and on the firing process (atmosphere, heat~ ingrate, soaking time at the peak temperature and time during other stages of firing). But during the firing process the clay-temper mixture is not within a thermodynamic phase equilibrium and the temperatures at which particular phases occur depend on kinetic and many other factors. In addition, changes in phase composition also sometimes occur during the course of the sherd's deposition in its archaeological context, e.g., second~ ary deposition of carbonates or rehydroxylation of clay minerals and decomposition of calcium silicates (e.g. gehlenite). The use of dynamic methods is decidedly preferable (in this author's view) because of the ambiguous interpretation of results associated with static methods. Analysis of Neolithic to Christian period pottery recovered from the Fourth Nile Cataract region (Sudan), has shown that determining the original firing temperature with this accuracy is sufficient as an indication of the technological level of the given period/culture, or of a production center/workshop (Daszkiewicz et al., 2003). The use of color in order to assess original firing temperatures was first proposed by Matson (1971), who fired raw materials which may have been used for making archaeological ceramics and subsequently compared the color of the fired briquettes to the color of the original archaeological ceramics. A similar method, the Thermal Color Test (TCT) was devised at the Laboratory for Ceramic Research (Department of Geology, Lund University, Sweden) for the purpose of determining original firing temperatures (Hulthen, 1976; Lindahl, 1986; Stilborg, 1997). In this test always the same ceramic fragment is re-fired at I00°C increments up to a

EXPERIMENTAL FIRING ANDRE- FIRING

505

temperature ofwoo°C and the Munsell Soil-Color Chart is used to classify the colors. The color codes are then transferred to diagrams and the temperature at which change occurs is identified. J. 1bis is only one example from an extensive model study of firing and re-firing ceramic samples at various temperatures (Daszkiewicz and Bobryk, unpublished). s. Gloss is a slip which due to repeated very fine levigation is enriched in potassium and iron and thus vitrifies earlier than a normal slip (but it is not a glaze composed like glass). Because of the vitrification a re-oxidation is limited. It makes a glossy surface and is typical for Attic black and red figured vases and Roman Samian Ware. Another possibility for black glossy surfaces used already in Neolithic periods is fumigation of polished vessels. 9· At an archaeometry conference held in Cologne in 2001 this name was suggested by M. Daszkiewicz in memory of Dr. H. Kilb and Prof. H. W. Hennike, who introduced the measurement of changes in values of apparent density versus re~firing temperature (Kilb and Hennicke, 1980 ). 10. Prior to this assessment, samples must be boiled in distilled water for two hours in order to fully saturate all open pores with water. The samples are then cooled to room temperature (the term "room temperature" refers to a temperature of 20°C) and weighed twice, making note of the mass of the sample immersed in water (mww), and the mass of the moist sample weighed in air (mw)· Next, the samples are weighed for a third time in air, having first been dried to a constant mass in a dryer at 105°C and cooled to room temperature in a desiccator. This is the method used fOr determining the mass of a dry sample (ms)· Open porosity, i.e. the percentage of the amount of water absorbed by a given volume of sample, c m -m was determined using the 10rmula p "' ' x 100 and expressed as a percentage.

" mw -m ww Water absorption, i.e. the percentage mass gain of the sample soaked in water in relation to the mass of the dry sample, was determined using the formula N

mw - m,, x 100 and m,

expressed as a percentage. Apparent density, i.e. the mass of the sample in relation to its volume, was determined using the formula d~ =

mw -mww

X pH 0

and expressed in g/cm 3

1

PH 20 =bulk density of water at temperature of measurement; in this analysis, the tempera~ ture of measurement is room temperature and Ptho = 1g/cm3). u. According to the hypothesis propounded by M. Daszkiewicz, this analysis allows ceramic workshops to be identified based on assessment of the degree to which the ceramic body was de-aired. This was tested on Terra Sigillata featuring makers' stamps, made at four workshops in the Roman production center ofRheinzabern (Daszkiewicz et al., 2001). 12. These observations are similar to those described in the sintering test devised at Lund University (Hulthen, 1976; Lindahl, 1986; Stilborg, 1997). In this test the same fragment is re-fired in 50°C intervals starting from woo°C and continuing until it reaches melting point (which could be up to 14oo'C); after every stage of re-firing the sample's behavior is noted.

REFERENCES Daszkiewicz, M. (1992). "Technologia wyrobu ceramiki plockiej XIV-XVI w" [Technology of Manufacture of Pottery from Plock from 14th-16th cent. AD]. Unpublished doctoral thesis, Faculty of History, Warsaw University.

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Daszkiewicz, M. and Baranowski, M. (2010). "Provenance Study of Late Classic and Hellenistic Black-Coated Pottery from Risan (Montenegro):' Novensia 21: 23-43. Daszkiewicz, M. and Bobryk, E. (2001). "Pottery Manufacturing Technology Detected from Ceramic Properties (K-H method):' Archiiometrie und Denkmalpjlege-Kurzberichte, U.Schiissler and R. Fuchs (eds), (ISSN 0949-4057), Cologne, 113-115. Daszkiewicz, M., Bobryk, E., el-Tayeb, M., Kolosowska, E., and Schneider, G. (zooz). "Composition and Technology of Pottery from Neolithic to Christian Periods from jebel el-Ghaddar and from the Karima-Abu Hamed Region, Sudan:' Archeologie du Nil Moyen 9: 65-87. Daszkiewicz, M., Bobryk, E., and Schneider, G. (2001). "Down-Up Sampling Classification of Pottery Using MGR-Analysis:' Abstracts of the 6th European Meeting on Ancient Ceramics EMAC'o1, Ceramic in the Society, Fribourg, Switzerland, October 3-6, 26. Daszkiewicz, M., Bobryk, E., and Schneider, G. (2003). "Continuity and Change in Pottery Making from the Mesolithic to Christian Period in the Fourth Cataract Region (Sudan):' ln: Paner, H. (ed), Gdansk Archaeological Museum African Reports 2: 81-89. Daszkiewicz, M. and Raabe, J. (1989a). "Wyznaczanie temperatury pierwotnego wypalania ceramiki zabytkowe( Archeologia Polski 34(1): 29-38. Daszkiewicz, M. and Raabe,). (1989b). "Zastosowanie elektronowego mikroskopu skaningowego do okreslania temperatury wypalania ceramiki zabytkowej:' Archeologia Polski 34(2): 259-264. Daszkiewicz, M. and Raabe,). (1995). "Technology of Firing of Grey Ware So Called 'Siwak' from Late Medieval Plock:' In: Vincenzini, P. (ed), The Ceramics Cultural Heritage, TechnoMonographs in Materials and Society 2: 349-359. Daszkiewicz, M. and Schneider, G. (2001). "Klassifizierungvon Keramik durch Nachbrennen von Scherben:· Zeitschrift fur Schweizerische Archiiologie und Kunstgeschichte 58: 25-32. Daszkiewicz, M., Schneider, G., and Bobryk, E. (2001). "Technologische Untersuchungen zur Keramik von Rheinzabern:' BAR International Series 929:59-71. Daszkiewicz, M., Schneider, G., and Bobryk, E. (2010). "The Application of Down-Up Sampling by MGR-Analysis in the Classification of Raw Materials Used for Pottery Making near the Site of Meqaber Ga'ewa (Ethiopia):' In: Wolf, P. and Nowotnick, U. (ed), Das

Heiligtum des Almaqah von Meqaber Gaewa in Ttgray!Athiopien, Zeitschrift fur OrientArchiiologie 3: 193-203. Garcia-Ten J., Orts M. )., Saburit, A., and Silva, G. (2010 ). "Thermal Conductivity ofTraditional Ceramics. Part I: Influence of Bulk Density and Firing Temperature:' Ceramic International 36: 1951-1959· Gosselain, 0. P. (1992). "Bonfire of the Enquiries: Pottery Firing Temperatures in Archaeology: What For?" Journal of Archaeological Science 19: 243-259. Harrison, S. (zooS). ''An Experimental Prehistoric Pottery Firing at Harray, OrkneY:' Antiquity 82:317. Heimann, R. B. (1982). "Firing Technologies and Ibeir Possible Assessment by Modern Analytical Methods:' In: Olin, ). S. and Franklin, ). D. (eds), Archaeological Ceramics (Washington, D.C.: Smithsonian Institution), 89-96. Hulthen, B. (1976). "On Thermal Colour Test:' Norwegian Archaeological Review 9: 1-6. Kilb, L. and Hennicke, H.W (1980). "Gefiigeanalytische Untersuchungen historischer steinzeugartiger Werkstoffe zur Behandlung archaometrischer Fragestellungen:' Keramische Zeitschrift 32(7): 370-375.

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Lindahl, A. (1986). Information through Sherds-A Case Study of the Early Glazed Earth ware from Dalby, Scania. Lund Studies in Medieval Archaeology 3(Lund: University of Lund, Institute of Archaeology). Lipovac Vrklian, G., Siljeg, B., Oianic Roguljic, I., and Konestra, A. (2012). "Experimental Archaeology-A Replica of a Roman Pottery Kiln:' Annales Instituti Archaeologici, 8: 149-154Livingstone-Smith, A. (2001). "Bonefire II: The Return of Pottery Firing Temperatures:· Journal of Archaeological Science z8: 991-1003. Maggetti, M. (1991). "Mineralogical and Petrographical Methods of Study of Ancient Pottery:' Atti del Convegno Europeo di ricerche archeometriche e studi archeologici sulla ceramica antica, Roma, October 10-12, 1991, Universiti degli Studi di Roma La Sapienza, Roma, 23-35. Maggetti, M., Neururer, Ch., and Ramseyer, D. (zon). "Temperature Evolution Inside a Pot during Experimental Surface (Bonfire) Firing:' Applied Clay Science 53: 500-508. Maritan, L. (2003). "Studio archeometrico di ceramiche di tipo etrusco padano dell'area veneta: indagini petrografiche, chimico-fisiche e confronto coni risultati ottenuti da prove speri~ men tali di cottura di materiali argillost:' Unpublished PhD thesis, University ofPadova. Maritan, L. (2004). 'Archaeometric Study of Etruscan-Padan Type Pottery from the Veneto Region: Petrographic, Mineralogical and Geochemical-Physical Characterisation:' European Journal ofMineralogy 16: 297-307. Maritan L., Mazzoli, C., and Freestone, I. (2007). "Modelling Changes in Mollusc Shell Internal Micro-Structure during Firing: Implication for Temperature Estimate in Shell-Bearing PotterY:' Archaeometry 49: 529-541. Maritan, L., Mazzoli, C., Nodari, L., and Russo, U. (zoos). "Second Iron Age Grey Pottery from Este (North-Eastern Italy): Study of Provenance and Technology." Applied Clay Science 29:31-44Maritan, L., Nodari, L., Mazzoli, C., Milano, A., and Russo, U. (zoo6). "Influence of Firing Conditions on Ceramic Products: Experimental Study on Clay Rich in Organic Matter!' Applied Clay Science 31: 1-15. Matson, F. L. (1971). 'A Study of Temperatures Used in Firing Ancient Mesopotamian PotterY:' In: Brill, R. H. (ed), Science and Archaeology (Boston, MA: MIT Press), 65-79. Nodari, L., Marcuz, E., Maritan, L., Mazzoli, C., and Russo, U. (2007). "Hematite Nucleation and Growth in the Firing of Carbonate-Rich Clay for Pottery Production:· Journal of the European Ceramic Society 27: 4665-4673Nodari, L., Maritan, L., Mazzoli, C., and Russo, U. (2004). "Sandwich Structures in the Etruscan- Padan type potterY:' Applied Clay Science 27: 119-128. Quinn, P. S. (2013). Ceramic Petrography. The Interpretation ofArcheological Pottery and Related Artefacts in Thin Section (Oxford: Archaeopress). Riccardi, M.P., Messiga, B., and Duminuco, P. (1999). 'An Approach to the Dynamic of Clay Firing:' Applied Clay Science 15: 393-409. Rice, P.M. (1987). Pottery Analysis (Chicago: University of Chicago Press). Rye, 0. S. (1981). Pottery Technology. Principles and Reconstruction (Washington, D.C.: Taraxacum Inc.). Schreiber, T. (1999). Athenian Vase Construction-A Potters Analysis (Malibu: The). Paul Getty Museum) Stilborg, 0. (1997). "Shards oflron Age Communications-A Ceramological Study oflnternal Structure and External Contacts in the Gudme-Lundeborg Area, Funen during the Late

--,508

MALGORZATA DASZKIEWICZ AND LARA MARITAN

Roman Iron Age:' Monographs on Ceramics, doctoral dissertation, Institute of Archaeology, Lund. Tenconi, M. (2013). "Study of the Production and the Regional and Interregional Relations between the Protohistory Communities from the Northern Italy, Particularly Focusing on the Middle- East Area, through the Archaeometrical Analysis of Their Pottery:' Unpublished PhD thesis, UniversityofPadova. Tenconi, M., Maritan, L., and Mazzoli, C. (2016). "Changes in Speleothem Microstructure during Firing: A Useful Tool in Temperature Estimation for Speleothems-Bearing Pottery:' doi: w.nn/arcm.12238. Ther, R. (2004). "Experimental Pottery Firing in Closed Firing Devices from the NeolithicHallstatt Period in Central Europe:' EuroREA r: 35-82. Ther, R. and Gregor, M. (2on). "Experimental Reconstruction of the Pottery Firing Process of Late Bronze Age Pottery from North-Eastern Bohemia:' In: Scarcella, S. (ed), Archaeological Ceramics: A Review of Current Research. BAR international Series 2193 (Oxford: Archaeopress), 128-142. Tile, M. S. (1969). "Determination of the Firing Temperatures of Ancient Ceramics by Measurement of Thermal Expansion." Archaeometry n: 131-143.

1

I

..................

~--------------

CHAPTER 28

FOURIER TRANSFORM INFRARED SPECTROSCOPY (FT-IR) IN ARCHAEOLOGICAL CERAMIC ANALYSIS SHLOMO SHOVAL

INTRODUCTION

Infrared Spectroscopy Studies of Ancient Pottery FT-IR spectroscopy has recently become widely utilized for investigation of ancient ceramic and archaeological artifacts (Roberts et a!., 2008; Kurap et a!., 2010; Nel et a!., 2010; Weiner 2010; Ravisankar et al., 2011, 2014; Shoval et al., zona; Rutherford et al., 2012; Izzo et al., 2013; Shoval and Paz, 2015). This method provides a mineralogical fingerprint of the ceramic and is preferred to other mineralogical techniques to identify the mineral composition of ancient ceramics (De Benedetto eta!., 2002, 2005). The major advantage of FT-IR spectroscopy is its ability to identify the composition of both crystalline minerals (Barilaro et a!., 2005, 2008; Akyuz eta!., 2007, 2008) as well as the pseudo-amorphous phases of the fired-clay ceramic (Shoval et a!., 2oua). Although the XRD (X-ray diffraction) method is the technique traditionally used for mineralogical analysis (Heimann and Maggetti, 1981; Maggetti, 1981), it unsuccessfully observes the pseudo-amorphous phases of the fired-clay ceramic, because they lack distinct XRD peaks. Moreover, analysis by FT-IR spectroscopy is almost non-destructive for the artifacts (Calia et al., 2011), since it requires only a small amount of ceramic material (approximately 1 mg), whereas the XRD method requires a significantly larger sample. FT-IR spectroscopy is a simple, fast, and reliable analytical tool and is relatively inexpensive. In addition, short analysis time means that researchers obtain results almost immediately, and with by portable apparatus the FT-IR analysis can be done in the field.

510

SHLOMO SHOVAL

Infrared spectroscopy is based on the manner in which radiation in the infrared range of the spectrum interacts with a material (Weiner, 2010). Infrared radiation is absorbed differentially by functional groups of the material according to the structure and vibration of their bonds and crystal lattice, The functional groups absorb infrared radiation frequencies which are resonant with their crystal structure (i.e. have the same energy as the transition energy of their bonds); therefore the frequencies absorbed by a material are characteristic of the structural-chemical composition of that materiaL In the infrared spectrometer, the sample material is irradiated with full spectrum infrared light and the output or unabsorbed radiation is measured by the detector. The absorption of specific wavenumbers (spatial frequency of a wave) by the material means that some frequencies of radiation do not reach the detector of the spectrometer. As a result, the intervals of absorption are recorded as series of bands (peaks) on the infrared spectra, The FT-IR spectra are usually depicted as absorption unites versus wavenumber units (in em·') at the range 4000-400 cm· 1• Each mineral has characteristic bands in the spectra which enable its identification (Farmer, 1974), These characteristic bands are used to identify the mineralogical composition of a materiaL

The Mineral Composition of Fired-Clay Ceramics FT-IRis a powerful technique for assessing the mineralogical composition of archaeological ceramics. These ceramics were produced by firing of clay raw materials. During firing, the primary clay of the raw material is transformed by a series of reactions to fired-clay ceramic (Maggetti, zoo9; Maggetti et aL, zon), Two main types of ceramics were produced in ancient times: calcareous (calcite-rich) ceramics and non-calcareous ceramics (Fabbri et al., 2014). Their mineral assemblages depend on the type of the raw material and the temperature of the firing (Shoval et aL, zona),

Mineral Assemblage ofNon-Calcareous Ceramic In the firing of non-calcareous raw material at temperatures no higher than 950°C the initial clay is transformed to fired-day, which is defined as meta-day (Shoval et aL, zona), This transformation occurs through a thermal process called dehydroxylation. Kaolinite clay transforms to meta-kaolinite, and smectitic (montmorillonitic) clay transforms to meta-smectite (Shoval et aL, 2011a; Shoval and Paz, 2015), In this process, the kaolinite clay dehydroxylates at approximately 450-soo'C (Frost and Vassallo, 1996; Dion et aL, 1998), forming meta-kaolinite, which is characterized by a pseudo-amorphous short-range ordered structure (Freund, 1974), Smectite (montmorillonite) clay dehydroxylates at approximately 6oo'C, forming meta-smectite with a pseudo-amorphous structure (Heller-Kallai and Rozenson, 1980 ), At fhe same time, illite clay dehydroxylates at approximately 550-9oo'C (Gualtieri and Ferrari, 2006), forming meta-illite. The consolidation of the ceramic body by sintering of the fired-day usually occurs in firing around 90o'C (Grimshaw, 1971; Rice, 1987), In this process, the meta-day grains stick to each other. In heating of kaolinite above 95o'C the meta-day progressively transforms to a defect spinel-type phase and at higher temperature to poorly crystallized cubic mullite (Shoval et aL, zonb ), The formation of well-crystallized phases of mullite is observed at approximately 12oo'C The major phases formed by the progressive heating of smectite have been identified as spinel, mullite, cordierite, and cristobalite (Seyama and Soma, 1986),

FT-IR IN ARCHAEOLOGICAL CERAMJC ANALYSIS

511

Mineral Assemblage of Calcareous Ceramic In firing of calcareous raw material, the presence of calcite affects the thermal reactions. The calcite decomposes through a thermal process called decarbonation. During decar· bonation, carbon dioxide (CO,) is released, and free-lime (CaO) is formed (Fabbri et al., 2014). Under prolonged ceramic firing the decarbonation takes place at temperatures between 6oo and 8oo°C, depending on the form of the calcite, the impact of the clay, and the firing conditions (Shoval et al., 1993; Maggetti et al., 2011). In parallel to decarbon· ation, a process of dehydroxylation of the clay to form the pseudo-amorphous phase of meta-day takes place (Shoval, 1988). In ceramic firing above 8oo°C, the free-lime from the decarbonated calcite generates newly formed firing silicates by reaction with the fired-clay. These firing silicates include minerals such as gehlenite, anorthite, larnite and diopside-wollastonite (Maggetti, 1982; Shoval, 1988; Dondi et al., 1999; Cultrone et al., 2001; Trindade et al., 2009 ). After firing, recarbonation of the excess free-lime takes place by the reaction with water vapour and carbon dioxide from the air, forming crystalliza· tion of fine reformed (recarbonated) calcite within the ceramic material (Shoval et al., zona; Fabbri et al., 2014).

SAMPLE PREPARATION FOR

FT-IR SPECTROSCOPY

The spectra presented in this work were obtained using a )asco FT-IR spectrom· eter (Series 4000) with Spectra Manager software. Part of the spectra was recorded using ThermoScientific Nicolet (Series DXC) with Omnicsoftware. KBr (potassium bromide) disk was used as carrier transparent material for the analysis of the sample in the apparatus. A small sample of the ceramic is first powdered, dispersed in KBr, and then pressed into a disk. For that, 1mg of the powdered sample was mixed with 150 mg ofKBr by grinding in an agate mortar. Before analyzing, the disk can be also dried in an oven at no°C and then repressed to improve the resolution of the spectra. Analysis of the bulk ceramic gives the composition of the ceramic matrix mixed with the temper particles (the latter known also as non-plastic component and inclusions). Particular pottery attributes, such as separated pastes, temper particles, binders, glazes, slips, paints, and pigments can also be analyzed after picking under a zoom stereomicroscope.

FT-IR SPECTRA AND

SPECTRAL

ANALYSIS OF CERAMIC

Representative FT-IR Spectra of Archaeological Ceramic Figures 28.1 and 28.2 show original spectra and spectral analysis by curve-fitting and by second-derivative. The figures display the IR spectra in the range !800-400 em-• of representative Iron Age pottery from Levantine sites and Bronze Age pottery from Canaanite sites. The figures illustrate the different minerals composing the ceramic

512

SHLOMO SHOVAL

according to their indicative bands. Diagnostic bands are: 1030-1090 cm- 1 of firedclay (meta-clay), 1420-1450 em-' of calcite, 778 and 798 (band-doublet) of quartz; 912915 cm- 1 of silicates.

Spectral Analysis by Curve-Fitting and Second-Derivative In order to improve the identification of different minerals and minor phases of the ceramic> the original spectra were analyzed by curve-fitting and by second-derivative (Figures 28.1 and 28.2). The spectral analyses presented in this work were obtained using the GRAMS/ AI 32 software package of the 1bermoScientific Corporation. The curve fitting of the spectra were carried out with the "peak fitting function" of the software. Lorentzian band shape and in several spectra Gaussian band shape were chosen for the fitting. Second-derivatives of the spectra were obtained with a derivative "gap" function of the "Grams» software. The FT-IR spectra of the pottery may exhibit composite bands often representative of mixtures of minerals. These composite bands may overlap partially, appearing as asymmetric bands or as band-shoulders. For example, in the spectra of the ceramic the main SiO band arises from contribution of meta-smectite, meta-kaolinite, and quartz, which bands are partly overlapped (Figures 28.1 and 28.2). The spectral analysis enables the separation of these partial overlay band> and improves identification of individual compositional phases in the ceramic fabric (De Benedetto et aL, 2002; Shoval eta!., zona). The curve-fitting technique has the ability to convert the composite bands into its components, which are easily quantified. In this manner, the broad bands, asymmetric bands, and band-shoulders are separate into their components. The second-derivative technique enables us to identify the exact frequencies (wavenumbers) of the composite band components. For example, spectral analysis enables the separation of the main SiO band to components of meta-smectite, metakaolinite, and quartz (Figure 28.2).

Quantification by FT-IR Spectroscopy The FT-IR method adds a quantitative dimension to mineralogical analysis of archaeological ceramics. The relative intensities or the relative integrated areas of the absorption bands and their components of individual minerals in the curve-fitted FT-IR spectra (Figure 28.1) are proportional to their concentrations and thus enable quantification of the detected minerals. Calibration curves, prepared for the ceramic with known concentrations of a mineral, are used as references for the calculations.

Relative Amount of Calcite The relative amount of calcite in the ceramic can be detected by the intensities or the integrated areas of the main C03 band of calcite at 1420-1450 em-' relative to that of the main SiO band of the fired-clay (meta-day) at 1030-1090 em-' (Shoval, 2003). For example, the higher intensity of the C0 3 band in the spectra of Figure 28.1a compared with its intensity in Figure 28.1b indicate a larger concentration of calcite in the fabric of the former. The overall percentage of calcite in the ceramic is calculated from the relative intensities or the relative

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1000

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Ceramic matrix rith in silicate

Ceramic matrix rich in quartz

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minerals (without quartz} SiO

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1 complex (A500 ) is divided by the area under the Raman bands at woo em·• (Aw 00), the polymerization index, IP' is calculated (Colomban et al., 2003, 2004b ). The value of the IP ratio is strongly correlated to the polymerization degree and thus characteristic for the composition of the glaze. Based on the IP ratio, the processing temperature of glass structures, like glazes, can be estimated (Table 29.1) (Colomban eta!., 2003). In a Pb-based glassy matrix, for instance, the IP ratio is much smaller than in transparent glazes. Note also that the center of gravity of the Pb-based glassy Si-0 stretching mode is ca. 950 em·', but that it is at ca. 1050-noo em·> in the K/Ca-based colorless glaze (Colomban et al., 2003, 2004b; De San tis eta!., 2012). In 2001, Colomban and Treppoz introduced five different stretching bands, whose convolutions produce the broad experimental band at about 1000 em·•. These five different components are denominated as Q 0 , Q, Q,, Q3, Q 4 , and Q 5, and correspond, respectively, to SiO 4 units with zero, one, two, three, and four bridging oxygen atoms (Col omban et al.,

Table 29.1 Based on the lp ratio, the processing temperature of glass structures can be estimated Processing temperature (in oc}

Polymerization index, IP

1400

~

1000

~1.3

600 or less

~

7 0.3

RAMAN SPECTROSCOPY AND STUDY OF CERAMIC MANUFACTURE

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FIGURE 29.4 Plot of the polymerization index as a function of the main Si-0 stretching component wavenumber (Redrawn from Colomban, 2006).

2003, 2004b; DeSantis et al., 2012). Knowledge of the components mentioned above allows classification based on the glaze structure. 1his can be done in several ways. For example, to classify different types of glassy silicates the I, index is plotted as a function of the position of the main Si·O stretching component wavenumber (i.e. the peak maximum wavenumber): from top to bottom, classification is a function of tbe melting/processing temperature, ranging from porcelain at the top to low-temperature-processes silicate glasses at the bottom. From left to right, classification is carried out as a function of the main fluxing agent. This is depicted in Figure 29.4 (Colomban eta!., zoo6). In the study of Kutahya wares, the On components were used to discriminate between different ceramic production processes which are debated among scholars. As a lot of infor· mation about the production process remains within the micro/nanostructure of the sam~ ples, the On components were used to understand the production process and classify the objects. The study shows that the production homogeneity can be represented by plotting the area of each component On as a function of their peak positions. Furthermore, the similarity between composition and nanostructure of glazes could be deduced from the comparison of the 0, center of gravity and relative area ratios of the On components (Colomban et al., zoos).

FUTURE PROSPECTS In many publications concerning pottery analysis, ceramics are clustered according to their chemical composition using different statistical methods, such as principal component analysis (PCA) or linear discriminant analysis (LDA). PCA is used to reduce the dimensions

540

JOLIEN VAN PEVENAGE AND PETER VANDENABEELE

of multivariate problems. It is an unsupervised pattern recognition method because no assumptions are made about underlying data distribution. The correlation among a large number of variables is expressed in terms of underlying factors, called principal components (PCs). These orthogonal variables are a linear combination of original variables with the first PC explaining the largest portion of variance, the second PC the second-largest, and so on. LDA, on the other hand, is a supervised discriminant analysis method. In this classification method, the variances between categories are maximized and the variances within categories are minimized (Carrero et al., 2010). In practice, to execute multivariate data analysis, quantified compositional data for the ceramics is reported as elements or element oxides, acquired using analytical techniques such as ED-XRF or ICP-MS. Raman data can also be analyzed using these data processing methods. For the distinction of copper phthalocyanines in paint layers, for example, Defeyt et al. (2013) used micro- Raman spectroscopy in combination with chemometrical analysis. Copper phthalocyanine is often identified as an important pigment (PB15) in twentieth-century artworks. It is used in different polymorphic forms and identification of it can retrieve information on the production process of the pigment at the moment. Using LDA with intensity ratios as variables, the crystalline structure of a PB15 pigment can be predicted in unknown paint samples (Defeyt et al., 2013). However, multivariate data analysis is rarely done in combination with Raman spectroscopy, but it has been proven effective. This provides opportunities and avenues for future research concerning pottery analysis.

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1#r

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543

Vandenabee]e, P. (2013). Practical Raman Spectroscopy: An Introduction (Chichester: fohn Wiley & Sons, Ltd). Vandenabeele, P., fehlicka, f., Vitek, P., and Edwards, H. G. M. (2012). "On the Definition of Raman Spectroscopic Detection Limits for the Analysis of Biomarkers in Solid Matrices." Planetary and Space Science 62(1): 48-54. Vandenabeele, P. and Moens, L. (2004). "Pigment Identification in Illuminated Manuscripts." In: Janssens, K. and Van Grieken, R. (eds), Non-Destructive Microanalysis of Cultural Heritage Materials (Amsterdam: Elsevier). Vandenabeele, P. and Moens, L. (2012). "Some Ideas on the Definition of Raman Spectroscopic Detection Limits for the Analysis of Art and Archaeological Objects:' Journal of Raman Spectroscopy 43(11): 1545-1550. Vandenabeele, P., Moens, L., Edwards, H. G. M., and Dams, R. (2oooa). "Raman Spectroscopic Database of Azo Pigments and Application to Modern Art Studies:' Journal of Raman Spectroscopy 31(6): 509-517. Vandenabeele, P., Wehling, B., Moens, L., Edwards, H., De Reu, M., and Van Hooydonk, G. (2ooob ). "Analysis with Micro- Raman Spectroscopy of Natural Organic Binding Media and Varnishes Used in Art:' Analytica ChimicaActa 407(1!2): 261-274. Vandenabee]e, P., Verpoort, F., and Moens, L. (2001). "Non-Destructive Analysis of Paintings Using Fourier Transform Raman Spectroscopy with Fibre Optics." Journal of Raman Spectroscopy 32(4): 263-269. Van de Voorde, L., Van Pevenage, f., De Langhe, K., De Wolf, R., Vekemans, B., Vincze, L., Vandenabeele, P., and Martens, M. P. ). (2014). "Non-Destructive In Situ Study of 'Mad Meg' by Pieter Bruegel the Elder Using Mobile X- Ray Fluorescence, X- Ray Diffraction and Raman Spectrometers:' Spectrochimica Acta Part B: Atomic Spectroscopy 97: 1-6.

CHAPTER 30

X-RADIOGRAPHY OF ARCHAEOLOGICAL CERAMICS INA BERG AND JANET AMBERS

HISTORY IN 1895, Wilhelm Rontgen discovered a new type of radiation, which he termed "X-rays;' while experimenting with vacuum tubes. These rays proved to be more penetrative than light and thus could be used to produce images of dense materials. The first X-ray image ever published was that of Rontgens wife's hand with her ring clearly visible on her finger (Rontgen, 1896). The scientific community rapidly recognized the potential of the technique and almost immediately began to use X-rays to illuminate a wide variety of medical problems (Posner, 1970 ). Rontgen was awarded the Nobel Priz.e in 1901 in recognition of his important discovery. The technique's power was by no means limited to medical uses and it quickly became an invaluable tool in art and archaeology, where it has since been applied to a great variety of materials, including human and animal bones, metals, ceramics, paper, paintings, and soils (for a recent summary see Lang and Middleton, 2005). The earliest application of X-radiography to ceramics dates to 1935 when Titterington published a radiograph of seven sherds from North American Indian burials in order to illustrate differential proportions of inclusions. A decade later, Digby employed the technique to investigate a defect in the construction of a Peruvian stirrup-handled pot (1948). However, it was only in 1977> when Rye laid down the fundamental rules of ceramic X-radiography, that the analytical potential of this technique was fully appreciated (1977; 1981). A comprehensive summary of the technique and its application to ceramics was published in the 1990s (Carr, 1990; Carr and Riddick, 1990) and further expanded and updated by Berg (zoo8).

RADIOGRAPHY AND CERAMIC TECHNOLOGY Radiography offers many advantages for the study of ceramics which make it a very effec-

tive technique for archaeologists and conservators alike, whether used on its own or in

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conjunction with other methods such as microscopy or conventional destructive provenance analyses. Although almost all published radiographic studies of ceramics focus on clay vessels, the underlying technological principles make it a suitable investigatory technique for almost any kind of clay object. Its advantages are manifold as it provides access to the internal structure of an object, is non-destructive, can be used on both fragments and complete objects, is comparatively rapid and cheap, and suitable medical or industrial facilities are easily and generally available worldwide. X-radiography is most commonly applied to cultural materials to answer a number of questions, particularly: identifrcation of the object and its condition; identification of the material(s) present; identification of manufacturing method(s); identification of joins, faults, breaks, repairs, and reuse; identification of finishing methods and decoration; .. identification of forgeries. In the case of archaeological ceramics, radiography is used extensively to answer many of these questions, particularly to study condition and repairs to inform conservation treatments and questions of authenticity. However, two of these themes-namely, the identification of materials and of manufacturing methods-have received by far the greatest attention, with work specifically concentrated on the characterization of clay fabrics through inclusions or tempers and the identification of manufacturing details (Carr, 1990 ). These two subjects are discussed in more detail in the following section.

Characterizing Clay Fabrics Under the right conditions, that is when the clay body and inclusions are of different radiodensities and vessel walls are not too thick, X-radiographs can be used successfully to characterize ceramic fabrics by determining the size, proportion, type, and general mineralogy of inclusions and/or tempering materials. Scholars have been able to distinguish between classes of minerals, such as felsic, mafic, and opaque, by considering the radiographic density and morphology of the particles, and the presence, number, and angle of their crystal faces. More specific attribution of minerals is often problematic, especially when inclusions/particles/grains have a similar chemical composition and exhibit similar morphology and radiodensities (e.g. chert, quartz, pure sandstone) (Carr and Komorowski, 1991). Grog, for example, is most visible when it is of different clay from the surrounding clay body (Foster, 1985). In contrast, organic inclusions (such as straw, wood, sponge, insects, seeds, shell) and the burnt-out voids left by them are easily recognizable, since the density of the ceramic body is significantly different from that of air. Once inclusions have been characterized, their volumetric proportion and (size) distribution within the vessel can be measured and used to determine fabric groups (Rye, 1977; Braun, 1982; Maniatis et a!., 1984; Foster, 1985; Blakely eta!., 1992). Blakely and colleagues tested the potential of radiography to assign vessels to fabric groups, and the technique was able to successfully divide their sherd assemblage of Pompeian red ware into two major fabric groups. Petrology and heavy mineral analysis were subsequently able to confirm the

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INA BERG AND JANET AMBERS

validity of these two groups (Blakely et al., 1989). In a related study, X-radiographs were used to successfully determine whether body sherds found in close proximity to each other during excavation belong to the same vessel or to different ones, providing certainty where macroscopic analysis is ambiguous (Carr, 1990: 21, 1993: 103-105). However, success of Xradiography for establishing fabric groups is variable, as demonstrated by Adan-Bayewitz and Wieder (1992), and depends upon the exact nature of the fabric(s) under investigation. It seems most prudent, therefore, to consider radiography as a complementary tool rather than a replacement for petrography and chemical analyses.

Identifying Vessel Formation Procedures First used by van Beekin 1969, X-radiography has since established itself as a powerful technique for the identification of primary forming methods, in particular differentiating among pinching, drawing, coil-building, slab-building, molding, and wheel throwing. It was Rye who first recognized that "the application of pressure to plastic clay causes mineral particles, voids, and organic fragments to take up a preferred orientation'' which affect the entire ceramic body. The resulting alignment and distribution of inclusions, as well as the shape and orientation of voids, is characteristic of each forming method, and these features are not normally obliterated or obscured by secondary forming/shaping or decorative techniques (1977: zo6, 1981; Carr, 1990; Berg, zooS). Much innovative X-ray work in this field was carried out in the 198os and early 1990s. However, waning technical support for xerora~ diography (see the section entitled 'Xeroradiography') in the late 1990s has led to a noticeable interruption in research activity. It is only now, with a better appreciation for the power of imaging software programs and increasing availability of industrial and medical X-ray equipment, thatX-radiographic research into ceramics is once again gaining momentum. Many scholars have successfully employed radiography to gain a better understanding of manufacturing techniques (see e.g. van Beek, 1969; Foster, 1983; Ellingson et al., 1988; Carmichael, 1990, 1998; Henrickson, 1991; Nenk and Walker, 1991; Vandiver et al., 1991; Philpotts and Wilson, 1994; Vandiver and Tumosa, 1995; Levi, 1999; Giannoulaki et al., zoo6; Berg, 2009; Laneri, 2009; Berg and Ambers, zona; Corfield, n.d.), but the two most detailed case studies currently available were undertaken by scholars working in the Near East (Glanzman, 1983; Glanzman and Fleming, 1986; Vandiver, 1987, 1988). In their diachronic study ofBaq'ah pottery, Glanzman and Fleming were able to show that, contrary to the common assumption of an evolutionary sequence from hand-building techniques to the potter's wheel, the Baq'ah LB I wheel-throwing tradition was replaced by a coil-building tradition in the LB II and Iron lA periods. Vandiver, on the other hand, employed xeroradiography to reconstruct a specific forming technique, called sequential slab-building, in widespread use in the Zagros region around 3000 sc. Not only was Vandiver able to identify the technique in general, but she was also able to determine the precise shape, size, and sequence with which each slab was applied to form a vessel (1987). Some of the most intriguing case studies have utilized X-radiography to detect hidden vessel parts and added sections, such as the whistling mechanism in Peruvian pots and the fake spout of Aegean stirrup jars (Digby, 1948; Leonard et al., 1993). Secondary forming techniques, such as scraping, trimming, smoothing, and adding sections, are more difficult to identify radiographically because tbey do not generally involve

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severe enough modification of the clay to be reflected in an X-radiograph (Berg, 2008). 1hese secondary modifications and technologies are, therefore, best identified macroscopically. 1he exception to this rule is the paddle and anvil technique which applies so much pressure to the preshape that it can obliterate all radiographically visible attributes of the primary forming technique (Rye, 1981). Similarly, severe turning of the entire vessel is often identified by the complete lack of evidence/traces of the original forming technique combined with thin vessel walls.

THEORETICAL BACKGROUND 1he use of radiography in the study of ceramic composition and forming techniques is based on the distribution, alignment> and nature of inclusions and voids within the fabric. In terms of simple compositional studies this is self-explanatory: materials which differ in radiographic density from the clay body can become visible, and hence can be analyzed and interpreted through X-radiographs. 1he use of radiography to look at ceramic forming techniques is rather more complex. Pressure applied during the formation and shaping of a vessel frequently creates characteristic alignments and orientations of inclusions and voids that become radiographically identifiable within the vessel fabric. Figure 30.1, based on the pioneering work of Rye (1977, 1981), provides a summary of the characteristics whicb might be expected for different forming techniques. Radiography reveals these alignments nondestructively. It should once again be emphasized that the success of radiography in identifying manufacturing techniques is dependent upon the visibility of these features; that is, they must have different optical densities from the matrix material, as well as the amount of secondary reworking. We advocate, therefore, that small-scale trials or pilot projects always be carried out on unknown or previously unradiographed ceramic types prior to any major commitment of resources. Pinching-forming shapes by squeezing clay between fingers and thumbs-is probably the simplest of the ceramic forming techniques. It does not result in the type of dramatic orientation of inclusions produced by other forming methods, but can still leave diagnostic traces in the vessel fabric. Figure 30.1a illustrates these features: in cross-section inclusions lie parallel to the surface while in plan view no horizontal or vertical orientation is visible. 1he surface may also show indentations from the pinching motion. Figure 30.1b illustrates the distribution patterns expected for coil- or ring-built vessels. It is extremely difficult to attain perfect cohesion for every coil joint, however expert the potter, and despite careful secondary worldng to smooth out and strengthen these joins, in most cases some evidence will survive somewhere within the vessel fabric. As a result, coil joins are often visible as voids between the coils and are typically roughly concentric on the base and roughly horizontally parallel on the vessel sides. joining techniques, such as overlapping, smearing, or crushing individual coils, are sometimes applied to strengthen coil joints. In these cases it can be necessary to vary the angle of the X-ray shots to capture the joins and, sometimes, even to resort to the "thick section" method of examination (described below in "Tips and Tricks") to capture proof of coiling. In addition, the coils themselves, having been prepared as long rolls prior to vessel formation, may exhibit a degree of horizontal parallel orientation with inclusions sometimes visible in the X-ray image (Figure 30.2).

548

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FIGURE 30.1 Characteristic X-ray features of the main pottery forming techniques (after Rye, 1981; Carr, 1990: figure 1; Middleton, 1995: figure 4.8), showing, from left to right, vessel, distribution of voids and inclusions in the vessel side, distribution of voids and inclusions in the vessel cross-section. Techniques shown are (a) pinching, (b) coil building, (c) wheel throwing, (d) slab building, (e) secondary working using the paddle and anvil technique.

Inclusion alignment in a clay coil. Normal view (left) and cross-section (right). Enhanced positive radiographic image. Exposure parameters: Faxitron, 0.5 mm focal spot, 6o em focus-to-film distance, 70 kV, 150 s, 3 rnA. FIGURE 30.2

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Wheel-thrown vessels do not exhibit joins but the combined upward and rotational movement associated with pulling the walls of a vessel results in a spiral orientation of voids and inclusions (Figure 30.1c). In cases where a vessel is complete, X-rays are able to pass through both the near and far walls, and the resultant X-radiography will show superimposed images of both sides of the vesseL Wheel throwing, therefore, can reveal itself in the radiograph as either a series of diagonal lines in the vessel's surface or as two sets of diagonal lines in apparently opposing directions (this effect can be avoided by placing film inside a complete or near complete vessel in order to capture only one side). The initial suggestion by Rye that the angle of these lines reflects the speed of the wheel is not supported experimentally (Berg, 2008), but the same study did show that it is possible, in some circumstances, to differentiate between wheel-made ceramics, where the entire forming process is carried out on a turning wheel, and wheel-shaped or wheel-finished vessels, where items initially made by other techniques are then finished and improved on a fast wheeL Joins between flattened sheets of clay are the primary radiographic evidence for slab-built vessels (Figure 30.1d). The orientation of inclusion in these sheets is dispersed and unaligned as a consequence of flattening of the clay sheets. Other manufacturing techniques, notably molding, are more difficult to identify radiographically. For molding, the nature of the method means there is little or no development of preferred particle orientation within the clay, but thickening of the clay along the lines where the separate parts of the molds meet frequently occurs, and it is sometimes possible to successfullyidentify mold-made ceramics in this way. A wide range of secondary forming processes are used in ceramic construction in order to increase strength and resistance or simply to improve appearance. They are seldom detectable by radiography and do not normally impact the visibility of primary forming techniques (Berg, 2008), except in cases where a large proportion of the wall thickness is removed. The one notable exception is the paddle and anvil technique, whose use may make the identification of the primary forming method more difficult. The effects on alignment and orientation of particles and voids in the vessel created/modified by the paddle and anvil technique are shown in Figure 30.1e. This technique, designed to thin and shape vessel walls, consists of beating one side of the vessel wall (usually the exterior) with a paddle, while the inside is supported with the smooth hard surface of a tool or implement, often a pebble. This "beating" causes localized distortions of voids and inclusions in the vessel walls, and the resultant variation in thickness and distinctive star~shaped cracks around large mineral particles are dearly visible in X-radiographs and are among the easiest ceramic features to identify radiographically. In contrast, very severe turning of the entire vessel may potentially be identifred by the total lack of traces of the original forming technique and thin vessel walls, as demonstrated in an unpublished study of Bronze Age Cypriot vessels investigated by one of the authors (Ambers). Based on our experience with ancient vessels) together with experimental data from replica vessels, a firm identification of forming techniques should be possible for approximately 70% of vessels within an assemblage. Success rates will be lower when the vessel walls are very thick, when clay body and inclusions have a similar radiodensity, or when the pots have been heavily turned.

550

INA BERG AND JANET AMBERS

METHODOLOGY

Historical Development The earliest X-radiographic investigations of ceramics (van Beek, 1969; Rye, 1981) used conventional film radiography and met with only limited success. In order to characterize archaeological ceramics it is necessary to locate and identify small particles with densities only minimally different than an already radiographically light matrix. With skill and care such subtle changes can be identified on unmodified X-ray films, but the process is not easy and requires considerable expertise. The development of a novel radiographic technique in the 1970s, xeroradiography, made the identification of such small changes in density much more accessible, and was followed by an explosion in the number of ceramic studies dependent on radiography published.

Xeroradiography Xeroradiography is an X-radiographic technique in which the image is collected on an aluminum sheet coated with a uniformly deposited film of amorphous selenium, rather than on a photographic film or a digital imaging plate, within an otherwise conventional radiographic setup. The plate is electrically charged before use, and during exposure this charge dissipates differentially in proportion to the dose of radiation it receives, thereby generating a latent image which can be fixed onto paper by processing with oppositely charge particles (usually in the form of a blue colored powder), as a variation of the Xerox photocopying process (Boag, 1973; Lang and Middleton, zoos). While this method cannot produce highresolution images, it has other advantages which established its importance for a range of medical applications, most notably mammography. Xeroradiography has a wide exposure latitude, is virtually impervious to scatter, and, because of the way in which the dry toner responds to electrical fringing between high- and low-charged areas, shows a pronounced edge enhancement effect (Figure 30.3). These characteristics make it particularly suitable for the examination of small differences in density, particularly if they have sharp, well-defined edges. Originally developed for medical examination, xeroradiography was rapidly taken up by the archaeometric community for a number of purposes, but most particularly for the study of ceramics (see e.g. Vandiver, 1987). Xeroradiography is now effectively obsolete, as it has long been replaced in medicine by techniques which require lower doses of radiation. Instead radiographers have turned to digital image manipulation to extract similar information from radiographic images, as discussed in detail in the section entitled "Image Enhancement" (O'Connor eta!., zooz).

Modern Practice A wide range of X-ray equipment, which can broadly be divided into medical and commercial/research setups, is now available to archaeologists. Medical units can be found in

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FIGURE 30.3 Xeroradiographs of two stirrup jars showing both the blue color and edge enhancement inherent to the technique. The scratch across a) is an unfortunate result of the use of ageing equipment. a) Stirrup jar with solid false central spout from mainland Greece (BM registration number G&R1978,0701.4); b) Cretan stirrup jar with hollow false central spout (BM registration number G&Rr857,0825.2).

hospitals, private clinics, and veterinary surgeries (Figure 30-4a), while commercial/research machines can be found in industrial settings, museums, and universities (Figure 30-4b). The key difference between them is that medical setups are designed to minimize the radiation dose to living tissue, and are, therefore, only designed to permit short exposure times. As a consequence, the voltage (kV) has to be proportionately greater to achieve penetration, resulting in images with reduced contrast. However, in industrial and research settings the imperative to minimize patient dosage does not exist. This means that exposure times can be increased and the kV kept low in order to achieve high-contrast images. For this reason, if the opportunity to work with a commercial/research setup is available, this is to be preferred over a medical facility. The advantages of using radiographic equipment at medical facilities, on the other hand, are their relative abundance, comparative ease of access, and potential portability (many large animal veterinary practices and some hospitals have mobile equipment). If medical equipment is to be used, it is best to avoid specialist mammography units, because mammography film is generally only available in very small sizes and also tends to be too responsive to very small thickness changes, making it overly sensitive for ceramic analysis. 'TI1e truth, however, is that it is possible to work with most commercial, research, and medical X-ray units and achieve a reasonably detailed image. One further choice exists when selecting X-ray equipment: whether to use digital or conventional wet( -film) processing. At the time of writing there are few qualitative differences

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INA BERG AND fA NET AMBERS

FIGURE 30.4 Examples of types of radiographic equipment available. (a) Portable medical Sirio no/loo CR system; (b) Faxitron single-cabinet X-ray unit.

between the two; currently available instrumentation digital image quality is as good as that of film and the speed of technical development is such that digital may soon overtake conventional film radiography. Digital equipment has several practical advantages: the image can simply be downloaded without having to be scanned; the latitude of exposure is greater; the lack of processing time means digital work tends to be quicker than film radiography; and, while the

initial outlay for equipment is higher, there are no recurrent costs for film and chemicals. "There are currently two types of digital systems available, which differ in the image collection method used: CR (computed radiography) and DR (direct radiography).ln CR, a reusable phosphor plate is used in place of film in a conventional system, while in DR the image is captured on a fixed plate and transmitted directly onto a computer screen. DR systems are currently considerably more expensive, but, at present, the image quality of the two systems is similar. An archaeologist's choice of system will most likely be governed by availability and training, but looking into the future, chemical processing is slowly being phased out in all areas, and digital X-ray machines will soon become the norm. A radiographic imaging technique called computed tomography (Cf or CAT) may occasionally be available to researchers. In addition to presenting a frontal view of an object, like regular X-rays, CT can also "slice" through an object, providing the researcher with cross-sectional views.

Image Enhancement Whatever the initial image collection method, the minimal differences in radiographic density between ceramic bodies and the voids and inclusions within them mean that some form of image enhancement is necessary prior to interpretation of the radiographs. In xeroradiography, edge enhancement was an integral part of the method, but for conventional X-radiography edge enhancement must be artificially produced by digital manipulation of

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the image. In order to do this, the images must first be in a digital format and of the highest resolution possible. With the increasing availability of digital radiography no interim stage may be necessary, but, given that archaeology tends to be both poorly funded and conducted in areas with limited resources, at the time of writing, most radiography of ceramic materials will have been recorded on film. Low-cost methods of film digitization exist (films can be scanned on office-style flatbed scanners with transmission capacity or placed on a light box and imaged with a standard digital camera), but by far the best results are obtained using specialist X-ray scanners (O'Connor and Maher, 2001; Lang et al., zoos). These are designed to maximize the information collected from film radiographs and have high dynamic ranges (dynamic range is defined as the range of optical densities that can be recognized in the image), and high resolution (resolution is the number of pixels per unit length in the image; for most specialist equipment the pixel pitch will be so microns (c.s12 pixels per inch) or better) and a bit depth of 12 or more (bit depth controls the number of shades of gray which can be distinguished within the image; in an 8-bit system zs6 shades of gray can be defined, in a 12-bit system 4,096, and in a 16-bit system 6S,S36). Such specialist equipment is very expensive and its purchase is not cost effective for most museum and academic departments. However, demand for the storage of industrial images means that commercial scanning services are readily available at reasonable rates, particularly when judged against the cost in time and effort of producing high-quality radiographic images in the first place. Regardless of how the digital image is produced, it is important that it is generated and stored in an accessible and widely supported format, partly for ease of publication by the researcher, but also, and crucially, for archiving purposes; much archaeometric data has been lost over the years owing to the use of data formats which have become redundant. Most digital radiography or radiograph scanning equipment produces data in both proprietary and generic formats. For archaeometric images, it is important that a widely available generic and uncompressed format is selected for archiving. At the time of writing (2013), this will be either as TIF or DICOM files. DICOM is a lossless data format originally devised for the distribution of medical images but now adopted into the industrial world in the form of DICONDE. It is possible that both these formats may eventually be superseded, but they are currently so prevalent that it is difficult to foresee a time when conversion programs for these formats are no longer available. Once an adequate digital image has been generated it must be enhanced to make the edges of the included materials visible for interpretation. One way to achieve this is first to detect and then enhance the edges, a process generally carried out using a kernel-based algorithm. A detailed study of suitable edge detectors (O'Connor et al., 2002) suggested that a Kirsch edge detector was the most suitable for archaeometric work. While most commonly available imaging programs, such as Adobe's Photoshop and Corel's PaintShop Pro, have the capacity to run such specialized filters as add-ons, they are not generally included in the off-the-shelf version. However, experimentation by the authors has found that in the majority of cases the use of the Unsharp Mask filter, originally devised to increase the resolution of photographic images and conventionally included in most digital imaging packages, provides a perfectly adequate and more accessible alternative to these more expensive add-on features.

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FIGURE 30.5 Radiographs of a Middle Minoan amphora (BM registration number G&R1906,m2.90) from the British Museum. All radiographs were recorded on Kodak Industrex MX film in a hard plastic cassette with 0.25 mm lead sheets on either side of the film. (a) Whole side of vessel, unenhanced image. Exposure parameters: Siefert DSr, o.s mm focal spot, I m focus-to-film distance, 70 kV, 25mA mins. (b) Image from 4a, enhanced using Adobe Photoshop Unsharp Mask filter. (c) Detail oflower body from sb showing diagonal voids characteristic of rotative kinetic energy. (d) Detail of central zone from sb showing parallel joins characteristic of coil forming and evidence of secondary working. (e) Detail of upper body from sb showing evidence of coil forming.

A dramatic example of the successful use of a scanned film radiograph, enhanced with Unsharp Mask, is given in Figure 30.5. Here a Middle Minoan III oval-mouthed amphora (BM registration number G&R 1906,m2.90) was radiographed using Kodak Industrex MX film. The film was then digitized using an Agfa RadView scanner with a so micron pixel size and 12-bit resolution, and the resultant image enhanced using the Unsharp Mask filter within Adobe Photoshop. Figure 30.5a shows the unenhanced scanned image, while 30.5b shows the same image with an Unsharp Mask filter applied. Figures 3o.sc, d, and e illustrate individual details of the lower, center, and upper body of the vessel, individually processed for the greatest clarity. In Figure 30.5c, clear diagonal voids can be seen representative of evidence of the rotative kinetic energy of wheel throwing. Parallel joins in Figure 30.5d show that this zone was produced by coil forming, and the localized distortion indicates that there was secondary reworking of this area. Figure 30.5e, the

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shoulder at the top of the amphora, also reveals parallel joins indicative of coil build-

ing, but here there was no secondary treatment, thus making the coil joins more easily recognizable.

RADIOGRAPHY OF CERAMICSPRODUCING THE BEST RESULTS

Crucial for the radiographic study of archaeological ceramics is the generation of a highcontrast radiograph. In order to achieve this, the kV should be kept low and the exposure time long. In work carried out by the authors, using either a Faxitron cabinet with a 3mA fixed tube current or a Siefert DSr 320 kV industrial X-ray tube, voltages between 55 and 70 kV were found to produce the best images of ancient and modern ceramics with a range of wall thicknesses, although such parameters will vary between equipment and between film and digital setups. The exposure chart in Table 30.1 provides some basic guidance for Faxitron users using standard industrial-type film. Exposure times will be considerably shorter for digital capture and other X-ray setups will require experimentation to determine the most suitable exposure parameters. It is important to note that exposure time and kV are directly related to the thickness of the ceramic object-the thicker the vessel, the longer the exposure and/or the greater the kV. None of the many clays and tempering materials tested in experiments by the authors have showed any deviation from this basic rule. To find the correct exposure for each pot, simply measure the thickness at several points along the vertical axis of a pot; vessels typically change thickness most radically from base to rim. Select the exposure time and range that best fits with the thickness range of the majority of the area to be imaged. In circumstances where the pot has drastic thickness changes, one will have to take several images at different exposure parameters to capture the entire vessel accurately. It is important to remember, however, that one must double the wall thickness when X-raying a complete vessel to ensure that the X-ray beam penetrates both sides of the object. While it is always best to position objects at the center of the focal spot of the X-ray tube, in order to keep geometric distortion to a minimum, several small ceramic objects of similar thickness can be imaged together in the same exposure without loss of quality, helping to keep costs low and conduct a project speedily. Larger objects may each require their own plate. X-ray translucent supports can be used to prop up objects, prevent them from rolling off their spot, and align them as parallel as possible to the horizontal surface of the film, cassette, or imaging plate being used. For most exposures, pieces of bubble-wrap or plastizote are suitable supports. The object should be in as much direct contact with the cassette as possible and cassettes can be either solid or flexible. In most circumstances, a solid cassette will suffice, but flexible cassettes have advantages for the examination of complete vessels because they can be bent to fit inside objects, allowing an image to be collected for a single side of a vessel. Because of the low energies employed in ceramic radiography, the use of filters (lead, aluminum, etc.) to remove low-energy scatter and sharpen the image, essential for the radiography of denser objects, is unnecessary for ceramics.

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Table 30.1 Exposure times and kV for clay objects using a Faxitron cabinet X-ray machine with a 0.5 mm focal spot. 60 em focus-to-film distance, 3 mA, and Agfa Structrex 04 Film. The kV shown here only present a guide-radiographs should always be taken using the lowest possible kV to improve image contrast Clay thickness

55 kV

70 kV

(mm)

19

150 sec

18

150 sec

17

150 sec

16

120 sec/150 sec

15

120 sec/150 sec

14

105 sec/120 sec

13

105 sec/120 sec

12

90 sec/1 05 sec/120 sec

11

120 sec

10

105sec/120sec

90sec

9

105 sec/120 sec

90sec

8

105 sec/120 sec

90sec

7

90 sec/1 05 sec

6

90 sec/105 sec

5

75 sec/90 sec

4

75 sec/90 sec

3

75sec

90 sec/105 sec/120 sec

Tips and Tricks Experience has shown that there are a number of tips and tricks that can increase the likelihood of producing good images, the quality of the images, and/or increase visible detail, and, as a result, our ability to analyze and interpret a ceramic object confidently. (1) The inclusions and clay body are normally sufficiently different in radio-density to allow successful interpretation of features. Despite this, it is highly recommended that a pilot study of the assemblage be conducted to avoid disappointment and/or

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wasted time and resources, because some ceramics have characteristics which make their analysis difficult. These difficulties include: inclusions and clay body with similar radio-densities, for example grog; large and abundant inclusions that obscure subtle features; the vessel walls are very thick, for example large storage vessels; and/ or the vessel was heavily turned, as was the case in the above-mentioned Bronze Age Cypriot pots. (2) When radiographing a complete or largely complete vessel for the purpose of determining forming technique, it is always advisable to take two views: one from above (a plan view) and a side view. This is because some voids, such as the spiral void arrangement of wheel-thrown pots, are sometimes only or more visible in one view than the other. There does not seem to be a discernible and persistent pattern as to which view will provide the clearest view of these features. Consequently, it is only by taking both views that an accurate identification is possible (Figure 30.6). (3) Always base interpretations only on clearly visible patterns. When determining a forming technique, there is always the potential danger of assigning meaning to a random or unrepresentative alignment of voids or inclusions. One way to counter this tendency is to turn the radiograph through 90 degrees and look for the alignments again. If you find alignments along this rotated axis, then it is most likely that they are not true alignments and the radiographs do not provide a clear indication of how the vessel was made. If there is any doubt about the interpretation of features in the radiograph, analysts should err on the side of caution. Also, since different people perceive black and light areas on radiographs differently, it is sometimes helpful to reverse the grayscale of a radiograph, making previously light sections darker and dark sections lighter.

30.6 Radiographs of a bell-shaped handled cup (Middle Minoan I) from Knossos (BM registration no G&R1950,uo6.r6) Taken from the side (a) and above (b). The diagonally stretched voids indicate that rotative kinetic energy (RKE) was used in the making of this vessel and hence that the main body is wheel-thrown. The handle was pulled and its bottom attachment only lightly pressed onto the body. The details of the handle can only be seen in a, while the spiral pattern of inclusions in the main body is far clearer in b. Exposure parameters for both exposures: Siefert DSr, 0.5 mm focal spot, I m focus-to-film distance, 6o kV, 20 rnA rnins, Kodak Industrex MX film. Enhanced using Adobe Photoshop Unsharp Mask. FIGURE

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( 4) In cases where it is possible to conduct destructive analysis, thick-sectioning,

a variation on the standard X-ray method, can be used to attain a more detailed understanding of vessel formation. Thick-sectioning was pioneered by Vandiver, who used it to reconstruct the precise size of each clay slab and building sequence of slab-built vessels (1987: plates 5-7; Vandiver et al. 1991: figures 8-11). Thicksectioning involves cutting a vessel or sherd vertically into thin slices with a radiograph being taken of each slice's cross-section. The resulting images display features diagnostic of the chosen forming technique and often provide clues about the building sequence. (5) It is absolutely essential that any radiographic interpretation is based on a deep and thorough understanding of formation processes as well as the characteristic radiographic fingerprint of each technique. We therefore strongly recommend that scholars work together with a practicing potter to create a control group of modern replicas against which they can compare radiographs of archaeological ceramics.

CASE STUDIES To demonstrate the power of radiography as a technique for the study of archaeological ceramics and to illustrate its potential contribution to the development of a more detailed understanding of sociocultural patterns and changes, we provide a summary of three case studies of objects in the collections of the British Museum.

Case Study 1: the Cretan Bronze Age In zoo6, the authors collected X-ray images of twelve open and closed Middle Bronze Age vessels with a firm Cretan (Knossian) provenance from the British Museum's collection (Berg and Ambers, zona). Analysis of the radiographs indicated that two vessels, a jug and an amphora, were produced by coiling, and a jar, a jug, an amphora, and two cups were manufactured by wheel throwing; no forming technique could be conclusively determined for four vessels, an amphora, a cup, a heavily restored jar, and a jug. The most exciting finding, however, was that one amphora (BM registration number G&R 1906,1112.90) was made using three different techniques in sequence (Figure 30.5): the diagonally stretched voids around the lower body indicate that this section was wheel-thrown using rotative kinetic energy (Figure 30.5c). The middle section or vessel body is characterized by parallel joins indicative/diagnostic of coil-building, although these are partially concealed by secondary shaping visible as the differential thickness of the wall (Figure 30.5d). This secondary working is also apparent as elongated vertical lines on the radiograph. These vertical lines probably represent drawing marks, although there is no evidence of preferential vertical orientation of the inclusions or voids to confirm this, and there is a chance that this feature results from the use of the paddle and anvil technique using a rod-shaped paddle. The vessel's shoulder was also made using coils) but did not receive any secondary treatment, leaving the coil joins more easily recognizable (Figure 30.5e).

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At its most basic, this case study demonstrates the great variability in forming techniques employed by Bronze Age potters on Crete. On a more detailed level, it hints at a degree of specialization within the potting tradition of Crete with small, open vessels generally being wheel~thrown, while large, closed vessels are often handmade. This observation was subsequently tested in a larger X-ray-based project and found to apply throughout the Cretan Bronze Age and across all of Crete (Berg 2009, 2015). Most intriguing, however, was the recognition that the potters sometimes combined several methods to manufacture a single vessel. Additional examples of vessel formation using a combination of techniques were identified during the large-scale X-ray study, as well as in the literature. Two important points about ceramic manufacture emerge from analysis of these vessels: first, when the wheel is employed on these large vessels, it is utilized for the basal and lower body sections which are comparatively easy to make. Second, the height of the wheel~thrown sections is approximately 16 em, the maximum average height achieved using this technique by potters across Crete. It is possible that this height restriction was a consequence of limitations in the design of the potter's wheel, making it unable to store momentum for sufficiently long periods oftime to throw large vessels in one sequence (Berg, 2015). Rather than modify or develop a better potter's wheel, Cretan potters employed an alternative technique, wheel-shaping (termed "wheel-coiling" in recent literature), that allowed them to construct vessels in stages, using a preshape made by coiling, and subsequently modify the shape and appearance of the pot with rotative kinetic energy (for the wheel-coiling technique, see Courty and Roux, 1995; Roux and Courty, 1998).

Case Study 2: Aegean Stirrup Jars The stirrup jar is a distinctive vessel shape from Bronze Age Greece which first appeared in the Middle Bronze Age and reached its greatest popularity in the Late Bronze/Mycenaean period. These vessels are characterized by a central, false spout closed off with a disk. Two handles reach from this spout to the shoulder where a second, and functional, pouring spout is positioned. Large undecorated stirrup jars functioned as transport containers for olive oil, while smaller, decorated versions were used to store perfumed oils. Owing to the desirability of their contents, stirrup jars were produced in many workshops both inside and outside Greece and traded widely throughout the Mediterranean. Analysis of thirty-nine jars in the British Museum by Leonard and his colleagues in 1993 used NAA to investigate vessel provenance, XRF and XRD to determine the composition of the paint, and xeroradiography to establish whether individual manufacturers and/or workshops could be identified by their differential use offorming techniques (Leonard et al., 1993). The radiography results were illuminating and two different methods of manufacturing stirrup jars could be documented. In one tradition, the vessel and fake spout were built in one sequence, resulting in a hollow fake spout. '!he other tradition attached a solid fake spout, thrown as a separate piece, to the completed vessel during the leather-hard stage (Figure 30.3). These distinct manufacturing methods were shown to be indicative of different regional potting traditions, with Attic and Rhodian pots favoring the solid fake spout method and Cretan potters manufacturing vessels in a single process. An important result of this study is the reminder that similar vessel shapes can be created using very different formation techniques and manufacturing processes, and that the

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transfer of practical knowledge can create local or regional forming traditions. Therefore, it is valuable/essential to identify these traditions and technologies using X-radiography.

Case Study 3: Mycenaean Pottery Our knowledge of production equipment, forming techniques, and organization of pottery production in Late Bronze Age mainland Greece, during the Mycenaean period, is surprisingly limited. This is partly owing to the dearth of archaeological evidence from this period that relates to ceramic manufacture; for example, only two wheel heads survive from the Middle Bronze Age. The lacuna is partly also a consequence of research traditions and priorities uninterested or engaged with questions related to ceramic manufacture in general and forming techniques in particular. For example, most archaeologists never explicitly state or appear to investigate manufacture technologies and formation techniques utilized to create Mycenaean ceramic assemblages; and yet there is a tacit assumption that almost all vessel shapes and wares were mass-produced by wheel throwing (Berg, 2013: table 1). It is only

30.7 Radiographs of a Mycenaean krater (BM registration number G&R1898,120L112) taken from the side (a) and above (b). The vessel has undergone extensive modern restoration with the long straight lines representing adhesive joins and the speckled area near the center of the rim being modern infill. Nonetheless, clear evidence survives of the use of coil building in the form of numerous elongated voids along the coil joins with rotative kinetic energy applied subsequently creating irregular rilling. The coil joins are particularly clear in the image taken from above. Exposure parameters for both exposures: Siefert DS1 tube, 0.5 mm focal spot, I m focus-to-film distance, 6o k\1, 20 rnA mins, Agfa Structrex D7 film. Enhanced using Adobe Photoshop Unsharp Mask FIGURE

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with reference to the earlier Middle Bronze Age, during which it is generally accepted that a wide variety of potting technologies and methods were in use, that scholars list forming techniques in their catalogue entries. In order to throw some light upon this under-researched aspect of Mycenaean potting traditions and to investigate the existence of other forming techniques, the authors conducted a pilot study of Mycenaean vessels in the British Museum's collections (Berg and Ambers, zonb). The results are as follows: three vessels are wheel-thrown (two bowls and a small jar), one vessel is handmade (a miniature jug), and three vessels are wheel-shaped (two kraters and a bowl) (Figure 30-7). Two alabastra and a rhyton are manufactured using a combination of handmade and wheel-made techniques. These vessels demonstrate the great variability in forming techniques and/or potting traditions employed by Mycenaean potters. Like potters in the preceding Middle Bronze Age, it is now confirmed that Mycenean potters also utilized a wide range of techniques and methods for ceramic manufacture and frequently combined several methods to produce a single vessel. Thus, the tacit assumption that all Mycenaean pottery was wheel-thrown has been demonstrated to be inaccurate by this radiographic analysis. The consequences of this research are farreaching and potentially paradigm-shifting because it imposes a reassessment of our understanding of pottery production in this period, alerts scholars to the need for detailed ceramic analysis, and reminds us always to test our assumptions against the archaeological record.

REFERENCES Adan-Bayewitz, D. and Wieder, M. "Ceramics from Roman Galilee: A Comparison of Several Techniques for Fabric Characterization:' Journal ofField Archaeology 19(1992): 189-205. Berg, I. (zooS). "Looking through Pots: Recent Advances in Ceramics X-RadiographY:' Journal ofArchaeological Science 35:1177-1188. Berg, I. (2009). "X-Radiography of Knossian Bronze Age Vessels: The Potential of a New Technique for Identifying Primary Forming Methods:' Annual of the British School at Athens 104:137-173Berg, I. (2013). '"!he Potter's Wheel in Mycenaean Greece: A Re-Assessment:' In: Graziadio, G., Guglielmino, R., Lenuzza, V., and Vitale, S. (eds), Philiki Synavlia. Studies in Mediterranean Archaeology for Mario Benzi (BAR International Series 2460) (Oxford: Archaeopress), 113-122.

Berg, I. (2015). "Potting Skill and Learning Networks in Bronze Age Crete:' In: Gauil, W., Klebinder-Gauil, G., and von Rueden, C. (eds), The Distribution of Technological Knowledge in the Production of Ancient Mediterranean Pottery (Vienna: Verlag der 6sterreichischen Wissenschaften), 17-34. Berg, I. and Ambers, J (2011a). "Identifying Forming Techniques in Knossian Bronze Age Pottery: The Potential of X-radiographY:' In: Vlasaki, M. and Papadopoulou, E. (eds), Proceedings of the wth International Cretological Congress, Chania, 2006 (Heraldion: Etairia Kritikon Istorikon Meleton), 367-380. Berg, I. and Ambers, ). (2onb). "New Insights into Forming Techniques of Minoan and Mycenaean Pottery from the British Museum Using X-RadiographY:' Poster presented atthe nth International Cretological Congress, Rethymnon, 2011.

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Blakely, Jeffrey A., Brinkmann, R., and Vitaliano, C.) (1989). "Pompeian Red Ware: Processing Archaeological Ceramic Data:' Geoarchaeology 4:201-228. Blakely, Jeffrey A., Brinkmann, R., and Vitaliano, C.). (1992). "Roman Mortaria and Basins from a Sequence at Caesarea: Fabric and Sources:' In: Vann, R. L. (ed), Straton's Tower, Herod's Harbour, and Roman and Byzantine Caesarea (Ann Arbor, MI: University of Michigan), 194-213. Boag, John W. (1973). "Xeroradiography:' Physics in Medicine and Biology u8: 3-37. Braun, David P. (1982). "Radiographic Analysis ofTemper in Ceramic Vessels: Goals and Initial Methods:' Journal ofField Archaeology 9:183-192. Carmichael, Patrick H. (1990 ). "Nasca Pottery Construction:' Nawpa Pacha 24: 31-48. Carmichael, Patrick H. (1998). "Nasca Ceramics: Production and Social Context:' In: Shimada, I. (ed), Andean Ceramics: Technology, Organization, and Approaches. MASCA Research Papers in Science and Archaeology 15 (Suppl.) (Philadelphia, PA: Museum Applied Science Center for Archaeology/University of Pennsylvania Museum of Archaeology and Anthropology), 213-231. Carr, C. (1990 ). ''Advances in Ceramic Radiography and Analysis: Applications and Potentials:' Journal ofArchaeological Science 17: 13-34. Carr, C. (1993). "Identifying Individual Vessels with X-Radiography:' American Antiquity s8: 96-u7. Carr, C. and Komorowski, ).·C. ( 1991). "Nondestructive Evaluation of the Mineralogy of Rock Temper in Ceramics using X-RadiographY:' In: Vandiver, B., Druzik, )., and Wheeler,). S. (eds), Issues in Art and Archaeology II. Materials Research Society Symposium Proceedings 185 (Pittsburgh, PA: Materials Research Society), 435-440. Carr, C. and Riddick, E. B. )r (1990). ''Advances in Ceramic Radiography and Analysis: Laboratory Methods:' Journal of Archaeological Science 17: 35-66. Corfield, M (n.d.). Radiography in Archaeology(London: English Heritage). Courty, Marie A. and Roux, V. (1995). "Identification of Wheel Throwing on the Basis

of Ceramic Surface Features and Microfabrics." Journal of Archaeological Science 22: 17-50.

Digby, A. (1948). "Radiographic Examination of Peruvian Pottery Techniques:' In: Actes du xxviii Congres International des Amiricanistes (Paris: Musee de l'Homme), 6os-6o8. Ellingson, William A., Vandiver, P. B., Robinson, T. K., and Lobick, ). ). (1988). "Radiographic Imaging Technologies for Archaeological Ceramics:' In: Sayre, E. V., Vandiver, P. B., Cruzik, )., and Stevenson, C. (eds), Materials Issues in Art and Archaeology (Materials Research Society Symposium Proceedings 123) (Pittsburgh, PA: Materials Research Society), 25-32. Foster, George V. (1983). "Kourion Votive Figures: A Study Using Xeroradiography." MASCA 2:179-181.

Foster, George V. (1985). "Identification oflnclusions in Ceramic Artifacts by Xeroradiography:' Journal of Field Archaeology 12: 373-376. Giannoulaki, M., Argyropoulos, V., Panou, Th., Moundrea-Agrafioti, A., and Themelis, P. (2oo6). "The Feasibility of Using Portable X-ray Radiography for the Examination of the Technology and the Condition of a Metals Collection Housed in the Museum of Ancient Messene, Greece:' £-Journal of Science and Technology 1:48-63. Glanzman, William D. (1983). "Xeroradiographic Examination of Pottery Manufacturing Techniques: A Test Case from the Baq'ah Valley, Jordan:' MASCA 2:163-169.

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Glanzman, William D. and Fleming, S. ). (1986). "Technology. Fabrication Methods:' In: McGovern, P. E. (ed), The Late Bronze and Early Iron Ages of Central Transjordan: The Baq'ah Valley Project, 1977-1981, (Philadelphia, PA: University Museum, University of Pennsylvania), 164-177Henrickson, Robert C. (1991). "Wheelmade or Wheel-Finished? Interpretation of 'Wheelmarks' on Pottery:' In:. Vandiver, P. B., Druzik, G. S., and Wheeler, G. S. (eds), Materials Issues in Art and Archaeology II (Pittsburgh, PA: Materials Research Society), 523-541. Laneri, N. (2009). Biograjia di un Vasa. Tecniche di Produzione del Vasellame Ceramico nel Vicino Oriente Antico tra il Veil II Millennia a. C. Serie Tekmeria 10 (Paestum: Pandemos). Lang, J. and Middleton, A. (eds) (2005). Radiography of Cultural Material (London: Elsevier). Lang, )., Middleton, A., Ambers J., and Higgins, T. (zoos) "Radiographic Images:' In: Lang, J. and Middleton,V. (eds), RadiographyofCulturalMaterial (London: Elsevier), 20-48. Levi, Sara T. (1999).Produzione e Circolazione della Ceramica nella Sibaritide Protostorica. I. Impasto e Dolii (Florence: A1l'Insegna del Giglio). Maniatis, Y., Jones, R. E., Whitbread, I. K., Kostikas, A., Simopoulos, A., Karakalos, Ch., and Williams, C. K., II. (1984). "Punic Amphoras Found at Corinth, Greece: An Investigation of Their Origin and Technology." Journal of Field Archaeology n: 205-222. Nenk, B. and Walker, H. (1991). "An Aquamanile and a Spouted Jug in Lyveden-Stanion Ware:'

Medieval Ceramics 15:25-28. O'Connor, S. and Maher, ). (2001). "The Digitisation of X-radiographs for Dissemination, Archiving and Improved Image Interpretation." The Conservator 25: 3-14 O'Connor, S., Maher, J., and Janaway, J. (2002). "Towards a Replacement for Xeroradiography:'

The Conservator 26: wo-n+ Philpotts, Anthony R. and Wilson, N. (1994). "Application of Petrofabric and Phase Equilibria Analysis to the Study ofPotsherd:' Journal ofArchaeological Science 21: 607-618. Posner, E. (1970 ). "Reception of Rontgen's Discovery in Britain and the USA:' British Medical Journal4: 357-360. Rontgen, Wilhelm C. (1896). "On a New Kind of Rays:' Nature 53: 274-276. Roux, V. and Courty, M.A. (1998). "Identification ofWheel-fashioningMethods: Technological Analysis of 4th-3rd Millennium BC Oriental Ceramics:' Journal of Archaeological Science 25:747-763. Rye, Owen S. (1977). "Pottery Manufacturing Techniques: X-Ray Studies:' Archaeometry 19: 205-211.

Rye, OwenS. (1981). Pottery Technology. Principles and Reconstruction. Manuals on Archeology (Washington, D.C.: Taraxacum). Titterington, Paul F. (1935). "Certain Bluff Mounds of Western Jersey County, Illinois:' American Antiquity r: 6-46. Van Beek, G. (1969). I-lajar Bin I-lumeid. Investigations at a Pre-Islamic Site in South Arabia (Baltimore, MD: Johns Hopkins Press). Vandiver, Pamela B. (1987). "Sequential Slab Construction; A Conservative Southwest Asiatic Ceramic Tradition, ca. 7000-3000 Be:' Paliorient 13: 9-35. Vandiver, Pamela B. (1988)."Reconstructing and Interpreting the Technologies of Ancient Ceramics:' In: Sayre, E. V., Vandiver, P. B., Cruzik, J., and Stevenson, C. (eds), Materials Issues in Art and Archaeology (Materials Research Society Symposium Proceedings 123 (Pittsburgh, PA: Materials Research Society), 89-102.

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Vandiver, Pamela B., Ellingson, W A., Robinson, T. K., Lobick, ). )., and Seguin, F. H. (1991). "New Applications ofX-Radiographic Imaging Technologies for Archaeological Ceramics."

Archeomaterials s: 185-207. Vandiver> Pamela B. and Tumosa, C. S. (1995). "Xeroradiographic Imaging:' American Journal

ofArchaeology 99: 121-124.

CHAPTER 31

ORGANIC INCLUSIONS MARTA MARIOTTI LIPPI AND PASQUINO PALLECCHI

INTRODUCTION

CERAMIC artifacts are made with clay hardened by kiln firing. The general term "clay" indicates a mixture of one or more clay minerals (hydrous aluminum phyllosilicates) containing small amounts of other mineral phases and organic compounds. Clay deposits may also contain microfossils, such as pollen, diatoms, and other animal and plant remains. One of the important considerations for ceramic manufacture is the performance of the clay during firing. If the right balance between clay minerals and inclusions is not maintained, ceramics can slump or fail during firing. To avoid this, temper is often added to the clay. Tempers may consist of inorganic, non-plastic materials, such as minerals, rock fragments, and grog (crushed pottery and firebricks), and/or animal and plant matter. The mixture of clay and temper improves both the plasticity of the paste and the thermal properties of the vessel. 1he type and amount of temper used depend upon the manufacture technology used to produce the vessel and its ultimate use/function. The selection of a specific organic temper may depend upon local availability of resources, ease of access to recycled materials, and/or be dictated by cultural factors and intended usage of the resulting artifact. In this text, organic inclusions are regarded as remains of biological matter; that is, portions of organisms or even entire small organisms, which are trapped in ceramic paste.

THE ORIGIN AND NATURE OF THE ORGANIC INCLUSIONS

Organic inclusions may occur naturally in the raw materials used to manufacture ceramics or they may be intentionally added to the clay paste by potters. During the firing, organic compounds undergo a partial or complete destruction, creating pores in the ceramic fabric. These pores make the vessel permeable and resistant to temperature changes and therefore suitable for cooking and as food storage containers (Maggetti, 1994). Minute charred organic

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materials or their heat-resistant mineral components are often found in these pores and can be extremely useful in the identification of the type of organic material included in the paste. Biological remains, when present, can be detected in the paste of ceramic artifacts and sometimes even on their surface: they appear as small spots or pits and their size is usually so small that they are hardly visible to the naked eye. In most cases, only magnifying lenses and microscopes can detect the presence ofbiological remains and reveal their shape. When the observation of the morphological features of organic inclusions in ceramic paste does not permit identification, microanalytical investigations can determine chemical composition and reveal important information about the type of temper employed. The study of organic inclusions in ceramics is, therefore, a promising source of information about ancient environments, sourcing of raw materials, and ceramic manufacturing techniques. When we study organic inclusion in ceramic wares, one of the first logical question is whether the inclusions were present in the raw material; that is, the natural deposit from which the clay was taken. Were the inclusions accidentally trapped in the paste during the kneading process and, therefore, present in the environment where the pottery was produced? Or rather, were they deliberately added to the paste in the form of temper to improve the plasticity of the clay? In some instances, the high concentration and type of inclusion leave us ill no doubt, but it is not always easy to find a definite answer to these questions.

Organic Inclusions Occurring in Raw Materials Organic inclusions that naturally occur in clay deposits and therefore may be found in ceramic paste can be entire microscopic organisms or fragments and/or parts of macroscopic plants or animals. A good example is the pottery of 'Thailand's Ban Chiang region (c.36oo BC-200 AD), where fre'shwater diatoms and sponge spicules were detected in ceramic wares. Tempers of different composition were intentionally added to Ban Chiang pottery throughout its history: since freshwater diatoms and sponge spicules are always found in the ceramic paste of wares from all periods in spite of diverse temper combinations, this sug~ gests that they were present in the clay deposits of local lakes that supplied the raw material (McGovern, 1989). Diatoms are unicellular algae belonging to Bacil/ariophyta, widely distributed in damp and aquatic habitats. Their cell wall (called frustule) is composed of two overlapping thecae or valves: the larger one is called epitheca and the smaller hypo theca. The frustule is mostly made of silica (hydrated amorphous silicon dioxide, SiO,.nH,O ); it has a peculiar shape with sculptures, that is, surface relief, and perforation patterns, which are valuable in systematics. When the algae die, the frustules sink and are preserved in sediments at the bottom of water bodies. Some types of diatoms only survive within a restricted range of ecological parameters, making diatom analysis useful for the environmental reconstruction of ancient artifacts. Beside diatoms, many other microscopic organisms may be preserved in clay sediments and survive the firing process, such as, for example, foraminifera, ostracods, radiolaria, and silicoflagellates (for references, see Quinn and Day, 2007). Sponge spicules are siliceous or calcareous structural elements produced by sponges in freshwater, brackish, and marine environments. Siliceous spicules, which occur in a wider morphological variety than the calcareous ones, are divided in megascleres and microscleres depending upon their size. Once sponges are dead, their organic elements decompose and

ORGANIC INCLUSIONS

FIGURE 31.1

567

Fan-shaped phytolith from modern rice (r mm).

their spicules accumulate at the bottom of water bodies: chemical composition, symmetrical axes, shape, and dimensions of these spicules are useful tools for the identification of the sponges. Phytoliths are another type of organic inclusion commonly found in ceramic paste: the term refers to all mineral (generally siliceous) plant deposits and often disarticulated remains surviving the decomposition of organic matter (Figure 31.1). In growing plants, silica may be deposited inside the epidermal cell walls, in intercellular spaces, or inside the cell lumen: the latter deposits are more properly termed silica bodies. Silica deposits have distinctive shapes useful for plant identification. An International Code for Phytolith Nomenclature was published for standardizing phytolith classification and descriptive parameters (Madella et al., 2005). Phytoliths may occur naturally in clay sediments used for pottery manufacture, or their presence in ceramic wares may result from the intentional use of vegetable temper. The quantity of phytoliths in the artifact generally provides clues as to their origin: when phytoliths appear in negligible amounts they are usually found in clay deposits. Conversely, if they reach significant quantities they were most likely added together with the temper. Unusual organic findings in ceramic are the well-preserved palynomorphs that were discovered in half-burnt potsherds from a Chalcolithic-Early Historic site in West Bengal, India (Ghosh et al., 2006). The palynomorphs include algal remains, spores, and pollen, presumably coming from the surrounding area. It is interesting to note the presence of fossil disaccate pollen grains (cf. Striatopodocarpites) of Permian origin. The preservation of the pollen grains is thought to be due to the short duration of the firing process. Organic inclusions may also be accidentally trapped in the clay paste during the kneading process: in this case their presence is infrequent. An example of accidental inclusion is the barley caryopsis (Hordeum vulgare) found in a potsherd from the Caverna dell'Aquila at Finale Ligure, Italy (Arobba and Caramiello, 2006). '!he caryopsis was completely burnt out during the firing, leaving a void in the paste. It is proposed that the barley was present at or around the location of ceramic manufacture.

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FIGURE 31.2 Thin section of rice~ tempered ceramic from Sumhuram, Sultanate of Oman: dark (above) and bright (below) rice lemmas/paleas. "Ihe bright one was more severely affected by oxidation during firing (1 mm).

Intentionally Added Organic Materials A large variety of organic materials were used as tempering agents in archaeological ceramics. During firing, some types of organic tempers are preserved in a carbonized state (Figure 31.2), while others are completely destroyed, leaving only impressions in the paste and pits on the surface of the artifacts. These impressions-the negative imprints of the organic inclusionsresult in tiny holes that increase porosity of the ceramic body and make the artifacts lighter and more permeable than those where mineral tempers were employed. When organic ternper contains mineral components, such as cereal chaff or mollusk shells, these are more easily preserved during firing than organic compounds such as mollusk bodies. The deliberate addition of a specific temper often introduces a small amount of"contamination" into the paste. For example, since weeds are harvested together with crops, cereal chaff normally incorporates weed seeds; their quantity depends on the degrees of weed infestation in the fields (Harvey and Fuller, 2005). Organic tempers may be divided into two main groups: plant temper and animal temper. They may be used alone or mixed with other organic or inorganic tempers.

Plant Tempers Plants used as tempering agents include numerous species, but generally consist ofbyproducts of the cereal crop processing waste and include different portions of the plant: stalks, husks, and ear bristles. The use of this tempering technique appears to have been quite common in the Prehistoric Old World, and survived to recent times in restricted areas: cattail fuzz was still used as ceramic temper in Afghanistan, near Kandahar, during the second half of the twentieth century (Matson, 1974); in Palestinian pottery, the tempering ingredients, threshing-floor straw, and cattail fuzz together with animal dung, shells, or sand, were added

ORGANIC INCLUSIONS

569

during wedging and worked into the clay to improve workability and reduce shrinkage (johnston, 1974). The use of cereal chaff as ceramic temper has been attested in many Asian archaeologi~ cal sites. It is related to cereal farming and, consequently, availability of cereal processing byproducts. On the other hand, since pottery was widely used in trade, the presence of cereal chaff in wares does not necessarily indicate local cultivation, but may indicate the geographical area of production of the ceramic artifacts. The local provenance of the wares may be verified by comparing the mineral composition of the ceramic paste with those of the clay deposits occurring in the area. Otherwise, local cereal cultivation may be identified by means of pollen analysis or detection of cereal phytoliths in the soil. The use of cultivated cereal chaff for tempering ceramic is first documented in southern China in w,ooo cal BP, where rice husks (Oryza sativa) were used as temper in Neolithic pottery of the lower Yangtze River region. Among other plant remains the ceramic contained fan-shaped rice phytoliths (Jiang and Liu, 2006). In Northern India, rice chaff-tempered pottery dating between c.2500-10oo BC was recovered in several Neolithic sites (Bellwood et al., 1992; Fuller, 2006). At Khok Phanom Di in Thailand, pottery from the second half of the second millennium BC was found to contain foreign rice temper: although rice Was naturally available in the area, apparently the local pottery industry did not exploit it. Indeed, petrographic analysis indicates that clay was sourced north of the area, in the upper Bang Pakong Valley (Vincent, 2003). A similar situation also occurred in Bali, where rice husk-tempered pottery appears to have been imported from India, although rice was grown locally and is attested by phytoliths in the soil (Bellwood et al., 1992). Rice-tempered ceramics were discovered at several locations outside the area of ancient rice cultivation, such as the Red Sea and coastal region of the Arabian Peninsula (Figures 31.2 and 31.4a); these findings indicate the existence of trade routes throughout the area around the Indian Ocean (Mariotti Lippi et al., 2011; Tomber et al., 2011). In the Arabian Peninsula, cereal chaff was found in ceramic fragments from the first millennium BC at Qala'at al-Bahrain: since three grains of barley were also found impressed in the pottery, the chaff was tentatively identified as two-row hulled barley (Hordeurn distichon). The provenance of the object is unknown (Willcox, 1994). Cereal chaff-tempered ceramics were also found in Sahelian Africa. Listed in chronological order from Neolithic to Iron Age, the dominant taxa are Sorghurn, Setaria, Panicum, and Pennisetum (Fuller, 2013). Most interesting, ceramics tempered with Sorghum husks were recovered at Essouk-Tadmakka in Mali (c.11o0-1300 AD); as the site bore no evidence of sorghum processing or consumption, this confirms the hypothesis that the wares were imported to Essouk-Tadmakka from the Niger Bend, where stylistically similar pottery was produced (Nixon et al., 2011). In Europe, the use of cereal chaff seems to have been be uncommon; plant fragments, possibly Triticum sp. chaff, were however found in Early Neolithic clay figurines, in Hungary (Kreiter et al., 2014), while unidentified chaff dating to sooil BC, was found in pre-Roman Iron Age vessels in Sweden (Stilborg, 2001). In addition to cereal byproducts, other plants were intentionally collected for tempering ceramics. A few meaningful examples are listed here by geographical area. For centuries in far East Russia (Asia), coarsely chopped grass was added to the clay for ceramic vessels (Miermon, 2006; Ponkratova, 2oo6); conifer needles were used with similar purposes in far East Russia during the Neolithic (Ponkratova, 2006). Sizeable fragments of stems and leaves of sedge (Cyperaceae), horsetail (Equiseturn), and burdock (Arctiurn lappa, Asteraceae family)

570

MARTA MARIOTTI LJPPI AND PASQUINO PALLECCHI

were found in Neolithic ceramics from South Sakhalin (Zhushchikhovskaya and Shubina, zoo6).ln Africa, leaf fragments of sedges (Cyperaceae) and impressions of other wild plant materials were observed in pre-Pastoral and Pastoral sherds at Gobero (south Sahara). The use of these vegetable fragments suggests the intentional gathering of wild plants for ceramic production and indirectly the absence of crop byproducts (Fuller, 2013). In Europe, a mixture of mosses, mostly Neckera crispa, was commonly used for tempering ceramics in France and Belgium during the Neolithic (Constantin and Kuijper, 2002). In South America, particularly in Amazonia, one of the most common organic tempers consisted of ashes and microcharcoals made by burning the bark of trees belonging to several genera of the Chrysobalanaceae family, particularly Licania spp. The barks of these plants contain silica bodies in parenchymatous and epidermal cells, and often their cell walls are also silicified (Cronquist, 1981; De Walt et al., 1999). Native populations living in the Amazon have used this material as temper for generations (Evans and Meggers, 1962; Costa et al., 2009, 2011). It is important to mention that most plants used as temper contain phytoliths and are therefore so-called Si-accumulating plants: in other words, they are capable of absorbing silicon from soil solutions (more precisely mono-silicic acid) and accumulating it as silica. Si-accumulating plants most commonly used for temper are Equisetum; Poaceae cereals and grasses; sedges (Cyperaceae family); Asteraceae. Silica is also present in the bark of Chrysobalanaceae and the needles of gymnosperms (Hodson et al., 2005). InPoaceae, silicon dioxide (silica) can reach 15% of the plant's dry weight (Neethirajan et al., 2009). When these plant tempers are used in pottery making and burn out during firing, their phytoliths may be preserved in the voids, thus allowing the identification of the plant. Finally, organic inclusions in ceramics may also be due to the use of biochemical sedimentary rocks as tempering agent. For example, the addition of diatomite to the paste introduces algal microfossils (i.e. diatoms) in the ceramic.

Animal Tempers Many organic tempers are animal in origin: bones and shells (Figure 31.3a) are the most common. Bone-tempered ceramics were spread through Europe during the Neolithic and Bronze

FIGURE 31.3 Shell-tempered ceramic from Sumhuram, Sultanate of Oman: (a) fracture surface showing shell fragments (stereomicroscope); (b) EDS spectrum indicating the presence of calcium in the animal material.

ORGANIC INCLUSIONS

571

Age (Stilborg, 2001; Freudiger-Bonzon, 2005). Before being used in ceramic manufacture, bones were subjected to a heat treatment, a necessary precursor to crushing or grinding them into minute fragments. In the ceramic artifact, these fragments generally have an angular outline and a smooth surface: at high magnification, their histological features and canals may be visible. When these diagnostic characteristics are not present, the tiny fragments are often insufficient to determine the type and origin of the bone used. Bone-tempered ceramics have a high phosphorus content, much higher than the lowvalues of natural clay(P ,05 = 0.1-0.5 wt.%);however, the high phosphorus pentoxide content is not sufficient to attest the use ofbones as temper, more generically indicating the employment of animal temper (Freudiger-Bonzon, zoos). An unknown and unusual temper of animal origin was found in the Neolithic ceramics at Quadrate di 1orre Spaccata, near Rome (Italy). Petrographic analysis revealed voids in the shape of parallelepipeds and energy dispersive X-ray spectrometry (EDS) analysis indicated high phosphorus values, both suggestive of animal temper. According to Pallecchi (1995), these voids likely result from the charring of organic matter, possibly meat, which was cut or processed to produce a regular pattern. Crushed shells of freshwater and saltwater mollusks are often found in pottery from the Neolithic period onward. For example, large surface pits with a peculiar shape were found on the exterior and on the breaks of Neolithic pottery from Sakhalin Island (northern Pacific). The shape of the pits recalls mollusk shell fragments: indeed, small shell fragments are sometimes found in the pits. Morphometric analysis of the pits enabled the identification of several types of mollusks still growing in rivers, estuaries, and coastal waters of the area (Zhushchikhovskaya and Shubina, zoo6). Among them, the most frequent species is Corbicula japonica, which has a very fragile shell. The consistently high phosphorus content of these wares suggests that both mollusk shells and bodies were used as temper: the shells prevented the clay from cracking during drying and firing, while the bodies were used to increase the porosity of the artifact (Zhushchikhovskaya and Shubina, zoo6). Prehistoric Oceanic pottery was tempered with a wide variety of organic materials. Among them were calcareous sands composed primarily of biogenic reef debris, such as the remains of corals, mollusk shells, foraminifera, and so on (Dickinson, zoo6), and burnt coral, used to temper pottery in the Yap Islands, Micronesia (Intoh, 1988).

FIGURE 31.4 Fracture surface of a potsherd from Sumhuram, Sultanate of Oman: (a) rice chaff fragment (stereomicroscope); (b) EDS spectrum indicating the presence of silicon in the plant material.

572

MARTA MARIOTTI LIPPI AND PASQUINO PALLECCHI

l

" ~~

I

[j

FIGURE

31.5 Renaissance ceramic tempered with wool (polarized 1 mm).

Sponge spicules have been found in Iron Age ceramics from Africa (inland Niger delta) and South America, especially in the Amazon Basin (Evans and Meggers, 1962; Costa et a!., 2009; Nixon, 2009; Costa, 2011). In these ceramics, spicules often have parallel orientation and occur in clusters. This particular orientation and grouping, rather than the overall number of spicules in a vessel or sherd, suggests that sponge fragments were intentionally added to the paste, and excludes the possibility that the spicules were originally in the deposits where the clay was collected. Many other animal tempers are occasionally found in clay wares worldwide: feathers, fish scales, dung, fibrous materials such as baleen, wool (Figure 31.5), and animal fur; for example, deer and horse hair. (London, 1981; Miermon, 2006; Ponkratova, 2006, Kiryushin eta!., 2012). A remarkable application of animal material in ceramic manufacture consists of using animal hair as a framework during the shaping of vessels with the coiling technique: bunched hairs are arranged as filler in the seams between the coils and added to the paste, coating the vessel before baking. An example of this technique is the use of horsehairs in comb-patterned ceramics recovered at Tytkesken-2 in Russia. This tradition was also widespread in western Siberia from the early to the last Neolithic period (Kiryushin eta!., 2012).

LABORATORY METHODOLOGIES In order to identify organic inclusions in archaeological ceramics it is necessary to observe and identify their structure and micromorphology with instruments of sufficient magnification to detect diagnostic features. Generally, an initial screening of the material at low magnification is the first step in order to identify the potsherds potentially containing organic inclusions. A simple magnifying lens (magnification 6-15x) held close to the eye might be sufficient to notice discontinuities in color and reflectivity or pitting in the vessel walls, all potential indicators of temper. However, owing to their small size, the identification of organic

ORGANIC INCLUSIONS

573

inclusions requires greater magnification, achieved by using a stereomicroscope (magnification commonly up to 6ox) or even a compound light microscope (LM) (magnification up to 100 ox), Both these microscopes utilize the interaction of the objects with visible light; however, they provide different information about the material: the former is useful for identifying the general tridimensional shape and micromorphology of the organic inclusions, while the latter allows us to see their inner structure and micromorphology. The stereomicroscope is used for a variety of analyses over the course of the analysis because it allows a rapid s~rface screening of the specimen. The instrument is easy to use (even though many researchers utilize it under suboptimal conditions), does not require a previous preparation of the specimen to be examined, and allows direct observation of objects of rather large size, such as potsherds. Observation under LM, on the other hand, always requires laboratory preparation of the sample or specimen. Since light must pass through the sample in LM, the thickness of the specimen must be minimal, usually ranging from 1 to 10 ~m for biological specimens and 30 ~m for minerals. When the thickness of the sample exceeds these dimensions it is necessary to cut it in sections prior to viewing. The sec~ tions are then placed on a slide and covered with a coverslip, using aqueous or non-aqueous solutions as mounting medium. When analyzing ceramics, the thin sample Sections are attached to a flat slide with epoxy resin, abraded to reach optimal thickness (25-30 ~m), At about 30 ~m of thickness, all the sample components are translucent and can be observed under LM. The sample section is covered with a coverslip, again using epoxy resin as mounting medium. The presence of the coverslip unfortunately excludes any successive microanalysis. Although polarizing light microscopy is successfully employed in petrographic analysis, it is generally not useful in the study of organic inclusions, which lose their original optical properties with charring. Moreover, organic inclusion might turn into cavities during combustion and later appear simply as dark areas in the thin sections. When we observe material cut into thin sections all the components appear two-dimensional and their shape depends on the inclination of the cutting plane, Only by JCTION BY ORGANIC RESIDUE ANALYSIS

645

Patrick, M., de Koning, A.)., and Smith, A. B. (1985). "Gas Liquid Chromatographic Analysis of Fatty Acids in Food Residues from Ceramics Found in the Southwestern Cape, South Africa:' Archaeometry27: 231-236. Pearsall, D. M. (1978). "Phytolith Analysis of Archaeological Soils: Evidence for Maize Cultivation in Formative Ecuador:' Science 199:177-178. Petraglia, M., Knepper, D., Glumac, P., Newman, M., and Sussman, C. (1996). "Immunological and Microwear Analysis of Chipped~Stone Artifacts from Piedmont Contexts." American Antiquity 61:127-135. Pevzner, P. A., Kim, S., and Ng, ). (zooS). "Comment on 'Protein Sequences from Mastodon and Tyrannosaurus Rex Revealed by Mass Spectrometry:" Science 321: 1040. Pollard, A.M. and Bray, P. (2007). "A Bicycle Made for Two? The Integration of Scientific Techniques into Archaeological Interpretation:' Annual Review of Anthropology 36: 245-259Rafferty, S.M. (zoo6). "Identification of Nicotine by Gas Chromatography/Mass Spectroscopy Analysis of Smoking Pipe Residue:' Journal of Archaeological Science 29:897-907Rainey, F. and Ralph, E. K. (1966). "Archeology and Its New Technology:' Science 153: 1481-1491. Reber, E. A. and Evershed, R. P. (2004). "Identification of Maize in Absorbed Organic Residues: A Cautionary Tale:' journal of Archaeological Science 31:399-410. Regert, M., Langlois, J., Laval, E., Le H6, A. S., and PagCs-Camagna, S. (2006). "Elucidation of Molecular and Elementary Composition of Organic and Inorganic Substances Involved in 19th Century Wax Sculptures Using an Integrated Analytical Approach." Analytica Chimica Acta 577:140-152. Reuther,). D., Lowenstein,). M., Gerlach, S.C., Hood, D., Steuenstuhl, G., and Ubelaker, D. H. (zoo6). "1be Use of an Improved Pria Technique in the Identification of Protein Residues." Journal ofArchaeological Science 33: 531-537. Ribechini, E., Colombini, M.P., Giachi, G., Modugno, F., and Pallecchi, P. (2009). "A MultiAnalytical Approach for the Characterization of Commodities in a Ceramic Jar from Antinoe (Egypt):' Archaeometry 51: 480-494. Robinson, N., Evershed, R. P., Higgs, W H., Jerman, K., and Eglinton, G. (1987 ). "Proof of Pine Wood Origin for Pitch from Tudor (Mary Rose) and Etruscan Shipwrecks: Application of Analytical Organic Chemistry in Archaeology:' Analyst 112: 637-644. Rottlander, R. C. A. and Schlichtherle, H. (1983). "Chemical Analysis of Fat Residues in Prehistoric Vessels:' Naturwissenschaften 70: 33-38. Rovner, I. (1975). "Plant Opal Phytolith Analysis in Midwestern archaeology:' Michigan Academician 7(2): 129-137. Rullkotter, ). and Nissenbaum, A. (1988). "Dead Sea Asphalt in Egyptian Mummies: Molecular Evidence:' Naturwissenschaften 75: 618-621. Schiffer, M. B. (1988). "The Structure of Archaeological Theory:' American Antiquity 53' 461-485. Schoeninger, M. )., DeNiro, M. )., and Tauber, H. (1983). "Stable Nitrogen Isotope Ratios of Bone Collagen Reflect Marine and Terrestrial Components of Prehistoric Human Diet:' Science 220: 1381-1383. Schweitzer, M. H., Marshall, M., Carron, K., Bohle, D. S., Busse, S.C., Arnold, E. V, Barnard, D., Horner, ). R. and Starkey, ). R. (1997). "Heme Compounds in Dinosaur Trabecular Bone:' Proceedings of the National Academy of Sciences of the United States of America 94: 6291-6296. Schweitzer, M. H., Zheng, W, Organ, C. L., Avci, R., Suo, Z., Freimark, L. M., Lebleu, V.S., Duncan, M. B., Vander Heiden, M. G., Neveu,). M., Lane, W S., Cottrell,). S., Horner,).

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PART

VII

DATING CERAMIC ASSEMBLAGES

L_

CHAPTER

35

TYPOLOGY AND CLASSIFICATION EUGENIO BORTOLINI

INTRODUCTION that an archaeologist was abruptly brought to a table covered with the most dispa~ rate objects: a mug, a cookie jar, a spoon, a miniature car, a bicycle bell, a light bulb, a shoe, a glass, a stapler, a nail, a book, a sponge, a note pad, pens, a fork, a pair of keys, a pipe, and many others. Imagine now the same archaeologist being asked to sort all the items covering the table in an ordered and logically sound way; a way that possibly represented the flow of time or the basic mechanisms of interaction between the individuals that made and/or deposited these items. The sorting should be flexible, replicable, and yet designed for the case at hand. How would our archaeologist divide them? Would she or he look at their shape, color, and overall appearance? Would it be preferable to think of their constituent materials? Or, rather, would it be better to start from their function? Should she or he look at the entire object or should IMAGINE

she or he focus on some specific elements? This fictive example is not dissimilar to the actual challenge archaeologists face when they uncover a context for the first time, or when they want to analyze an already known or familiar set of materials from a completely new perspective. Archaeological materials provide information about their producers and/or consumers, and their respective social, cultural, and economic contexts. However, this vast and fluid data needs to be ordered and divided in more manageable units, so that inferences about causal processes and/or relationships are possible. Ordination techniques in archaeology have been developed for precisely this reason, to "put order into disordered evidence" (Renfrew and Bahn, 2004: n8). Variability in material culture derives from the cumulative effect of individual choices, copying errors, social preference, interaction, taphonomic processes, and multiple loss-of-knowledge events. If researchers want to identify directions in this sea of variation Without sinking or getting lost, they need to produce a map in which landmarks are clearly indicated. A systematic arrangement of material culture is the archaeologist's map towards understanding and explanation. Nevertheless, there is no definitive classificatory structure that can encompass all possible

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datasets and answer all possible questions. In fact, many different approaches have developed over time, and scholars have often proposed antithetic explicit definitions or implicit uses for the terms type, class, group, and assemblage. Most of the archaeological approaches to typology and classification draw on the different directions that emerged from the archaeological debates of the 1940s and 1950s. Studies on typology, classification, and ordination techniques have always involved a number of cultural expressions, from early lithic industries to complex pyrotechnical products. Among the latter, ceramics acquired a particularly relevant status partly owing to their abundance in later prehistoric and historic archaeological contexts, which can be in turn ascribed to the durability of pottery compared to more perishable materials, but mostly because they were increasingly used to measure time in terms of relative chronology where absolute dating was unavailable (O'Brien and Lyman, 2006). Observation of change in the formal and, potentially, functional attributes of pottery has been the key to building models of diachronic variability (ibid.). Therefore, the theory and practice of archaeological typology and classification is strongly interwoven with the study of ceramic materials.

TYPOLOGY OR CLASSIFICATION? SOME PRELIMINARY DEFINITIONS The terms typology and classification are often thought of as synonymous and interchangeable (Adams, 2008). However, a thorough examination of these terms and their definition suggests that this is not the case. Archaeologists, and researchers involved in many other disciplines, developed methods for systematizing and ordering the archaeological record in order to analyze the emerging picture of past human activities. Analyze literally means to divide something into manageable and interpretable units, and to infer the dynamic relationship between them. Classification refers to a series of methods that can be used for the deductive categorization of observable phenomena. Approaches that rely on different or sometimes antithetical principles should not be confused with classification but instead be identified as inductive or grouping methods (after Dunnell, 1971; see the section "Classes and Groups" for a detailed explanation). Typology is a technique developed by archaeologists in which artifacts are arranged according to perceived or measurable similarity between observed data and specific analytical units. These units, called types, are aggregates of diagnostic attributes recorded at a particular sampling site at a particular moment. Similarity is therefore based on the quality or the quantity of diagnostic attributes that types and data appear to share. Types can either be conceived as abstract models-theoretical units with no actual counterpart in the real world-or as real, empirical entities (see Hill and Evans, 1972, for discussion). While a typology can be a particular form of classification, the opposite is not always true (Adams and Adams, 1991; Adams, 2008). It follows, therefore, that the terms typology and classification cannot be used interchangeably because each term has a precise meaning and background in archaeological ordination.

,

__

TYPOLOGY AND CLASSIFICATION

653

,,

DEVELOPMENT OF THE CoNCEPTS OF TYPOLOGY AND CLASSIFICATION

The Beginning Systematization in archaeology dates back to the nineteenth century, when the large amount of evidence uncovered by antiquarians started to be rigorously compared, European prehistory offered the first framework for the identification of diagnostic artifacts and assemblages. The main objective of this early systematization was to determine a suitable chronological ordering for dividing collections in museums and other public and private institutions. Scandinavian scholars are renowned for having formulated the famous "three-age system" based on the ordered succession of three main cultural stages, that is Stone Age, Bronze Age, and Iron Age. The system drew on the direct observation of materials repeatedly used in different assemblages over a period of time, and ordering relied upon the idea of a progressive and unidirectional technological development The system, already known from Classical authors and endorsed by many Danish collectors, was first used in 1819 by Christian Jurgensen Thomsen to arrange temporally the prehistoric collections of the Danish National Museum (the method was published in 1836 in Danish and later translated into English; see Ellesmere, 1848). Further archaeological investigations across Europe made it immediately clear that this simple and effective scheme could be adopted for the entire continent This moment represented a shift towards the identification of novel types. A type-as intended at this early stage-can be generally defined as a single artifact which embodies a specific stage of cultural development with defined temporal and spatial coordinates. At the same time, John Lubbock formalized the "Palaeolithic-Neolithic" sequence (Lubbock, 1865), and the idea of a sequential, linear development of humanity was further cemented by the acceptance of geological stratigraphy (Lyell, 1863). In this context, Oscar Montelius developed the three-stage idea of European Later Prehistory into a series of local or regional chronologies that could be directly compared and refined into a succession of subperiods. His relative dating was based on the presence of artifact types or "good finds" (Montelius, 1899: 308), which helped to seriate phases in different contexts through cross-site comparison. Montelius coined the terms "typological evolution'' and "typological series" (ibid.), and his approach inspired directional trends on a continental scale over more than two millennia. Refinement of the concept of type proceeded with the work of William Matthew Flinders Petrie (1899 ), who developed five methods to arrange artifacts from funerary contexts according to their plausible original chronological order. Among these methods, Petrie proposed the analysis of "development or degradation of form" (Petrie, 1899: 297) to be performed through the "grouping of similar types" based on stylistic resemblance (ibid., emphasis added). By sorting pottery according to these principles, Petrie was able to chronologically seriate vessel types over the whole study period, and to arrange them in a single-rooted genealogy with just one main branch based on formal resemblance (Figure 35.1). Although the model of shape evolution he proposed was simplistic and relied upon the concept of unilinear development,

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EUGFN1(1 BORTOLINI

FIGURE 35.1 Two graphical representations of Petrie's chronological ordination of archae~ ological types. On the left there is a summary of diachronic trends articulated in seven successive stages. Some diagnostic vessel shapes exhibit continuity between adjacent stages. The graphs on the right consists instead of an attempt of genealogical sorting. Petrie's assumption ,,vas that of unilinear and unidirectional change over time. (Reprinted with permission from Petrie, 1899, plates XXXI fig. 1 and XXXII fig. 3 respectively.)

Petrie succeeded in creating types that had a chronological value and alto wed him to explore issues of"functional versus stylistic" variability over time.

Culture History 111e early t'\ventieth century represented a moment of divergent trends in the use of archae~ ological typology and classification, especially in Europe and the New World. On the one hand, scholars involved in the study of European and Asian prehistory built upon typologies that functioned as the basic observational unit for the different archaeological cultures documented by researchers. These "cultural markers" facilitated the systematization of the conspicuous amount of data continually emerging from new excavations on the Continent and in the Mediterranean. This work developed from the seminal contribution ofVere Gordon Chi! de (1925, 1929, 1930, 1932), and many specialized trends across Europe originated from it. For example, just to mention two cases for their abundance of programmatic and method~ ologicalliterature on the topic, French prehistorians focused on production techniques (the concept of chafne opCratoire is an example) and on the formal as well as functional attributes of artifacts (Laplace 1966, 1968; Bordes, 1988, among others). Italian prehistorians focused instead on the highly articulated and hierarchical arrangement of pottery and other artifacts,

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655

based upon the occurrence of specific formal attributes (Peroni, 1967, 1998, among others). These complex and rigidly defined ordination systems were empirically determined by grouping together observed materials in order to identify basic types. Their normative character favored the emergence and spread of an essentialist approach towards archaeological types. This meant that many archaeologists advocated the existence of types in the real world; that is, the existence of material expressions of mental templates which are immanent and invariable, models whose essence can be reconstructed by archaeologists or directly grasped by ethnographers (Hull, 1965a, 1965b; Sabloff and Smith, 1972). 1be term typology, therefore, began to indicate a systematization based on formal resemblance between observed data and empirical types. This similarity was measured either on a number of diagnostic attributes or on the object as a whole. New World archaeology proceeded slightly differently. Although it adopted the same approach as in Europe, archaeologists started looking at typology and classification as a means to address specific questions of relative chronology and human interaction (Adams and Adams, 1991; Adams, 2008). Alfred Kroeber refined and used types in order to produce effective relative chronologies by observing increase, peak and decrease in their relative frequency at different sampling sites (the method is known as frequency seriation; Kroeber, 1904, 1916a, 1916b, 1919, 1948, 1952). Chronologies obtained by frequency seriation have been used to investigate the genealogy of cultural types, going beyond the strict unilinear model proposed by Petrie (Kroeber 1948). Although Kroeber was explicitly referring to his types as artificial units imposed by the archaeologist over the continuous variability of human material culture, he also revealed an essentialist approach (1916a, 1916b; see Sabloff and Smith, 1972 and Lyman and O'Brien, 2006: 27--70 for a more detailed discussion).

A Brief Digression: Frequency Seriation The method of frequency seriation assumes that a portion of total variation expressed by formal attributes is a function oftime (see Figure 35.2). In other words, if time and human interaction are considered the main factors governing change in formal attributes (or some aggregate of the same attributes, i.e. types), time can be represented as a gradient along which sites or assemblages are sorted. 'The chronological scaling of sampling sites follows the relative abundance of chosen attributes or types at each location. More specifically, sites are arranged so that each attribute/type shows the longest possible historical continuity and its frequency distribution through time is unimodal. Graphic representations of such ordinations are often symmetric curves traditionally labeled battleship-shaped curves (Petrie, 1899; Phillips eta!., 1951; Dunnell, 1970; Neiman, 1995; Lipo eta!., 1997; O'Brien and Lyman, 1999; Lyman and O'Brien, 2006; Smith and Neiman, 2007). The imposition of a unimodal or roughly normal distribution represents a strong analogywith ecological and biological phenomena. Species follow a unimodal distribution along environmental gradients, with the highest frequency around optimal values (mean) and decreasing abundance towards the tails (Hutchinson, 1957; Hill, 1973). The same principle can be applied to the ideas embedded in material culture. Ctiltural elements are first introduced into a population and its cultural background, then gradually spread until they reach a peak in popularity (i.e. they become the modal class at a specific location in time), and

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FIGURE 35.2 An example of frequency seriation. The relative abundance in sixteen sampling sites of four variants (A-D, expressed in percentage) is arranged so that their overall frequency/probability presents a unimodal distribution. These battleship-shaped curves effectively represent the flow of time due to the apparent trends in popularity of the observed types or classes. The graph shows that the space occupied by the earliest variant (A) is pro· gressively invaded by two, low-frequency traits (B, C). These are in turn are replaced by a later innovation (D) that progressively leads to the extinction of all other variants. As sug· gested by the double time-arrow on the right, frequency seriation gives no preliminary indication of time directionality. This has to be archaeologically inferred. (Reprinted with permission from Dunnell, 1970:312, fig. 3.)

eventually decrease to extinction as they are replaced by other, newer ideas (Phillips et al., 1951: 220; Dunnell1970: 309). This working assumption has been further developed by observing (Dunnell, 1978, 1980, 1986; Teltser, 1995) and demonstrating (Neiman, 1995) that the frequency distribution of specific formal traits (e.g. decorative attributes) predicted by frequency seriation resembles that of non-selective alleles studied in biology and genetics. This parallel suggests that when cultural elements, not subject to any functional preference or social bias, are free to vary over time according to the exchange of information between humans (i.e. in the presence of cultural drift), they produce a unimodal distribution analogue to that of non-selective genetic variants (determined by genetic drift; see Cavalli-Sforza and Feldman, 1981, and Boyd and Richerson, 1985, for a detailed discussion of parallels between genetic and cultural tranSmission). Ordinations generated through seriation are merely formal and their chronological value must be inferred. For this inference to be robust, frequency seriation must meet three conditions: (i) all sampling groups or sites must have the same or comparable duration in time, so that frequency distribution is not affected beyond sample-size effects; (ii) all groups in a seri· ation must be homologous; in other words, deriving from a shared ancestor and presenting

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heritable continuity aside from historical continuity (Cochrane, 2009); and (iii) seriation has to be conducted to an appropriate spatial scale, so that attribute or type frequency distribution can be considered as determined by chronology rather than geographical distance, information transfer, and migration (Dunnell, 1970: 316; Lipo et aL, 1997 ).

Early Debates over the Notion Type The first epistemological discussion on typological ordination appeared within the framework of Americanist arcbaeologyby!rving Rouse (1939) and Alex Krieger (1944). The meaning that Rouse assigned to the term type was radically different from that established by early nineteenth-century archaeologists. In his words, the concept type indicates a theoretical unit, a class to which empirical objects can be assigned if they present a set of necessary and sufficient modes or attributes (Rouse, 1939:9). Rouse's type was intended to be immutable, and its origin, diffusion, persistence, decreasing popularity, and replacement could be used to investigate change in a given culture (Rouse, 1939: 14; see Dunnell, 1986: 169-176, for further discussion). Rouse's units were based on stylistic and formal attributes and-Similarly to Kroeber's-could be used to generate relative chronologies (Rouse, 1939: 18). Krieger expanded upon Rouse's work from both a theoretical and practical perspective. In his words, an archaeological type "should represent a unit of cultural practice;' that is, the fossil of an ethnographically observable cultural trait (Krieger, 1944: 272). The function of types was to identify patterns in material culture that would facilitate inferences about the mechanisms of information transfer, human interaction, and culture change. Types were, therefore, "organizational tools" that enabled researchers to divide artifacts into groups with "demonstrable historical meaning" (Krieger, 1944) (see Figure 35.3). Krieger refused the use of hierarchical arrangements of artifacts or assemblages (i.e. taxonomic classifications) and envisaged a six-stage process named "the typological method" (Krieger, 1944: 279-281). The process started by grouping together artifacts that could be the product of similar design or mental templates. Groups were progressively refined, and clusters with comparable distributions were merged into higher-level types. Consistency and robustness of the obtained types were iteratively tested through comparison with independent information and other collections. Types were then formally described and finally used for cross-cultural comparisons. In Krieger's work, ,types emerged as artificial entities which defined particular instances of association between a determined number of variables. These units were distinct from the empirical objects that may or may not have belonged to a given type (Dunnell, 1986: 171; O'Brien and Lyman, 2002: 39-40). At the same time, when Krieger proceeded toward interpretation and archaeological inference, types were implicitly considered as phenomena of the real world, a conflation of analytical units with observed patterns (Krieger, 1944; Cochrane, 2001; O'Brien and Lyman, 2002). Therefore, his seminal paper reiterated the idea of types having a chiefly chronological relevance, as well as the incongruence between "types as mere tools" and "types as existing entities or mental templates:' The post-war discussion on typology is exemplified by the so-called Ford-Spaulding debate. james Ford's contribution to the notion of type consisted of a long sequence of problem-oriented works, aimed primarily at systematizing ceramic materials of the American southeast (Ford, 1938, 1952; see also Dunnell, 1986, for a more detailed discussion),

658

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determination of series of linked types; (b) determination of material-culture complexes; (c) determination of type relationships in related cultures.

FIGURE 35·3 The original diagram by which Krieger explained in detail the procedure for a correct application of his typological method. (Reprinted \Vith permission from Krieger, 1944:279, fig.2s.J

and of a single, programmatic paper on the concept of type (1954a). Ford's work effectively shifted the focus of typology from lithic industries and other classes of material culture to pottery (Ford, 1938, 1952; Dunnell, 1986). Ford used types as instruments, abstract concepts that were arbitrarily formed by selecting specific attributes. In his view space, time, chance, and the derivative mechanism of cultural drift strongly affected the formation of archaeological records (Ford, 1954: 52). Therefore, archaeological types encompassed these processes in addition to actual individual choices (ibid.). In the same years, Albert Spaulding published a paper (1953) in which he strongly opposed the notion of types as artificial instruments created ad hoc by archaeologists. If, as culture historians claimed, types represented mental templates equivalent to ethnographic cultural behaviors, they had to be considered as real entities belonging to the past. 1he only way for archaeologists to avoid discretion in type description was to make types emerge as non-random patterns from raw data. This could be achieved through the application of rigorous and explicit statistical techniques based on attribute association. Spaulding's approach, predating the requirements of Processualism and New Archaeology, aimed at replacing the iterative testing of the Krieger-Ford approach, and directly addressed the issue of types' cultural-behavioral value. Spaulding explicitly relied on an essentialist view of types, that is, he considered types as real entities (Hull, 1965a, 1965b; Sabloff and Smith, 1972), and his method was purely inductive. This created a problem of an overlap between the definition of types and their empirical test (Dunnell, 1982, 1986; Cochrane 2001), and did still not eliminate subjectivity from the critical step of attribute choice.

TYPOLOGY AND CLASSIFICATION

659

Spaulding's paper was followed by a heated debate (Ford 1954a, 1954b, 1954c; Spaulding 1954a, 1954b) in which two fundamentally opposed views--that of types as theoretical, artificial constructs functional to specific enquiries and that of types as existing entities that could naturally emerge from the noise of empirical data-confronted each other. Ultimately, Spaulding won the debate and had a greater influence on the research of the following decades, as it was more in line with the changing attitude of archaeologists toward function and behavior.

CLA§§E§ AND GROUP§

Over the last thirty years, archaeological sorting methods have been refined, elaborated on, and perfected. Nevertheless, all typologies and classificatory arrangements in the literature, no matter how sophisticated, are rooted in one of the models proposed by Rouse-KriegerFord on the one hand and Spaulding on the other. All systematic arrangements may be conveniently divided into deductive (top-down) classifications and inductive (bottom-up) grouping methods (after Dunnell, 1971). Deductive classification consists of generating theoretically derived units (classes). In other words, a number of diagnostic attributes and a particular observational scale are selected depending upon the initial research question. Membership in each class, by any of the observed objects, is defined by the exhibition of these attributes (Dunnell, 1971: 15). Deductive classificatory processes constantly test and update theoretical units based upon the available evidence (as suggested by Krieger). Classes, therefore, are tools produced to verify expectations about the relationship between categories (Dunnell, 1971: 24). In a deductive classification, a class can be structured according to two different principles: monothetic classes, which assume diagnostic attributes that are mutually exclusive and represent the necessary and sufficient condition for an object to be included in a given class; and polythetic classes, in which classes are defined by the collocation of a number of diagnostic attributes, none of which alone can ever be considered as necessary or sufficient. In a polythetic system attributes are never mutually exclusive. An example of monothetic approach is paradigmatic classification (Dunnell, 1971; O'Brien et al., 2001, 2002; O'Brien and Lyman, 2002a, 2002b). This system produces a non~ hierarchical arrangement of classes defined by the necessary and sufficient exhibition of equally weighted, mutually exclusive attributes. The high level of redundancy offered by this method has proven to be particularly useful in tracking change over time and investigating cultural phylogenies (O'Brien and Lyman, 2003). The primary weakness of monothetic arrangements is that, in order to create classes that are strictly defined by necessary and sufficient conditions, the number of attributes that can be used is considerably lower than all the possible dimensions of variation observable in the data. Therefore, this classificatory approach simplifies empirical reality by focusing on only a limited number of diagnostic variables. The term polythetic was first coined in biology by Sakal and Sneath (1963), and was adopted into archaeology by David Clarke in 1978 (Clarke, 1978: 35ff.). Clarke claimed that, unlike natural phenomena, cultural entities could not be forced into strictly monothetic parameters. Artifacts and products of human culture could be systematically described, but

660

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not severely defined by necessary and sufficient attributes. A polythetic approach to classification enables the archaeologist to preserve most of the available infOrmation about artifact variability and respects the idea of continuous variation in the real world, although these features make it more challenging for the analytical and inferential stages of research. A theory-driven or deductive classification, whether monothetic or polythetic, conceives of classes and types as heuristic tools, in other words theoretical units with no necessary counterpart in the real world, and uses these tools to answer specific research questions about a specific dataset (Klejn, 1982). Deductive classes are abstract models distinct from the groups of objects they create, and function as an ideational meter of comparison for empirical observations. In inductive grouping archaeological materials are observed and divided according to shared attributes, and types emerge from the analysis itself. Therefore, groups are not predetermined theoretical units; they are purely empirical units overlapping with their own definition, with no distinction being made between actual assemblages and the conditions for membership in each group. This approach derives from Spaulding's definition of type and has benefited from the increasingly efficient development of clustering and distance-based phylogenetic algorithms (Whallon, 1972, 1982; Read, 1982; Whallon and Brown, 1982). The inductive method is both viable and indicated for the initial exploration of archaeological datasets through pattern-recognition techniques (Christenson and Read, 1977; Aldenderfer and Blashfield, 1978; Hodson, 1982; Legendre and Legendre, 1998; Smith and Neiman, 2007). Among its objectives are explicit methodological explanation and a tendency towards quantification. However, as in the case of theoretical classes, inductive grouping methods have some important limitations (Dunnell, 1971, 1986). For example, the approach is not designed to test hypotheses or to infer processes assumed a priori (Read, 1987). In addition, this approach supports an essentialist view, in which "natural" types emerge from data and represent mental templates existing in the real world (Hull, 1965a, 1965b; Read, 1987; although see Hill and Evans, 1972, for a critical review of this epistemological problem). To conclude, groups and types obtained by inductive ordination may result from generalizations based only on observed phenomena (Willer and Willer, 1973; Dunnell, 1982; Cochrane, 2001 ). The potential issue is that units obtained through empirical generalizations are easily falsifiable; they are unable to change or adapt. Rather, these units are stretched to cover an increasing diversity in the available evidence, and eventually succumb to continuously emerging exceptions.

How MANY

TYPOLOGIES AND CLA§§UICATWNS?

The systematic arrangement of materials, particularly ceramics, is one of the most common and critical activities in archaeology. Researchers can adopt different theoretical perspectives, a number of possible methods, and almost infinite attributes to describe variation in equally valid and useful ways (Sinopoli, 1991: 44). Specialist, applied, and generalist literature on the topic is considerable, and every author explicitly or implicitly emphasizes the approaches and perspectives that she or he considers more applicable.

F TYPOLOGY AND CLASSIFICATION

661

But '\.vhich is the right ordination method?" The quick answer is that there is no right or wrong arrangement of artifacts or ordination method (Hull, 1970; Sinopoli, 1991). There are simply techniques that can be designed and adapted for individual datasets or to answer specific questions. Some arrangements may not be appropriate for some contexts, but this does not make them invalid in other contexts or for other questions. Every systematic approach has its problems and limitations. It is important to be aware of these issues, and to be explicit in detailing the chosen method and its pitfalls (Krieger, 1944; Dunnell, 1971). The first choice that researchers have to make when designing a classificatory strategy is between structuring their types, classes, or groups in qualitative or quantitative terms. The former refers to the identification of nominal or categorical variables as diagnostic attributes (color, shape, formal aspects, decorative motifs) in order to observe their presence or relative frequency within a context. The latter refers to higher-level variables that can be quantified at ordinal, interval, or ratio scale (Shennan, 1998: 8-12) and usually focus on aspects of avessel that are directly measurable, such as height, width, diameter, angles, percentages of ware components, and so on. Describing the distribution of attributes in a quantitative fashion is the most appropriate way to provide explicit, sharable, replicable, and testable units or types. However, it is worth remembering that any ordination process is based on the subjective discrimination of specific qualities over others. In other words, archaeologists choose what to observe and measure, depending on their questions and objectives. This choice is arbitrary by defini tion. Therefore, any systematic description consists first of a qualitative process drawing on discrete variables or attributes, followed by the quantification of attribute distributions (Dunnell, 1971: 54-55). It follows, therefore, that the mandatory first step in any classification is attribute selection (Rice, 1987: 285). Ceramics possess a seemingly infinite number of measurable attributes, characteristics, and dimensions. Therefore, the choice of diagnostic attributes should be oriented toward answering specific questions on specific sets of data. Attributes might constilute the best scale of analysis, in which case they should be consistently observed through time and space. Alternatively, spatially and/or temporally bounded aggregates of chosen attributes can be selected. In the latter case, observational units consist of the product of an ordination process, whether these are types, classes, or groups. As far as the systematic description of ceramics is concerned, dimensions of pottery variability may be roughly divided into formal dimensions and technological dimensions (Sinopoli, 1991: 56-65: Orton et al., 1993: 152-165). The former refer to observations concerning the shape of the entire vessel, the shape of any specific components of the vessel, or any type of surface treatment (Rice, 1987: 287). Entire vessel shapes can be described by using established typological categories or developing new ones. Some formalized descriptions of individual vessel parts have been published (Gardin, 1976, 1978, among others), and can be used to achieve a more standardized and replicable representation of vessel design. Alternatively, and preferably, description of shapes can be reached through direct measurement and quantification of relevant attributes. The use of complete or almost complete vessels is preferable, in order to reduce the risk of sample inflation and inference over a non-representative assemblage, although a number of techniques have been developed to overcome these limitations (Orton et al., 1993; Orton, zooo). An entire vessel shape might be directly compared with abstract or primitive geometric forms (truncated or overlapping ¥

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EUGENIO BORTOLINI

cones, cylinders, spheres, ellipsoids, etc.) or '.vith several composite forms in order to systematically measure volume (Shepard, 1956: 233; Gandon et aL, 20u). Measurement of both complete vessels and fragments of shapes is possible by theoretically slicing the vessel into standardized horizontal sections and 'measuring the absolute radius of each slice (Wilcock and Shennan, 1975), the relative distance from a tangential imaginary line, or mathematically describing body curves (see Orton et aL, 1993: 159-163, for a detailed discussion). These methods have greatly benefited from the increasing use of informatics (Gilboa et aL, 2004; Kampe! and Sablatnig, 2007; Martinez-Carrillo et al., 2009, to quote some recent examples). Vessel size is most commonly a measurement of absolute height and diameter, lip angles, shoulder angles, angles at the base, thickness of rim, neck, body, and base (see Sinopoli, 1991: 61--62). It is also possible to classify vessels according to ratios between pairs of the above-mentioned measures, so that individual specimens are more directly comparable (see Figure 35.4). These procedures can be used to infer differences in the manufacturing process, the transmission of knowledge, and the skills of individual pot· ters (Roux, 1990; Gandon et al., 20u). Surface treatment comprises observations on surface color, level of elaboration, smoothness, the presence of glazing or slips, and the presence of appliques or comparable

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!I· TYPOLOGY AND CLASSIFICATION

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ornaments. All these elements can be systematically described and useful classifications can be drawn on such data. Because quantification is often more difficult for surface attributes, archaeologists tend to divide them into categorical units (either presence-absence or multistate variables) and quantitatively treat their distribution through space and time. The classification of decorative patterns as categorical attributes has been fruitfully employed to investigate mechanisms of cultural transmission, adoption, and selection responsible for the formal evolution of material culture (Neiman, 1995; Shennan and Wilkinson, 2001; Cochrane, 2009). Interesting correlations between formal attributes and potentially functional characters have also been explored (Steele eta!., 2010) (see Figure 35.5). In addition, technological dimensions can be chosen for ceramic description. Typologies based on technological characters are comparatively rarer (Rice, 1987: 286-287). One of the most explored attributes of ceramic wares is their composition. The chemical and mineralogical analysis of ceramic fabrics is often used to infer the potential raw material sources (Neff, 1995; Mery, 2000). Tempers are used to distinguish different technical traditions, to make inferences about functional aspects of the finished vessels that influenced individual and group choices, and/or to generate hypotheses about the temper sources chosen by potters (Feathers, 2006). Firing techniques can be investigated through the analysis of minerals and components in different wares, as well as through the color of both surface and core (for example to distinguish between oxidizing and reducing kiln environments; see Rye, 1981: 114-118).

CONCLUSION In summary, it is important to remember that: Ordination methods have been developed to systematically arrange disordered information contained in the empirical record. The systematic description of material culture is at the root of archaeological practice and significant effort has been invested in the classification of archaeological ceramics in particular. 1he systematic arrangement of archaeological phenomena originated from the need for reliable chronological sequences. Initial typological and classificatory efforts led to normative approaches and involved the classifiCation of cultures supported by a unilin~ ear and progressivist view of human societies. Later developments focused on typology and classification as tools for generating effective relative chronologies (frequency seriations), and to investigate the interaction between individuals and human groups. The term type, although it generally refers to an aggregate of particular characteristics in space and time, has been used alternatively to refer to actual objects, abstract units, mental templates, analytical tools, and groups of real entities. As emerged in the debates over typology in the l940S and l950S, all systematic arrangements, no matter how sophisticated, can be divided into deductive and inductive approaches. The first generate abstract or theoretical units starting from a particu~ lar set of research questions. These units (classes) are then used to divide observable

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phenornena, and each class may or may not have an actual counterpart in the real world. 1be second approach allows analytical units to emerge from empirical data as "natural" groups based on shared attributes, It is impossible to create a single classificatory structure for general purposes or to answer questions that are not theory and context specific (Hull, 1970 ), In fact, different sorting methods need to be developed to meet the requirements of different contexts and datasets. In addition to the choice of an appropriate observational scale, attribute selection is the most critical step to build effective units (types, classes, or groups), The explicit definition of categories and the replicability of their quantitative evaluation make classificatory practices the most amenable to communication and problemoriented archaeological enquiry, Ceramic materials can be arranged according to a vast number of variables. These comprise both formal dimensions (shape and size of entire vessels or their portions, surface treatment), and technological dimerJsions (composition, firing techniques, tempering, and manufacturing processes). A famous quote by Box on model building stated that "all models are wrong, but some are useful" (Box and Draper, 1987: 424), This means that all abstract representations of reality elaborated by researchers are, by definition, distinct from reality itself (from a linear meter to increasingly complex simulations, from weight units to mathematical abstractions). By pointing at selected elements models offer useful and often repeatable comparisons with observed phenomena. For us to understand and explain the empirical world, models need to be rejected and hypotheses need to be tested; only then can causal processes be inferred. In the same way, one could state that all classes and types are wrong, but some are usefuL All arrangements of empirical objects conducted by researchers are models of reality, Types, classes, and ordination systems constitute, for the archaeologist, a door connecting a theoretical, abstract) or ideational level to an empirical, material, or phenomenological level (Dunnell, 1971: 26-30). In order to generate knowledge, the archaeologist has to move between these worlds in both directions, which means she or he must view material culture both deductively (from theoretical to empirical, or top-down) and inductively (from empirical to theoretical, or bottom-up; Willer and Willer, 1973), Types and classes, therefore should offer a controlled, repeatable, and formally testable background against which observed phenomena can be measured in order to answer specific questions. As in the case of models, building problem-oriented types and effective classificatory systems implies the simplification of reality. The large amount of variability expressed by human actions at an individual level has unpredictably broad consequences at the population leveL Artifact variation in a population generally results from the cumulative effect of change, innovation, and taphonomic processes through space and time. If an ordination system is limited by the investigator's criteria and purposes) it cannot encapsulate this immense range of variability. Rather) it must consistently represent a smaller number of dimensions in order to account for at least some of their causative processes, and to avoid drowning the investigator in the flood of data generated by the richness of individual creativity (Filippucci, 20ll:l90). It has been pointed out that there is no fixed or optimal number of attributes that an

archaeologist should include in her or his descriptive system. On the one hand, the more attributes or characteristics analyzed the more accurate the description. However, if a

666

F.Ue Type Concept Revisited:' American Anthropologist s6: 42·-s+ Ford,). A. (1954b). "Comments on A. C. Spaulding, 'Statistical Techniques for the Discovery of Artifact Types: American Antiquity 19: 390-391. Ford,). A. (1954c). "Spaulding's Review of Ford:' American Anthropologist 56:109-112. Gaudon, E., Casanova, R., Sainton, P., Coyle, T., Roux, V., Bril, B., and Bootsma, R. (2011). ''A Proxy of Potters' Throwing Skill: Ceramic Vessels Considered in Terms of Mechanical Stress." journal of Archaeological Science 38: 1080-1089. Gardin,). -C. (1976). Code pour lima lyse des formes de poteries (Paris: CNRS). Gardin,). -C. (1978). Code pour /'analyse des ornements (1956, revised 1973) (Paris: CNRS). Gilboa, A., Karasik, A., Sharon, !., and Smilansky, U. (2004). "Towards a Computerized Typology and Classification of Ceramics:' Journal ofArchaeological Science 31: 681-694. Hill,). N. and Evans, R. K. (1972). "A Model for Classification and Typology:' In: Clarke, D. L (ed), Models in Archaeology (London: Methuen), 231-27+ Hill, M. 0. (1973). "Reciprocal Averaging: An Eigenvector Method of Ordination:' Journal of Ecology 6r: 237-249. Hodson, F. R. (1982). "Some Aspects of Archaeological Classification." In: Whallon, R. and Brown,). A. (eds), Essays on Archaeological Typology (Evanston, IL: Center for American Archaeology Press), 21--29. Hull, D. (1965a). "The Effects of Essentialism on Taxonomy-Two Thousand Years of Stasis(!):' British Journal for the Philosophy of Science 15( 6o ): 314-326. Hull, D. (1965b). "The Effects of Essentialism on Taxonomy--Two Thousand Years of Stasis (II)". British Journal for the Philosophy ofScience 16( 61): 1-18. Hull, D. (1970). "Contemporary Systematic Philosophies:' Annual Review of Ecology and

S'ystematics 1: 19-54. Hutchinson, G. E. (1957). "Concluding Remarks:' Cold Spring Harbor Symposia on Quantitative Biology 22(2): 415-427. Kampe!, M. and Sablatnik, R. (2007). "Rule Based System for Archaeological Pottery Classification." Pattern Recognition Letters 28: 740-747Klejn, L. S. (1982). Archaeological Typology. BAR International Series (Oxford: Archaeopress). Krieger, A. D. (1944). "The Typological Concept:' American Antiquity 9:271-288. Kroeber, A. L. (1904). "Types of Indian Culture in California:· University of California Publications in American Archaeology and Ethnology 2: 81-103. Kroeber, A. L. (1916a). "Zuni Culture Sequences:' Proceedings of the National Academy of Sciences 2: 42-45. Kroeber, A. L. (1916b). "Zuni Potsherds:' American Museum of Natural History Anthropological Papers 18: 1-37. Kroeber, A. L. (1919). "On the Principle of Order in Civilization as Exemplified by Changes of Fashion." American Anthropologist 21: 235-263. Kroeber, A. L. (1948). Anthropology: Culture Patterns and Process (New York: Harcourt Brace). Kroeber, A. L. (1952). The Nature of Culture (Chicago: University of Chicago Press). Laplace, G. (1966). Recherches sur l'origine et /'evolution des complexes leptolithiques. Melanges d'archeologie et d'histoire/Ecole fran,aise de Rome (Paris: de Boccard). Laplace, G. (1968). "Recherches de Typologie analityque:' Origini 2:7-64.

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CHAPTER

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DIRECT DATING METHODS SOPHIE BLAIN AND CHRISTOPHER HALL

INTRODUCTION

an artifact or an archaeological site is a critical component of any archaeological investigation, providing not only chronological weight and facilitating determination of the duration of its use or occupation, but also situating the object or site within a (pre-/proto-) historic context 1hese questions, and those contingents upon them, can only be answered by a thorough dating of the object or site. In the case of ceramics, regardless of whether they have an aesthetic, domestic, or architectural function, their primary chronological attribution is typically achieved typologically. The difficulty with relying upon typological dating, established by analogy and comparison of shapes and styles, is that it is often based upon circular reasoning: if a type, considered to be a chronological marker, is dated incorrectly, then the house of cards collapses since all the other ceramics which have been dated by comparison will also be incorrectly dated. Therefore, it is necessary, if not fundamental, for these typologies to be built upon a robust foundation, that is, on indubitably dated objects. Furthermore, typochronologies are usually only applicable to prestigious or fashionable pottery which goes into and out of vogue, and not to ubiquitous common and utilitarian wares, such as cooking pots and storage vessels. And yet, dating the latter would facilitate the dating of many archaeological contexts for which stratigraphic and/or radiocarbon dates are not possible or practical. During the second half of the twentieth century, a number of archaeometric methods were developed aimed at dating archaeological ceramics directly, using their physicochemical properties rather than formal or stylistic attributes. Tbe choice of which direct dating method to use depends largely upon the material and archaeological question to be answered. Tbe type and quantity of the former determine the type of analysis (destructive or not) which can be carried out, and the latter conditions both the selection of the samples (their representativeness) and the analytical method used. It is also important to consider the precision of the analytical method and confirm that it fits with the chronological resolution required to answer the archaeological question. Furthermore, a retlection must be made on the dated event while applying chronometric methods on a ceramic: is the event dated the artifact itself or an element associated to it? What is the connection between them? Does dating a ceramic mean dating the occupation of the site? Furthermore, it must be kept in DATING

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mind that dating a ceramic artifact might only provide a terminus post quem to the archaeological occupation of the site or the building of the wall; for example, if the manufacture of the object is not strictly contemporary to the archaeological event. The most suitable dating method is the one which is best adapted to the nature of the material to be dated, its context, and the specific research question. Two of these methods, luminescence and rehydroxylation dating, are discussed in detail below.

LUMINESCENCE DATING Although the idea of using this progressive phenomenon was suggested by Daniels, University of Wisconsin (USA), in 1953, it is mainly the Oxford Luminescence Dating Laboratory (UK) that played the fundamental role in stimulating the worldwide development of luminescence dating (Zoller and Wagner, 2015). At the end of the 1960s, the first reliable thermoluminescence (TL) dates were obtained for archaeological ceramic material (Mazess and Zimmermann, 1966; Ralph and Ham, 1966), first on pottery and later on architectural bricks (Kasa et al., 198+ Goedicke C., 1985). The optically stimulated luminescence (OSL) method, deriving from TL, was developed in the 198os-90s and its first applications on archaeological ceramic were published in zooo for both pottery (Oke and Yurdatapan) and brick (Bailiff and Holland). An overwiew of the method applied on pottery and bricks is given by Bailiff (2015).

Background Physics of the Phenomenon TL and OSL are radiogenic dating methods that use the property exhibited by certain crystals of emitting light when stimulated with heat or light following irradiation with ionizing radiation (Aitken, 1985, 1998; Duller, 2015). Within ceramic materials, minerals such as quartz, feldspars, and other aluminosilicates have the capacity to store the cumulative effects of ionizing radiation. Natural sources of radiation are present within the ceramic and its environment in the form of isotopes of uranium, thorium, potassium, and rubidium. These isotopes undergo radioactive decay and emit alpha and beta particles, and gamma rays. Cosmic rays also make a minor contribution as a radiation source. These types of radiation carry energy which is absorbed by the ceramic (referred to as the absorbed dose), and during this process, atoms within crystals are ionized, liberating electrons. Some of the electrons are subsequently trapped by crystal defects and the number of trapped electrons builds up over time. During firing of the ceramics bodies (above 4oo'C), all previously trapped electrons are released and, following this resetting process referred to as the zeroing event, the crystal defects or traps begin to acquire electrons again. Since the radiation dose received is delivered at a low and steady rate (depending on the concentration in naturally occurring radionuclides in the ceramic and its environment), the total quantity of trapped electrons, which is related to the cumulative radiation dose, is proportional to the time elapsed since the

DIRECT DATING METHODS

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