Raman spectroscopy in archaeology and art history. Volume 2 978-1-78801-347-5, 1788013476, 978-1-78801-138-9, 978-1-78801-565-3

Table of contents :
Content: Analytical Raman Spectroscopy of Inks
Raman Spectroscopic Analysis of Romano-British Wall Paintings: A Comparison Between Geographically Different Sites at the Northern Fringe of the Roman Empire
Evidence of Pentimenti for the Authentication of Paintings: A Challenge for Analytical Science at the Interface with Art History
Dancing on Eggshells: A Holistic Analytical Study of a Ballet Dancer on Regency Porcelain
Pigments and Colourants
Micro Raman Spectroscopy of Epipalaeolithic Decorated Pebbles from Arroyo Moreras 2 (Parque Darwin, Madrid)
Raman Microscopy as a Primary Technique for Identifying Micro-residues Related to Tool-use on Prehistoric Stone Artefacts
Biological Materials of Significance to Cultural Heritage
Discrimination of Contraband Ivories Using Long Wavelength Portable Raman Instrumentation
Micro-Raman and Provenance Studies: The Case of Levantine Ceramics
Raman Spectroscopy for the Identification of Materials in Contemporary Painting
Application of Micro-spatially Offset Raman Spectroscopy to Street Art Paintings
Raman Spectroscopy as a Cultural Heritage Forensic Tool
Outdoor Bronze and Its Protection
Analysis of the Degradation of Medieval Mural Paintings in the Open Air Abandoned Church of Ribera, North of Spain
Miniaturized Raman Spectrometers Applied to Gemstone Analyses on Works of Art
New Case Studies: Diamonds, Jades, Corundum and Spinel
The Cultural Meanings of Color: Raman Spectroscopic Studies of Red, Pink, and Purple Dyes in Late Edo and Early Meiji Period Prints
Raman Spectroscopy Applied to the Analysis of Typomorphic Minerals in Various Provenance Investigations of Cultural Heritage Objects
Pitfalls in Raman Spectroscopy Applied to Art and Archaeology: A Practical Survival Guide for Non-specialists
Subject Index

Citation preview

Published on 26 October 2018 on https://pubs.rsc.org | doi:10.1039/9781788013475-FP001

Raman Spectroscopy in Archaeology and Art History

Volume 2

Published on 26 October 2018 on https://pubs.rsc.org | doi:10.1039/9781788013475-FP001

View Online

Published on 26 October 2018 on https://pubs.rsc.org | doi:10.1039/9781788013475-FP001

View Online

Raman Spectroscopy in Archaeology and Art History Volume 2

Edited by

Peter Vandenabeele

Ghent University, Belgium Email: [email protected] and

Howell Edwards

University of Bradford, UK Email: [email protected]

Published on 26 October 2018 on https://pubs.rsc.org | doi:10.1039/9781788013475-FP001

View Online

Print ISBN: 978-1-78801-138-9 PDF ISBN: 978-1-78801-347-5 EPUB ISBN: 978-1-78801-565-3 A catalogue record for this book is available from the British Library © The Royal Society of Chemistry 2019 All rights reserved Apart from fair dealing for the purposes of research for non-commercial purposes or for private study, criticism or review, as permitted under the Copyright, Designs and Patents Act 1988 and the Copyright and Related Rights Regulations 2003, this publication may not be reproduced, stored or transmitted, in any form or by any means, without the prior permission in writing of The Royal Society of Chemistry or the copyright owner, or in the case of reproduction in accordance with the terms of licences issued by the Copyright Licensing Agency in the UK, or in accordance with the terms of the licences issued by the appropriate Reproduction Rights Organization outside the UK. Enquiries concerning reproduction outside the terms stated here should be sent to The Royal Society of Chemistry at the address printed on this page. Whilst this material has been produced with all due care, The Royal Society of Chemistry cannot be held responsible or liable for its accuracy and completeness, nor for any consequences arising from any errors or the use of the information contained in this publication. The publication of advertisements does not constitute any endorsement by The Royal Society of Chemistry or Authors of any products advertised. The views and opinions advanced by contributors do not necessarily reflect those of The Royal Society of Chemistry which shall not be liable for any resulting loss or damage arising as a result of reliance upon this material. The Royal Society of Chemistry is a charity, registered in England and Wales, Number 207890, and a company incorporated in England by Royal Charter (Registered No. RC000524), registered office: Burlington House, Piccadilly, London W1J 0BA, UK, Telephone: +44 (0) 20 7437 8656. Visit our website at www.rsc.org/books Printed in the United Kingdom by CPI Group (UK) Ltd, Croydon, CR0 4YY, UK

Published on 26 October 2018 on https://pubs.rsc.org | doi:10.1039/9781788013475-FP005

Foreword Raman spectroscopy did not feature in my undergraduate degree in Archaeological Sciences in the 1980s. At the time, Howell Edwards was actively extending research applications of Raman spectroscopy at my alma mater, the University of Bradford, UK, but in the Department of Chemistry in an adjoining building on the campus. Today, thanks to Howell, Peter Vandenabeele and many other researchers, Raman spectroscopy is included in the teaching of a much wider range of degree subjects spanning the archaeological, heritage, environmental and forensic sciences. This is testimony to the versatility of Raman spectroscopy as a diagnostic analytical tool. Furthermore, the research horizons of the technique have continued to expand and this timely follow up to the 2005 volume is welcome. In the late 1990s and early 2000s, Raman spectroscopy was acquired by several of the major museum science and conservation laboratories. Following the installation of a Raman microscope in the British Museum in May 1999, the first dedicated conference on Raman Spectroscopy in Art and Archaeology was held in the Museum in November 2001. The technique has been used at the British Museum since then to study minerals, including pigments and gemstones, some organic dyestuffs, corrosion products and so on. The technique is often used in conjunction with other techniques, notably X-ray fluorescence and X-ray diffraction. The increasing miniaturisation and portability of analytical kit, fuelled by developments in lasers, detectors, filters and more, is exemplified by the diverse situations where Raman is now being deployed. Raman and micro-Raman spectroscopy features in the multi-technique MOLAB or mobile laboratory platform providing access to portable technologies for in situ non-destructive investigation of artworks. Various spectrometers have been used to produce immediate results in the field to guide sampling strategies for ongoing archaeological excavations. Looking ahead to 2020,   Raman Spectroscopy in Archaeology and Art History Volume 2 Edited by Peter Vandenabeele and Howell Edwards © The Royal Society of Chemistry 2019 Published by the Royal Society of Chemistry, www.rsc.org

v

View Online

Published on 26 October 2018 on https://pubs.rsc.org | doi:10.1039/9781788013475-FP005

vi

Foreword

the Mars microbeam Raman spectrometer, a component of the Scanning Habitable Environments with Raman & Luminescence for Organics & Chemicals (SHERLOC), will be mounted on the NASA Mars 2020 Rover and will search for organics and minerals that may be associated with signs of past life on the red planet. Another miniaturised Raman laser spectrometer (RLS) will feature for first-pass analytical screening on board the ESA/IKI Roscosmos ExoMars 2020 mission in the search for life signatures. The study of our heritage relies on close co-operation between curators, conservators and scientists. All techniques must be subject to continuous critical evaluation so that the advantages, disadvantages and implications are understood clearly. I am delighted to see this second volume extending the applicability of Raman spectroscopy to a wider range of topics and themes in cultural heritage. Carl Heron Director of Scientific Research The British Museum, London, UK

Published on 26 October 2018 on https://pubs.rsc.org | doi:10.1039/9781788013475-FP007

Preface This book forms a sequel to the first volume which appeared under the editorship of John Chalmers and Howell Edwards in 2005, comprising some twenty-five contributed chapters from eminent authors and researchers over a wide-ranging field of topics, which all had the common theme of the applications of Raman spectroscopy to the characterisation of materials of relevance to art history and to archaeological artefacts. The idea for this first volume was generated by a ground-breaking meeting on the same topic held at the British Museum in London in November 2001, sponsored jointly by the Royal Society of Chemistry (Molecular Spectroscopy Group, Analytical Division) and the British Museum under the joint chairmanship of Dr Ian Freestone of the British Museum Research Laboratories and Professor Howell Edwards of the Chemical and Forensic Sciences Department of the University of Bradford. It was apparent at this meeting that a synergy existed between analytical Raman spectroscopists who were leading the application of their technique towards the rather novel area of art materials and archaeological artefacts and the special sampling considerations and data interpretation that these demanded and the conservation scientists, museum curators and archaeologists who required novel information to facilitate the restoration and preservation of the objects in their curacy. It is certainly the case that most vibrational spectroscopic studies of artwork and archaeological artefacts carried out up to the last quarter of the 20th century were exclusively the preserve of the infrared spectroscopist; there are several reasons for this, but the most important are that earlier Raman spectroscopic instrumentation used Toronto mercury arc excitation (of up to 3 kW power output), operating mainly at 435.8 nm, and photographic plates, or later, photoelectric recording. This required rather large quantities of pure samples that were stable to high-energy visible radiation and the total absence of fluorescence emission, which could swamp the   Raman Spectroscopy in Archaeology and Art History Volume 2 Edited by Peter Vandenabeele and Howell Edwards © The Royal Society of Chemistry 2019 Published by the Royal Society of Chemistry, www.rsc.org

vii

View Online

Preface

Published on 26 October 2018 on https://pubs.rsc.org | doi:10.1039/9781788013475-FP007

viii

Figure 1 Overview of the number of research papers published on Raman spectroscopy of cultural heritage. Based on ISI Web of Science.

much weaker Raman scattering intensity. In the late 1970s, however, the classic marriage of a laser Raman spectrometer with an optical microscope with sensitive photon detectors revolutionised the range of applications that could be undertaken using the new laser Raman microscopy and almost immediately resulted in the first brief description of artefact analysis using this novel instrumentation. In a recent survey of the literature in the decade 1997–2007, which has addressed Raman spectroscopic applications to art and archaeology by Vandenabeele et al. (2007), the growth of the technique can be clearly seen expressed as a proportion of the total number of papers published in art and archaeology and this is reflected in data presented in the Web of Science where an almost exponential increase in Raman papers published in art and archaeology should be noted (Figure 1). Also, a greater awareness is now apparent across several disciplines at the arts/science boundaries, and particularly in the field of scientific conservation and restoration, because publications using Raman spectroscopic techniques, and also complementary data, for studying artworks have appeared in journals which hitherto had not attracted research work of this kind, for example, Studies in Conservation, Journal of Archaeological Science, Archaeometry, and Antiquity as well as in the more mainstream spectroscopic literature. The growth of work specifically in the area of Raman spectroscopy applied to art and archaeology has stimulated the acquisition of novel spectroscopic instrumentation and trained specialists by museums and a new focus directed at the communication of the results forthcoming from these studies. In addition, the analytical information derived from optical, spectroscopic and diffraction experiments on artwork is being used increasingly to provide evidence for the authentication of high-value artwork in museum collections and in the private domain and also for the scientific provenancing of unknown artworks; the success of this approach is dependent upon

View Online

Published on 26 October 2018 on https://pubs.rsc.org | doi:10.1039/9781788013475-FP007

Preface

ix

the acquisition of data derived from the materials comprising the art object or artefact at both the elemental and molecular levels. In the twelve years that have passed since the publication of the first volume on Raman Spectroscopy in Archaeology and Art History in 2005, a steady growth in output in this field has occurred: from the first conference mentioned earlier in the British Museum in 2001, dedicated international meetings on Raman Spectroscopy in Art and Archaeology (RAA) have been held in Ghent (2003), Paris (2005), Modena (2007), Bilbao (2009), Parma (2011), Ljubljana (2013), Wroclaw (2015) and Evora (2017). Other mainstream spectroscopy and art analysis conferences now hold dedicated sessions on Raman spectroscopy in art and archaeology, for example, the International Conference on Raman Spectroscopy, GeoRaman, InArt, Technart and IRUG (formerly the Infrared Users Group and now the Infrared and Raman Users Group). Additionally, several topics which were presented as novel examples or as typical case studies in the 2005 publication have now themselves become more widely applicable: a particularly apposite example of one of these is the adoption of non-destructive, handheld or mobile Raman spectrometers for the interrogation of artworks and artefacts in situ and in the field. In this second volume, the original idea of offering full peer-reviewed chapters supported by individual case studies that describe the application of Raman spectroscopy to specific examples selected from the area or artworks and archaeology has been maintained. This book will give the reader a measure of the important contribution that the Raman spectroscopic technique is making currently to the provision of information about the analytical molecular composition of material relevant to artworks and archaeological artefacts. The major questions that archaeologists, conservators and art historians have regarding the characterisation of their specimens can be summarised as follows: ●● There is an artefact that requires analysis; what is the composition of the material present? ●● How much of that material is present – are there any other materials present that we should know about? ●● Where did this material originate? ●● What, if anything, has happened to it in the burial environment, if appropriate? Is there evidence of environmental or biological degradation and, if so, is this still ongoing? ●● Are there “unusual materials” present which warrant further study? Is there any evidence that the specimen has undergone unrecorded restoration? ●● Is the specimen or artefact genuine or a fake? ●● The specimen is subject to strict protocols of preservation and only non-destructive analysis is acceptable – can this be assured? Whereas most of these can be addressed by the adoption of analytical Raman spectroscopy, the main purpose of any data acquisition must be incorporated in a holistic forensic approach that necessarily involves the

View Online

Published on 26 October 2018 on https://pubs.rsc.org | doi:10.1039/9781788013475-FP007

x

Preface

consideration of historical data and all available documentation in a science/ arts amalgamation. For example, although the establishment of a chronological database of pigments used in art is well established, the recognition of a particular pigment in an out-of-context situation in an artwork does not imply that the artwork is a fake: Prussian blue, synthesised by Diesbach in 1706 was a mainstay of blue pigment colours over the next two centuries but its presence detected in an otherwise Renaissance painting from the 16th century does not condemn that artwork to be a forgery. Unrecorded restoration is a major reason for the discovery of such materials in these situations. Another example is that of chrome yellow synthesised by Vauquelin in 1807, but its presence on an ancient Egyptian cartonnage does not imply a restorative procedure carried out in the 19th century, as lead(ii) chromate is a naturally occurring mineral which has a Raman spectrum that is indistinguishable from that of synthetic chrome yellow. Hence, the interpretation of Raman spectral data should always be accomplished with an interdisciplinary awareness of the background provenancing or history. Finally, the question has sometimes been raised in meetings as to the provision of an all-encompassing database of Raman spectral data that would facilitate the interpretation of the often complex data produced in the analytical interrogation of artworks. A major advantage of Raman spectroscopy is the ability to provide spectral data from complex mixtures containing inorganic and organic moieties and species without effecting their separation chemically or mechanically. A particular advantage arising from this is the recognition of characteristic biomarkers that indicate unambiguously that biological degradation of an artwork or artefact has taken or is taking place. This is especially valuable information for curators, who need to assess the integrity of their specimens for storage and display: it has been shown on many occasions that Raman spectroscopy can provide an early warning system for the presence of ongoing biological degradation in a sensitive biological sample such as a human mummy, textile, or vellum manuscript before that degradation becomes visible to an observer. This volume serves to illustrate a selected number of examples of the information that Raman spectroscopic analysis can supply to assist the objective understanding of the material composition of artefacts and artworks: this information has been obtained through the micro-destructive or non-­ destructive sampling of the specimens concerned and the increasing role that mobile instrumentation has played in the acquisition of the necessary spectral data. Peter Vandenabeele and Howell G. M. Edwards

Published on 26 October 2018 on https://pubs.rsc.org | doi:10.1039/9781788013475-FP011

Contents Chapter 1 Analytical Raman Spectroscopy of Inks  Howell G. M. Edwards

1.1 Introduction  1.2 The Detection of Ancient Inks  1.2.1 Raman Spectroscopy  1.3 Case Studies  1.3.1 The Vinland Map  1.3.2 The Voynich Manuscript  1.3.3 The Beato de Valcavado Manuscript  1.4 Conclusion  References  Chapter 2 Raman Spectroscopic Analysis of Romano-British Wall Paintings: A Comparison Between Geographically Different Sites at the Northern Fringe of the Roman Empire  Howell G. M. Edwards, Rebecca Widdowson and Jennifer Proctor



2.1 Introduction  2.2 Experimental  2.2.1 Villa Sites and Samples  2.2.2 Raman Spectroscopy  2.3 Results and Discussion  2.4 Conclusions  References 

  Raman Spectroscopy in Archaeology and Art History Volume 2 Edited by Peter Vandenabeele and Howell Edwards © The Royal Society of Chemistry 2019 Published by the Royal Society of Chemistry, www.rsc.org

xi

1 1 5 6 8 8 10 11 12 13

16

16 20 20 21 24 27 28

View Online

Contents

Published on 26 October 2018 on https://pubs.rsc.org | doi:10.1039/9781788013475-FP011

xii

Chapter 3 Evidence of Pentimenti for the Authentication of Paintings: A Challenge for Analytical Science at the Interface with Art History  Timothy J. Benoy , William A. Edwards and Howell G. M. Edwards

3.1 Introduction  3.2 The de Brécy Tondo  3.3 Historical Provenancing  3.4 Scientific Analysis  3.5 Conclusions  References  Chapter 4 Dancing on Eggshells: A Holistic Analytical Study of a Ballet Dancer on Regency Porcelain  Howell G. M. Edwards, Alexander P. H. Surtees and Richard Telford



4.1 Introduction  4.1.1 Ballet History  4.2 The Porcelain Connection  4.3 Raman Spectroscopic Analysis of the Spill Vase  4.3.1 Raman Spectroscopic Data and Discussion  4.4 Conclusions  References  Chapter 5 Pigments and Colourants  Peter Vandenabeele, Anastasia Rousaki, Mafalda Costa, Luc Moens and Howell G. M. Edwards



Acknowledgements  References  Chapter 6 Micro Raman Spectroscopy of Epipalaeolithic Decorated Pebbles from Arroyo Moreras 2 (Parque Darwin, Madrid)  A. Hernanz, J. M. Gavira-Vallejo, P. Bueno-Ramírez, R. de Balbín-Behrmann, J. Morín de Pablos and C. de Juana Ortín



6.1 Introduction  6.1.1 Initial Remarks  6.1.2 Archaeological Background  6.2 Experimental  6.3 Results and Discussion  6.3.1 Pebble C-AM-86 

31

31 35 38 40 42 43 46

46 48 50 52 53 57 59 61

66 66

68

68 68 69 69 73 73

View Online

Published on 26 October 2018 on https://pubs.rsc.org | doi:10.1039/9781788013475-FP011

Contents



xiii

6.3.2 Pebble C-AM-245  6.3.3 Pebble C-AM-246  6.4 Conclusion  Acknowledgements  References  Chapter 7 Raman Microscopy as a Primary Technique for Identifying Micro-residues Related to Tool-use on Prehistoric Stone Artefacts  Linda C. Prinsloo and Luc Bordes



7.1 Introduction  7.2 Archaeological Background  7.3 Experimental Methods  7.3.1 Sample Preparation  7.3.2 Raman Analysis  7.3.3 Cleaning and Analysis Procedures  7.3.4 Reference Material  7.4 Results and Discussion  7.4.1 Sediment  7.4.2 Experimental Tools  7.4.3 Archaeological Artefacts  7.5 Conclusions  Acknowledgements  References  Chapter 8 Biological Materials of Significance to Cultural Heritage  Elizabeth A. Carter



8.1 Introduction  8.2 Human Tissue  8.2.1 Keratin Proteins  8.2.2 Morphological Structure  8.2.3 Characteristic Raman Spectra of Keratin Proteins  8.2.4 Mummified Remains  8.2.5 Hair  8.3 Skeletal Remains  8.3.1 A Comparison of Ancient and Modern Teeth  8.4 Brain Matter  8.4.1 The Heslington Brain  8.4.2 St John the Evangelist Church  8.5 Calculi  8.5.1 Gristhorpe Man  8.5.2 Oluz Höyük 

74 75 78 78 79

81 81 82 82 82 84 84 84 85 85 85 90 95 95 95 97 97 98 98 98 100 101 106 108 109 115 115 116 117 117 118

View Online

Contents

xiv

Published on 26 October 2018 on https://pubs.rsc.org | doi:10.1039/9781788013475-FP011



8.6 Conclusion  Acknowledgements  References  Chapter 9 Discrimination of Contraband Ivories Using Long Wavelength Portable Raman Instrumentation  Sarah Kelloway, Howell G. M. Edwards, Brad Swarbrick and Elizabeth A. Carter



9.1 Introduction  9.1.1 Previous Raman Spectroscopy Studies of Ivories  9.2 Experimental  9.2.1 Materials  9.2.2 Raman Portable Spectrometer  9.2.3 Spectral Analysis  9.3 Results  9.3.1 Spectral Analysis  9.3.2 Partial Least Squares Discriminant Analysis (PLS-DA)  9.4 Discussion and Conclusions  Acknowledgements  References 

Chapter 10 Micro-Raman and Provenance Studies: The Case of Levantine Ceramics  Laura Medeghini, Danilo Bersani, Silvano Mignardi, Caterina de Vito and Pier Paolo Lottici

10.1 Introduction  10.2 Experimental  10.3 Results and Discussion  10.3.1 Technological Level  10.3.2 Provenance of the Raw Material  10.3.3 Burial Conditions  10.4 Concluding Remarks  References 

Chapter 11 Raman Spectroscopy for the Identification of Materials in Contemporary Painting  Silvia Bruni and Vittoria Guglielmi

11.1 Introduction  11.2 Surface-enhanced Raman Spectroscopy (SERS) Applied to Coloured Inks and Fluorescent Pigments 

118 119 119

123

123 127 130 130 132 132 133 133 133 137 138 138 141

141 142 143 143 152 152 153 154 157 157 158

View Online

Contents

Published on 26 October 2018 on https://pubs.rsc.org | doi:10.1039/9781788013475-FP011





xv

11.3 Portable Raman, Reflection FTIR and FT-Raman Non-invasive Study of 20th Century Household and Automotive Paints  11.4 Raman Analysis of Pigments in Contemporary Paintings by Portable Instrumentation  11.5 Conclusions  References 

Chapter 12 Application of Micro-spatially Offset Raman Spectroscopy to Street Art Paintings  C. Conti, A. Botteon, C. Colombo, M. Realini and P. Matousek

12.1 Introduction  12.2 Micro-spatially Offset Raman Spectroscopy  12.3 Materials  12.4 Methods  12.4.1 Full Micro-SORS  12.4.2 Defocusing Micro-SORS  12.5 Results and Discussion  12.6 Conclusions  References 

Chapter 13 Raman Spectroscopy as a Cultural Heritage Forensic Tool  Catarina Miguel and António Candeias

13.1 Unveiling the Authenticity of an Artwork Destroyed by a Fire  13.2 Authenticity Evaluation of an Artwork Intercepted in the Trade Markets  13.3 Unveiling the Placement’s Authenticity of Early Brazilian Printed Stamps Through Raman Microscopy  13.4 Final Remarks  References 

162 167 172 172 174

174 175 176 176 177 177 178 182 183 184

184 187 189 194 194

Chapter 14 Outdoor Bronze and Its Protection  P. Ropret and T. Kosec

196



196 198 198 200 200

14.1 Introduction  14.2 Experimental  14.2.1 Sampling  14.2.2 Materials  14.2.3 Instrumentation 

View Online

Contents

Published on 26 October 2018 on https://pubs.rsc.org | doi:10.1039/9781788013475-FP011

xvi



14.3 Results and Discussion  14.3.1 Case Studies  14.3.2 Protection Systems  14.4 Conclusion  References 

Chapter 15 Analysis of the Degradation of Medieval Mural Paintings in the Open Air Abandoned Church of Ribera, North of Spain  Juan Manuel Madariaga, Ilaria Costantini and Kepa Castro

15.1 Introduction  15.2 Experimental  15.2.1 Instrumentation  15.2.2 In Situ Analysis  15.2.3 Micro-sampling and Laboratory Instrumental Setup  15.3 Results  15.3.1 Pigments and Paintings  15.3.2 Soluble and Insoluble Efflorescence Salts  15.3.3 Biopatinas  15.4 Discussion and Conclusions  Acknowledgements  References 

Chapter 16 Miniaturized Raman Spectrometers Applied to Gemstone Analyses on Works of Art  Jan Jehlička and Adam Culka





16.1 Introduction  16.2 Specifics of Portable Instrumentation  16.3 Loose Gemstones and Minerals and Their Spectroscopic Investigation Using Portable Instruments  16.4 Using a Miniaturized Raman Spectrometer for Fast Detection of Gemstones from an 18th Century Monstrance While Working in a Monastic Treasury Environment  16.5 Using a Miniaturized Raman Spectrometer to Learn About Mounted Stones from a 19th Century Torah Shield: A Museum Repository Study  16.6 Summary  References 

201 201 205 209 210

213

213 217 217 218 218 220 220 222 226 228 230 230 234 234 237 239

241

247 250 251

View Online

Contents

xvii

Published on 26 October 2018 on https://pubs.rsc.org | doi:10.1039/9781788013475-FP011

Chapter 17 New Case Studies: Diamonds, Jades, Corundum and Spinel  Lore Kiefert, Pierre Hardy, Klaus Schollenbruch and Wenxing Xu

17.1 Introduction  17.2 Case Studies  17.2.1 Diamonds  17.2.2 Jades  17.2.3 Application of Raman Spectroscopy on Corundum Inclusions  17.2.4 Heat Treatment of Spinel  17.3 Summary  References 

Chapter 18 The Cultural Meanings of Color: Raman Spectroscopic Studies of Red, Pink, and Purple Dyes in Late Edo and Early Meiji Period Prints  Anna Cesaratto, Marco Leona and Federica Pozzi

18.1 Introduction  18.2 Experimental  18.2.1 Materials  18.2.2 Methods  18.3 Results and Discussion  18.3.1 Natural Red Dyes: From Safflower Red to Cochineal  18.3.2 The Introduction of Eosin and Detection of Binary Mixtures with Cochineal  18.3.3 From Natural to Synthetic Reds: Cochineal is Superseded by Acid Red Dyes  18.3.4 The Evolution of Purple: From Safflower Red to Aniline Dyes  18.4 Conclusion  Acknowledgements  References 

Chapter 19 Raman Spectroscopy Applied to the Analysis of Typomorphic Minerals in Various Provenance Investigations of Cultural Heritage Objects  B. Łydżba-Kopczyńska

19.1 Introduction  19.2 Typomorphic Minerals 

254

254 255 255 259 262 266 268 268

271 271 273 273 274 276 276 279 281 283 285 286 286

289 289 291

View Online

Contents

xviii

Published on 26 October 2018 on https://pubs.rsc.org | doi:10.1039/9781788013475-FP011



19.3 Case Studies  19.3.1 Experimental  19.3.2 Ceramic. Provenance Investigation of Archaeological Ceramic from Giles (Poland)  19.3.3 Archaeological Minerals  19.3.4 Painting Materials  Acknowledgements  References 

Chapter 20 Pitfalls in Raman Spectroscopy Applied to Art and Archaeology: A Practical Survival Guide for Non-specialists  D. L. A. de Faria and H. G. M. Edwards

20.1 Introduction  20.2 The Pitfalls  20.2.1 Instrumentation  20.2.2 Samples and Sampling  20.2.3 Data Interpretation  20.3 Conclusions  Acknowledgements  References  Subject Index 

293 293 294 298 305 310 310

314 314 316 316 330 336 340 341 341 344

Published on 26 October 2018 on https://pubs.rsc.org | doi:10.1039/9781788013475-00001

Chapter 1

Analytical Raman Spectroscopy of Inks Howell G. M. Edwards* School, of Chemistry and Biosciences, Faculty of Life Sciences, University of Bradford, Bradford BD7 1DP, UK *E-mail: [email protected]

1.1  Introduction Many of the earliest studies of manuscripts involving Raman spectroscopy focused upon the analysis of coloured mineral pigments in historiated manuscripts from which much novel information could be obtained about their composition and preparation technologies. However, complementary studies of these inks have generally been less frequent, yet as will be seen, this can often provide interesting and supportive information on the holistic preparation of manuscripts and printed works of art. The distinction between a paint and an ink is not easily defined as both contain pigments dissolved or suspended in a carrier liquid or solvent with added binders and drying agents to produce a coloured fluid: the major difference, therefore, is one of application rather than composition and in some cases printing inks can be used as paints and vice versa with an adjustment of pigment content. Generally, paint is applied more thickly than ink, and often the drying process is chemically different, depending upon the ingredients used in the ink or paint.

  Raman Spectroscopy in Archaeology and Art History Volume 2 Edited by Peter Vandenabeele and Howell Edwards © The Royal Society of Chemistry 2019 Published by the Royal Society of Chemistry, www.rsc.org

1

View Online

Published on 26 October 2018 on https://pubs.rsc.org | doi:10.1039/9781788013475-00001

2

Chapter 1

The adoption of fluid inks and reed pens for their application has been attributed to China around 2700 BCE; hence, ink can be accredited to almost 5000 years of human history. The name ink is believed to originate from the Latin incaustum and the later mediaeval French encre; as was experienced with pigment minerals, both have been found to apply to the earliest carbon-based inks and to the later iron gallotannate (iron gall) inks.1–3 The earliest ink, formulated in China from carbon black suspended in an aqueous solution of water and gum arabic, is now known as Indian ink because the best carbon supplies at that time for this purpose were sourced in India; the carbon was synthesised by burning wood such as pine, in which the partially combusted resin helped to bind the sooty deposits, in a limited amount of air under an upturned iron or ceramic dish. The gum arabic had a multifunctional role in keeping the carbon particles in suspension whilst also thickening the writing fluid for ease of application using quill or reed pens. Other carbons were sourced from the calcination of animal bone and ivory, which produced a deeper black colour – these contained residues of calcium phosphate derived from the hydroxyapatite component and provide a useful analytical Raman spectroscopic signature for the detection of bone black or ivory black, with the characteristic wavenumber of phosphate ion stretching at 960 cm−1, which can be used to discriminate between vegetable and animal origins for the source of the amorphous carbon used in the manufacture of ancient inks.4 The discovery of natural mineral oils and petroleum afforded another opportunity for the production of a deep black sooty residue upon combustion in a limited supply of oxygen. A hierarchical basis for recipes for the production of carbonaceous soot existed in which certain botanical materials were highly prized for combustion to form the blackest inks, such as peach stones, almond shells and vine twigs. There was much empiricism in the formulation of early inks as evidenced by the universal adoption of gum arabic as a binding agent; in addition to assisting the suspension of the insoluble carbon particles in the aqueous ink medium, the water-soluble gum arabic modified the viscosity of the ink, so assisting in the writing flow when applied with reed pens, quills and brushes and also improved the adhesion of the ink to the writing substrate. However, the addition of too much gum arabic resulted in a brittleness of the applied ink when dry and a tendency for the writing to flake off – hence, the debris found between the leaves of ancient manuscripts frequently contains particles of ink from the associated script that can provide a rich source of sampling to derive analytical information without involving the further destruction of the manuscript text. Different names have been recorded for carbon black inks through the ages, dependent upon their formulation or source, such as bistre,5 an extract from sooty fires that possessed a warm brown colour, and sepia, a dark, semi-transparent ink from cuttlefish, which was much used by the Roman scribes. In mediaeval times, iron gall ink replaced carbon black ink as the favoured medium of writing; although iron gall ink has recently been detected6 using X-ray spectrometry on the Codex Eusebii Evangelorum (the Vercelli Gospels),

View Online

Published on 26 October 2018 on https://pubs.rsc.org | doi:10.1039/9781788013475-00001

Analytical Raman Spectroscopy of Inks

3

the oldest existing version of the Gospels written in Latin and dating from the 4th century CE. Iron gall ink, more correctly described as an iron gallotannate, was the first water-based ink to be made from a chemical reaction between aqueous solutions of iron(ii) sulfate and extracts of oak galls with the addition of gum arabic. Oak galls are spherical, nut-like protuberances resulting from the egg-laying of wasps on oak trees. The best galls were those fully developed from which the emerging wasp larvae had hatched. As encountered with the carbon-based inks, there are many empirical recipes in existence for the manufacture of iron gall inks; indeed, as we have noted above, the chronology for the first appearance of iron gall inks actually predates the mediaeval period and Pliny in the 1st century CE describes in detail the preparation of aqueous gall solutions that blacken in the presence of copperas, an iron sulfate ore. However, Pliny was specifically referring to the detection of the adulteration of verdigris by the addition of cheaper copperas through the formation of a black colouration on exposure to an infusion of nutgalls. Outside of the Vercelli Gospels, the first record of the use of iron gall ink as a writing medium seems to have occurred in the Dead Sea Scrolls, from the late 3rd century CE. The preparation of iron gall ink was a rather complex alchemical procedure, as indicated by the following ancient recipe for the manufacture of the highest quality iron gall ink:    8 oz powdered Aleppo galls; 4 oz logwood chips; 4 oz iron sulfate; 3 oz powdered gum arabic; 1 oz copper sulfate or verdigris (basic copper acetate); 1 oz sugar; all heated and triturated in 12 pounds water followed by filtration and the addition of alum, ammonia, beer, lemon juice, oil of cloves, ground walnuts, lavender, wine, boiled oil, and extract of amber or shellac in brandy to minimise the growth of mould.    An understanding of the chemistry of the preparation of iron gall inks reveals the roles of the iron complex and its formation: the enzyme tannase from the fungus Aspergillus niger in oak galls releases gallic acid, a triphenol carboxylic acid, C6H2(OH)3COOH, and glucose through the catalytic hydrolysis of gallotannic acid ester. Iron(ii) ions from ferrous sulfate then form a dark grey 1 : 1 iron gallate complex, which releases hydrogen ions and is then oxidised by aerial oxygen on the manuscript to a ferric pyrogallate complex that is black in colour. An excess concentration of iron(ii) causes the ink to gradually fade, a problem experienced with the multifarious recipes in existence in the Middle Ages, and this also stimulates the release of hydroxyl ions and the formation of hydrogen peroxide through a Fenton reaction. It is this last property that causes the destructive damage effects noted on ancient manuscripts involving iron gall inks. Iron gallotannate inks quickly became the medium of choice for mediaeval scribes because, unlike the carbon-based inks they replaced, they interacted physically and chemically with cellulose substrates, conferring better adhesion and permanence of the writing on the script.7,8 Even when used with

View Online

Published on 26 October 2018 on https://pubs.rsc.org | doi:10.1039/9781788013475-00001

4

Chapter 1

parchments and vellum, the iron gall inks had a noteworthy adherence to their substrate and could only be removed by mechanical detachment and scraping, unlike the carbon-based inks which could be more easily erased and washed off. However, this improvement in the writing permanence of iron gall inks caused severe corrosion problems for paper manuscripts in particular. In some cases, this process resulted in the formation of holes in the manuscript (lacunae) in place of the writing; many manuscripts have suffered irreversibly in this way and pose problems for their conservation and the preservation of their integrity.9,10 It has been found that arresting the decay can be achieved by the application of calcium bicarbonate, lime, magnesite and calcium phytate, but generally, irreparable damage has been done to the original script and text.11–13 The corrosive effect of iron gallotannate inks upon cellulosic substrates can be related to the iron-catalysed breakdown of cellulose in an acidic environment.14 It will be seen below that the formation of the iron(ii) gallate complex releases hydrogen ions and decreases the pH significantly to about 2; in this process, excess Fe2+ ions then react with acidic decomposition products of the cellulose to form hydroxyl and oxygenyl radicals, from which the subsequent creation of hydrogen peroxide destroys the cellulose substrate and oxidises the iron15 to Fe3+. Hence, it has been suggested14 that measurement of the Fe2+/Fe3+ ratio in an ancient iron gall ink could provide a means of assessing its age, although clearly the actual rate of degradation of the ink would be dependent upon several environmental factors, not the least of which would be the recipe and formulation of the original ink, which was certainly not standardised in any way. The elemental migration of iron atoms into the substrate also can provide a measure of the age of the script, as determined from Auger spectroscopy, but pitfalls can be encountered particularly in the form of hair follicles in vellum substrates,16 which provided a route of penetration of the ink components into the lower regions of the substrate. It may perhaps be inferred from this discussion that iron gall inks used on vellum are not subject to the extensive corrosive material degradation and destruction noted for their cellulose analogues. This is not strictly the case since even the preparation of high quality vellums and parchments for scriptorial purposes resulted in the presence of chemical residues in the writing substrate, such as alum, lime and bicarbonate, which of course can react with the iron gallotannate fluids that are applied along with the ink. Another problem arising from the excess of iron(ii) ions in gall inks from preparations that utilised too high a ratio of copperas to oak galls was their oxidation to ferric ions, creating a brown halo surrounding the inked regions.8 Analytical Raman spectroscopy can identify the presence of exogenous chemical components and residues present in treated vellums and the effects of acid degeneration of the skin proteins resulting from the gall ink additives, which itself can be an early warning for conservators of manuscripts and ancient documents. Examples of the definitive Raman spectral signals from iron gall inks will be provided in several case studies outlined later.

View Online

Published on 26 October 2018 on https://pubs.rsc.org | doi:10.1039/9781788013475-00001

Analytical Raman Spectroscopy of Inks

5

Later developments in ink manufacture occurred in the mid-to-late 19th century, when a new range of organic dye-based coloured inks became available following upon Perkin's synthesis of mauveine. At the London Society of Arts in 1858 the advent of this new range of brightly coloured dyestuffs was advocated first for ink manufacture with the additional adoption of graphite to replace soot for carbon-based inks. It is true that whereas most ancient manuscript texts and writing have been accomplished using black ink, a rather limited range of other colours have been identified; examples include red inks (utilising cinnabar, dragon's blood, Brazil wood extracts for pigmentation), purple (using folium, caput mortuum and purpurum extracts for pigmentation) and gold. The major problem that was identified early on with the use of alternatives to carbon black or iron gall based inks is that unless the pigment was a mineral, such as cinnabar or in some much rarer cases haematite, extracts from botanical or marine sources were dyestuffs, which were badly affected by light and handling – such was the case for folium (also known as turnsole) and purpurum. The ancient scribes and artists termed these dyes “fugitive” and thereby recognised their impermanence17,18 and unsatisfactory adoption for scriptorial work.

1.2  The Detection of Ancient Inks Outside of conservation, a major problem that faces analytical scientists and art historians is the dating of inked manuscripts. Unlike historiated manuscripts, many ancient texts and maps often do not have any colouring pigments associated with them so the identification of the chemical composition of the ink could be an important analytical source of information. Radiocarbon dating procedures are usually not practicable for the dating of ancient inks because of the quantities of a specimen required in the destructive analysis, although of course, some useful ancillary information can result from the radiocarbon dating of the manuscript substrates themselves. Traditional methods of characterisation of ancient inks3,16 involve the application of techniques such as proton-induced X-ray emission (PIXE) spectroscopy, thin layer chromatography, ultra-violet visible spectroscopy, infrared spectroscopy, Raman microscopy, micro X-ray fluorescence spectroscopy, capillary electrophoresis, Rutherford back-scattering spectroscopy, scanning electron microscopy, scanning Auger spectroscopy and mass spectrometry.19,20 The major problem facing analysts arises from unrecorded variations in the ink composition and empirical formulations used over the centuries. The central analytical discrimination for the differentiation between iron gall inks and carbon-based inks is the recognition of elemental carbon signals for the former versus those of metallic iron for the latter. Secondary issues relate to the analytical identification of potential additives such as gum arabic, shellac and copper; in this respect, infrared spectroscopy and mass spectrometry provide valuable molecular information that other techniques do not. Thin layer chromatography has not been found to be particularly useful for the compositional discrimination of ancient inks.20

View Online

Published on 26 October 2018 on https://pubs.rsc.org | doi:10.1039/9781788013475-00001

6

Chapter 1

In contrast, the identification of elemental iron by SEM/EDAXS, micro-XRF and PIXE techniques is often used to indicate the presence of an iron gall ink in preference to a carbon-based ink from the detection of iron elemental signals. Iron gall inks possess an ultraviolet absorption with a sharp, strong band at 215 nm and a shoulder at 269 nm, characteristic of an iron gallotannate complex, compared with corresponding bands at 218 and 274 nm for the uncomplexed gallotannic acid. However, a word of caution should be advanced in adoption of this either/or concept regarding carbon-based inks and iron gallotannate inks as recent analytical studies have revealed that in some cases mixtures were used and in one example,21 mixtures of carbon black, iron gall and logwood-derived inks were used in the same manuscript. During the restoration of the 18th century manuscript of F.M. da Ponticelli entitled Nova Rhetorica, changes in the colour of the inks were noted from well-defined black to reddish-brown smudged portions on the same page: Raman spectral signatures of iron gall inks and also logwood inks to which had been added metal salts were indicated. The addition of metal salts, especially iron, conferred a darkening of colour on the reddish logwood ink, but also assisted the dispersion of the ink into the surrounding substrate, giving rise to a smudging effect. It has been suggested that this unusual procedure occurred as a result of a shortage of iron gallotannate inks in the scriptorium. Studies have been reported of logwood inks complexed with metals such as iron and chromium and also with aluminium from alum residues in the vellum, which compromise the preservation and colour of the resultant script.22,23

1.2.1  Raman Spectroscopy Raman spectroscopy has been used to detect amorphous and graphitic carbon and has been applied to the analysis of ancient carbons and carbon-based inks: a typical Raman spectrum of an ancient carbon derived from a botanical source gives two features (Figure 1.1), a broad band at 1320 cm−1 ascribed to sp3-hybridised carbon atoms (the D band) and a sharper band at 1580 cm−1 attributed to sp2-hybridised carbon atoms (the G band). It has already been mentioned above that an additional feature can occasionally be observed at 960 cm−1, which is the symmetric P–O stretching band of orthophosphate ions, characteristic of the presence of calcium hydroxyapatite, a basic calcium orthophosphate, which is indicative of a source for carbon that has been derived from the thermal treatment of animal bones (usually cow or ox bones) or ivory. During the low temperature combustion process in a furnace or kiln with a limited supply of air, the organic matter is converted to amorphous carbon, leaving the inorganic phosphatic matrix: at higher temperatures the carbon is burnt off to leave a white deposit of predominantly calcium triphosphate, Ca3(PO4)2, which is used as “bone ash” after fine grinding in the production of bone china and phosphatic porcelains.24 Several scribes and artists professed favour towards ivory black or bone black, as these products were called, because of their greater depth

View Online

Published on 26 October 2018 on https://pubs.rsc.org | doi:10.1039/9781788013475-00001

Analytical Raman Spectroscopy of Inks

7

and intensity of colour. Examples can be found of carbon from animal and vegetable sources that have been identified by Raman spectroscopy in ancient manuscripts, whether in the inks or in the black pigments in historiated texts. In contrast with the well-established Raman spectroscopic signatures that have been defined for carbon-based inks, those of iron-gall inks have been correspondingly much more difficult to attain, it is assumed because of their complexity of composition and the presence of potentially fluorescent additives, which render the detection of the weaker intensity bands definitive of the Fe-gallotannate complexation to be recognised.25,26 Hence, a survey of the previous literature reveals that the presence of iron gall inks

Figure 1.1  Raman  spectral stack plot of carbon black ink from four manuscripts:

(i) AMS2, 1631–1635 AD; (ii) AMS4,1697–1711 AD; (iii) AMS6, 1668– 1680 AD; (iv) AMS10, 1726–1747 AD, all from the collection at Santo Domingo de Silos Monastery, Castile y Leon, Spain. All spectra show the characteristic D and G bands of carbon near 1320 and 1600 cm−1. Three different sources for the carbon used in the manufacture of the inks are indicated. Reproduced with permission from ref. 30, Copyright 2016 The Author(s).

View Online

Published on 26 October 2018 on https://pubs.rsc.org | doi:10.1039/9781788013475-00001

8

Chapter 1

is inferred by the absence of carbon signatures, as defined above, and vice versa. Generally, too, unless special care is taken with the choice of laser excitation, the onset of background spectral emission from the inked areas on a potentially degraded manuscript with visible laser wavelengths can result in rather broad ill-defined carbon signatures situated on a larger than expected broadband emission background, so making these carbon signatures rather difficult to observe anyway! It is dangerous to assume that because carbon signals are noted from a manuscript ink, the absence of an iron gall component may be inferred. As will be seen in an example given below, the spectrum of an ancient manuscript demonstrates the presence of a mixture of carbon and iron gall, and iron gall and logwood extracts in the same inked script!

1.3  Case Studies As an illustration of the information that can be deduced from the ink analysis of ancient manuscripts and works of art, three case studies will now be presented here:    1. The Vinland Map. 2. The Voynich Manuscript. 3. The Beato de Valcavado manuscript.    The Vinland Map and the Voynich Manuscript are two important and highly controversial manuscripts purporting to be from the 15th century. One of these, the Vinland Map, possesses only black ink on two sheets of vellum,5,27 whereas the other, the Voynich Manuscript, is polychrome and comprises 240 sheets of vellum, but again, with only black ink script.28,29 Both manuscripts were discovered in the early-to-mid 20th century with limited historical provenances and have since been the subject of some intense analytical, eschatological and historical research, from which diverse conclusions have been forthcoming. The Beato de Valcavado manuscript is of a Visigothic 10th century origin and, unlike the previous two examples, has an impeccable provenance but still has some surprises in store for the pigments analyst and ink specialist.30 These three examples will now be discussed in more detail.

1.3.1  The Vinland Map The Vinland Map is a vellum map of the Old World (Figure 1.2), measuring approximately 28 × 40 cm, that identifies an area in the Western Atlantic, Vinilanda Insula, the so-called Vinland of Scandinavian Viking folklore, showing an area to the north-east of North America, described thereon as “a new and fertile land to the west”. It first appeared in 1957 bound together with a manuscript known as the Tartar Relation (the Historia Tartarorum), which had an unusual composition of vellum and paper, two leaves of vellum

View Online

Published on 26 October 2018 on https://pubs.rsc.org | doi:10.1039/9781788013475-00001

Analytical Raman Spectroscopy of Inks

9

Figure 1.2  The  Vinland Map. Reproduced with permission from Beinecke Rare Book & Manuscript Library. Yale University.

alternating with six of paper, the latter exhibiting bulls' head watermarks, which were identifiable with the Basle Council of the 1430 s. The cartographic importance of the Vinland Map centred upon its pre-dating the voyage of Christopher Columbus and his epic discovery of the New World in 1492 by approximately 60 years and fed the rumour that Columbus could actually have used such a map based on earlier Viking seafaring exploits, notably those of Leif Ericsson.5 In 1957, the Vinland Map and Tartar Relation were examined by British Museum experts in ancient maps and incunabula.27 The philanthropist Paul Mellon donated them to the Beinecke Rare Book and Manuscript Library in Yale University and in 1972 the Yale University Library commissioned an analysis of the Vinland Map, thereby initiating a controversy which has raged for over 45 years and is still ongoing. The scientific analysis of the Vinland Map opened with a detailed polarised microscopic and X-ray diffraction (XRD) analysis of the inked areas,31 from which Walter McCrone concluded that the presence of anatase in the ink, a polymorphic form of titanium(ii) oxide, dated the map firmly to the 20th century32 indicating the Vinland Map could be a fake.33 Further analyses using scanning electron microscopy and energy-dispersive X-ray (EDX) analysis34,35 determined that the ink was not an iron gallotannate as found on the associated Tartar Relation but was carbon black. The ink and parchment of the Vinland Map were re-analysed36 using proton-induced X-ray emission (PIXE) spectroscopy and yielded results that challenged the conclusion of McCrone.13 Radiocarbon dating of the vellum37 gave a date of 1432 ± 11 ACE, which agreed to within

View Online

Chapter 1

Published on 26 October 2018 on https://pubs.rsc.org | doi:10.1039/9781788013475-00001

10

one standard deviation with the watermarked date on the associated paper in the Tartar Relation. In 2002, a definitive Raman microspectroscopic study by Brown and Clark38 of the Vinland Map was undertaken with 632.8 nm laser excitation. The inked areas were apparently composed of two parts: a yellow line that was strongly adherent to the parchment substrate and an overlaid black line, which showed evidence of severe loss in parts due to the black pigment “flaking off”. Analysis of the black ink gave the characteristic D and G bands for amorphous carbon at 1325 and 1580 cm−1, respectively. The presence of anatase was evident, with characteristic bands at 142 and 398 cm−1 and seems to be indicative of a clever forgery; however, care must be taken as anatase has actually been identified in genuine archaeological artefacts significantly pre-dating its established synthesis in the 20th century.39,40

1.3.2  The Voynich Manuscript In 1912, Wilfrid Voynich revealed the discovery of his eponymous manuscript which apparently dates to the early 15th century: the 240 vellum pages with black script and historiated polychrome figures, now labelled the “World's most mysterious manuscript”, resembles a herbal compilation of botanical medicine and alchemy. An example is shown in Figure 1.3. Believed to be written either in a secret code or in a lost language, the major problem with this manuscript is that it has thus far defied all attempts at translation. The historical provenance of the Voynich Manuscript, like that of the Vinland Map, is steeped in international intrigue.28,29 A recent comprehensive and elegant analysis of the iron gall ink on the Voynich manuscript has been undertaken41 using polarised light microscopy, SEM/EDAXS spectrometry, micro XRD and IR spectroscopy.

Figure 1.3  The  enigmatic Voynich Manuscript. Reproduced with permission from Beinecke Rare Book & Manuscript Library. Yale University.

View Online

Published on 26 October 2018 on https://pubs.rsc.org | doi:10.1039/9781788013475-00001

Analytical Raman Spectroscopy of Inks

11

Unlike the Vinland Map, the Voynich Manuscript is historiated and has the advantage over other inked documents in having the presence of supporting analytical information resulting from the interrogation of the associated pigments to assist in the chronology,42–48 which seems to be scientifically well established and supportive of an assignment of the manuscript to the mediaeval period.

1.3.3  The Beato de Valcavado Manuscript Towards the end of the 8th century, in 776 CE, a monk called Liebana prepared an illuminated manuscript on the Apocalypse of St. John in the monastery of Santo Martin. Although this original is now lost, it generated several commentary texts over the next two or three centuries addressing heretical disputes and the coming of the first Millennium. Some 32 of these so-called Beato manuscripts are known, and the most complete is the Visigothic Beato de Valcavado (the Codex de Valladolid) now in the Biblioteca del Colegio de Santa Cruz, Valladolid, in Castile y Leon, Spain, which was completed in 970 and comprises 230 sheets of vellum with 87 historiated miniatures.49 A further five sheets reside in the National Library of Spain, detailing the genealogy of Christ. This Beato is unique among the contemporary Beato copies in that it contains the signature of its author and the dates of its commencement and completion, namely the 8th June and the 9th of September, 970; in addition to its very high quality, it is unique eschatologically in that it is identifiable as the work of the single scribe, Obeco. A Raman spectroscopic study of this Beato de Valcavado was undertaken30 and several important pigments were identified from the historiated scenes: of particular relevance here, is that iron gall ink has been used not only for the script but as a black pigment in the historiated scenes; not carbon black as suspected. In another specimen from a comparative 10th century Beato from the Najera monastery, now in Santo Domingo de Silos, iron gall ink was found in the admixture with the bright red mineral cinnabar, mercury(ii) sulfide, to produce a dark red colour. Later manuscripts from the collection50 in the Santo Domingo Monastery in Silos dating from 17th century exhibited mixtures of iron gall ink and carbon black in their black pigmentation. An interesting Raman spectroscopic study of carbon black inks on several of these manuscripts held in the same collection as the Beato de Valcavado manuscript in the Monastery of Santo Domingo de Silos shows, firstly, the confirmation of their assignment as carbon-based inks and, secondly, information about the possible sourcing of the carbon from which the inks were made. All spectra show the characteristically broad D and G bands of amorphous carbon peaking around 1320 and 1590 cm−1. A spectral stack plot of four manuscripts from the Santo Domingo de Silos collection, comprising AMS2 from the 17th century, AMS4 from the 17th and 18th Centuries, AMS 6 from the 17th century and AMS10 from the 18th century. The spectra of AMS 2 and AMS4 have D and G bands at 1318 ± 2 and 1591 cm−1, indicative of a bone or ivory black, but the absence of the phosphate band

View Online

Chapter 1

Published on 26 October 2018 on https://pubs.rsc.org | doi:10.1039/9781788013475-00001

12

Figure 1.4  Iron  gall ink: Raman spectrum excited at 785 nm. Reproduced with permission from ref. 30, Copyright 2016 The Author(s).

at 960 should be noted, ascribed to the excitation wavelength of 785 nm used here.51 AMS6 has a pronounced high wavenumber shoulder at 1608 cm−1 on the G band centred at 1578 cm−1 and a lower D band centred at 1308 cm−1, indicative of a charcoal produced using a resinous material, and a higher relative band intensity for the G band over the D band. Finally, AMS10 shows a G band at 1601 cm−1 and a D band at 1316 cm−1 with similar relative intensity to that for AMS2, indicating a soot-based carbon source based on “black chalk”. In contrast, the Raman spectrum of iron gall ink from the manuscript collection and the 10th century Beato de Valcavado is shown in Figure 1.4: characteristic Raman signature bands of iron gall ink are found at 1577 mw broad, 1480 s broad, 1424 mw shoulder, 1341 m broad, 937 w, 774 w, 705 w, 614/550 m broad, 402 w, all in cm−1. The band at 1341 varies in wavenumber25,26,30 between 1350 and 1310, whilst that at 614/550 can vary between 640 and 490 cm−1.

1.4  Conclusion The identification of and analytical discrimination between ancient inks and the recognition of the corrosive nature of iron gallotannate inks is now well documented,52,53 but the dating of specimen manuscripts with any precision is still generally not feasible solely by examination of the ink composition alone. The consideration of associated information from radiocarbon dating of the manuscript substrates, eschatology, lexicography and chronological placement of historiated pigments materially assists in the verification of the antiquity of a manuscript. Analytical spectroscopy has demonstrated the novel presence of iron gall inks in an admixture with other inks such as carbon black and logwoods often in the same manuscript, reinforcing the tenet that it is not simply an either/or choice but perhaps reflects the availability of the inks available to the scribes at that time and their experience

View Online

Analytical Raman Spectroscopy of Inks

13

Published on 26 October 2018 on https://pubs.rsc.org | doi:10.1039/9781788013475-00001

of temporary shortages. Finally, the use of iron gall ink as a black pigment for the historiation of written scripts alongside the more usual mediaeval pigments and even in an admixture with them is also recorded analytically.

References 1. J. C. Thompson, Manuscript Inks: A Personal Exploration of Materials and Modes, Caber Press, Portland, Oregon USA, 1996. 2. R. L. Brunelli and K. R. Crawford, Advances in the Forensic Analysis and Dating of Writing Ink, C.C. Thomas Publications, Springfield, Massachusetts, USA, 2003. 3. P. Cradock, Scientific Investigation of Copies, Fakes and Forgeries, Elsevier Butterworth-Heinemann, Oxford, 2009. 4. H. G. M. Edwards, Ancient inks: a forensic historical perspective, in Encyclopaedia of Scientific Dating Methods, ed. W. J. Rink, J. Thompson, A. J. T. Jull, J. B. Paces and L. Heamann, Springer, Heidelberg, Germany, 2015, pp. 48–52. 5. K. A. Seaver, Maps, Myths and Men, Stanford University Press, Stanford, 2004. 6. M. Aceto, A. Agostino, E. Boccaleri and A. C. Garlanda, X-Ray Spectrom., 2008, 37, 286. 7. D. V. Thompson, Materials and Techniques of Mediaeval Painting, Dover Publications, New York, 1956. 8. E. W. Zimmermann, Iron gallate inks–liquid and powder, J. Res. Natl. Bur. Stand., 1935, 15, 35. 9. B. Reissland and S. de Groot, Ink corrosion: comparison of currently used aqueous treatments for paper objects, in 9th Ink Congress of IADA, 1999, p. 121. 10. B. Reissland, Iron gall ink corrosion – progress in visible degradation, in Contributions to Conservation, ed. J. A. Mesh and N. H. Tennent, James & James, London, 2002, p. 113. 11. V. Rouchon-Quillet, J. Bernard, A. Wattiaux and L. Fournes, Appl. Phys., 2004, 79, 389. 12. W. J. Barrow, Manuscripts and Documents: Their Deterioration and Restoration, University of Virginia Press, Charlottesville, USA, 1972. 13. E. Delage, M. Grange, B. Kusko and E. Menei, Rev. Egyptol., 1990, 41, 213. 14. K. Proost, K. Janssens, B. Wagner, E. Bulska and M. Schreiner, Nucl. Instrum. Methods Phys. Res. B, 2004, 213, 723. 15. E. Bulska and B. Wagner, The study of ancient manuscripts exposed to iron-gall ink corrosion, in Non-Destructive Micro-Analysis of Cultural Heritage Materials, ed. K. Janssens and R. van Grieken, Elsevier, Dordrecht, The Netherlands, 2004, ch. 17. 16. M. de Pas and F. Flieder, History and prospects for black manuscript inks, in Conservation and Restoration of Pictorial Art, ed. N. Broumelle and P. Smith, Butterworths, London, 1976. 17. D. Lee, Nature's Palette: The Science of Plant Color, University of Chicago Press Chicago, 2007.

View Online

Published on 26 October 2018 on https://pubs.rsc.org | doi:10.1039/9781788013475-00001

14

Chapter 1

18. P. Ball, Bright Earth: The Invention of Colour, Viking/Penguin Books, London, 2001. 19. G. M. la Porte and J. C. Stephens, Analytical techniques used for the forensic examination of writing and printing inks, in Forensic Chemistry Handbook, ed. L. Kobilinskiy, J. Wiley & Sons, New Jersey, USA, 2012, pp. 225–248. 20. J. Senvaitiene, A. Beganskiene, S. Tautkus, A. Padarauskas and A. Kareiva, Chemija, 2005, 16, 34. 21. M. Bicchieri, M. Monti, G. Piantanida and A. Solo, J. Raman Spectrosc., 2008, 39, 1074. 22. S. A. Centeno, P. Ropret, E. Del Federico, J. Shamir, B. Itin and A. Jerschou, J. Raman Spectrosc., 2010, 41, 445. 23. S. A. Centeno, M. Bronzato, P. Ropret, A. Zoleo, A. Verzo, S. Bognalli and D. Badorco, J. Raman Spectrosc., 2016, 47, 1422. 24. H. G. M. Edwards, Swansea and Nantgarw Porcelains: A Scientific Reappraisal, Springer, Dordrecht, The Netherlands, 2017. 25. A. S. Lee, P. J. Mahon and D. Creagh, Vib. Spectrosc., 2006, 41, 170. 26. A. S. Lee, V. Otieno-Alego and D. Creagh, J. Raman Spectrosc., 2008, 39, 1079. 27. R. A. Skelton, T. Manston and G. D. Painter, The Vinland Map and the Tartar Relation, Yale University Press, New Haven, Connecticut, USA, 1965. 28. G. Kennedy and R. Churchill, The Voynich Manuscript: The Unsolved Riddle of an Extraordinary Book Which Has Defied Interpretation for Centuries, Orion Books, London, 2004. 29. M. E. D'Imperio, The Voynich Manuscript: An Elegant Enigma, CreateSpace Independent Publishing Platform, 2012. 30. E. A. Carter, F. Rull Perez, J. M. Garcia and H. G. M. Edwards, Philos. Trans. R. Soc., 2016, 374, 20160041. 31. W. C. McCrone and L. B. McCrone, Geogr. J., 1974, 140, 212. 32. R. L. Gettens and G. L. Stout, Painting Materials: A Short Encyclopaedia, D. Van Nostrand, New York, 1942. 33. A. D. Baynes-Cope, Geogr. J., 1974, 140, 208. 34. W. C. McCrone, Anal. Chem., 1988, 60, 1009. 35. W. C. McCrone, Microscope, 1999, 47, 71. 36. T. A. Cahill, R. N. Schwab, B. H. Kusko, R. A. Eldred, G. Moeller, D. Dutshke and D. L. Wick, Anal. Chem., 1987, 59, 829. 37. D. H. Donahue, J. S. Olin and G. Harbottle, Radiocarbon, 2002, 44, 45. 38. K. L. Brown and R. J. H. Clark, Anal. Chem., 2002, 74, 3658. 39. H. G. M. Edwards, N. F. Nik Hassan and P. S. Middleton, Anal. Bioanal. Chem., 2006, 384, 1356. 40. H. G. M. Edwards, P. S. Middleton and J. Wild, A Roman Paint Pot from Castor, Normangate Field, and its Contents, in An Archaeological Miscellany: Papers in Honour of K.F. Hartley, ed. G. B. Dannell and P. V. Irving, Journal of Roman Pottery Studies, Oxbow Publishing, Oxford, 2006, vol. 12, pp. 204–208.

View Online

Published on 26 October 2018 on https://pubs.rsc.org | doi:10.1039/9781788013475-00001

Analytical Raman Spectroscopy of Inks

15

41. J. G. Barabe, Materials Analysis of the Vinland Map: A Report to the Curator of Modern European Books and Manuscripts, Beinecke Rare Book & Manuscripts Library, Yale University, USA, 2009, pp. 1–6. 42. P. Birren, History of Colour in Painting, Van Nostrand/Reinhold, New York, 1965. 43. Artists' Pigments: A Handbook of Their History and Characteristics, ed. R. L. Feller, National Gallery of Art, Washington, and Oxford University Press, Oxford and New York, 1966, vol. 1. 44. Artists' Pigments: A Handbook of Their History and Characteristics, ed. A. Roy, National Gallery of Art, Washington, and Oxford University Press, Oxford and New York, 1993, vol. 2. 45. Artists' Pigments: A Handbook of Their History and Characteristics, ed. E. W. Fitzhugh, National Gallery of Art, Washington, and Oxford University Press, Oxford and New York, 1997, vol. 3. 46. Artists' Pigments: A Handbook of Their History and Characteristics, ed. B. H. Berrie, National Gallery of Art, Washington, and Oxford University Press, Oxford and New York, 2007, vol. 4. 47. N. Eastaugh, V. Walsh, T. Chaplin and R. Siddall, Pigment Compendium: A Dictionary of Historical Pigments, Elsevier Butterworth-Heinemann, Oxford, 2004. 48. R. L. Harley, Artists' Pigments, 1600-1835, Butterworths Scientific, London, 1982. 49. J. M. Ruiz Asencio, El Codice del Beato de Valcavado, Valladolid, Spain, University of Valladolid Press, Valladolid, Spain, 1993. 50. A. Boylan, The Library at Santo Domingo de Silos and its catalogues, XI-XVIIIth centuries, Rev. Mabillon, 1992, 3, 59. 51. A. Coccato, J. Jehlicka, L. Moens and P. Vandenabeele, J. Raman Spectrosc., 2015, 46, 1003. 52. K. D. Charlton, A. E. Smith and D. M. Goltz, Anal. Lett., 2009, 42, 2533. 53. D. M. Goltz, Anal. Lett., 2012, 45, 314.

Published on 26 October 2018 on https://pubs.rsc.org | doi:10.1039/9781788013475-00016

Chapter 2

Raman Spectroscopic Analysis of Romano-British Wall Paintings: A Comparison Between Geographically Different Sites at the Northern Fringe of the Roman Empire Howell G. M. Edwards*a, Rebecca Widdowsona and Jennifer Proctorb a

School of Chemistry and Biosciences, Faculty of Life Sciences, University of Bradford, Bradford, BD7 1DP, UK; bPost-Excavation Manager, Pre-Construct Archaeology Ltd., Unit 19A, Tursdale Business Park, Durham, DH6 5PG, UK *E-mail: [email protected]

2.1  Introduction The Roman conquest of Britannia commenced in 43 AD, following the initial invasions of Julius Caesar in 55 BC, with a force of four legions (II, IX, XV and XX) under Emperor Claudius commanded by General Aulus Plautius. The invasion force departed Boulogne and established an initial beachhead in the South, probably near Rochester in Kent, and expanded outwards into major fortifications at Colchester (Camulodunum), London (Londinium)   Raman Spectroscopy in Archaeology and Art History Volume 2 Edited by Peter Vandenabeele and Howell Edwards © The Royal Society of Chemistry 2019 Published by the Royal Society of Chemistry, www.rsc.org

16

View Online

Published on 26 October 2018 on https://pubs.rsc.org | doi:10.1039/9781788013475-00016

Raman Spectroscopic Analysis of Romano-British Wall Paintings:

17

and St Albans (Verulamium). There followed an intense period of military activity but stability was not achieved for many years; indeed, the Boudiccan Revolt of 60/61 AD with attacks of the Iceni on these Roman garrisons came close to repulsing the invaders.1,2 In the following two centuries, the Roman legions moved North and West to establish forts such as those at Chester (Deva), Caerleon (Isca Augusta) and York (Eboracum), linked in a communications system with roads such as Ermine Street, Watling Street, Dere Street and the Fosse Way. During this period, three phases of Roman occupation in Britain have been identified, namely, military, colonisation and settlement, as the stabilisation and integration of the Romano-British community increased.3,4 Close to large cities in the Roman Empire, Roman villas were lavish buildings and were designed to impress visitors with the wealth and social standing of their owners; however, the situation at the far reaches of the Empire was necessarily more functional in that the villa often served as the focus of a farming estate that relied upon the protection afforded by the occupying army. Nevertheless, the grandness of the villa still defined the personal wealth and stability of the local community.5,6 Although there is no definitive Romano-British art style resulting from the fusion of the ancient Celtic and incoming Roman traditions, a common theme in Romano-British wall paintings was believed to have been the use of a rather simple palette based on locally sourced pigments wherever possible. We have studied hitherto wall painting fragments from several Romano-British villa sites in the South of the country from the 1st to the 4th centuries and have characterised by Raman spectroscopy the pigments involved in the three occupational phases3,6,7 identified above. As anticipated, the earliest military phase involved the use of locally sourced pigments only, but as the society stabilised the importation of pigments from other geographical sources became evident; for example, cinnabar and lapis lazuli, two very desirable and expensive pigments (sourced probably from Spain and Afghanistan) were found in villas belonging to the settlement stage, reflecting the greater economic prosperity and social stability of that area of Roman Britain at that time.6,7 The presence of the rare form of natural haematite, caput mortuum, was identified in a Romano-British villa of this period,8 which has been noted in only some 1% of Roman villas in Europe, several of these being prestigious sites in Pompeii and Herculaneum5 – and to find this mineral in a wall painting in a villa near the fringe of the Roman Empire was indeed significant historically. Previous Raman spectroscopic studies of Roman wall-paintings have also provided novel information about the technologies employed for pigment and substrate preparation, especially regarding pigment mixtures and the use of limewash putty as a wall painting substrate, reinforcing the textual descriptions of Roman authors and subsequent art historians.3,6–10 The Roman army had advanced northwards and conquered the Brigantes by early AD 70s, although the land had not yet been consolidated by the construction of the full network of forts. Major forts were established at

View Online

Published on 26 October 2018 on https://pubs.rsc.org | doi:10.1039/9781788013475-00016

18

Chapter 2

Carlisle and Red House, Corbridge in the early 70s and these were supplemented by others, such as Vindolanda, along the Tyne–Solway isthmus. Agricola (AD 77–83) began his governorship by completing the fort-building programme and extended his activities beyond the Tyne–Solway isthmus.11 The main route into northern Britain, Dere Street, was established along the eastern side of the country and forts were built along its line in the Flavian period in County Durham at Ebchester and Binchester.12–14 The strategic importance of the crossing of the River Tees by Dere Street suggests that there was probably a fort of Flavian date at Piercebridge, although the location of a fort of this early date has never been identified.15 A fort was established in the Flavian period at Catterick, 15 km south of the Tees crossing, and an associated roadside settlement may have been established as early as the AD 80s.16 Another important north–south supply route led from Brough-on-Humber to the fort at Newcastle passing through the Tees lowlands. The northernmost segment is known as Cade's Road and although its date of origin is unknown, it is likely to have been in existence by the earlier Hadrianic period17 (Bidwell and Hodgson 2009, Fig. 5 and 14). Construction of Hadrian's Wall along the Tyne–Solway isthmus began in AD 122 and was almost complete when it was largely abandoned by early AD 140s and the frontier moved north to the Forth–Clyde isthmus. A fort was established between Ebchester and Binchester at Lanchester on Dere Street in the Antonine period and Binchester was reoccupied ca. AD 150.12,13 The Antonine Wall was abandoned ca. AD 158–163 and Hadrian's Wall was re-established as the northern frontier.11,18 By AD 160 a large fort had been established at Catterick and associated with this was a large civilian town and roadside settlement, which extended for at least 4 km along Dere Street.16 A thriving civilian community was also in existence at Piercebridge by the 1st century; a huge increase in activity ca. AD 170–180 including a settlement south of the river suggests the arrival of a military unit, but a fort of this date has not been discovered.15 Unrest came to the northern frontier in the late 2nd century AD and major rebuilding work took place along Hadrian's Wall and the hinterland forts in the Severan period and into the 3rd century. Following the Severan campaigns into Scotland in the early 3rd century, a long period of stability was established on the northern frontier lasting throughout that century.1 The 4th century saw a return of unrest on the northern frontier with attacks by the Picts culminating in the “Barbarian Conspiracy” of AD 367. There is little archaeological evidence to suggest the destruction of Wall forts at this time, but the rebuilding of several forts took place in the late 4th century.19 Recently, an opportunity has been presented for the undertaking of a Raman spectroscopic analysis of wall painting fragments from four sites situated in the northern frontier zone; three in the Tees Valley ca. 50 km to the south of Hadrian's wall, and one just 20 km from the frontier. The network of forts in this frontier zone with their associated civilian settlements were occupied throughout the Roman period. This area had long been characterised as a landscape populated by native homesteads and Roman military

View Online

Published on 26 October 2018 on https://pubs.rsc.org | doi:10.1039/9781788013475-00016

Raman Spectroscopic Analysis of Romano-British Wall Paintings:

19

sites where the negative impact of the Roman army resulted in an absence of “Romanisation” amongst the local population.20 Recent excavations and reappraisals of earlier investigations are, however, providing a very different picture and it appears that the roads, towns and forts brought new opportunities to some local populations.21 Investigations at Quarry Farm, Ingleby Barwick, on the southern banks of the River Tees in 1997–2000 explored an Iron Age settlement which developed into a villa complex in the 2nd century with occupation continuing until at least the late 4th century.22 The main villa building was preserved in situ but a large aisled structure and a small one-roomed bathhouse which functioned as a caldarium was excavated. At Chapel House Farm, Dalton on Tees, a programme of field walking, geophysical survey and limited excavation at the site in 1996–1997 recorded a simple winged corridor villa and a large aisled building.23 Three apses at the back of the aisled building had walls decorated with painted plaster and a painted concrete floor; samples from the walls were analysed. At the time of writing full analysis of the artefactual material had not been undertaken, but the pottery assemblage indicates that the settlement had Late Iron Age origins and was occupied into the late 4th century. At Holme House, on the south banks of the Tees, opposite the location of where Piercebridge fort was to be built, excavation in 1969–1970 revealed a simple “cottage house” constructed within an Iron Age enclosure.24 The date of origin of this villa was not established, but it was enlarged in the Antonine period with a bath suite and apsidal suite containing heated dining and reception rooms; painted plaster from these structures was analysed. Occupation at this villa was relatively short-lived, ending by AD 180. An unenclosed settlement established at Faverdale, located 4 km north of the River Tees, in the 1st century AD, was succeeded by a large habitation enclosure set within an extensive network of enclosures occupied throughout the 2nd century.25 Plough truncation of the interior of the enclosure had removed all traces of structures, with the exception of a small two-roomed stone bathhouse which had been decorated with painted wall plaster, samples of which were submitted for analysis. The plan and form of the structure indicated that it had functioned as a small steam room with vestibule. Following a hiatus of occupation in the 3rd century within the excavated area, late 4th century activity was recorded. At East Park, Sedgefield, ca. 20 km north of the River Tees and ca. 35 km south of Hadrian's Wall, an extensive roadside settlement which seems to have been established ca. AD 120 has been identified by geophysical survey and smallscale excavation.13 Such a roadside settlement, commonplace further south, is the first to be discovered in the hinterland of the Wall and was evidently inhabited by the indigenous population and not established through military intervention.12,13 Another possible villa site may have been located at Old Durham on the south side of the River Wear, to date the most northerly in Britain just 20 km south of Hadrian's Wall. A small bathhouse was excavated here in the 1940s following its discovery during gravel quarrying; no associated dwelling was discovered and it is interpreted as a detached bathhouse probably constructed by the 2nd century with occupation at the site

View Online

Chapter 2

20

Published on 26 October 2018 on https://pubs.rsc.org | doi:10.1039/9781788013475-00016

26

continuing into the 4th century. The bathhouses had a vestibule, laconium, caldarium and cold bath. Painted wall plaster recovered from demolition deposits in the hypocaust of the caldarium was submitted for analysis. Like the settlements investigated more recently in the Tees Valley, Old Durham may also have its origins as a Late Iron Age/early Roman period ditched enclosure, as indicated by elements of a large ditch encountered at a few locations at the site. The picture that is now emerging from rural settlements in the frontier zone south of Hadrian's Wall is that some members of the indigenous population had much greater levels of contact with the Roman military and the associated extra-mural settlements attached to the forts. The presence of the Roman military obviously had a major impact on the economy of the region, however, some settlements were evidently benefiting from this military occupation. These sites were evidently able to generate surplus agricultural products, both arable produce and animals, and were engaged in trade at some level with the Roman military and associated settlements enabling them to acquire items of Roman material culture such as pottery and jewellery and construct Roman style buildings. The cost of these structures would not just have been in the materials required such as box flue tiles, but in the specialised labour needed for aspects such as the painted walls. The evidence from these settlements indicates that their inhabitants apparently selected, rejected and hybridised Roman material culture and elements of a Roman lifestyle that were available to them in this frontier zone, whilst maintaining certain aspects of their own traditions.25 Thus, at Faverdale, large quantities of local handmade pots continued to be produced, but alongside the traditional jar forms, pots imitating Roman forms were also manufactured and fine ware pots produced in Roman Britain and across the empire were acquired. The small heated buildings associated with some of these settlements also appear to be a local adaptation of the Roman bathhouse. It is of considerable interest therefore to evaluate the strategy that may have been adopted for the decoration of buildings at these four sites, which were located within the hinterland of the frontier, and to compare this with the situation that pertained in the south of the country at that time. Painted plaster from these four sites were selected as described below and we sought any special technologies or usage of pigments that may reflect their location at the extreme fringe of the Roman Empire.

2.2  Experimental 2.2.1  Villa Sites and Samples The four sites from which the specimens were selected for analysis were as follows: Faverdale East, Darlington (FAV), excavated in 2004 (J. Proctor), six specimens. The site was established in the 1st century AD. In the 2nd century a

View Online

Published on 26 October 2018 on https://pubs.rsc.org | doi:10.1039/9781788013475-00016

Raman Spectroscopic Analysis of Romano-British Wall Paintings:

21

large habitation enclosure established with a small heated building inside set within an extensive network of enclosures, seemingly abandoned in the 3rd century with 4th century reoccupation. There are pottery remains and evidence of metal working on site. Holme House, Piercebridge (HOL), excavated in 1969–1970 (D. W. Harding and P. R. Scott), 11 specimens now in the Bowes Museum, Barnard Castle. Occupation phases have been identified from the Iron Age to the 4th century AD – the villa was aggrandised in the mid-2nd Century and then abandoned. This was the second most northerly villa found in the Roman Empire. The most interesting accumulation of wall painting debris occurred in the bath house and apsidal suites of the villa and comprised geometrical shapes and patterns in mottled red and black and remains of human figures. Chapel House Farm, Dalton-on-Tees (DOT), excavated in 1996–1997 (J. Brown), nine specimens; from apsidal rooms of an aisled building, a high status, classic winged corridor villa, measuring 30 m by 17 m, with a suggestion of late occupation into the 4th century AD. Old Durham (OLD), Shincliffe Bridge, Durham, excavated in 1941–1943 (Rev. T. Romans and R. P. Wright), seven specimens. This is the most northerly villa known in the Roman Empire. All sites were contained (Figure 2.1) within a 20 km2 area in the North of England and located 25–50 km from Hadrian's Wall, a defensive fortification at the limit of the Roman army's occupation of Britannia. Of the 184 available specimens of wall painting fragments unearthed archaeologically in total from these four sites, a total of 33 specimens of wall painting fragments were selected for analysis by Raman spectroscopy. The colour palette exhibited in these selected specimens is tabulated in Table 2.1.

2.2.2  Raman Spectroscopy Specimens were analysed using a Bruker IFS 66/FRA 106 FT Raman spectrometer operating in macro mode with Nd3+/YAG laser excitation at 1064 nm, with the accumulation of 500 spectral scans obtained with a spectral resolution of 4 cm−1 over a wavenumber range of −3500 cm−1 from a sample footprint of 100 microns in diameter. A Renishaw In Via confocal microscope was also employed using 785 nm excitation, with 16 spectral accumulations obtained with a spectral resolution of 2 cm−1 using a 50× lens objective giving a sample footprint of about 2 microns in diameter over a wavenumber range of 200–3500 cm−1. Particularly useful analytical information emerges from the Raman spectroscopic interrogation of wall-painting substrates in that it is possible to discriminate molecularly between Roman plasters that have been derived from the use of limewash putties based upon limestone (calcite, chalk), seashells or corals (aragonite) and dolomitic limestone or magnesite (calcium magnesium carbonate, magnesium carbonate and hydromagnesite).

View Online

Chapter 2

Published on 26 October 2018 on https://pubs.rsc.org | doi:10.1039/9781788013475-00016

22

Figure 2.1  Location  map of the Roman villas studied showing their proximity to Hadrian's Wall, the defensive northern limit of the Roman Empire. Reproduced with permission from ref. 25 with permission from Pre-Construct Archaeology.

The spectral signature of calcium hydroxide in calcined and moistened limewash putty appears as a very broad electronic transition band centred at 790 cm−1 in the Raman spectrum excited with near infrared radiation at 1064 nm. Incomplete conversion of the sourced limestone variant upon

View Online

Raman Spectroscopic Analysis of Romano-British Wall Paintings:

23

Published on 26 October 2018 on https://pubs.rsc.org | doi:10.1039/9781788013475-00016

Table 2.1  Distribution  of specimens and associated pigments.

Red White Green Yellow Orange Black Pink Brown Blue Grey

Faverdale (FOV)

Holme House (HOL)

Dalton-on-Tees (DOT)

Old Durham (OLD)

X X X X X X x

X X X X

X X X X X

X X X X

X X x

X X x

X

Figure 2.2  Raman  spectral stack plot of calcite and aragonite, indicating the discrimination possible between these two white pigments, which are both chemically calcium carbonate, CaCO3.

calcination leaves residual signatures of the mineral carbonate used, which can be differentiated in the observed Raman spectra, an example of which is shown in Figure 2.2 (bearing a stack plot of the Raman spectra of calcium carbonate and aragonite). Since calcite and aragonite both have a carbonate ion stretching band at 1086 cm−1, dolomite at 1094 cm−1 and magnesite at 1112 cm−1; calcite and aragonite can be distinguished from each other by the presence of bands at 712 and 283 cm−1 in the former and 713 and 203 cm−1 in the latter.27 On reaction of the moist limewash putty with atmospheric carbon dioxide, the formation of calcite occurs, but the conversion is only partial28 and the resulting spectrum generally shows evidence for both the

View Online

Chapter 2

Published on 26 October 2018 on https://pubs.rsc.org | doi:10.1039/9781788013475-00016

24

Figure 2.3  Raman  spectrum of haematite in a Romano-British wall painting, indi-

cating that the pigment used was reasonably crystalline from the narrow bandwidths of the Raman signals.

original putty and calcite together (Figure 2.3). This extent of this conversion is dependent upon the dampness of the depositional environment and the protection afforded by the outer skin of hardened calcite formed, which limits the accessibility of atmospheric carbon dioxide to the inner regions of unconverted lime.

2.3  Results and Discussion The distribution of specimens and their associated pigments is presented in Table 2.1; although the palette is perceived to be rather simple21 (A. Barbet, 1990), the distribution of colours used in the wall paintings is very diverse. Only red, white, green and yellow are common to all the sites studied here. As expected for such a palette, the red colour is obtained from haematite (Figure 2.3), the yellow from goethite (Figure 2.4, yellow ochre), white from calcite and green from terre verte; this complies with the findings from other Romano-British villa sites, but differs in that there is no evidence at all in our spectra for the use of more exotic and imported colours such as cinnabar, orpiment, lead white, lapis lazuli, verdigris and malachite, which have been identified at other sites. The most common colour is red, which is found in 28 of the 33 samples analysed. As expected perhaps from the most ubiquitous mineral found in rock art, frescoes and wall-paintings over the ages,29–31 red ochre has been generically applied to describe this colour32,33 but some care needs to be applied in this terminology since it is possible to differentiate analytically between the

View Online

Published on 26 October 2018 on https://pubs.rsc.org | doi:10.1039/9781788013475-00016

Raman Spectroscopic Analysis of Romano-British Wall Paintings:

25

Figure 2.4  Raman  spectrum of goethite in a Romano-British wall painting, an

iron(iii) oxide hydroxide and yellow pigment, which is converted thermally to haematite.

parent mineral haematite, hydrated iron(iii) oxide, and its admixture with clays and sand, or even calcite and limewash. In some cases, the haematite component of a red ochre may have been prepared from heating goethite,34,35 a hydrated iron(iii) oxyhydroxide, FeO(OH). xH2O, to a temperature in excess of 300 °C. Clearly, it is important to be able to differentiate analytically a “red ochre”, which has been produced historically using a technological process such as heating or mechanical mixing and grinding, with that of a pure mineral form of haematite. This is especially relevant for pigment production where the particle size achieved by grinding the raw mineral can have a significant effect upon the resultant colour. A very good example of this can be seen in the red ochres sourced from the ancient Clearwell Caves site in the UK,36 where a range of reds through to a purple colour have been analysed using Raman spectroscopy and other techniques to demonstrate conclusively that the same original mineral haematite was used.37 All colour hues were achieved with different particle sizes and degrees of grinding. This is also manifest in our studies of the Romano-British villas, where we observe the sole use of mineral haematite and through its admixture with fine quartz sand, limewash and calcite. A particularly relevant discovery found only in the Faversdale villa is a mixture of haematite and aragonite, a polymorph of calcium carbonate found in the shells of marine animals and corals. We have not seen evidence of

View Online

Published on 26 October 2018 on https://pubs.rsc.org | doi:10.1039/9781788013475-00016

26

Chapter 2

this reported in Roman wall paintings hitherto and its location at this site must be related to the presence of molluscs that the local inhabitants were able to acquire. The colours orange, black, pink, brown, blue and grey are not found at every site – but, where analysed, these pigments seem to be readily available on a local basis; black is achieved through use of amorphous carbon of vegetable origin rather than bone black obtained from calcined bones or ivory, grey through the admixture of carbon black and calcite, orange is a mixture of goethite and haematite, which could possibly have been achieved through the heating of goethite at a temperature in excess of 300 °C until the desired hue was achieved, pink is achieved through the admixture of calcite and haematite, brown through the admixture of haematite and carbon and blue through the use of azurite, a basic copper carbonate. Other villa sites have demonstrated a wider use of pigments such as orpiment, realgar, pararealgar, malachite, hydrocerussite, pyrolusite and lapis lazuli,5 which could possibly reflect the greater availability of these minerals to painters located in more stable environments. Despite this, some unusual features can be derived from the Raman spectra which are worthy of note; in particular, FAV 094 has a pink painted area which demonstrates the Raman bands for aragonite and haematite. This discovery generates the question as to the origin of this calcium carbonate polymorph source for white pigment – oyster, mussel and cockle shells were found at the site and clearly this marine source could provide the necessary base for grinding to produce the pigment mixture. At this site it should be noted that the limewash putty is probably composed solely of calcined limestone and there is no evidence of aragonite residues remaining through incomplete thermal conversion in the production of the lime, as has been noted in other cultures.38 Hence, we can exclude the presence of aragonite arising from its incorporation into a calcined lime production for substrate preparation and we therefore maintain that its discovery in the pigment mixture must occur as a result of deliberate inclusion by the artist, possibly to give a special tone or finish to the intended pink colour. The specimen HOL 100 has a yellow pigment that analyses reveal to be massicot (Figure 2.5), a lead(ii) oxide that was in use in ancient times, and which has been seen before in Roman villa wall paintings in northern Spain39 but has not been recorded hitherto in Romano-British sites. This is the only occasion where this mineral pigment has been identified other than the ubiquitous goethite for provision of a yellow colour in these Roman villa paintings.5 Other comments relate to the use of quartz sand identified in many samples from its Raman signature at 464 cm−1; this has been noted hitherto3,4,6,7 as an additive to aid the grinding of mineral pigments for painting preparation to achieve the desired particle size and hue. The green and blue pigments are uncommonly found at these sites and have been identified here as originating, respectively, from the natural copper containing minerals, terre verte and azurite.40

View Online

Published on 26 October 2018 on https://pubs.rsc.org | doi:10.1039/9781788013475-00016

Raman Spectroscopic Analysis of Romano-British Wall Paintings:

27

Figure 2.5  Raman  spectrum of yellow lead(ii) oxide, massicot, which is different spectrally from the formulaically identical litharge, a red pigment.

2.4  Conclusions The Raman spectroscopic analysis of 33 specimens of Romano-British wall painting fragments from three of the most northerly villa sites and a rural settlement at the fringe of the Roman Empire has revealed several important pieces of information in comparison with other sites that have been examined hitherto:    ●● A simple palette of natural mineral pigments that are available and sourced locally has been used exclusively; there is no evidence for the use of more exotic imported pigments such as cinnabar, lapis lazuli, orpiment, caput mortuum and malachite, which have been noted elsewhere in the southern Roman villa sites. It could be conjectured that this may result from the difficulty in transportation of non-essential items to isolated locations that were subjected to insurrection and periods of social instability, despite the archaeological evidence that these villas were themselves impressive structures. It could also be concluded that these northern villas were predominantly working farmsteads rather than centres of colonial regional government and military importance. ●● The presence of limewash putty substrate is ubiquitous at all sites and the spectra indicate that its conversion to calcite through aerial exposure to carbon dioxide has only been partially accomplished even after almost two millennia; this correlates with our previous spectroscopic studies of archaeological Norman and mediaeval lime mortars. Only limestone has been used in the calcination technology since there is no evidence of the production of calcium oxide and hydroxide for putty preparation from marine mollusc sources despite the archaeological evidence for mussel shell deposits at the Faverdale site.

View Online

Chapter 2

28

Published on 26 October 2018 on https://pubs.rsc.org | doi:10.1039/9781788013475-00016

●●

●●

●●

  

The predominant pigment colour is red, achieved through the use of haematite, either alone or in an admixture with calcite to produce a lighter shade and carbon to produce a darker shade. Out of the 24 red pigmented samples analysed only eight proved to be solely haematite (in the villas at Faverdale and Old Durham) and the rest comprised various admixtures of calcite and haematite to effect colour variations. In one case, at Faverdale, aragonite has been detected in an admixture with haematite to form a pink colour; the source of this marine polymorph of calcium carbonate can be attributed to oyster, mussel and cockle shells that have been found at this site, demonstrating the partiality of the occupants for seafood. We have not discovered this situation elsewhere thus far in Roman Britain. Yellow colours were achieved through the use of goethite, except for one specimen from Holme House villa where massicot was detected; again, this represents the first and only occasion that this has been found in a wall painting in Roman Britain. Preparative technologies are evidenced by the use of admixtures of haematite, carbon and calcite to make a brown colour, goethite and haematite for orange, haematite and calcite or carbon for shades of red, carbon from vegetable sources for black and carbon and calcite for grey. In some cases, particularly at Faverdale, the use of quartz sand to aid the grinding of minerals to produce pigments is evidenced.

References 1. S. S. Frere, Britannia: A History of Roman Britain, Routledge and Kegan Paul, London, 3rd edn, 1987. 2. T. Rice Holmes, Ancient Britain and the Invasions of Julius Caesar, Oxford, University Press, London, 2nd edn, 1936. 3. P. S. Middleton, H. G. M. Edwards and S. E. Jorge Villar, Coloured in Colchester: a Raman spectroscopic study of Romano-British painted wall plaster from the Roman Town of Colchester, in A Victory Celebration: Papers on the Archaeology of Colchester and Late Iron Age –Roman Britain, ed. P. Ottaway, Colchester Archaeological Trust, Colchester, UK, 2006, ch. 6, pp. 69–74, ISBN: 0-89-7719-124. 4. H. G. M. Edwards, P. S. Middleton and M. D. Hargreaves, Spectrochim. Acta, Part A, 2009, 73, 553. 5. H. Bearat, Quelle est la gamme exacte des pigments romains? Confrontation des resultats d'analyse et des textes de Vitruve et de Pline, in Roman Wall Painting: Materials, Technologies, Analysis and Conservation, Proceedings of the International Workshop on Roman Wall Painting, Fribourg, ed. H. Bearat, M. Fuchs, M. Maggetti and D. Pauvier, Institute of Mineralogy and Petrography, Fribourg, Switzerland, 1996, pp. 11–34. 6. H. G. M. Edwards, L. F. C. de Oliveira, P. S. Middleton and R. L. Frost, Analyst, 2002, 127, 277.

View Online

Published on 26 October 2018 on https://pubs.rsc.org | doi:10.1039/9781788013475-00016

Raman Spectroscopic Analysis of Romano-British Wall Paintings:

29

7. H. G. M. Edwards, P. S. Middleton, S. E. Jorge Villar and D. L. A. de Faria, Anal. Chim. Acta, 2003, 484, 211. 8. L. F. C. de Oliveira, H. G. M. Edwards, R. L. Frost, J. T. Klopprogge and P. S. Middleton, Analyst, 2002, 7, 536. 9. Vitruvius, On Architecture in Two Volumes, transl. F. Granger, Loeb Classical Library, Cambridge, Mass., 5th edn, 1985, vol. II. 10. Pliny the Elder, Natural History in Ten Volumes, Books XXXIII-XXXV, transl. H. Rackham, Loeb Classical Library, Cambridge, Mass., 3rd edn, 1968, vol. X. 11. D. J. Breeze and B. Dobson, Hadrian's Wall, Penguin, London, 4th edn, 2000. 12. D. Petts and C. Gerrard, Shared Visions: The North East Regional Research Framework for the Historic Environment, Durham County Council, Durham, 2006. 13. D. Mason, Curr. Archaeol., 2010, 239, 22. 14. I. M. Ferris, The Beautiful Rooms Are Empty: Excavations at Binchester Roman Fort, County Durham 1976–1981 and 1986–1991, Durham County Council, Durham, 2010. 15. Roman Piercebridge: Excavations by D.W. Harding and P.R.Scott, 1969–1981, ed. H. E. M. Cool and D. J. P. Mason, Architectural and Archaeological Society of Durham and Northumberland Research Report Number 7, 2008. 16. P. Wilson, H. E. M. Cool, J. Evans, A. Thompson and J. Wacher, Cataractonium: Roman Catterick and its Hinterland. Excavations and Research 1958–1997, London, CBA Research Report 128, 2002. 17. P. Bidwell and N. Hodgson, The Roman Army in Northern England, The Arbeia Society, Newcastle upon Tyne, 2009. 18. N. Hodgson, Hadrian's Wall 1999–2009, Cumberland and Westmoreland Antiquarian and Archaeological Society and the Society of Antiquaries of Newcastle upon Tyne, Kendal, 2009. 19. D. J. Breeze, The Northern Frontiers of Roman Britain, Batsford, London, 1982. 20. K. Dark and P. Dark, The Landscape of Roman Britain, Sutton Publishing, Gloucester, 1997. 21. A. Smith, M. Allen, T. Brindle and M. Fulford, The Rural Settlement of Roman Britain, Britannia Monographs, Society of the Promotion for Roman Studies, London, 2016, vol. 29. 22. A Roman Villa at the Edge of Empire: Excavations at Ingleby Barwick, Stockton-on-Tees, 2003-04, CBA Research Report 170, ed. S. Willis and P. Carne, CBA, York, 2013. 23. J. Brown, Romano-British Villa Complex, Chapel House Farm, Dalton-onTees, North Yorkshire, Yorkshire Archaeological Society, Roman Antiquities Section, Bulletin No. 16, 1999. 24. D. W. Harding and P. R. Scott, The Holme House Villa, in Roman Piercebridge: Excavations by D.W. Harding and P.R. Scott, 1969–1981, ed. H. E. M. Cool and D. J. P. Mason, Architectural and Archaeological Society of Durham and Northumberland Research Report Number 7, 2008.

View Online

Published on 26 October 2018 on https://pubs.rsc.org | doi:10.1039/9781788013475-00016

30

Chapter 2

25. J. Proctor, Faverdale, Darlington: Excavations at a Major Settlement in the Northern Frontier Zone of Roman Britain, ed. V. Ridgway, Pre-Construct Archaeology Ltd., Darlington, Monograph No. 15, 2012. 26. I. A. Richmond, T. Romans and R. P. Wright, I – A civilian bath house of the Roman Period at Old Durham, Archaeol. Aeliana, 1944, 22, 1–20. 27. H. G. M. Edwards and D. W. Farwell, J. Raman Spectrosc., 2008, 39, 985. 28. J. R. Partington, Textbook of Inorganic Chemistry for University Students, McMillan & Co., London, 1921. 29. E. E. Wreschner, R. Bolton, K. W. Butzer, H. Detporte, A. Hausler, A. Heinrich, A. Jacobson-Widding, T. Malinowski, C. Masset, S. F. Miller, A. Ronen, R. Solecki, P. H. Stephenson, L. L. Thomas and H. Zollinger, Curr. Anthropol., 1980, 21, 631. 30. M. Hyman, S. A. Turpin and M. E. Zolensky, Rock Art Res., 1996, 13, 93. 31. M. P. Pomies, M. Menu and C. Vignaud, Archaeometry, 1999, 41, 275. 32. P. Ball, Bright Earth: The Invention of Colour, Viking-Penguin Group, London, 2001. 33. R. L. Gettens and G. L. Stout, Painting Materials: A Short Encyclopaedia, Dover Books, New York, 1966. 34. D. L. A. de Faria, S. V. Silva and M. T. de Oliveira, J. Raman Spectrosc., 1997, 28, 873. 35. D. Bersani, P. P. Lottici and A. Montenero, J. Raman Spectrosc., 1999, 30, 355. 36. L.-J. R. Marshall, J. R. Williams, M. J. Almond, S. D. M. Atkinson, S. R. Cook, W. Matthews and J. L. Mortimer, Spectrochim. Acta, Part A, 2005, 61, 233. 37. D. Bikiaris, S. Daniilia, S. Sotiropoulou, O. Katsimbiri, E. Pavlidou, A. P. Moutsatsou and Y. Chryssoulakis, Spectrochim. Acta, Part A, 1999, 56, 3. 38. H. G. M. Edwards, D. W. Farwell, D. L. A. de Faria, A. M. F. Monteiro, M. C. Afonso, P. De Blasis and S. Eggers, J. Raman Spectrosc., 2001, 32, 17. 39. S. E. Jorge Villar and H. G. M. Edwards, Anal. Bioanal. Chem., 2005, 382, 283. 40. R. J. H. Clark, Chem. Soc. Rev., 1995, 24, 187.

Published on 26 October 2018 on https://pubs.rsc.org | doi:10.1039/9781788013475-00031

Chapter 3

Evidence of Pentimenti for the Authentication of Paintings: A Challenge for Analytical Science at the Interface with Art History Timothy J. Benoy a, William A. Edwardsa and Howell G. M. Edwards*b a

The de Brécy Trust, de Brécy House, Lammas, Norfolk, NR 10 5JJ, UK; School of Chemistry and Biosciences, Faculty of Life Sciences, University of Bradford, Richmond Road, Bradford, BD7 1DP, UK *E-mail: [email protected]

b

3.1  Introduction The provenancing and authentication of works of art afforded by the complementary combination of scientific analysis and historical research is now well established and several books have addressed the major contributions that the analytical interrogation of artworks have made to specific case studies in a forensic art context.1–7 Much scientific research on oil paintings specifically has concentrated on the characterisation of pigments, varnishes, resins and extenders to facilitate the attribution of the paintings to particular

  Raman Spectroscopy in Archaeology and Art History Volume 2 Edited by Peter Vandenabeele and Howell Edwards © The Royal Society of Chemistry 2019 Published by the Royal Society of Chemistry, www.rsc.org

31

View Online

Published on 26 October 2018 on https://pubs.rsc.org | doi:10.1039/9781788013475-00031

32

Chapter 3

periods and timelines associated with the established usage of pigments and from these studies it has been demonstrated that later copies or fakes can be exposed.8 The presence of synthetic pigments that had not been known at the supposed time of painting was enough to label an art work a fraud and painted with the intent to deceive is now well-established.9 Although scientific analysis alone can rarely identify a particular artist it can be a powerful source for the identification of copies through out-of-context pigments. Hence, the Raman spectroscopic pigment analyses carried out10 on the oil painting “Young Woman Seated at a Virginal” were instrumental in affirming its origins to Vermeer, despite reservations by some art experts that the painting itself was of “insufficient quality”. However, some caution needs to be applied in the interpretation of elemental and molecular data from pigment analysis alone since several synthetic pigments whose usage in art works can be temporally located to within a narrow time frame also have natural counterparts, which have been adopted and used for centuries before, and often it is a difficult task to discriminate between these natural and synthetic forms.11,12 Examples include lead(ii) chromate and chrome yellow (synthesised in 1809), and lapis lazuli and ultramarine (synthesised in 1828). In the case of anatase, a titanium(iv) oxide polymorph, the statement13 that its synthesis in 1923 therefore means that its analytical occurrence and discovery in a Renaissance or mediaeval art work can infer that it is a fake is actually incorrect, as anatase does occur naturally and is often found as a component or contaminant in clay minerals. For example, in kaolin (china clay), Raman spectroscopic signatures of anatase have been recognised in archaeological shards of Ming porcelains from the early 17th Century,14 which significantly predate the “cut-off” dateline for anatase of 1923 as suggested by Gettens and Stout.13 Additional information about the particulate size and shape of the anatase particles is critical for the analytical interpretation of its presence in an artwork: such is the case of the controversial Vinland Map, which has been hailed by some as a highly important document in which the northeastern coast of North America is delineated accurately, with a watermarked date of 1436, some 60 years or so before Columbus' voyage15,16 and, conversely by some experts, as a clever fake. Analytical Raman spectroscopy has determined the presence of anatase particles associated with black iron gall ink,17 which seriously challenges the acceptance of originality of the Vinland Map, but there is much argument in the literature about the sphericity and uniform size of the anatase particles. Finally, the restoration of art works often occurs unrecorded several centuries after their initial composition, frequently involving the use of contemporary materials that had superseded the originals and whose presence could therefore be misinterpreted on the basis of pigment timelines. The presence of chrome yellow (synthesised in 1809) or Prussian blue (synthesised in 1706) in a suspected high Renaissance painting should not therefore be taken as an absolute indicator that the painting is a fake, as later restorers could have

View Online

Published on 26 October 2018 on https://pubs.rsc.org | doi:10.1039/9781788013475-00031

Evidence of Pentimenti for the Authentication of Paintings: A Challenge for Analytical 33

used strongly coloured and stable pigments as replacements for degraded historical examples of inferior colour intensity such as yellow ochre and azurite, respectively.18 The scientific examination and analysis of a painting is not simply reflected in the pigment analysis as carried out using infrared and Raman spectroscopy, X-ray fluorescence spectroscopy and scanning electron microscopy/ EDAXS spectrometry. Penetrative techniques using optical microscopy, X-ray diffraction, and illumination using infrared and ultraviolet radiation have revealed important subsurface information from which the methodology and technology used by the artist in the construction of the painting can be inferred: from these measurements, the stratigraphy, canvas preparation and underdrawing, with evidence of carbon pouncing, can all be determined. This information can be assimilated into a holistic scientific approach which sits alongside and supports the available historical research for establishing the construction of the painting.9,19–22 In this context, one very important discovery revealed from the subsurface scientific analysis of a painting is a pentimento (from the Italian, pentirsi, meaning to repent): this can be defined as an alteration made by the artist when actually working on composition of the art work, which usually means that the original composition is overpainted and is then not visible later. In reality, therefore, what is seen in the finished article is not necessarily what was created originally as a work in progress. In this respect, the presence of a pentimento is an extremely valuable entity which supports the conclusion that a painting is an original composition – so, by inference, therefore, refuting any later suggestion that the painting could be the work of a copyist, who would have been engaged upon copying an existing painting as seen! The identification of a pentimento in an art work can occur in one of two ways: by analytical interrogation of the subsurface using penetrative radiation such as IRR or XRD, or by direct visual observation, where the overlaying paint has worn away to expose the original composition. It should be recognised here that there is a subtle distinction between a pentimento and a more generic alteration in the composition in a painting that is made later in its history for a variety of reasons: the former is an alteration carried out by the artist during the actual construction and composition of the painting and is therefore truly a useful indicator of originality, whereas the latter can be described as a later alteration made on the grounds of a change in social taste and examples include the covering up of naked figures or the removal of a particular figure from the art work. An example of a painting alteration that does not qualify as a pentimento is provided by the Bronte family portrait of Branwell and his three literary sisters, Emily, Anne and Charlotte, wherein the figure of Branwell was removed by the painter after or near to its completion. To illustrate this, the Bronte family portrait, painted by Branwell Bronte, now hanging in the National Portrait Gallery, London, is shown in Figure 3.1. The painter's unsuccessful attempt to erase himself can be seen in the shadowy figure towards the right of centre, only partially masked by a pillar, between

View Online

Published on 26 October 2018 on https://pubs.rsc.org | doi:10.1039/9781788013475-00031

34

Chapter 3

Figure 3.1  The  Bronte family portrait painted by Patrick Branwell Bronte in about

1834, showing the three sisters from left, Anne, Emily and Charlotte and a shadowy region between Emily and Charlotte where their brother, Branwell, has erased himself and substituted a pillar between Emily and Charlotte. Copyright © National Portrait Gallery, London, acquisition number NPG 1725, where it is now undergoing scientific analysis to enhance the missing image. Reproduced with permission from the National Portrait Gallery, London.

Anne and Emily at the left and Charlotte on the right. This painting is now undergoing restoration and analysis at the National Portrait Gallery, London. Examples of true pentimenti reported in the scientific literature and discovered using penetrative IRR or XRD radiation of art works are to be found in Raphael's Madonna of the Goldfinch,3 Raphael's Portrait of Pope Julius II,21 Jan van Eyck's The Arnolfini Marriage,23 and Hans Memling's triptych The Last Judgement,2 all of which exhibit alterations made by the artist during construction of the painting that were never intended to be seen by an observer in the finished work. It is interesting that the identification of the underdrawing and pentimenti in the Madonna of the Goldfinch during its recent scientific analysis, at the National Gallery laboratories, were instrumental in the acceptance of the painting as an original Raphael, when prior to this it was considered to be only a copy.19,21 The converse can sometimes occur, as in the case of a putative 15th century Renaissance painting of an Italian untitled portrait group of members of the Montefeltro family of Urbino, acquired by the National Gallery in 1923, and which was later shown to be a fake through extensive scientific investigation21 in the late 1990s. This included the identification of the presence of several modern pigments, including cobalt blue, chrome yellow and cadmium yellow.

View Online

Published on 26 October 2018 on https://pubs.rsc.org | doi:10.1039/9781788013475-00031

Evidence of Pentimenti for the Authentication of Paintings: A Challenge for Analytical 35

In this present case study we shall consider the de Brécy Tondo, a Madonna and Child oil painting which has been subjected to analyses, including a Raman spectroscopic study, which have defined pigments and associated materials compatible with the Renaissance period. Clear evidence of several different pentimenti, including a carbon underdrawing discovered from a subsurface analysis and an artistic change exposed through the erosion of superficial paint layers, are supported by detailed historical research. This is an illustrative example of a strong analytical and historical case study of a Renaissance painting at the arts/science interface that is still considered by expert opinion as possibly constituting a later copy – although the holistic scientific and historical evidence seems to dictate otherwise. Effectively, therefore, the question needs to be addressed: when is a pentimento deemed to be unacceptable as evidence of originality, especially when its presence is supported by a thorough analytical scientific pigment analysis?

3.2  The de Brécy Tondo The Tondo is a life-sized Madonna and Child portrait, comprising a full faced circular depiction of a woman wearing a robe, shawl and scarf and cradling a naked male child, which is closely reminiscent of a region of the larger oil painting on canvas entitled “The Sistine Madonna”, originally painted by Raffaello Sanzio in 1513 for the Church of St Sixtus in Piacenza. The theme of this painting is a full-size Madonna with her Child floating in a sky with a background host of cherubs, flanked by a supplicant St Sixtus with a papal crown and St Barbara. With several significant differences in composition, the subject of the Tondo and its respective area of the Sistine Madonna are very closely similar indeed: they are of approximately the same size, as can be seen in Figure 3.2, which shows the Tondo on the right and the appropriate circular area transcribed from the Sistine Madonna on the left (taken from an exhibition in St Patrick's Chapel, Westminster Cathedral, London, in 2012). It appears reasonable that the Tondo (Figure 3.3) could have been undertaken as a study or cartoon for the full Sistine Madonna, as evidenced by the presence of pentimenti in the Tondo: the overt pentimento in the lower left of the painting, projecting from the Child's right elbow can be cited as the best evidence of the originality of this work. This can be clearly seen in Figure 3.3, as a continuation of the Madonna's scarf extending beyond the Child's arm, which has been exposed through wear and erosion of the thin overpaint. There is no suggestion of the presence of this scarf in the similar region of the Sistine Madonna. It is clear that this pentimento was made at the underdrawing stage of the painting: this is evidenced by infrared photography, which reveals that the faces of the cherubs – and particularly the cheek of one cherub as shown in Figure 3.4 – are painted over the scarf. Also, there is no differentiation in the pattern of the surrounding craquelure, which might be expected if anything extraneous had been added.

Published on 26 October 2018 on https://pubs.rsc.org | doi:10.1039/9781788013475-00031

View Online

Figure 3.2  The  de Brecy Tondo digital facsimile exhibited alongside the analogous area taken from an image of the Sistine Madonna, sourced from a Bridgeman Art Library image; on public exhibition in Westminster Cathedral, London, 2012. Reproduced with permission from the De Brecy Trust.

Figure 3.3  The  de Brecy Tondo, showing the pentimento of the Madonna's scarf clearly visible below the Child's right hand. Reproduced with permission from the De Brecy Trust.

View Online

Published on 26 October 2018 on https://pubs.rsc.org | doi:10.1039/9781788013475-00031

Evidence of Pentimenti for the Authentication of Paintings: A Challenge for Analytical 37

Figure 3.4  Infrared  enlargement of the area of the Tondo painting showing the

Child's right elbow and the pentimento of the Madonna's scarf curled near the right hand, exposed by erosion of the thin painted overlay, with details of the background cherubic faces, one of which is superimposed upon the underlying scarf. Reproduced with permission from the De Brecy Trust.

It was not until the Tondo received conservation and was photographed in monochrome at the National Conservation Centre, Liverpool, in early 2000 that it became clear what this particular pentimento represents. It is clearly a continuation of the Madonna's scarf, terminating in a scroll-like ball. The elliptic folds of material, the regular parallel lines of embroidery and the twist in the scarf in the pentimento are complementary to the shawl visible over the Madonna's left shoulder. It is apparent that if the painting had been completed in accordance with this pentimento, it would have created a noticeably triangular design to the picture and, consequently, a very different appearance to the final portrait. In an earlier study of the Tondo, Lothian24 commented that the pentimento to the viewer's left of the Child's right elbow would seem to be produced by a similar process to that used in some of Raphael's panel paintings as identified by Buchanan,25 who analysed the notes of Hacquin, who was responsible in 1798 for the transfer of some of Raphael's work from panel to canvas, including the Madonna di Foligno. The immediately preceding altarpiece to the Sistine Madonna is the Madonna di Foligno.26,27 Raphael's black chalk preparatory study for this is at the British Museum and it is interesting to note his several attempts at finding an elegant solution to the position of the Child's left hand and arm – culminating in the artist's decision in the final painting to show the hand holding the Madonna's shawl, rather than as shown in the study drawing. It strongly resembles the treatment of the pentimento and the final depiction in the de Brécy Tondo, but in reverse, and in relation to the Child's right hand and arm rather than His left as in the Madonna di Foligno. Mr Hacquin mentioned that in all the works of Raphael which he had transferred from the old panels to canvas, there appeared on the white ground of

View Online

Published on 26 October 2018 on https://pubs.rsc.org | doi:10.1039/9781788013475-00031

38

Chapter 3

the picture a very fine but firm line in black crayon, or, what he termed pierre d’italie and that this fine line, or first tracing of his subject, was afterwards strengthened with the pencil (a fine paint-brush) by a transparent brownish, or bistery colour, called by the French painters “stil du grain”. He then appeared to have passed a thin transparent glazing over this preparation, generally of a warm hue, somewhat like mummy, over which he painted the picture. Pierre noire or pierre d’italie is a shale that leaves an indelible mark, of which the tone is from black to grey. Draughtsmen did not begin to use it regularly until towards the end of the fifteenth century, although it was known from ancient times. Michelangelo, Raphael and the Caracci are said to have produced some remarkable anatomical drawings with it. It is extremely difficult to envisage the circumstances in which an expert copyist, commissioned to reproduce the final painting, would feel able to substantially experiment in this way with the copied image and to create something which is not apparent in the final rendition. Additionally, X-ray examination of the paint surface reveals additional pentimenti in the faces of both the Madonna and the Child. It appears that the artist has experimented with three different levels for the eye-line of the Madonna, before deciding on the highest level which imparts a distinctly long nose to the subject. There is evidence that the Madonna's mouth has also been adjusted and there is considerable working to the eyes of the Child, which is evident in the infrared image. It can be concluded that the existence of these pentimenti specifically provide a powerful argument in support of the de Brécy Tondo being an original art work and very possibly a study by Raphael for his Sistine Madonna in 1513, which it probably therefore predates.

3.3  Historical Provenancing Following a thirty-year research programme in the UK, the painting has been recently examined by a scholar at the forefront of Raphael research,26 Professor Dr Jürg Meyer zur Capellen of the University of Münster, Germany, and of the Raphael Project. He has confirmed the historical significance of the work by linking it to the famous early 17th century Royal Stuart picture collection of King Charles I and Queen Henrietta Maria in the UK, to the Vatican's generosity at that time of gifting works of art in support of Catholicism, to Rome as the place where the painting was produced, and subsequently to the cultural history of Wales and the influential aristocratic Welsh Family the “Wynns of Gwydir”. Henrietta Maria was the daughter of King Henry IV of France and Queen Marie de Medici, sharing with her mother a devotion to the Virgin Mary as her patron saint and fondness for Marian imagery. Sir Richard Wynn, 2nd Bt. (1588–1649) was Treasurer and Receiver General to Queen Henrietta Maria (1609–1669) from 1629 to 1649, Groom of the Bedchamber to the King and Queen from 1629 and was responsible for the accounts relating to her art collection. He was a prominent Royalist and was in a position to assist the secreting away of Queen Henrietta Maria's art works from the depredations of the iconoclastic Cromwellian forces, of which several are recorded

View Online

Published on 26 October 2018 on https://pubs.rsc.org | doi:10.1039/9781788013475-00031

Evidence of Pentimenti for the Authentication of Paintings: A Challenge for Analytical 39

as being gifts from Cardinal Barberini of the Vatican between 1632 and 1640 in recognition of the Queen's staunch support of Catholicism.24 Research has proposed that one of these paintings is the Tondo and that it eventually passed into the possession of Sir Richard Wynn24: it may have been accepted as a pledge for money lent to the Queen or he may have been asked to house it securely after the royal departure from London. It may also have been a gift from the Vatican delegation for “services rendered”. In 1642, he was appointed Keeper of the Queen's Palace at Wimbledon, continuing in the role until his death in 1649. One of his first actions was to have all the valuable pictures, mainly Marian in nature and by Italian artists, put away in one room under a special lock and key.28 Gwydir Castle, the Wynns fortified family seat outside Llanrwst, North Wales, is 200 miles from London and would have made an ideal, isolated hiding place for contentious items of art for the duration of the Civil War, affording several safe and secret underground store-houses. The positioning of the painting in the Queen's art collection is evidenced by the presence of a cipher similar to her personal monogram, revealed by infrared photography on the reverse of the canvas. The painting eventually came into the ownership of a cadet branch relative of Sir Richard Wynn, Mrs Violet Hope Fairbairn Wynne-Eyton, who died in 1981 and whose estate at Leeswood Hall, near Mold, North Wales, was auctioned off soon afterwards. The painting passed by purchase, being described as “after Raphael” by the auctioneers, into the collection of George Lester Winward (1934–1997), the founder of the charitably-established de Brécy Trust. A number of interesting features in the painting indicate that it could be by the hand of the Italian Renaissance Master, Raphael. The most significant of these are first, the underdrawing (pentimento) appearing in the lower left of the picture, and, secondly, pounce marks (pricking holes) revealed on the X-ray photographs around the knuckles of the Madonna's right hand and the Child's bicep, indicating the use of an auxiliary cartoon. Such pentimenti and auxiliary cartoons have been held by art historians to be powerful evidence of Raphael's work. Other important features include the pigment usage for the blue colouration in the picture, established by scientific analysis, of an unusual vegetable-derived dye called turnsole, an indicator dye of the orcein family, which includes litmus.29 This has never been recorded in a painting as distinct from manuscript illumination for which it was in regular use in medieval times and subsequently fell out of use around 1600. It is known that during Raphael's later career in Rome he became very interested in thin painting techniques, at a time when European artists were experimenting with transparent and luminous artistic effects in their paintings. Raphael was an influential member of the Vatican court and would have known the della Rovere Pope, Julius II. On 1st October, 1509, Raphael was appointed to the office of Scriptoria Brevium at the Vatican, where the turnsole pigment would have been freely available to him.24 The facial features of the Madonna in the Tondo bear a striking resemblance to those of Raphael's Madonna with the Fish (ca. 1512–1514)27 and to Saint Mary in his Lo Spasimo di Sicilia (1516–1517),27 both of which reside

View Online

Published on 26 October 2018 on https://pubs.rsc.org | doi:10.1039/9781788013475-00031

40

Chapter 3

in the Prado Museum. The model for the de Brecy Madonna is clearly the same one that was used by Raphael for these paintings. An inscription on the reverse of the canvas of the Tondo is “Felic” in a flowing, ornate script, which is believed to refer to Felice della Rovere, natural daughter of Pope Julius II, the most powerful woman in early 16th Century Rome and one of the wealthiest in Italy, who married into the Orsini Family in 1506, having two sons and two daughters. It was an established custom at that time for artists to depict their powerful patrons as the Sacra Famiglia and it would have been quite acceptable to portray Felice della Rovere and her son as the Madonna and Child in this Tondo. It has been further suggested that the Sistine Madonna is a della Rovere family group: with Pope Julius II depicted as St Sixtus, Eleonora della Rovere as St Barbara and Felice and her son as the Madonna and Child.24 A painting of a female subject believed to be Felice della Rovere by Sebastiano del Piombo shows a very similar facial likeness30 with the model in both the Sistine Madonna and the Tondo. Lothian24 concluded that the Tondo predates the Sistine Madonna and is likely to be the prototype painted by Raphael for his celebrated Sistine Madonna altarpiece. Over the centuries, elements of the Sistine Madonna have been reproduced in religious works of art in many countries but it is intriguing that many of these depict a Tondo-like composition: a good example is the mosaic in the Premonstratensian monastery in Tepla in the Czech Republic. In 1520, just seven months after Raphael's death, Cardinal Bibbiena, the Vatican Treasurer, bequeathed to Raphael's friend Baldassare Castiglione a Madonna by Raphael whose description (a circular image on a square canvas) matches that of the Tondo. Bibbiena was aware of the personal affection between Felice della Rovere and Castiglione and after Castiglione's death his own portrait by Raphael, together very possibly with the Tondo, passed into the ownership of the Duke of Urbino. Upon the Duke's death in 1631, part of his estate passed into the Medici Collection, now housed at the Uffizi in Florence, and would have been available to the Vatican for transfer as gifts to Queen Henrietta Maria in England in support of her Catholic faith. Cardinal Francesco Barberini, nephew of Pope Urban VIII, wrote to Mazarin, lately appointed Nuncio extraordinary to the court of Louis XIII: “The statues go on prosperously, nor shall I hesitate to rob Rome of all her most valuable ornaments, if in exchange we might be so happy as to have the King of England's name amongst the princes who submit to the Apostolic See”.31

3.4  Scientific Analysis The scientific analysis of the Tondo has involved the acquisition of chemical elemental and molecular data of the pigments used, micrographs of the stratigraphy, craquelure varnish assessment, XRD and IR photography. The following conclusions were reached:   

View Online

Published on 26 October 2018 on https://pubs.rsc.org | doi:10.1039/9781788013475-00031

Evidence of Pentimenti for the Authentication of Paintings: A Challenge for Analytical 41

* The paint layer on the Tondo is very thin, approximately 10 microns in thickness. Microphotographs of cross-sections of the paint layer showed several distinct strata of paint, usually three; the craquelure between the heads of the Madonna and her Child was discrete and showed no evidence of other paint layers.32,33 * Pigments identified by microscopic analysis were burnt sienna; red madder lake; yellow ochre; lead white and possibly scattered particles of Prussian blue.34,35 * Blue paint samples from seven diverse areas of the painting were specifically tested for the presence of Prussian blue by EDAX Elemental Analysis. No evidence for this pigment was found in any of the samples.36 * Chemical analysis of blue paint samples identified the presence of a natural, vegetable-derived indicator dye from the family orcein – probably turnsole.36 * Three paint samples analysed by Raman spectroscopy37 from the blue painted region at the junction of the gilt surround found the presence of the yellow pigment lead(ii) oxide, massicot (Figure 3.5). This pigment is usually associated with Renaissance works of art as in the 17th century stronger yellow colours were being developed that rapidly subsumed massicot in artists' palettes.38 It is interesting that Raman microscopy did reveal the presence of an isolated blue particle (Figure 3.6), which analysed as Prussian blue: it was concluded that this probably arose from an unrecorded restorative attempt of the blue dye made in the 18th or 19th centuries, which has now almost completely worn away. Raman spectroscopy also determined the presence of lead

Figure 3.5  Raman  spectrum of a yellow particle of massicot, lead(ii) monoxide, which fell into disuse as an artist's pigment in the late Renaissance and early 17th century.

View Online

Chapter 3

Published on 26 October 2018 on https://pubs.rsc.org | doi:10.1039/9781788013475-00031

42

Figure 3.6  Isolated  particle of Prussian blue found in a blue area of the Tondo, characterised by the CN stretching vibrations in the Raman spectrum near 2100 cm−1.

white, basic lead(ii) carbonate, Pb(OH)2·2PbCO3, and amorphous carbon. * Raman spectroscopy37 found the presence of starch used as the probable substrate binding medium.    Scientific analysis is indicative of the pigments and substrate being consistent unequivocally with an attribution of the artwork to the Renaissance period, with evidence of some possible unrecorded later restoration having taken place.

3.5  Conclusions Considering together holistically the quality of production, the extensive historical research, the scientific conclusions and the highly important presence of the pentimenti, underdrawings and pounce marks, the inevitable conclusion must be that the de Brécy Tondo is a Renaissance masterpiece, logically perhaps predating the Sistine Madonna. It was very likely a study for this very large canvas completed by Raphael in 1513. In this context, a statement in the text on Raphael discussing the Sistine Madonna by Jones and Penny27 published in 1983 is quite prophetic:    “Raphael spent more time working on ideas for half-length Madonnas, and it is significant that a circle drawn around the Madonna's veil and the Christ-child would enclose an admirably designed tondo, like the approximately contemporary Madonna della Sedia (authors' note, ca. 1514, now in the Pitti Palace, Florence). It is in this circular area of the composition that the celestial light irradiating the picture is at its most golden”.   

View Online

Published on 26 October 2018 on https://pubs.rsc.org | doi:10.1039/9781788013475-00031

Evidence of Pentimenti for the Authentication of Paintings: A Challenge for Analytical 43

As Jones and Penny were unaware of the existence of the de Brecy Tondo at that time, their hypothesis is all the more remarkable in the emergence of the subsequent historical research studies of Dr Murdoch Lothian.24 The pigments are certainly contemporary with Renaissance usage, as is the starch substrate. The indicative presence of turnsole is a tantalising discovery, which could act as a unique pointer to a possible artistic or atelier origin. The most interesting conclusion, however, is that despite this wealth of evidence pointing to a Renaissance origin for the de Brecy Tondo with strong threads of connection to Raphael that is accepted by several art experts, others are still of the opinion that the painting is a much later copy. Finally, aside from the scientific conclusions relating to the pigment composition and usage, there can surely be no denial of the pentimenti as the strongest evidence of the Tondo's originality, which addresses the theme of this case study: how can the Tondo be still considered as a copy of a well-known work of Renaissance art when the pentimenti would dictate otherwise and surely be indicative of its originality, perhaps even predating its larger analogue study known as the Sistine Madonna?

References 1. Science in Art: The Painted Surface, ed. A. Sgamellotti, B. G. Brunetti and C. Miliani, Royal Society of Chemistry Publishing, Cambridge, 2014. 2. I. Szmelter, L. Cartechini, A. Romani and L. Pezzatt, Multi-criterial Studies of the Masterpiece ‘The Last Judgement’ attributed to Hans Memling at the National Museum of Gdansk, 2010–2013, in Science in Art: The Painted Surface, ed. A. Sgamellotti, B. G. Brunetti and C. Miliani, Royal Society of Chemistry Publishing, Cambridge, 2014, ch. 11, pp. 230–251. 3. M. Ciatti, Science and conservation at the Florentine OPD and Raphael's Madonna of the Goldfinch in the Uffizi Gallery, Florence, in Science in Art: The Painted Surface, ed. A. Sgamellotti, B. G. Brunetti and C. Miliani, Royal Society of Chemistry Publishing, Cambridge, 2014, ch. 12, pp. 252–268. 4. R. Bellucci and C. Frosinini, Underdrawing in paintings, in Science in Art: The Painted Surface, ed. A. Sgamellotti, B. G. Brunetti and C. Miliani, Royal Society of Chemistry Publishing, Cambridge, 2014, ch. 13, pp. 269–286. 5. J. Nadolny, Rev. Conserv., 2003, 4, 1. 6. J. Moreno, L. Stodulski, K. Trentelman, J. Jourdan and L. I. McCann, An examination of the materials used in the creation of Tintoretto's The Dreams of Men, in Art et Chimie La Couleur, ed. J. Goupy and J.-P. Mohen, Actes du Congres de 1er Congres International: Art et Chimie, Paris, 1998, CNRS Editions, Paris, 2000, pp. 60–64. 7. Raman Spectroscopy in Archaeology and Art History, ed. H. G. M. Edwards and J. M. Chalmers, Royal Society of Chemistry Publishing, Cambridge, 2005, vol. 1.

View Online

Published on 26 October 2018 on https://pubs.rsc.org | doi:10.1039/9781788013475-00031

44

Chapter 3

8. P. Craddock, Scientific Investigation of Copies Fakes and Forgeries, Butterworth-Heinemann/Elsevier, Oxford, 2009. 9. D. Bersani, C. Conti, P. Matousek, F. Pozzi and P. Vandenabeele, Anal. Methods, 2016, 8, 8395. 10. L. Burgio, R. J. H. Clark, L. Sheldon and G. D. Smith, Anal. Chem., 2005, 77, 126. 11. H. G. M. Edwards, Historical pigments: a survey of analytical chemical archaeometric usage and terminology with a Raman spectroscopic agenda, in Encyclopaedia of Analytical Chemistry, ed. R. Myers and Y. Ozaki, J. Wiley & Sons, Chichester, UK, 2015, pp. 1–12, DOI: 10.1002/9780470027318.a9527. 12. H. G. M. Edwards, Infrared and Raman spectroscopy in the study of artworks, in Encyclopaedia of Spectroscopy and Spectrometry, ed. J. C. Lindon, G. E. Tranter and D. W. Koppenaal, Elsevier, Oxford, 3rd edn, 2016, vol. II, pp. 378–393. 13. R. J. Gettens and G. L. Stout, Painting Materials: A Short Encyclopaedia, Chapman & Hall Ltd., London, 1942, p.161. 14. E. A. Carter, M. Wood, D. de Waal and H. G. M. Edwards, Heritage Sci., 2017, 5, 17. 15. R. A. Skelton, T. E. Marston and G. D. Painter, The Vinland Map and the Tartar Relation, Yale University Press, New Haven and London, New Edition, 1995. 16. H. G. M. Edwards, The Vinland Map: an authentic relic of early exploration or a modern forgery – Raman spectroscopy in a pivotal role? in Infrared and Raman Spectroscopy in Forensic Science, ed. J. M. Chalmers, H. G. M. Edwards and M. D. Hargreaves, John Wiley and Sons, Chichester, 2012, ch. 7.2, pp. 401–408. 17. K. L. Brown and R. J. H. Clark, Anal. Chem., 2002, 74, 3658. 18. H. G. M. Edwards, P. Vandenabeele and T. J. Benoy, Spectrochim. Acta, Part A, 2015, 137, 45. 19. Art in the Making: Underdrawings in Renaissance Paintings, ed. D. Bomford, National Gallery, London, 2002. 20. M. E. Wiesemann, A Closer Look: Deceptions and Discoveries, National Gallery London/Yale University Press, London, 2010. 21. A. Kirsh and R. S. Levinson, Seeing Through Paintings: Physical Examination in Art Historical Studies, Yale University Press, New Haven, Connecticut, USA and London, 2002. 22. Scientific Examination for the Investigation of Paintings: A Handbook for Conservator-Restorers, ed. D. Pinna, M. Galeotti and R. Mazzeo, Centro Di Publishing, Florence, 2010. 23. L. Campbell, The 15th Century Netherlandish Paintings, National Gallery, London, 1998. 24. M. Lothian, PhD thesis, The Methods Employed to Provenance and to Attribute Putative Works by Raphael, University of Liverpool, 1991. 25. W. Buchanan, Memoirs of Painting, ed. R. Ackerman, London, 1824, vol. I, p. 338.

View Online

Published on 26 October 2018 on https://pubs.rsc.org | doi:10.1039/9781788013475-00031

Evidence of Pentimenti for the Authentication of Paintings: A Challenge for Analytical 45

26. J. Meyer zu Capellen, Raphael: A Critical Catalogue of His Paintings in 5 volumes: Volume 1: The Beginning in Umbria and Florence ca. 1500–1508, Arcos Verlag, Landshut, Germany, 2001; Volume 2: The Roman Religious Paintings ca. 1508–1520, Arcos Verlag, Landshut, Germany, 2005; Volume 3: The Roman Portraits ca. 1508–1520, Arcos Verlag, Landshut, Germany, 2008; Volume 4: Wall Paintings and Tapestry Cartoons, and Volume 5: Works Produced by Raphael's Workshop, are currently awaiting publication. 27. R. Jones and N. Penny, Raphael, Yale University Press, New Haven, USA, and London, 1983, p. 128. 28. R. J. Milward, Wimbledon in the Time of the Civil War, Wimbledon Society Museum Press, 2011, p. 81. 29. Dr Arie Wallert, Curator/Scientific Examination, Department of Paintings, Rijksmuseum, Amsterdam, private communication. 30. C. P. Murphy, The Pope's Daughter, Faber & Faber, London, 2004. 31. C. Oman, Henrietta Maria, Hodder & Stoughton, London, 1931, p. 92. 32. H. H. Bland, UK Forensic Science Services Ltd, Report to G. L. Winward, dated 24th February, 1988. 33. H. H. Bland, UK Forensic Science Services Ltd, Report to G. L. Winward, dated 5th September, 1988. 34. W. McCrone, Report of McCrone Research Associates Ltd. to G. L. Winward, dated 23rd November, 1983. 35. Cambridge Environmental Research Consultants Ltd., Dept. of EarthSciences, University of Cambridge, Report to G. L. Winward, dated 22nd February 1988. 36. H. H. Bland, UK Forensic Science Services Ltd, Report 3 to de Brecy Trust, dated 2nd August 1999. 37. H. G. M. Edwards and T. J. Benoy, Anal. Bioanal. Chem., 2007, 387, 837. 38. H. G. M. Edwards, Analyst, 2004, 129, 956.

Published on 26 October 2018 on https://pubs.rsc.org | doi:10.1039/9781788013475-00046

Chapter 4

Dancing on Eggshells: A Holistic Analytical Study of a Ballet Dancer on Regency Porcelain Howell G. M. Edwards*, Alexander P. H. Surtees and Richard Telford School of Chemistry and Biosciences, Faculty of Life Sciences, University of Bradford, Bradford BD7 1DP, UK *E-mail: [email protected]

4.1  Introduction Some years ago, a spill vase was acquired which was simply decorated with the figure of a young girl in Regency dress standing in a formal “plie” ballet pose (the First Ballet Position of the feet). The spill vase is devoid of factory markings but has a red enamel script pattern number “908” on its base. A photograph of the spill vase in transmitted light is shown in Figure 4.1, showing a flawless and translucent porcelain body. It transpires that the depiction of ballet figure painting on Regency and very early Victorian English porcelains dating from about 1815 to 1840 is a very rare occurrence indeed. Observational data on the spill vase reveals the following information:    ●● The spill vase is of cylindrical form, 105 mm high and of diameter 53 mm at the top and 64 mm at the base, with an exceptionally clear and white translucency. The figure painting is of a young girl in a yellow dress   Raman Spectroscopy in Archaeology and Art History Volume 2 Edited by Peter Vandenabeele and Howell Edwards © The Royal Society of Chemistry 2019 Published by the Royal Society of Chemistry, www.rsc.org

46

View Online

Published on 26 October 2018 on https://pubs.rsc.org | doi:10.1039/9781788013475-00046

Dancing on Eggshells: A Holistic Analytical Study of a Ballet Dancer on Regency

47

Figure 4.1  Spill  vase, cylindrical in shape, with the figure of a young girl in a ballet pose, First Position (Plie), and a yellow dress with a broad blue band and white slippers (ballet pumps), in an oval landscape with pink flowers (roses and peonies). There is simple line gilding at the edge and the moulding. Photographed in transmitted light, showing very clear translucency. Private collection.

●●

●●

with blue stockings, hair tied back and with her feet in white slippers. She is adopting a ballet “plie” (First Position) pose, bending forward, in the foreground of an idealised formal garden scene. The gilding is very simply and tastefully executed with concentric lines around the rim and the base mouldings. The style of decoration and dress places the chronology clearly in the Georgian Regency period, ca. 1810–1830, through the reigns of King George III, King George IV and up to the start of the reign of King William IV. The porcelain factory, probably English, is likely to be one of the following: Minton, Spode, Davenport, Ridgway or Coalport. Worcester and Derby are excluded on translucency grounds. A similar spill vase with an

View Online

Chapter 4

Published on 26 October 2018 on https://pubs.rsc.org | doi:10.1039/9781788013475-00046

48

●●

oval landscape decoration has recently appeared at auction, identical in measurement, shape and moulding with the spill vase under study here, being catalogued as “Davenport, bone china porcelain, circa 1830”, with no pattern number given. Lockett and Godden1 state that “Little is known of pre-1830 Davenport porcelains except that they were of very high quality…and that they could compete in decoration with the finest Derby and Swansea”. It is relevant to note here that recently a further example of the type of landscape decoration, which appears to be en suite with the Davenport spill vase described above, has surfaced at auction, being a lidded powder box from a dressing table set. This has a Davenport mark in blue stencil script on its base along with a blue anchor rebus, confirming its attribution to this factory. John Davenport first started making a hybrid porcelain in the early 1800s in Longport, Staffordshire, England, and for the period 1806–1815, the Davenport factory concentrated on producing soft paste porcelain items and then bone china2 with simple but effective decoration, including landscapes which were accompanied by the simplest of gilding such as that exemplified here in Figure 4.1. The translucency of the spill vase under investigation here is much finer than its Bloor Derby analogue from a similar period: in addition, upon close inspection, the Bloor Derby equivalent would be observed to suffer from the usual glaze crazing, whereas the Swansea equivalent, for example, would have the characteristic duck-egg colouration in transmitted light.3 Little can be divined from the Davenport pattern books from the earliest period as the first factory work book that is now extant2 starts at pattern number 1000, almost 100 later than that shown in red enamel on the marked spill vase shown in Figure 4.1. However, from the dates given in this first surviving pattern book, it can be estimated that pattern 908 would have been in use around the period 1815–1820.

4.1.1  Ballet History Ballet, from the Italian word meaning “to dance”, originated in the Italian Renaissance courts in the 15th Century as a spectacle of lavish dance, theatrical performance and music. Catherine de Medici, Queen of King Henri II, brought it to France from Italy in the 16th century and founded ballet centres there as part of their elaborate and extravagant festivals. The first formal ballet on record, “Le Paradis d'Amour”, was performed at the wedding of Catherine and Henri's daughter, Marguerite de Valois, to Henri of Navarre in 1573. King Louis XIV of France was a passionate dancer and he is recorded as participating in Le Ballet de Nuit, a 12-hours long extravaganza, at the age of 15 in 1657 as the Sun God Apollo, hence giving rise to his sobriquet of “The Sun King”. He founded the Paris Opera Ballet in 1661 and he actively encouraged the transition of ballet from the French Court

View Online

Published on 26 October 2018 on https://pubs.rsc.org | doi:10.1039/9781788013475-00046

Dancing on Eggshells: A Holistic Analytical Study of a Ballet Dancer on Regency

49

to the stage in the form of opera ballet productions. By the mid-1700s the French court encouraged the separation of operatic and ballet productions, introducing the concept of a ballet d'actif, which gave rise to the classical narrative ballet productions of the early 19th century, such as Giselle. It was only at this stage that romantic ballet movements started to be performed by dancers on tiptoe, called “en pointe”, and the wearing of a specially designed ballet costume or a tutu in tulle was introduced. One of the earliest professional ballerinas4 was Marie Taglioni, a pioneer of dancing “en pointe”, who first performed as lead dancer in Didelot's Zephire et Flore in London in 1830. Ballet companies were later formed in major cities from the 1850s. This brief chronological history of ballet is useful for a correct historical placement in the context of ceramics decoration and is particularly relevant for the case study reported here. John Twitchett5 has commented on the extreme paucity of ceramic art decorated with pictures of ballerinas: the first recorded depiction of a ballerina, on Derby porcelain, is that of Marie Taglioni, the most famous romantic ballerina in the 19th century, born in Stockholm in 1804, who features on a cobalt blue ground colour Bloor Derby spill vase. This Bloor Derby spill vase5 is marked on its base with the Bloor Derby crown over a Gothic D stencilled in red enamel with the name of Taglioni added in script. The spill vase was painted by John Haslem, later chronicler6 of the output and painters of the Derby China Works. Taglioni's most famous role as the wood nymph in La Sylphide was performed in 1832 in Paris. She retired to Ca d'Oro on the Grand Canal in Venice in 1847 and died in 1884 in Marseilles; she is buried in Pere Lachaise Cemetery, Paris, where her grave is a focus for young ballet dancers who leave their worn shoes there as a tribute to the first en pointe “toe dancer”. A second possible example of an early ballet pose depicted in porcelain decoration is provided by the Nantgarw porcelain plate of “The Three Graces” painted by James Plant in John Sims' London enamelling atelier7: these are the three daughters of Thomas Coutts, banker to King George III, and his actress wife Elizabeth Starkey – called Elizabeth, Frances and Sophia – at one time these young ladies were the most eligible heiresses in Regency England.3 This plate, dating from the period 1817–1819, is described in the book of John et al.8 on Nantgarw porcelain. The three girls are in Georgian gowns and satin slippers and are adopting classic dance poses, which might not at first appear to be attributable specifically to ballet. There are reports of several ceramic figures of ballerinas in later classic poses, one of which is represented in Twitchett's book5 (page 135, colour plate 84), where the figure is ascribed to the Derby China Works with a footnote: “Known to be Marie Taglioni, who with her father introduced French ballet in the London Theatre; the ballet was called La Sylphide, Marie taking the title role”. The figure was enamelled in colour but the dress and slippers were not of the standard ballet form that were depicted later. Recently, a further example of Nantgarw decorated porcelain has surfaced at auction depicting two young women in Georgian

View Online

Published on 26 October 2018 on https://pubs.rsc.org | doi:10.1039/9781788013475-00046

50

Chapter 4

dress, which is stated to be decorated en suite with the Three Graces plate described earlier and with an identical gilding pattern. Again, the period of 1817–1819 for this plate seems to pre-date the adoption of formalised ballet dress, which can be tentatively dated historically to Taglioni around 1830 and not earlier from the above discussion. Perhaps the earlier description of ballet as “dynamic theatre” better describes the dancing pose of the young girls in long Georgian dresses.

4.2  The Porcelain Connection It is not surprising that figures of notable personalities from the world of ballet are found to be represented in porcelain later in the Victorian era from about 1850, as for many years hitherto theatrical figures had been depicted by many factories: for example, the Derby China Works had a large range of figures from public life, including politicians, statesmen, world leaders, religious characters, the judiciary, icons from literature, classical subjects, military heroes and actors – and sets of these figures were made, such as the Mansion House Dwarfs who used to parade outside the Lord Mayor's residence in London advertising their wares, which were sold by the Derby factory at the time as Grotesque Punches. It should be noted that the purpose of a porcelain figure originally was for dinner table decoration as a conversation piece and this habit can be traced back to about 1760. The Bow and Chelsea factories produced figures in only a limited range of subjects, including birds and animals. Other factories produced figures in fancy dress from stage productions of the Commedia del Arte, see for example a comprehensive study of figure subjects in Dr Peter Bradshaw's book on English porcelain figures of the 18th century.9 The Derby China Works alone produced several hundred different figures which were listed in Haslem6 – many of which were actors and stage performers, such as John Kean as King Richard III, and John Liston in several roles, and Rockingham produced others.10 Most significantly, however, for the purposes of the present research, porcelain painted with ballerinas dating prior to Marie Taglioni 1830 would have probably therefore shown them in shorter dresses and slippers, but only perhaps recognisable characteristically from their classic ballet dancing poses. Only after the impact of the dancing of Marie Taglioni in the early 1830s did ballerinas come to be represented in their now more characteristic dress and costume, comprising a tutu or long ballet dress and ballet pumps. Hence, we can place chronologically the subject of our spill vase to a date before 1830 and probably from her dress and hair style to the decade of 1815–1825, which therefore predates that of Marie Taglioni on the Bloor Derby spill vase. An interesting and exceptionally rare and fine Derby biscuit porcelain figure, designed by Jean-Jacques Spangler and modelled by Joseph Hill, of a Georgian girl depicted in the style of Flora after the earlier sketches of Angelika Kaufmann and dated to about 1795, described as “A Paris Opera Girl in the Style of Flora” is shown in Figure 4.2: here, the elegant dress and classical

View Online

Published on 26 October 2018 on https://pubs.rsc.org | doi:10.1039/9781788013475-00046

Dancing on Eggshells: A Holistic Analytical Study of a Ballet Dancer on Regency

51

Figure 4.2  William  Duesbury Derby biscuit porcelain, ca. 1795, William Duesbury II period, showing an elegant young woman dressed as Flora in a classical pose wearing a long dress and typical shoes of the period with buckles and heels, carrying a garland of flowers. Height 12 inches. Marked on the base with the Duesbury mark of an incised crown, crossed batons and six dots, a number “390” and the incised triangle mark of Joseph Hill. Modelled by Jean-Jacques Spangler after a character of Angelika Kaufmann, “A Paris Opera Girl in the Role of Flora”. Private collection.

pose are noteworthy and befitting a formal Georgian ball or theatre in the late 18th century and perhaps were suitable for the dynamic theatre, as ballet dancing would have been described in the Regency period! This figure has been illustrated and discussed in Dr Bradshaw's book9 (page 217, Plate 129), where its extreme rarity is highlighted. It is recorded that Marie Taglioni was the first ballet dancer to use special satin slippers for “en pointe” dancing on her toes in the early 1830s. These are very similar in style to those depicted some 15 years earlier on the young ladies on the Nantgarw plates described above. It is appropriate here to consider another aspect of porcelain design and manufacture which has thus far not been elaborated: a spill vase is

View Online

Published on 26 October 2018 on https://pubs.rsc.org | doi:10.1039/9781788013475-00046

52

Chapter 4

not the most common piece of porcelain to have survived undamaged for some two hundred years or more. The main output of porcelain factories in the late 18th and early 19th centuries was undoubtedly services for the consumption of tea and coffee and for dessert and dinner courses. These would comprise plates, teapots, coffee pots, sucriers, slop bowls, plates, tureens, platters and serving dishes of various sizes. Special services could be created for breakfast, which would include further items such as muffin dishes, egg cups and large breakfast cups. However, a special type of “functional” item such as ice pails, central dessert comports, water coolers, custard cups, cabaret sets, desk sets, bough pots, violeteers and spill vases were ordered by clients to special commission; these were sensibly different from purely decorative items of porcelain such as cabinet plates, cabinet cups and saucers, and special display vases. It is interesting, therefore, that the spill vase under investigation here has a pattern number, “908”, implying that it came as a special part of a commissioned service or set of porcelain items, which presumably depicted several scenes en suite on a dance theme. Unusually, the pattern number is not accompanied by a factory identifier mark so one has now to recourse to the following to determine the source china factory:    ●● Consultation of available contemporary factory pattern books to compare existing records of any pattern 908; this generally affords a description of floral groups or geometric patterns. ●● Comparison of the spill vase shapes and dimensions from different factories. ●● Spectroscopic analysis to determine the porcelain body composition for an assessment to be made of the components of the porcelain, such as the presence of bone ash, feldspar, soaprock (chinastone), kaolin and gypsum to differentiate between hard paste and soft paste porcelains. A non-destructive requirement for the analytical requirement is essential for the interrogation of this item as it seems to be very rare or even unique and is in perfect condition. Hitherto, much porcelain analysis has been carried out on porcelain shards from kiln damaged pieces and from broken pieces of finished porcelain from used services in collections, where further damage occasioned by destructive sampling or preparation for instrumental examination is not forbidden.3,11

4.3  Raman Spectroscopic Analysis of the Spill Vase A major problem facing analysts of fine ceramics is the destructive nature of the sampling procedure imposed on the specimen by the adoption of a particular technique: even microsampling involves the excision of small specimens of porcelain paste for analytical purposes – usually in the form of a small drill boring or of a small chip taken from a masked area such as a footrim base. This is perfectly acceptable in the case of shards excavated

View Online

Published on 26 October 2018 on https://pubs.rsc.org | doi:10.1039/9781788013475-00046

Dancing on Eggshells: A Holistic Analytical Study of a Ballet Dancer on Regency

53

from a factory site waste dump and the analysis can then be effected with a minimal loss of material. The non-destructive analysis of this spill vase can now be reported using Raman spectroscopy: no mechanical or chemical pretreatment of the specimen is necessary, so the specimen can be returned to its display case unharmed after the investigative procedure. The Raman spectroscopic experiments were carried out using a Renishaw RX210 RIAS portable spectrometer operating at a laser wavelength of 785 nm with a nominal power at the sample of 50 mW and a spectral resolution of 10 cm−1 over a wavenumber range of 100–2000 cm−1. The RX210 was equipped with a 1-metre flexible fibre attachment coupled with a 20× Olympus lens objective in a 5 : 1 arrangement offering a laser footprint of 100 microns at the sample with a standoff focal distance of 1 cm, which facilitates the interrogation of large specimens such as a dinner plate or a platter and the examination of the inside of cups, bowls and spill vases as exemplified here. The flexibility of this arrangement meant that samples of different sizes and shapes could be easily interrogated without any contact between the probe head and the specimen, which could be mounted vertically or horizontally. After an initial test-run to determine the correctness of the focal imaging, each spectral sampling point was examined for 30 co-accumulated spectral scans, each of 3 seconds duration, and several replicate analyses were carried out. Spectral data are presented as over two wavenumber regions from 2000–1000 cm−1 and 1050–100 cm−1. The presence of a transparent glaze has no untoward adverse effect since the laser beam can penetrate the glazed layer and interrogate the underlying ceramic body. The presence of individual minerals or materials is recognised from the observed spectral band wavenumber positions, which can be identified from literature databases. Philippe Colomban has established a sound basis for the interpretation of complex ceramic silicate spectra in terms of both the types of silicon–oxygen bonding present as well as the degrees of polymerisation of the silicate matrices, which have been subjected to elevated temperatures.12–18 In the current study, the prime intention is not to examine the glaze itself but to interrogate the porcelain bodies through the glaze coating: also, because the laser wavelength used in our studies is in the near infrared at 785 nm, this generally produces luminescence emission bands which appear in the same region as the Raman features.

4.3.1  Raman Spectroscopic Data and Discussion The Raman bands observed for the spill vase are collected and listed for the two wavenumber ranges:    A: between 2000 and 1000 cm−1; 1832, 1770, 1681, 1525, 1465, 1344, 1304, 1184 cm−1 (Figure 4.3). B: between 1050 and 100 cm−1; 997, 971, 960, 930, 915, 860, 837, 630, 588, 551, 510, 438, 409, 388, 350, 319, 273, 254, 151 cm−1 (Figure 4.4).   

View Online

Published on 26 October 2018 on https://pubs.rsc.org | doi:10.1039/9781788013475-00046

54

Chapter 4

Figure 4.3  Raman  spectrum of a spill vase; wavenumber region, 2000–1000 cm−1.

Figure 4.4  Raman  spectrum of a spill vase; wavenumber region, 1050–100 cm−1. In the higher wavenumber shift region between 1850 and 1000 cm−1, several broad and strong bands occur, which are characteristic of laser-excited electronic transitions from rare earth lanthanide complexes that are found naturally occurring in very small amounts approximating to only several micrograms per gm in silicates, which comprise the bulk of fired porcelain bodies. These have been reported previously in the literature by Widjaja et al.19 who studied ancient Yuan, Ming and Qing Chinese hard paste

View Online

Dancing on Eggshells: A Holistic Analytical Study of a Ballet Dancer on Regency

Published on 26 October 2018 on https://pubs.rsc.org | doi:10.1039/9781788013475-00046

20

55

porcelain shards, and a recent paper by Carter et al. discusses them in some detail: the Raman spectra in this latter paper were derived from Ming period porcelains recovered from the wrecks of Portuguese carracks that foundered off the Cape of Good Hope in the early 17th century. In a Ming Dynasty shard from the wreck of the Santa Maria Madre de Deus, luminescence bands were noted that show some similarity to those identified here for the spill vase. Although strictly belonging to the category of hard paste porcelains and fired at higher temperatures than their European soft paste porcelain counterparts, the silicate matrices in Chinese hard paste porcelains will have some structural commonalities and lanthanide element impurities, which cause the excitation of these electronic spectra by 785 nm laser excitation in the near infrared region of the electromagnetic spectrum. Hence, the bands that have peak wavenumbers of 1832 mw, 1770 mw, 1679 mw, 1465 ms, 1344 ms, 1304 vs, and 1184 m can all be assigned to the lanthanide electronic transitions in their host three-dimensional silicate matrix composed of –O–Si–O– and >Si=O bridging units, and composed of wollastonite, bytownite and other high temperature stable silicates. Widjaja et al.19 have quoted similar bands, but not at identical wavenumbers, in their studies of Chinese porcelains. This difference is to be expected as it is extremely unlikely that identical lanthanide elemental compound impurities would be found in the local Chinese kaolin sources compared with the analogous European sourced material. Whereas Widjaja et al.19 employed a spectral reconstruction technique, called BTEM (band target entropy minimisation, a self-modelling curve resolution technique), to remove the lanthanide luminescence bands from this wavenumber shift region of the Raman spectrum, so exposing underlying broad spectral bands arising from the complex silicates, this is actually not so helpful in determining the molecular compositional data in the lower wavenumber region, which is free from such lanthanide luminescent spectral interference. These authors report that the lanthanide spectra represented one component from six individual components identified in the spectral reconstruction process. Hence, it can be seen below that the bands in the wavenumber shift region of the Raman spectra between 1000 and 100 cm−1 are probably going to be most informative for the phosphatic, feldspathic, haematite and other components, from which information can be accessed without resorting to spectral data manipulation, itself subject to potential error introduction particularly for the weaker intensity bands. Earlier mention of these luminescent features and their attribution to lanthanide complexes undergoing resonant enhancement under near-infrared wavelength excitation has been noted13,19–23 for some porcelains and obsidians. A remaining broad feature centred at about 1525 cm−1 in our spill vase can be assigned to silicate bands from glass frit which has been added to a bone china base for porcelain manufacture. The spectral envelope in the higher wavenumber shift region is very similar to that observed for some of the finest English soft paste porcelains made in the late 18th and early 19th

View Online

Published on 26 October 2018 on https://pubs.rsc.org | doi:10.1039/9781788013475-00046

56

Chapter 4

centuries, including Derby, Pinxton and Coalport, and it is also very close to that seen for Swansea duck-egg porcelain.24 In the lower wavenumber shift region (Figure 4.4) occur weaker Raman bands which can be assigned to molecular vibrational modes of discrete entities comprising phosphates and silicates: the broad feature centred near 960 cm−1 can actually be deconvoluted into two components at approximately 968 and 958 cm−1, which can both be assigned to P–O stretching vibrations in phosphatic components such as apatite (from the addition of bone ash to the paste) and whitlockite. This feature is very characteristic of porcelains that have had bone ash, which analyses as predominantly calcium hydroxyapatite, as a component in the paste recipe before firing. Reactions between the phosphate radicals and the silicates at high temperatures in the kiln result in the formation of the phosphatic minerals described above. The observation of this feature near 960 cm−1 therefore is convincing spectroscopic analytical evidence for the inclusion of a bone ash component in the porcelain paste and would not be expected to be found, for example, in the hard paste porcelains of Chinese manufacture. Other bands in this low wavenumber region are two rather weak features at approximately 630 and 420 cm−1, which can be assigned to the bending vibrations of the >PO2 modes in phosphatic minerals or possibly the Ti=O stretching modes in rutile. The latter mineral occurs in low concentrations in kaolin deposits in Cornwall, which were believed to be the source of china clays for several manufactories of English and Welsh porcelains.3 An alternative assignment of the broad feature envelope near 968 cm−1 is the occurrence of wollastonite (key bands at 970, 638 and 340 cm−1), which itself provides a powerful support for the presence of a soft paste porcelain, as wollastonite is unstable at higher kiln temperatures so is not detected in hard paste porcelains fired at temperatures near 1400 °C. Hence, recent research on Ming Dynasty hard paste porcelains has failed to determine the presence of wollastonite, which has been detected in a number of European porcelains, including early examples of Medici porcelain of the 16th century.16,25 The broad phosphatic band centred near 960 cm−1 has an envelope similar to the Nantgarw phosphatic band envelope in this region, showing two peaks of approximately equal intensity at 964 and 958 cm−1, which can be interpreted as representing two major phosphate components, probably whitlockite and apatite. The creation of these phosphatic features is reflected in the bending modes' spectrum bands near 631 and 409 cm−1, again ascribed to slightly different phosphate structures in the porcelain. The doublet at 860 and 837 cm−1 is characteristic of a feldspathic type structural moiety and can be assigned to a plagioclase such as bytownite, created at high temperatures by reaction of phosphate with silicate, anorthite, or inosilicate pyroxene. This is certainly strongly indicative of the addition of feldspathic minerals to the porcelain paste. The 632 cm−1 feature is assignable to several possible silicate components, including mullite and muscovite, as well as a bending

View Online

Dancing on Eggshells: A Holistic Analytical Study of a Ballet Dancer on Regency

57

−1

Published on 26 October 2018 on https://pubs.rsc.org | doi:10.1039/9781788013475-00046

mode of phosphatic apatite. The series of bands at 409 cm and below could be Fe–O stretching modes of haematite from the fine river sand used in the recipe.

4.4  Conclusions Scientific analysis and historical porcelain provenancing taken together generally provide a reasonably accurate means of attribution to a factory, painter and date of manufacture of the individual items under investigation.3 In the present study:    ●● The simplicity of the spill vase, its refined decoration comprising the figure of a girl in a background landscape, and the simplicity of the line gilding employed are strongly suggestive of a Georgian English piece of porcelain, probably dating from the high Regency period from 1810– 1825. After this date, society in the later years of the reign of King George IV (1820–1829) and that of King William IV (1830–1837) demanded a more intense decoration in subject matter, with applied vivid pigments and ground colours and an increased intricacy in the mouldings and applied encrustation and their decoration, exemplified by the output from the Coalport, Ridgway, and Rockingham factories.10,26–28 With the accession of Queen Victoria in 1837, porcelain became even more revived baroque and rococo in style of shape and decoration. We can, therefore, confidently place the spill vase shown in Figure 4.1 stylistically in the much earlier Regency period, broadly between 1810 and 1825. ●● The style, shape and texture of the porcelain body identifies the spill vase as English porcelain: the hard paste porcelain from the continental factories of Sevres and Meissen has different texture and glaze characteristics and can immediately be excluded from the much softer and gentler soft paste and bone china being produced in England and Wales at that time. ●● The major English and Welsh factories have been considered as possible sources of this piece of porcelain: namely Worcester, Spode, Derby, Coalport, Ridgway, Minton, Davenport, Swansea and Nantgarw. An analysis of the translucency of the item is informative and it can be seen from Figure 4.1 that the transmission of white light in the visible region of the electromagnetic spectrum is extremely fine. This immediately excludes the Derby China Works of Robert Bloor, the Worcester china Works of Messrs. Barr, Flight & Barr and the china works of John Ridgway. The Swansea china works of Lewis Dillwyn would have either a very clear translucency with a duck-egg colouration or a muddier peach translucency from his trident marked soaprock body,3 whereas the Nantgarw works of William Billingsley would have a similar but an even better translucency; both Swansea and Nantgarw went out of

View Online

Chapter 4

58

Published on 26 October 2018 on https://pubs.rsc.org | doi:10.1039/9781788013475-00046

●●

●●

●●

production during our time period, viz. 1819–20. Coalport porcelain of this period has a fine translucency but with a rather creamier and muddier tone, sometimes verging on a pale greenish hue. The shape of the spill vase is extremely functional and simple: being cylindrical in section with a moulded foot and indented footrim at the base. Examination of scholarly texts affording examples of spill vases from the different factories under consideration can immediately exclude Worcester, Derby, Swansea, Nantgarw, Coalport, and Ridgway porcelains. From the previous two points we can therefore narrow down the factory possibilities to the following three: Minton, Spode and Davenport. All of these factories made quality porcelains in the Regency period. The pattern books for Minton and Spode exist and the pattern number “908” shown for our spill vase in Figure 4.1 does not match the decoration assigned to these numbers of the Minton and Spode factories. The former assigns painted floral groups in arabesque coloured and gilded borders to their pattern “908” and the latter is a deep blue background and heavily gilded – neither have landscape designs with figures for pattern numbers. By deduction, therefore, we are left with Davenport as our potential source factory for the spill vase under investigation here. However, it has already been stated above that Davenport made very fine porcelain from 1806, but, unfortunately the first Davenport factory pattern book does not exist: the earliest pattern on record is number 1000, dating it is believed from about 1815–20. This confirms the conclusion that pattern 908 on the spill vase would therefore date from a similar period as factory pattern numbers for services were usually assigned sequentially.3 Raman spectroscopic analysis confirms that the porcelain is of a bone china formulation, involving bone ash, feldspar, quartz sand and glass frit in its composition. The author can find only one reference to the composition of early formulations of Davenport porcelains in the literature and that is in the work of Eccles and Rackham,11 who analysed examples from 18 English, Welsh and Chinese porcelains in the Victoria & Albert Museum Collection in 1922. At the very end of their report they cite their results for a Longport porcelain (Davenport) mug painted with enamelled flowers and embellished with an AMM monogram in gold. The mug has an anchor mark and DAVENPORT in a crescent painted in red enamel on the underside. Eccles and Rackham give the following data: SiO2 38.64%, Al2O3 21.97%, CaO 22.38%, H3PO4 13.78%, PbO 1.02%, Na2O 1.46%, K2O 0.5% with a trace of MgO. They place Davenport porcelain in the “hybrid porcelain” category, which is basically a hard paste porcelain body with significant bone ash content – their phosphoric acid value correlates with a bone ash content of approximately 40% (as discussed in Edwards3) so the bone ash is certainly a significant component in this formulation. Interestingly, Eccles and Rackham11

View Online

Dancing on Eggshells: A Holistic Analytical Study of a Ballet Dancer on Regency

59

Published on 26 October 2018 on https://pubs.rsc.org | doi:10.1039/9781788013475-00046

place a strong similarity in body between this Davenport porcelain and a Coalport specimen from 1820 adjacent to it in their report, which has similarly high silica, calcium oxide, alumina and phosphoric acid percentages, but they classify Coalport as a “feldspar porcelain”.

   In summary, therefore, we can conclude that the spill vase shown in Figure 4.1 depicting a young dancer in a First Position “plie” ballet pose is a very early example of this genre and predates the Bloor Derby spill vase showing Marie Taglioni, dating from about 1830. As such, it represents a rather rare example of this theme: the interesting “pattern number” of 908 that appears in red script on the base of this spill vase implicitly assumes that other pieces from a set could exist – the standard items made for a dinner/dessert service would comprise plates, serving dishes, fruit comports, tureens and stands, whilst items such as spill vases, a centre comport and ice pails would be ordered by a special commission and decorated en suite with the major service. Alternatively, the spill vase could have been commissioned for a dressing table or cosmetic/boudoir set. It is interesting to speculate on the decoration and composition of the remainder of such a service with pattern number 908: would it show a range of dancers in different ballet poses, perhaps small groups of dancers as in the Nantgarw plates illustrated earlier, or even dancers in theatrical roles as in this period dynamic theatre was still transitional with the true ballet form which evolved from it?

References 1. T. A. Lockett and G. A. Godden, Davenport China, Earthenware and Glass, 1794–1887, Barrie & Jenkins, London, 1989. 2. T. A. Lockett, Davenport Pottery and Porcelain 1794–1887, David & Charles, Newton Abbott, Devon, 1972. 3. H. G. M. Edwards, Swansea and Nantgarw Porcelain: A Scientific Reappraisal, Springer, Dordrecht, The Netherlands, 2017. 4. C. J. Murray, Encyclopaedia of the Romantic Era, 1760–1850, Routledge, London, 2013. 5. J. Twitchett, Derby Porcelain: 1748–1848, Antique Collectors Club, Woodbridge, Suffolk, 2002. 6. J. Haslem, The Old Derby China Factory, 1876, reprinted by E.P. Publishing, Wakefield, 1973. 7. W. D. John, Nantgarw Porcelain, Ceramic Book Company, Newport, 1948. 8. W. D. John, K. Coombes and G. J. Coombes, The Nantgarw Porcelain Album, Ceramic Book Company, Newport, 1978. 9. P. Bradshaw, Eighteenth Century English Porcelain Figures 1745–1795, Antique Collectors Club, Woodbridge, Suffolk, UK, 1981. 10. A. Cox and A. Cox, Rockingham Porcelain, Antique Collectors Club Publishing, Woodbridge, Suffolk, UK, 2005.

View Online

Published on 26 October 2018 on https://pubs.rsc.org | doi:10.1039/9781788013475-00046

60

Chapter 4

11. H. Eccles and B. Rackham, Analysed Specimens of English Porcelain in the Victoria and Albert Museum, Victoria & Albert Museum, South Kensington, London, 1922. 12. P. Colomban, Asian Chem. Lett., 2001, 5, 133. 13. P. Colomban, Appl. Phys. A, 2004, 79, 167. 14. P. Colomban, A case study: glasses, glazes and ceramics, in Raman Spectroscopy in Archaeology and Art History, ed. H. G. M. Edwards and J. M. Chalmers, Royal Society of Chemistry Publishing, Cambridge, 2005. 15. P. Colomban, Arts, 2013, 2, 77. 16. P. Colomban and F. Treppoz, J. Raman Spectrosc., 2001, 32, 93. 17. P. Colomban, G. Segon and X. Faurel, J. Raman Spectrosc., 2001, 32, 351. 18. P. Colomban, V. Milande and H. Lucas, J. Raman Spectrosc., 2004, 35, 68. 19. E. Widjaja, G. H. Lim, Q. Lim, A. S. Mashadi and M. Garland, J. Raman Spectrosc., 2011, 42, 377. 20. E. A. Carter, M. L. Wood, D. de Waal and H. G. M. Edwards, Heritage Sci., 2017, 5, 17. 21. E. Smith and G. Dent, Modern Raman Spectroscopy: A Practical Approach, John Wiley & Sons, Chichester, 2005. 22. B. T. Bowie, D. B. Chase, I. R. Lewis and P. R. Griffiths, Anomalies and artifacts in Raman spectroscopy, in Handbook of Vibrational Spectroscopy, ed. J. M. Chalmers and P. R. Griffiths, John Wiley and Sons, Chichester, UK, 2002, pp. 2355–2378. 23. E. A. Carter, S. J. Kelloway, N. Kononenko and R. Torrance, Anal. Archaeol., 2012, 318. 24. H. G. M. Edwards, Swansea and Nantgarw Porcelains: An Analytical Perspective, to be published, Springer, Dordrecht, The Netherlands, 2018. 25. D. Mancini, C. Dupont-Logie and P. Colomban, Ceram. Int., 2016, 42, 14918. 26. G. A. Godden, Minton Pottery and Porcelain of the First Period 1793–1850, Barrie and Jenkins, London, 1968. 27. G. A. Godden, Coalport and Coalbrookdale Porcelain, Barrie & Jenkins, London, 1972. 28. G. A. Godden, The Illustrated Guide to Ridgway Porcelains, Barrie & Jenkins, London, 1972.

Published on 26 October 2018 on https://pubs.rsc.org | doi:10.1039/9781788013475-00061

Chapter 5

Pigments and Colourants Peter Vandenabeele*a,b, Anastasia Rousakib, Mafalda Costaa, Luc Moensb and Howell G. M. Edwardsc a

Ghent University, Department of Archaeology, Sint-Pietersnieuwstraat 35, B-9000 Ghent, Belgium; bGhent University, Department of Chemistry, Krijgslaan 281 (S-12), B-9000 Ghent, Belgium; cChemistry and Biosciences, Faculty of Life Sciences, University of Bradford, Bradford BD7 1DP, West Yorkshire, UK *E-mail: [email protected]

Colour has a substantial influence on how most people appreciate their environment. Therefore, it forms an important aspect of how we see art objects, and artists usually select their colours very consciously: as exemplars, one can think of the contrasting hues used on Warhol's iconic prints of Marilyn Monroe, or the pastel tones used by Monet to catch the subtle changes of light on the cathedral of Rouen. Artists can deliberately choose to make monotone artworks (e.g. Y. Klein) or selectively use a palette with very vivid colours (e.g. Keith Haring), to mention some options. Today, by using a wide range of techniques and materials that exist, artists have practically unlimited possibilities to vary their colour palette. When looking at historical artworks, it can be seen that some artworks are vividly coloured, whereas in other works the palette of colours is more limited. Historically, it is reasonable to assume that that the number of different painting materials may have been more restricted compared with today. Since the late 19th century the availability of synthetic organic materials for use in artefacts has provided artists with an almost unlimited number of   Raman Spectroscopy in Archaeology and Art History Volume 2 Edited by Peter Vandenabeele and Howell Edwards © The Royal Society of Chemistry 2019 Published by the Royal Society of Chemistry, www.rsc.org

61

View Online

Chapter 5

62

Published on 26 October 2018 on https://pubs.rsc.org | doi:10.1039/9781788013475-00061

1–3

pigment related materials at their disposal. Moreover, in contemporary art, artists do not limit themselves any more to “artists' materials”, but they tend to use diverse materials not primarily associated with art, which poses a serious challenge towards their conservation. On the other hand, when discussing the colours of ancient artefacts, one should appreciate that the colours we see on artefacts today are not necessarily the way they looked at their creation. A well-known example is the colour of antique Greek temples and statues. Today they appear white, but traces of pigments that have been retrieved from protected niches prove that these artefacts were originally very colourful. Colour changes can originate from natural degradation processes or from intrusive events occurring historically. When looking at mediaeval tapestries, for example, they often have a blueish tone. To understand this phenomenon, it is important to know that these tapestries were mainly coloured by using natural dyes, typically originating from animal or vegetable sources. These dyes are sensitive to degradation under the influence of time, temperature, oxygen and light. Yellow dyes are especially prone to fading, and as a consequence, in green zones composed originally of admixtures of blue and yellow pigments, the blue tones tend to become more prominent. Another example of natural colour change with environmental degradation is observed in old oil paintings. These artworks are typically covered with a layer of varnish. Varnishes are films of terpenoid origin and during curing a film is formed by (bio-)polymerisation occurring at the C=C double bonds.4 Over time, these C=C double bonds tend to react with oxygen radicals in the atmosphere. As a consequence, the varnish tends to turn yellow and even a deep brown in colour. Moreover, light may also initiate radical formation and thus enhance the degradative colour change. The yellowed varnish film acts as a coloured filter over the paint layers and a brown varnish can seriously obscure the painting or even render it invisible. On the other hand, the refractive index of linseed oil used as an extender for oil paints can change over time and thus paint layers tend to become more transparent. This is a well-known phenomenon that results in the underdrawing becoming visible through the superficial paint layers in several cases. In addition to natural reasons for colour changes, intrusive events during history influence the way we see antique artworks today. In some periods, artworks were intentionally damaged, due to changing interests in fashion, novel ideals on beauty or due to political sensitivities. Through iconoclasm many artworks were intentionally damaged, wall paintings were limewashed for their protection or manuscripts were destroyed. In other cases, the appearances of artworks, although not intentionally modified, were damaged through catastrophic events. An example is the change of colour through thermal events such as arson or accidental conflagration. In essence, therefore, pigments are chemicals that can react under the influence of heat and adverse environmental conditions. Also, the degradation of artworks under the influence of moisture or of biological attack can cause colour changes to their component pigments.

View Online

Published on 26 October 2018 on https://pubs.rsc.org | doi:10.1039/9781788013475-00061

Pigments and Colourants

63

In general, products that modify the appearance of an artwork can be described as colourants and two classes of colourant can be distinguished, namely, pigments and dyes.5 Pigments are applied as an ink or paint and are mixed with a binding medium that is responsible for film formation and to assist the adherence of the pigment grains to the substrate. Pigments are insoluble in the applied medium, and remain present as small, micrometer-sized grains. In principle, pigments do not migrate in the binder, but over time and depending on the pigment concentration and type of binder, bleeding or blooming can be observed, which results in a variability of colour intensity on the artefact. As opposed to pigments, dyes are perfectly soluble in a binder or carrier. They can be assigned to a natural or synthetic origin. As they are soluble in the carrier, it is necessary to fixate them before application. This can be achieved through chemically binding them to the substrate. This procedure results in a vat-dye, and the most well-known example of this is indigo. Another approach could be making the dye insoluble and then to bind it with a binding medium, i.e., transform the dye into a pigment. This can be achieved by either making an insoluble salt of the dye, or by fixing it to an insoluble salt. This is called a lake. A third approach is a combination of the first two, where a mordant is used to turn the dye in an insoluble complex and then chemically binding it onto textile fibres. Commonly, alum, ureum, or tannins are used as mordants. When dealing with colourants, one should be extremely careful regarding the terminology used. In ancient literature, there is often some confusion about the names used for the different pigments. A typical example is the red pigment “minimum”, which is etymologically linked to “miniature”, a word referring to mediaeval illuminations. In the Roman era, “minimum” was used for the red pigment vermilion (HgS), whereas in mediaeval times the word was preferentially and exclusively used for red lead (Pb3O4).1 Moreover, when using modern terminology, one can make the distinction between the mineral cinnabar (HgS) and the pigment vermilion (HgS), which is either of synthetic origin or of an unknown origin, i.e., (natural or synthetic). Today, there still exists some confusion about typical pigment names. Firstly, one should distinguish between pigment names and commercial, indicative, names of paint. Paint manufacturers often name their paint after a pigment, although this does not mean that this particular pigment is exactly prescribed for that particular paint. For example, the contemporary paint named ‘vermilion’ does not contain the pigment vermilion (HgS), as this would result in too much ecological damage and would invariably cause health problems for people working with this paint. Therefore, manufacturers now make a red paint that typically contains red synthetic organic pigments (often in an admixture) and has a similar red “vermilion” hue. Some manufacturers actually mention the pigments that are used in the paint on the bottle/tube, typically by using the Colour Index6 codes (e.g. PB15:3), where a P is used for pigment, the second letter indicates the colour (W = white, K =

View Online

Published on 26 October 2018 on https://pubs.rsc.org | doi:10.1039/9781788013475-00061

64

Chapter 5

black, B = blue, G = Green, Y = Yellow, R = Red, V = Violet, O = Orange, etc.) and the number indicates the actual molecule that is used. PB15, for example, is copper phthalocyanine, a commonly used blue pigment. In some cases, different crystalline forms exist, and these are indicated with a number after a colon. Pigment analysis can resolve a lot of potential archaeometrical questions. It is clear that knowledge of the specific materials used is important for conservation/restoration purposes. Moreover, identification of the materials used can shed light on the provenance of the artwork, or on the applied painting technique. Finally, the presence of certain materials can be indicative of a specific period, hence it can help in dating the work chronologically. However, the dates of use of pigments as found in the literature should often be treated with caution. The date of invention or synthesis of a pigment does not imply that this was the date of its first usage in an artwork. Moreover, some materials are also available as natural materials, but were only used from a specific date as an artist's pigment because of difficulties in their acquisition or rarity. Raman spectroscopy is a highly interesting tool for the investigation of artefacts.7,8 Indeed, being a molecular spectroscopic technique, it allows the identification of molecules present in minute samples, down to about one micrometer, which is the typical size of pigment grains. Provided the laser power density is kept sufficiently low, the technique can be considered as non-destructive. Indeed, when analysing a sample, the sample is not consumed and is still available for further investigation with other techniques. On the other hand, the Raman spectroscopic technique has been used for direct investigations of artworks, bypassing the need of sampling.9–12 The importance of Raman spectroscopy for art analysis has been recognised since the 1980s and has been well-appreciated in this application. The first investigations of works of art using Raman spectroscopy covered the pigment identification of mediaeval manuscripts.13,14 Often, small manuscripts or loose leaves were positioned under the Raman microscope and due to the confocal properties of the illumination arrangement excellent Raman spectra could be recorded. In other cases, investigations were made of minute samples, often acquired from particulate matter found as detritus between the leaves of a manuscript. Following these first investigations, new applications in art and archaeology were explored and the research area steadily expanded.7 Today, it is almost superfluous to add that Raman spectroscopy can be used in a relatively routine way for the identification of most pigments. However, it must be appreciated that the interpretation of the data must be subject to cross-referencing and the examination of alternative descriptions, especially for the identification of unusual pigments or for the deduction of any proposed degradation pathways. Discovery of pigments or pigment mixtures can also contribute to novel information relating to the technologies of their production processes. One of the advantages of Raman microscopy is its excellent spatial resolution. By recording spectra in a structured way from different positions

View Online

Published on 26 October 2018 on https://pubs.rsc.org | doi:10.1039/9781788013475-00061

Pigments and Colourants

65

on the sample surface it is possible to reconstruct an image of the spatial distribution of the pigment molecules. This mapping procedure, where at each point of the image a full spectrum is recorded, is a punctual measurement. Global imaging, on the other hand, is an approach that is used to obtain an image of the sample in a specific wavelength range, where the range is selected by using appropriate filters. The latter has the advantage that it proceeds faster as all the points are studied simultaneously, but it has the disadvantage that only partial information is obtained, in contrast with a full spectrum in the case of mapping. Recently, there have been some technological evolutions in the mapping arena involving line-shaped lasers and fast high-precision motors, allowing rapid acquisition of the recording of Raman maps. These technological evolutions have triggered a more frequent use of Raman mapping as an approach to visualise structures in pigmented samples. Another technological evolution that has seriously influenced the Raman spectroscopic analysis of colours and pigments was the development of small mobile instruments that can be brought into the field for direct analysis of artworks. Many in situ campaigns were elaborated in recent years, including the analysis of wall paintings in Pompeii,15,16 Egyptian wall paintings,17 rock art,18–21 stained glass windows,22 etc. These investigations are often performed under harsh conditions and the artworks are not always easily reached. The main advantage of this approach is that sampling can be avoided or minimised. Apart from the identification of pigments it is often also possible to examine degradation products from weathering or from biological degradation.23,24 Surface-enhanced Raman spectroscopy (SERS) is a technique that is frequently applied for the identification of dyes.25–27 The dye molecules are brought into close contact with a colloid and as a consequence certain Raman bands are enhanced, so permitting their identification. Different experimental approaches have been evaluated to reduce the sample size or to perform in situ experiments. Micro-spatially offset Raman spectroscopy (SORS) is a technique that allows one to probe deeper layers which perhaps are covered with a turbid (non-transparent) layer.28–30 This is achieved by having an offset between the position where the sample is irradiated with the laser and the zone where the Raman spectrum is recorded by defocussing the objective lens. These approaches were proven to be successful for the identification of pigmented layers on artworks. It was recently even possible to combine micro-SORS with mapping applications.31,32 As colour and paint play an important role in artworks, the importance of pigment identification is evident. Raman spectroscopy happens to be an excellent tool for this purpose. Although pigment identification was one of the first applications of Raman spectroscopy in the field of art analysis, it continues to be of importance, and technological developments are continuing to reveal new applications in this highly interesting research field.

View Online

66

Chapter 5

Acknowledgements Published on 26 October 2018 on https://pubs.rsc.org | doi:10.1039/9781788013475-00061

The authors thank Ghent University for its financial support through the Concerted Research Actions (GOA) programme.

References 1. R. J. Gettens and G. L. Stout, Painting Materials, A Short Encyclopedia, Courier Dover Publications, Dover, 1966. 2. W. Herbst and K. Hunger, Industrial Organic Pigments: Production, Properties, Applications, 3rd, Completely Revised Edition, Wiley-VCH Verlag, Weinheim, 2004. 3. H. Zollinger, Color Chemistry: Syntheses, Properties and Applications of Organic Dyes and Pigments, Wiley-VCH Verlag, Weinheim, 1991. 4. J. S. Mills and R. White, The Organic Chemistry of Museum Objects, Butterworths, London, 1987. 5. H. G. M. Edwards and J. M. Chalmers, Raman Spectroscopy in Archaeology and Art History, RSC, 2005. 6. Colour Index, The Society of Dyers and Colourists, 3rd edn, 1971. 7. P. Vandenabeele, H. G. M. Edwards and L. Moens, Chem. Rev., 2007, 107(3), 675–686. 8. D. Bersani, C. Conti, P. Matousek, F. Pozzi and P. Vandenabeele, Anal. Methods, 2016, 8, 8395–8409. 9. P. Vandenabeele and M. K. Donais, Appl. Spectrosc., 2016, 70(1), 27–41. 10. P. Vandenabeele, H. G. M. Edwards and J. Jehlicka, Chem. Soc. Rev., 2014, 43(8), 2628–2649. 11. P. Colomban, J. Raman Spectrosc., 2012, 43(11), 1529–1535. 12. D. Lauwers, A. G. Hutado, V. Tanevska, L. Moens, D. Bersani and P. Vandenabeele, Spectrochim. Acta, Part A, 2014, 118, 294–301. 13. B. Guineau, Stud. Conserv., 1989, 34, 38–44. 14. B. Guineau, C. Coupry, M.-T. Gousset, J.-P. Forgerit and J. Vezin, Scriptorium, 1986, XL(2), 157–171. 15. M. Maguregui, U. Knuutinen, K. Castro and J. M. Madariaga, J. Raman Spectrosc., 2010, 41, 1110–1119. 16. M. Maguregui, U. Knuutinen, I. Martínez-Arkarazo, A. Giakoumaki, K. Castro and J. M. Madariaga, J. Raman Spectrosc., 2012, 11, 1747–1753. 17. P. Vandenabeele, R. Garcia-Moreno, F. Mathis, K. Leterme, E. Van Elslande, F.-P. Hocquet, S. Rakkaa, D. Laboury, L. Moens, D. Strivay and M. Hartwig, Spectrochim. Acta A, 2009, 73, 546–552. 18. A. Tournié, L. C. Prinsloo, C. Paris, Ph. Colomban and B. Smith, J. Raman Spectrosc., 2011, 42(3), 399–406. 19. L. C. Prinsloo, W. Barnard, I. Meiklejohn and K. Hall, J. Raman Spectrosc., 2008, 39(5), 646–654. 20. A. Rousaki, C. Vázquez, V. Aldazábal, C. Bellelli, M. Carballido Calatayud, A. Hajduk, E. Vargas, O. Palacios, P. Vandenabeele and L. Moens, J. Raman Spectrosc., 2017, 48(11), 1459–1467.

View Online

Published on 26 October 2018 on https://pubs.rsc.org | doi:10.1039/9781788013475-00061

Pigments and Colourants

67

21. D. L. A. de Faria and F. N. Lopes, Vib. Spectrosc., 2007, 45, 117–121. 22. Ph. Colomban and A. Tournié, J. Cult. Heritage, 2007, 8(3), 242–256. 23. M. Maguregui, U. Knuutinen, I. Martínez-Arkarazo, K. Castro and J. M. Madariaga, Anal. Chem., 2011, 83(9), 3319–3326. 24. L. Burgio, R. J. H. Clark and S. Firth, Analyst, 2001, 126, 222–227. 25. F. Pozzi and M. Leona, J. Raman Spectrosc., 2016, 47, 67. 26. F. Casadio, M. Leona, J. R. Lombardi and R. P. Van Duyne, Acc. Chem. Res., 2010, 43, 782. 27. F. Pozzi, S. Porcinai, J. R. Lombardi and M. Leona, Anal. Methods, 2013, 5, 4205. 28. C. Conti, M. Realini, C. Colombo, K. Sowoidnich, N. K. Afseth, M. Bertasa, A. Botteon and P. Matousek, Anal. Chem., 2015, 87, 5810. 29. C. Conti, C. Colombo, M. Realini, G. Zerbi and P. Matousek, Appl. Spectrosc., 2014, 68, 686. 30. C. Conti, M. Realini, A. Botteon, C. Colombo, S. Noll, S. R. Elliott and P. Matousek, Appl. Spectrosc., 2016, 70, 156. 31. A. Botteon, C. Conti, M. Realini, C. Colombo and P. Matousek, Anal. Chem., 2017, 89, 792–798. 32. A. Rousaki, A. Botteaon, C. Colombo, C. Conti, P. Matousek, L. Moens and P. Vandenabeele, Anal. Methods, 2017, 9, 6435–6442.

Published on 26 October 2018 on https://pubs.rsc.org | doi:10.1039/9781788013475-00068

Chapter 6

Micro Raman Spectroscopy of Epipalaeolithic Decorated Pebbles from Arroyo Moreras 2 (Parque Darwin, Madrid) A. Hernanz*a, J. M. Gavira-Vallejoa, P. Bueno-Ramírezb, R. de Balbín-Behrmannb, J. Morín de Pablosc and C. de Juana Ortínb a

Departamento de Ciencias y Técnicas Fisicoquímicas, Facultad de Ciencias, Universidad Nacional de Educación a Distancia (UNED), Paseo de la Senda del Rey, 9, E-28040 Madrid, Spain; bÁrea de Prehistoria, Universidad de Alcalá de Henares (UAH), Colegios, 2, E-28801 Alcalá de Henares, Spain; cAUDEMA Arqueología, Santorcaz, 4, E-28002, Madrid, Spain *E-mail: [email protected]

6.1  Introduction 6.1.1  Initial Remarks Raman spectroscopy is an efficient technique to identify the materials present in rock art painting panels,1 particularly at microscopic scale.2–4 Stone artefacts5,6 and decorated stone tools may also be studied by Raman microscopy.7,8 Paint residues in prehistoric decorated pebbles from an archaeological site in the centre of the Iberian Peninsula are studied in this work by   Raman Spectroscopy in Archaeology and Art History Volume 2 Edited by Peter Vandenabeele and Howell Edwards © The Royal Society of Chemistry 2019 Published by the Royal Society of Chemistry, www.rsc.org

68

View Online

Published on 26 October 2018 on https://pubs.rsc.org | doi:10.1039/9781788013475-00068

Micro Raman Spectroscopy of Epipalaeolithic Decorated Pebbles

69

Raman microscopy. In Iberia, painted pebbles have usually been found in the north of the peninsula, in association with trans-Pyrenean relationships in the late Upper Palaeolithic. However, research carried out in recent years has increased the record numerically and enlarged it geographically. From the 13th to 8th millennia cal BC, different kinds of surfaces: rock walls in caves and in the open air, and portable objects, witnessed evolution and change in Upper Palaeolithic symbols, whose techniques and subject matter formed part of the cultural background of the hunter-gatherers.9–16 In this framework, the new finds from outside the north of the Iberian Peninsula, the painted pebbles from Arroyo de las Moreras (Madrid, Spain), are of great interest.

6.1.2  Archaeological Background Pigment residues on the three decorated pebbles C-AM-86, C-AM-245 and C-AM-246 with oval or convex cross-sections have been analysed. The first pebble, C-AM-86, is the best preserved and most closely resembles the classic objects from the north of Iberia. The main motifs are sinuous lines and zigzags, painted in red and black. These pebbles were found in a salvage excavation at Parque Darwin, archaeological sites discovered in the Holocene geological deposits near Arroyo de las Moreras, in the Tagus drainage basin in the Madrid region (see Figure 6.1). They form part of a single archaeological level, 27 m long. Both sites have been dated17 in the Epipalaeolithic by samples of charcoal from the level in Parque Darwin 2: 8470 ± 70 BP. The pebbles that have been analysed were found at this site, in a context of hearths and habitation structures. The researchers relate this site with the possible quarrying of flint in the area, as well as with hunting and subsistence strategies. The pebbles may have been used in activities connected with the preparation of plants or in other uses in the habitation contexts. They all display evidence of fire and were decorated before being used functionally. These pebbles are unique finds in the centre of the Iberian Peninsula, and their chronology is also unknown in interior regions. Therefore, the presence of pigment on the pebbles at Arroyo de las Moreras is important as they form a unique group of painted pebbles in a region where this type of object had never been found.

6.2  Experimental Three pebbles collected form the Arroyo de las Moreras site have been studied by micro Raman spectroscopy without any previous physical or chemical treatment (see Figures 6.2–6.4). They were placed on the stage of an Olympus BX41 microscope coupled to a Jobin-Yvon Lab-Ram-IR HR-800 confocal Raman spectrometer. Their surface was examined in order to find possible pigment residues. The micro Raman study was carried out using the 632.8 nm line of a He/Ne laser for Raman excitation with powers between 0.042

Published on 26 October 2018 on https://pubs.rsc.org | d

70

Figure 6.1  Location  of the Arroyo de las Moreras site, Madrid, Spain. Image courtesy of R. de Balbín-Behrmann.

Chapter 6

View Online

Published on 26 October 2018 on https://pubs.rsc.org | doi:10.1039/9781788013475-00068

Micro Raman Spectroscopy of Epipalaeolithic Decorated Pebbles

71

Figure 6.2  Pebble  C-AM-86 from the Arroyo de las Moreras site. The black circles indicate points with residues of amorphous carbon detected by Raman microscopy. The red triangles indicate points with residues of haematite detected by this technique.

Figure 6.3  Pebble  C-AM-245 from the Arroyo de las Moreras site. The black circles indicate points with residues of amorphous carbon detected by Raman microscopy. The red triangles indicate points with residues of haematite detected by this technique.

View Online

Published on 26 October 2018 on https://pubs.rsc.org | doi:10.1039/9781788013475-00068

72

Chapter 6

Figure 6.4  Pebble  C-AM-246 from the Arroyo de las Moreras site. The black circles indicate points with residues of amorphous carbon detected by Raman microscopy.

and 1.24 mW measured at the sample position. These low laser powers avoid the “graphitisation” of organic materials. The average spectral resolution in the Raman shift range of 100–1700 cm−1 was 1 cm−1 (focal length 800 mm, grating 1800 grooves/mm and confocal pinhole 100 µm). These conditions involved a lateral resolving power of ∼1–2 µm (100× objective lens) and ∼5 µm (50× LWD objective lens) at the specimen. The depth of laser focus is 0.34 and 1.10 µm for the 100× and 50× LWD objective lenses, respectively. An integration time of between 2 and 15 s and up to 50 accumulations has been used to achieve an acceptable S/N ratio. The linearity (sine bar linearity) of the spectrograph was adjusted using fluorescent lamps of the lab (zero order position) and the lines at 640.22 and 837.76 nm of a Ne lamp. The confocality of the instrument was refined using the 519.97 cm−1 line of a silicon wafer. The wavenumber shift calibration of this spectrometer was accomplished with 4-acetamidophenol, naphthalene and sulphur standards18 in the range 150–3100 cm−1. This resulted in a wavenumber mean deviation of Δνcal−Δνobs = 0.96 ± 0.75 cm−1 (tStudent 95%). Raman spectra from 33 to 49 points of the decorated side of each pebble with the rest of the pigments were obtained (see Figures 6.2–6.4). Spectral smoothing was not applied to the observed spectra. The software package GRAMS/AI v.7.00 (Thermo Electron Corporation, Salem, NH, USA) has been used to correct the spectral background of fluorescence radiation, as well as to assist in determining the wavenumber of the peaks.

View Online

Micro Raman Spectroscopy of Epipalaeolithic Decorated Pebbles

73

Published on 26 October 2018 on https://pubs.rsc.org | doi:10.1039/9781788013475-00068

6.3  Results and Discussion The irregular surface of the three pebbles has been examined with the Raman microscope in order to characterise the rock components and to detect the presence of possible pigment residues. The convex surface of the pebbles has not made Raman mapping possible. The results obtained are summarised in Table 6.1.

6.3.1  Pebble C-AM-86 The main component of the rock corresponding to the pebble C-AM-86 is α-quartz (α-SiO2) and rutile (TiO2) (see Figure 6.5). A microscopic scanning of the pebble surface revealed the presence of red and black pigments on one of its faces (see Figure 6.6). The distribution of the paint remains suggests traces and areas decorating the pebble (see Figure 6.2). Haematite (α-Fe2O3) (see Figure 6.7) and amorphous carbon have been identified in the red and black particles, respectively. Sometimes, both pigments appear together in the same trace (see Figures 6.2 and 6.6). Table 6.1  Pigments  and components of the rock substrates identified by Raman microscopy in the three pebbles.

Pebble

Rock substrate

Pigments

C-AM-86 C-AM-245 C-AM-246

α-Quartz, rutile Haematite, amorphous carbon α-Quartz Haematite, amorphous carbon α-Quartz, ε-Cu-phthalocyanine blue Amorphous carbon (contamination)

Figure 6.5  Raman  spectrum of particles of rutile (TiO2) from the rock corresponding to the pebble C-AM-86.

View Online

Chapter 6

Published on 26 October 2018 on https://pubs.rsc.org | doi:10.1039/9781788013475-00068

74

Figure 6.6  Microphotograph  of residues of black and red pigments from the surface of the pebble C-AM-86.

Figure 6.7  Raman  spectrum of particles of haematite (α-Fe2O3) from the surface of the pebble C-AM-86.

6.3.2  Pebble C-AM-245 As in the pebble C-AM-86, α-quartz is the main rock component of the pebble C-AM-245. Red and black particles of haematite and amorphous carbon (see Figures 6.8 and 6.9) are distributed over one of the pebble faces. The remains of both pigments indicate lines and traces of an ancient decoration (see Figure 6.3).

View Online

Published on 26 October 2018 on https://pubs.rsc.org | doi:10.1039/9781788013475-00068

Micro Raman Spectroscopy of Epipalaeolithic Decorated Pebbles

75

Figure 6.8  Microphotograph  of residues of black pigment from the surface of the pebble C-AM-245.

Figure 6.9  Microphotograph  of residues of red pigment from the surface of the pebble C-AM-245.

6.3.3  Pebble C-AM-246 α-Quartz is also the principal component of the rock used in the pebble C-AM-246 (see Figure 6.10). However, in this case only very weak black lines are observed in its surface. The broad Raman bands at 1386 and 1594 cm−1 of the spectra obtained from the black particles of these lines (see Figure 6.11) indicate that amorphous carbon (charcoal or soot)19,20 is the pigment used

View Online

Chapter 6

Published on 26 October 2018 on https://pubs.rsc.org | doi:10.1039/9781788013475-00068

76

Figure 6.10  Raman  spectrum of particles of α-quartz (α-SiO2) and amorphous carbon from the surface of the pebble C-AM-246.

Figure 6.11  Microphotograph  of residues of black pigment from the surface of the pebble C-AM-246.

to make the lines. These bands appear usually in the spectra of the pebble together with those of α-quartz from the substrate (see Figure 6.10). Some microscopic blue spots have been observed in the pebble surface (see Figure 6.12). Their Raman spectra (see Figures 6.13 and 6.14) revealed that they were from the synthetic pigment ε-copper-phthalocyanine blue,21–24 first produced about 1935 and commonly used in inks for pens and marker pens.

View Online

Published on 26 October 2018 on https://pubs.rsc.org | doi:10.1039/9781788013475-00068

Micro Raman Spectroscopy of Epipalaeolithic Decorated Pebbles

77

Figure 6.12  Microphotograph  of a spot of ε-copper-phthalocyanine blue from the surface of the pebble C-AM-246.

Figure 6.13  Raman  spectrum (low wavenumber region) of a spot of ε-copper-phthalocyanine blue from the surface of the pebble C-AM-246.

This type of contamination has also been observed in prehistoric paintings.25 It is extremely important to avoid contamination of archaeological objects, rough manipulation and labelling introduce strange materials in these pieces, even at the microscopic scale, that may mislead researchers (fakes, dating, origin…etc.).

View Online

Chapter 6

Published on 26 October 2018 on https://pubs.rsc.org | doi:10.1039/9781788013475-00068

78

Figure 6.14  Raman  spectrum (high wavenumber region) of a spot of ε-copper-phthalocyanine blue from the surface of the pebble C-AM-246.

6.4  Conclusion Despite the fact that the Epipalaeolithic pebbles collected from the site of Arroyo Moreras 2 had deteriorated, the detection by Raman microscopy of residual pigments on their surface in several areas and lines confirms a primitive decoration. Haematite and amorphous carbon were used as pigments. Sometimes micro-particles of both pigments are found together, but in other areas of the pebbles only one type of has been identified. In one case, pebble C-AM-246, only particles of amorphous carbon have been detected. The main rock component of the pebbles is α-quartz; additional rutile microcrystals have also been identified in pebble 86. Contamination with the synthetic pigment ε-copper-phthalocyanine blue, commonly used in pen inks, has been detected in pebble C-AM-246. Spots of this pigment observed with the microscope would be the result of careless handling of these archaeological pieces, something also detected in prehistoric paintings.25 These findings should serve as a call to prevent the contamination of archaeological objects. The analysis of the pigments used, together with their previously unknown chronology and open-air location, constitute a new point of reference for the technical and cultural uses of symbology among hunter-gatherers in southern Europe.

Acknowledgements The financial support of the project HAR2015-68595-P (Ministerio de Economía y Competitividad, Spain) and the European Regional Development Fund (ERDF) is acknowledged. We also thank Dr. Enrique Baquedano Pérez (Museo Arqueológico Regional de la Comunidad de Madrid) and AUDEMA Arqueología for the facilities provided to investigate the pebbles.

View Online

Micro Raman Spectroscopy of Epipalaeolithic Decorated Pebbles

79

Published on 26 October 2018 on https://pubs.rsc.org | doi:10.1039/9781788013475-00068

References 1. A. Hernanz, in Prehistoric Art as Prehistoric Culture, ed. P. Bueno-Ramírez and P. G. Bahn, Archaeopress, Oxford, UK, 2015, p. 11. 2. A. Hernanz, J. Chang, M. Iriarte, J. M. Gavira-Vallejo, R. de Balbín-Behrmann, P. Bueno-Ramírez and A. Maroto-Valiente, Appl. Phys., 2016, 122, 699. 3. M. Tascon, N. Mastrangelo, L. Gheco, M. Gastaldi, M. Quesada and F. Marte, Microchem. J., 2016, 129, 297. 4. M. Iriarte, A. Hernanz, J. M. Gavira-Vallejo, J. Alcolea-González and R. de Balbín-Behrmann, J. Archaeol. Sci. Rep., 2017, 14, 454. 5. C. Capel Ferrón, L. León-Reina, S. Jorge-Villar, J. M. Compaña, M. A. G. Aranda, J. T. López Navarrete, V. Hernández, F. J. Medianero, J. Ramos, G.-C. Weniger, S. Domínguez-Bella, J. Linstaedter, P. Cantalejo, M. Espejo and J. J. Durán Valsero, Archaeol. Anthropol. Sci., 2015, 7, 235. 6. E. A. Carter, S. J. Kelloway, N. Kononenko and R. Torrence, in Analytical Archaeometry: Selected Topics, ed. H. G. M. Edwards and P. Vandenabeele, The Royal Society of Chemistry, Cambridge, UK, 2012, p. 318. 7. Z. E. Papliaka, A. Philippidis, P. Siozos, M. Vakondiou, K. Melessanaki and D. Anglos, Heritage Sci., 2016, 4, 15. 8. R. Belli, G. Dalmeri, A. Frongia, S. Gianalella, M. Mattarelli, M. Montagna and L. Toniutti, in Proceedings of the 37th International Symposium on Archaeometry, ed. I. Turbanti-Memmi, Springer-Verlag, Berlin, Heidelberg, 2011, p. 187. 9. Th. Aubry, A. Santos and L. Luis, in Les arts de la préhistoire mycro-analyses, mise en contextes, conservation, ed. P. Paillet, PALEO, MADAPCA, Paris, 2014, p. 259. 10. P. Bueno-Ramírez and R. de Balbín-Behrmann, in Rock Art Studies. News of the World IV, ed. P. Bahn, N. Franklin and M. Strecker, Oxbow Books, Oxford, UK, 2012, p. 45. 11. P. Bueno-Ramírez and R. de Balbín-Behrmann, in Social Complexity in a Long Term Perspective, ed. J. Soares, Setúbal Arqueológica, Portugal, 2016, vol. 16, p. 41. 12. P. Bueno-Ramírez, R. de Balbín-Behrmann and J. Alcolea-González, L'Anthropologie, 2007, 111, 549. 13. P. Bueno-Ramírez, R. de Balbín-Behrmann and J. Alcolea-González, in Arte Prehistórico al aire libre en el Sur de Europa, ed. R. Balbín-Behrmann, Actas PAHIS, Junta de Castilla y León, Valladolid, Spain, 2009, p. 259. 14. C. Cacho, J. A. Martos, J. F. Jordá Pardo, J. Yravedra, M. Ruiz, L. Zapata, C. Sesé, B. Avezuela, J. Valdivia, P. Ortega and D. Arceredillo, in Los cazadores recolectores del Pleistoceno y del Holoceno en Iberia y el estrecho de Gibraltar. Estado actual del conocimiento del registro arqueológico, Fundación Atapuerca, Universidad de Burgos, Burgos, Spain, 2014, p. 568. 15. J. Casabo Bernard, Paleolítico Superior Final y Epipaleolítico en la Comunidad Valenciana, MARQ, Alicante, Spain, 2004, Serie mayor 3.

View Online

Published on 26 October 2018 on https://pubs.rsc.org | doi:10.1039/9781788013475-00068

80

Chapter 6

16. S. S. Figueiredo, P. Xavier, A. Silva, D. Neves and I. Dominguez García, in Sobre rocas y huesos: las sociedades prehistóricas y sus manifestaciones plásticas, ed. M. A. Medina-Alcaide, A. J. Romero Alonso, R. M. RuizMárquez and J. L. Sanchidrián Torti, Imprenta Luque, Córdoba, Spain, 2015, p. 192. 17. A. Pérez-González, J. Baena-Preysler, J. Morín de Pablos, I. Rus, S. Bárezm, D. Uribelarrea, in Primer Simposio de la Investigación y Difusión Arqueopaleontológica en el Marco de la Iniciativa Privada, ed. J. Morín, AUDEMA, Madrid, Spain, 2007, p. 121. 18. A.S.T.M. Subcommittee on Raman Spectroscopy, Raman Shift Frequency Standards: McCreery Group (ASTM E 1840), American Society for Testing Materials, Philadelphia, PA, 2015, http://www.chem.ualberta.ca/∼mccreery/raman.html (last accessed September 2017). 19. O. Beyssac, B. Goffé, J.-P. Petitet, E. Froigneux, M. Moreau and J.-N. Rouzaud, Spectrochim. Acta A, 2003, 59, 2267. 20. S. Potgieter-Vermaak, N. Maledi, N. Wagner, J. H. P. Van Heerden, R. Van Grieken and J. H. Potgieter, J. Raman Spectrosc., 2011, 42, 123. 21. L. I. McCann, K. Trentelman, T. Possley and B. Golding, J. Raman Spectrosc., 1999, 30, 121. 22. L. Burgio and R. J. H. Clark, Spectrochim. Acta A, 2001, 57, 1491. 23. T. D. Chaplin, R. J. H. Clark, A. McKay and S. Pugh, J. Raman Spectrosc., 2006, 37, 865. 24. C. Defeyt, P. Vandenabeele, B. Gilbert, J. Van Pevenage, R. Clootse and D. Strivaya, J. Raman Spectrosc., 2012, 43, 1772. 25. A. Hernanz, M. Iriarte, P. Bueno-Ramírez, R. de Balbín-Behrmann, J. M. Gavira-Vallejo, D. Calderón-Saturio, L. Laporte, R. Barroso-Bermejo, P. Gouezin, A. Maroto-Valiente, L. Salanova, G. Benetau-Douillard and E. Mens, J. Raman Spectrosc., 2016, 47, 571.

Published on 26 October 2018 on https://pubs.rsc.org | doi:10.1039/9781788013475-00081

Chapter 7

Raman Microscopy as a Primary Technique for Identifying Microresidues Related to Tool-use on Prehistoric Stone Artefacts Linda C. Prinsloo* and Luc Bordes Centre for Archaeological Science, School of Earth and Environmental Sciences, University of Wollongong, Wollongong, NSW 2522, Australia *E-mail: [email protected]

7.1  Introduction Stone tools are the most common artefacts excavated at archaeological sites dating from the Stone Age and they are, in many instances, the only remaining evidence of how people lived in the distant past. Analysis of ancient micro-residues preserved on stone artefacts can provide detailed information on the activities undertaken with such implements and forms a useful tool to reconstruct past human behaviours. The identification of ancient micro-residues, however, is only the first step in relating it to the original function of the tool, as the presence of a micro-residue may originate from multiple agencies other than transfer of contact material during use. For example, both organic and inorganic micro-residues can be transferred to stone tool surfaces via contact with sediments,

  Raman Spectroscopy in Archaeology and Art History Volume 2 Edited by Peter Vandenabeele and Howell Edwards © The Royal Society of Chemistry 2019 Published by the Royal Society of Chemistry, www.rsc.org

81

View Online

Published on 26 October 2018 on https://pubs.rsc.org | doi:10.1039/9781788013475-00081

82

Chapter 7

groundwater, bacteria, subterranean invertebrates and fungi. Contamination after excavation is also not negligible and can occur through handling by archaeologists during excavation, contact with storage material, or through laboratory conditions and physical contact with analytical instruments and facilities used to study the tools.1 Previously, Raman spectroscopy has been used to verify the identification of macro-residues on stone tools through optical microscopy by usewear specialists.2 In the methodology presented here, artefacts were not selected based on the presence of any visible macro-residues attached to the tools, but were systematically analysed using Raman spectroscopy as a primary technique for initially locating and identifying organic and inorganic micro-residues. This strategy was followed to avoid any bias that targeted preferentially larger residues or residues present only on polished edges and surfaces and to focus on particles less than 50 microns in size. These micron-sized residues can only be successfully and systematically analysed by a technique with high spatial resolution, such as Raman microscopy, with the added advantage that both inorganic and organic materials can be identified simultaneously.1 Furthermore, the technique is non-destructive and leaves the residues in context on the artefact, allowing for future study of the same artefacts. In this chapter, we use stone artefacts from Liang Bua (Flores, Indonesia) and Denisova Cave (Altai Mountains, Siberia) to illustrate the use of Raman spectroscopy as a primary method to identity ancient micro-residues preserved on stone artefact surfaces that are specifically due to prehistoric use as opposed to some form of ancient or modern source of contamination.

7.2  Archaeological Background Liang Bua is a limestone cave located on the island of Flores, Indonesia, with a cultural sequence spanning the past ∼190 thousand years.3 During this time, the cave was occupied successively by at least two human species, initially by Homo floresiensis and later by Homo sapiens (modern humans), currently with no evidence of temporal overlap.3,4 Denisova Cave was used as an occasional occupation site, initially by Neanderthals and Denisovans with some occupation periods overlapping,5 and later by Homo sapiens. The two sites have completely different climatic conditions and it is expected that the preservation of organic residues will be much higher at the lower average temperature in Denisova Cave (which is located in the Altai Mountains of southern Siberia) than in Liang Bua, which forms part of the tropical Indonesian archipelago.

7.3  Experimental Methods 7.3.1  Sample Preparation Working with micron-sized residues increases the possibility of contamination from various sources that can interfere with the correct interpretation of the archaeological relevance of a residue. For instance, during the course of this study, indigo was identified6 in fibres on artefacts originating

View Online

Published on 26 October 2018 on https://pubs.rsc.org | doi:10.1039/9781788013475-00081

Raman Microscopy as a Primary Technique for Identifying Micro-residues Related

83

Figure 7.1  Images  of indigo-coloured fibre on a Liang Bua artefact (A and B) and Raman spectrum of indigo using 532 nm excitation (C).

from Liang Bua (Figure 7.1), attracting considerable interest, as the island of Flores has a long history of batik work; a prehistoric presence of native Indigofera plant material (which has medicinal properties) would thus not have been out of place. Unfortunately, indigo fibres were also identified on glass slides placed in the same Raman laboratory for a week to test for airborne pollution sources. The results were positive and the conclusion was that micron-sized indigo-coloured cotton fibres are quite common in the air, which led to the re-classification of the indigo fibres on the stone tool as a contaminant.7 Being aware of the many sources of contamination that can influence the interpretation of archaeological data, we requested that the artefacts collected at Denisova Cave and Liang Bua should be excavated encased in sediment, eliminating exposure to ambient conditions at the excavation site. The stone tools were only removed from the sediment under clean laboratory conditions and for each artefact, the sediment in contact and 3 cm away from the artefact surface was collected. The artefacts were handled with nitrile gloves (latex, powder and protein free) and placed on a support fashioned with Blu-Tack® (a synthetic rubber compound) to accommodate its shape. This enabled the positioning of each sample under the Raman microscope with the incident laser perpendicular to the point of analysis. The support was covered with a piece of nitrile glove to prevent

View Online

Chapter 7

84

Published on 26 October 2018 on https://pubs.rsc.org | doi:10.1039/9781788013475-00081

®

contamination from the Blu-Tack (contamination from the nitrile glove is easy to recognise). Basic precautions, such as storing the samples in clean bags and boxes, were taken before and after analysis. Raman reference spectra were recorded for any material that was in contact with the artefacts and, together with spectra collected from glass slides placed in strategic positions in the laboratory to screen for air pollution, we formed a database of possible contaminants.1

7.3.2  Raman Analysis Raman spectra were recorded with a WITec® alpha 300R confocal Raman microscope (WITec® Instrument Corp., Germany) equipped with two UHTS300 spectrometers and two CCD detectors: (1) a visible DV401 detector for use with 532 nm excitation, and (2) a DV401 detector for 785 nm excitation. The excitation sources were two diode lasers operated at 532 nm and 785 nm wavelengths with 38 mW and 120 mW maximum power output, respectively. Zeiss® microscope objectives (20× and 50× magnifications) were used, achieving a sub-micron spatial resolution. The samples were placed on a piezo-driven, feedback-controlled scanning stage.

7.3.3  Cleaning and Analysis Procedures Once removed from the sediment crust, the samples were first photographed and macro-residues characterised using Raman spectroscopy. Samples were then cleaned by ultrasonication for 10 s in Milli-Q® water. A systematic search and analysis of the micro-residues on the washed artefacts were undertaken, concentrating on the edges of the artefact perimeter using a 50× objective, within a strip approximately 200 µm from the edge (on both the ventral and dorsal sides). This is a time-consuming task and in general ∼100 Raman spectra were recorded for each artefact from ∼500 spots probed by the oscilloscope. On encountering potentially significant micro-residues, investigations of the adjacent surfaces were conducted to document residue distributions and, if possible, Raman mapping was undertaken on small areas. Finally, a random check of both surfaces, away from the edges, was conducted with a 20× magnification objective, to document any other residue area(s) and to confirm the extent and depth of the micro-residue concentrations. Sediment samples taken from the sediment surrounding the samples and removed during ultrasonication were placed on microscope slides and also analysed.

7.3.4  Reference Material Micro-residues originating from both animal and plant material are often complex mixtures of nucleotides, proteins, lipids and carbohydrates and it is not expected that Raman spectroscopy will be able to identify all constituents, as is possible with techniques based on mass spectrometry.8 A first step in using Raman spectroscopy as a tool is to evaluate the range

View Online

Published on 26 October 2018 on https://pubs.rsc.org | doi:10.1039/9781788013475-00081

Raman Microscopy as a Primary Technique for Identifying Micro-residues Related

85

of residues that can be detected through their Raman spectra on artefacts with known micro-residues.9 Addressing this need, replicate stone tools were used to imitate tasks regularly performed in the Stone Age during food processing to detect the type and distribution of micro-residues related to specific tasks (e.g. sawing, cutting, scraping) on different materials (e.g. meat, wood, hide, bone). Some of these tools were used nearly 30 years ago as the basis for documenting residue and wear patterns and were used on a variety of materials, including animal flesh, bone and hide.10 New tool-use experiments were undertaken for comparison with the 30-year-old tools. Studying samples with known residues and functions forms a reference base to aid interpretation of the results from archaeological tools.

7.4  Results and Discussion 7.4.1  Sediment It is expected that residues associated with a stone tool will also occur in the surrounding sediment as degradation processes and dissolution through the working of groundwater might detach some original residues from the artefacts. Comparing the frequency of occurrence of a specific residue on a tool with the three sediment samples collected for each artefact is helpful in deciding if a residue present in the sediment was deposited on the artefact or, conversely, if the occurrence of a residue in the sediment is due to dissolution from the artefact. Sediment from Liang Bua consisted mainly of feldspar and α-quartz grains, but other common minerals such as calcium carbonate, goethite and anatase were frequently observed. Sediment attached to the artefacts from Denisova Cave consists mainly of amorphous phosphate particles interspersed with α-quartz and feldspar grains, with varying amounts of calcite present for some of them. Although kaolinite clay was identified in sediments from both Denisova Cave and Liang Bua using FTIR spectroscopy, it was not observed in the sediment using Raman spectroscopy.

7.4.2  Experimental Tools Table 7.1 summarises the results obtained from the experimental tools. The most common residues that were detected on tools used to process animal products 30 years ago were identified as collagen (amide I and amide III bands), bone (PO4 stretch at 962 cm−1) and saturated fatty acids (SFA) with CH2 and CH3 stretching vibrations between 2800 and 2950 cm−1, bending CH2/CH3 vibrational bands at 1463 and 1443 cm−1, a CH2 twisting mode at 1300 cm−1, and C–C stretching at 1133, 1105 and 1067 cm−1.11,12 Collagen fibres, small pieces of bone and individual fatty acid residues could be recognised visually (Figure 7.2). Saturated fatty acids and bone appeared smeared in areas where pressure was applied during the processing activity.

Published on 26 October 2018 on https://pubs.rsc.org | d

Material worked

Age

Function

Residue type

Frequency

Fresh possum skin

30 years

Scraping

Dry animal bone

30 years

Sawing

Meat

30 years

Cutting

Fresh bone

30 years

Scraping

Fallow deer bone

3 months

Fallow deer bone

3 months

Cleaning Extracting bone marrow Scraping Sawing

Fallow deer skin

3 months

Scraping

Smeared SFA Discrete SFA Protein fibre Protein Starch grain Bone + collagen Smeared bone Smeared SFA + bone Smeared SFA Collagen fibre Smeared protein SFA fibre Discrete SFA Bone and collagen Collagen fibre Lipids Plant fibre Smeared bone and collagen Bone and collagen Smeared SFA/UFA mixture Bone and collagen Smeared bone and collagen Smeared SFA/UFA mixture Protein Smeared SFA/UFA mixture Discrete SFA/UFA mix

Common Common Common Common Rare Very common Very common Very common Rare Very common Very common Uncommon Uncommon Very common Very common Uncommon Rare Very common Very common Uncommon Very common Very common Uncommon Rare Common Common

86

Table 7.1  Results  from residue identification on experimental tools. Adapted with permission from ref. 15, Copyright 2018 Elsevier Ltd.a

Chapter 7

Published on 26 October 2018 on https://pubs.rsc.org | d

2 weeks

Cutting

Rowan

2 weeks

Cutting and scraping

Siberian pine

1 month

Cutting and scraping

Birch bark

1 month

Cutting

Nettle

9 month

Cutting

a

Uncommon Rare Common Common Common Common Common Rare Rare Common Common Uncommon Uncommon Common Common Uncommon Common Common Common

 ery common: micro-residue widespread; common: micro-residues occur in limited areas or with specific distributions; uncommon: infrequently V detected; rare: only once or twice detected.

Raman Microscopy as a Primary Technique for Identifying Micro-residues Related

Fern

Collagen fibre Protein Plant fibre Carotenoid pigment Smeared carotenoid pigment Wood fibre Smeared wood fibre Oxalate Discrete SFA Smeared wood Wood fibre Plant fibre Smeared resin Smeared wood Wood fibre Plant fibre Plant fibre Smeared SFA/UFA Discrete SFA/UFA

87

View Online

Published on 26 October 2018 on https://pubs.rsc.org | doi:10.1039/9781788013475-00081

88

Chapter 7

Figure 7.2  Micro-residues  associated with processing animal material: (A) Discrete saturated fatty acid, (B) smeared saturated fatty acid, (C) collagen micro-fibres and (D) bone fragment.

In animal processing experiments, where tools were analysed one month after use (Table 7.1), similar residues were detected, but in some cases Raman spectra of discrete and smeared fatty acid residues had additional peaks at 1656 and 3010 cm−1 (C=C stretch and =C–H stretching, respectively) and a shoulder centred at 1260–1270 cm−1 (=C–H deformation) that can be attributed to unsaturated fatty acids.11,12 The presence of another C=C stretch band centred at 1679 cm−1 suggests the presence of a trans-isomer11 and a band at 1610 cm−1 (Figure 7.3) might be attributed to a conjugated cis-isomer mode with multiple C=C–C=C modes or an aromatic ring.13 It can be concluded that for the older samples, unsaturated fatty acids were degraded to their saturated counterparts during the 30 years of storage. The frequency and residue type on the tools used for processing animal products varied according to tool function. On artefacts used to saw or cut bone, bone and collagen residues were the most common; on tools used to cut meat, collagen fibres and smeared protein were the most common. Scraping animal skin resulted in mostly fatty acid residues, some as discrete residues with a specific shape and others spread over a larger area (Table 7.1). On most of the artefacts that were used to process fresh plant material (fern, rowan, Siberian pine and birch bark), the most common residues detected were plant fibres (high cellulose content, main bands at 1093 and 1121 cm−1),14 wood fibres (high lignin content, main band at 1600 cm−1)14 and carotenoid pigments (only for fern). Although discrete fatty acids were

View Online

89

Published on 26 October 2018 on https://pubs.rsc.org | doi:10.1039/9781788013475-00081

Raman Microscopy as a Primary Technique for Identifying Micro-residues Related

Figure 7.3  Comparison  between the Raman spectra of saturated fatty acid and sat-

urated/unsaturated fatty acid mixtures recorded on stone tools used to process fresh animal skin in the spectral regions (A) 100–1700 cm−1 and (B) 2600–3100 cm−1. Reproduced with permission from ref. 15, Copyright 2018 Elsevier Ltd.

detected on these tools (saturated and saturated/unsaturated mixtures) resulting in Raman spectra exactly the same as on the tools used to process animal products, their numbers were not significant and they were not smeared or spatially distributed in recognisable patterns that can be linked to usewear. However, on the artefact used to cut nettles, a plant rich in natural oils, saturated/unsaturated fatty acid mixtures were commonly recorded

View Online

Published on 26 October 2018 on https://pubs.rsc.org | doi:10.1039/9781788013475-00081

90

Chapter 7

as discrete and smeared residues (Table 7.1). Therefore, there is no single Raman spectrum that makes a chemical distinction between the artefacts used on animal and plant material, so the distribution of the residues and association with other materials becomes very important. Although discrete and smeared saturated/unsaturated fatty acids commonly occur on the artefact used to cut nettles, they occur in patches interspersed with plant fibre bundles and the smeared fatty acid residues are not as thick as for the artefacts used to process animal products.15

7.4.3  Archaeological Artefacts Stone tools used repeatedly to scrape, cut or saw particular materials sustain diagnostic use wear, including polish associated with changes in surface micro-topography, that can be visually identified under a light microscope.16 It has been shown experimentally that micro-residues are commonly found in areas with usewear17 and therefore an in-depth study of polish distribution for each artefact was undertaken after the Raman analyses and compared to the distribution patterns of the residues.15 Three different micro-residue groups were distinguished among the artefacts so far studied. The first group, for artefacts from Denisova Cave, consists of smeared fatty acid residues (Figure 7.4A), similar to those obtained on experimental tools used to process animal products and some plants, in addition to discrete fatty acid and protein residues.7,15 In general, these fatty acid residues are closely associated with areas of high polish (Figure 7.4B) and in some instances include unsaturated fatty acid residues similar to the one month-old experimental tools (see Section 7.4.2 and Figure 7.3). This indicates a high degree of preservation, as expected for the cold conditions in Denisova Cave. Although the very nature of a smeared residue classifies it as originating from the past use of a tool, a good correlation between polish and smeared fatty acid areas offers supporting information (Figure 7.4B). A closer look at the distribution patterns on the tool shown in Figure 7.4B shows that the correlation between polish and fatty acid distribution is very high and on the left long edge, smeared fatty acids and polish appear on both sides, implying that pressure was distributed to both sides of the tool during use, which is consistent with a cutting/sawing action. On the other edge of the tool, the smeared fatty acid zones and polish occur only on one side, corresponding to a scraping action. On the experimental tools used to process some animal products, small pieces of bone as well as areas of smeared bone were identified (Table 7.1). Although particles of amorphous phosphate (PO4 stretch at 950 cm−1, FWHM 25–35 cm−1)18 were found widespread on all the artefacts from Denisova Cave, they do not show any specific spatial distribution; as amorphous phosphate is the most common mineral identified in the sediment, it was probably transferred from the sediment to the artefact surfaces and on some artefacts formed a patina (phosphate skin). Collagen fibres associated with bone are commonly found on experimental stone tools used to work bone and meat,

91

Published on 26 October 2018 on https://pubs.rsc.org | d

of the distribution patterns of polish and saturated fatty acid residues on the same tool from Denisova Cave (B).

Raman Microscopy as a Primary Technique for Identifying Micro-residues Related

Figure 7.4  Map  (using the strong C–H stretch band) of smeared fatty acid residue on a stone tool from Denisova Cave (A) and comparison

View Online

Published on 26 October 2018 on https://pubs.rsc.org | doi:10.1039/9781788013475-00081

92

Chapter 7

but they were not found on Denisova stone artefacts in association with lipid micro-residues. Taking into account the prominent presence of both discrete and smeared fatty acid micro-residues, together with the absence of bone and collagen (which is well preserved in some bones excavated at Denisova Cave), a comparison with Table 7.1 suggests that these tools were most likely used to scrape animal skin. The residues most common for the second group of micro-residues are discrete fatty acids and proteins, protein/fatty acid mixtures and plant fibres. This group is typical for some artefacts from Liang Bua and the fatty acid residues commonly occur on polished areas, while the proteins are generally more randomly distributed. Figure 7.5 shows a typical distribution pattern of saturated fatty acids and plant fibres on an artefact and a representative spectra of plant/wood fibres. The main chemical components of plant fibres are cellulose (including hemicelluloses), moisture, lignin and pectins, which vary in abundance between species and growth conditions. Main cellulose bands occur at 1093 and 1121 cm−1 (C–O and O–C–O stretching modes) and the C–H deformation mode at 903 cm−1.14 Although Raman spectroscopy is not able to identify specific plant species, the aryl ring stretching bands characteristic of lignin are useful to broadly distinguish between wood and plants richer in cellulose. For example, a

Figure 7.5  (A)  Plant fibres detected on an artefact from Liang Bua, and (B) shown in relation to polished edges. (C) Raman spectrum of cellulose fibre suspected to be contamination due to high signal-to-noise ratio (a), and Raman spectra of other plant fibres analysed on stone tools from Liang Bua (b, c).

View Online

Raman Microscopy as a Primary Technique for Identifying Micro-residues Related

93

Published on 26 October 2018 on https://pubs.rsc.org | doi:10.1039/9781788013475-00081

−1

higher intensity of the lignin aryl stretching vibration at 1597 cm accompanied by a shoulder at 1654 cm−1 indicate that the fibres probably originate from wood.14 The presence of plant fibres and the absence of a strong presence of fatty acids and bone suggest that these artefacts were used to process plant material. The third set of micro-residue types and distribution patterns is extremely rich in a variety of residues and an example can be seen in Figure 7.6, where polish distribution is also indicated. Small pieces of bone commonly occur and are sometimes smeared; discrete as well as smeared fatty acid residues are common and in some instances are mixed with bone. Plant fibres occur in clusters and concentrations of protein residues were also detected. The dorsal distal part of this stone tool has the most intense polished area and also the highest number of bone apatite and lipid micro-residues. Plant fibres that occur in clusters were identified, but appear outside the main working zone, so their presence might be incidental to the main use of the tool. Artefacts with this group of residues are also from Liang Bua and, comparing the residue suite to Table 7.1, were probably used for butchering.

Figure 7.6  Example  of the third set of residue types and distribution pattern in comparison with polish distribution.

View Online

Published on 26 October 2018 on https://pubs.rsc.org | doi:10.1039/9781788013475-00081

94

Chapter 7

Figure 7.7  Raman  spectra of bone recorded on a stone tool from Liang Bua (A,

b–d) and Raman map of the position of the P–O stretch vibration on a small fragment of bone on the tool (B). Raman spectrum (A, a) is from a modern bone sample.

Bone consists of an inorganic part that is chemically similar to carbonate apatite (Ca5(PO4, CO3)3OH) and an organic part consisting mostly of collagen. Over time, bone undergoes taphonomic and diagenetic processes, influenced by environmental and burial conditions, which cause alteration of both the organic and inorganic components.19 Collagen deterioration, microbiological alteration, bioapatite dissolution and recrystallisation, ion depletion or uptake and the precipitation of secondary mineral phases can occur and has an influence on the Raman spectrum.20 Depletion of collagen can be seen by the disappearance of the peaks at 1254, 1451, 1675, 2880 and 2943 cm−1 present in the spectrum of a modern bone sample (Figure 7.7A, a) and absent in spectra recorded on a bone fragment on a tool from Liang Bua (Figure 7.7A, b–d). The presence of rare earth elements can be identified in two of the spectra (c, d) by fluorescence bands. A closer look at the Raman spectra recorded on the bone residue shown in Figure 7.7B shows the presence of two different phases of phosphate. In one part of the fragment, the symmetric stretch vibration of phosphate occurs at 950 cm−1 (FWHM 25–35 cm−1) and in other parts at 967 cm−1 (FWHM 15 cm−1). The appearance of both types of phosphate signals on a small bone fragment firmly attached to the stone tool clearly illustrates the coexistence of ongoing degradation or recrystallisation processes of bone. In classifying the residues as originating from tool use, we have followed very stringent guidelines, as set by researchers using optical microscopy to identify residues; namely micro-residue abundance and meaningful distributions.21,22 As all the artefacts were washed by 10 s sonication and the residues left on the artefacts are strongly attached, there is a high probability that many of the micro-residues that we rejected as possible contamination might in fact be archaeologically meaningful. On many of the artefacts

View Online

Published on 26 October 2018 on https://pubs.rsc.org | doi:10.1039/9781788013475-00081

Raman Microscopy as a Primary Technique for Identifying Micro-residues Related

95

we did not detect any significant numbers of micro-residues, but not all of the stone artefacts excavated at archaeological sites have actually been used as tools and might, instead, be stones produced during the process of lithic reduction and include shatter and production debris, and production rejects.

7.5  Conclusions The most common residues identified on stone tools from the three different groups are quite distinct. This can be attributed to different degrees of preservation due to climatic difference, but might possibly also be linked to distinct behaviours between human species. Precise archaeological interpretation is not possible at this stage, due to a small sample size, but the results of the present study have laid an important foundation for further work on the identification and interpretation of micro-residues. A comparison with GC-MS results on the same set of artefacts and a study on bone degradation at both sites (currently being conducted) will also contribute to a better understanding of the nature of the micro-residues on the artefacts.

Acknowledgements We thank T. Sutikna (University of Wollongong), M. W. Tocheri (Lakehead University, Canada) and E. W. Saptomo and Jatmiko (Pusat Penelitian Arkeologi Nasional, Indonesia) for supporting our work at Liang Bua, and A. P. Derevianko and M. V. Shunkov (Institute of Archaeology and Ethnography, Russian Academy of Sciences) for supporting our research at Denisova Cave. We appreciate the input of R. Fullagar (University of Wollongong) and E. Hayes (University of Wollongong) regarding polish distribution. This study was funded by the Australian Research Council through Australian Laureate Fellowship FL130100116 to R. G. Roberts (University of Wollongong), and by a University of Wollongong Postgraduate Award and an International Postgraduate Research Scholarship to L. B., with additional funding from the Smithsonian Institution's Humans Origins Program (to M. W. Tocheri) and Russian Science Foundation project number 14-50-00036 (to A. P. Derevianko and M. V. Shunkov).

References 1. L. Bordes, L. C. Prinsloo, R. Fullagar, T. Sutikna, E. Hayes, Jatmiko, E. W. Saptomo, M. W. Tocheri and R. G. Roberts, J. Raman Spectrosc., 2017, 48, 1212. 2. G. F. Monnier, T. C. Hauck, J. M. Feinberg, B. Luo, J. Le Tensorer and H. al Sakhel, J. Archaeol. Sci., 2013, 40(10), 3722. 3. M. J. Morwood and W. L. Jungers, J. Hum. Evol., 2009, 57, 437.

View Online

Published on 26 October 2018 on https://pubs.rsc.org | doi:10.1039/9781788013475-00081

96

Chapter 7

4. T. Sutikna, M. W. Tocheri, M. J. Morwood, E. W. Saptomo, Jatmiko, R. D. Awe, S. Wasisto, K. E. Westaway, M. Aubert and B. Li, et al., Nature, 2016, 532, 366. 5. V. Slon, C. Hopfe, C. L. Weiß, F. Mafessoni, M. de la Rasilla, C. LaluezaFox, A. Rosas, M. Soressi, M. V. Knul, R. Miller, J. R. Stewart, A. P. Derevianko, Z. Jacobs, B. Li, R. G. Roberts, M. V. Shunkov, H. de Lumley, C. Perrenoud, I. Gušić, Z. Kućan, P. Rudan, A. Aximu-Petri, E. Essel, S. Nagel, B. Nickel, A. Schmidt, K. Prüfer, J. Kelso, H. A. Burbano, S. Pääbo and M. Meyer, Science, 2017, 356, 605. 6. C. Coupry, G. Sagon and P. Gorguet-Ballesteros, J. Raman Spectrosc., 1997, 28, 85. 7. L. Bordes, PhD thesis, University of Wollongong, in writing. 8. S. Luong, E. Hayes, E. Flannery, T. Sutikna, M. W. Tocheri, E. W. Saptomo, Jatmiko and R. G. Roberts, Anal. Methods, 2017, 30, 4349. 9. E. A. Carter, S. J. Kelloway, N. Kononenko and R. Torrence, in Analytical Archaeometry, Selected Topics, ed. H. G. M. Edwards and P. Vandenabeele, RSC Publishing, London, 1st edn, 2012, p. 11. 10. R. L. K. Fullagar, PhD thesis, Department of Archaeology, La Trobe University, Melbourne, 1986, p. 382. 11. K. Czamara, K. Majzner, M. Z. Pacia, K. Kochan, A. Kaczor and M. Baranska, J. Raman Spectrosc., 2015, 46, 4. 12. J. De Gelder, K. De Gussem, P. Vandenabeele and L. Moens, J. Raman Spectrosc., 2007, 38, 1133. 13. M. Melchiorre, C. Ferreri, A. Tinti, C. Chatgilialoglu and A. Torreggiani, Appl. Spectrosc., 2015, 69, 613. 14. U. P. Agarwal and S. A. Ralph, Appl. Spectrosc., 1997, 51, 1648. 15. L. Bordes, R. Fullagar, L. C. Prinsloo, E. Hayes, M. B. Kozlikin, M. V. Shunkov, A. P. Derevianko and R. G. Roberts, J. Archaeol. Sci., 2018, 95, 52–63. 16. J. S. Bradfield, Afr. Archaeol. Bull., 2015, 70(201), 3. 17. V. Rots, E. Hayes, D. Cnuts, C. Lepers and R. Fullagar, PLoS One, 2016, 11(3), e0150437. 18. M. Kazanci, P. Roschger, E. P. Paschalis, K. Klaushofer and P. Fratzl, J. Struct. Biol., 2006, 156, 489. 19. D. B. Thomas, R. E. Fordyce, R. D. Frew and K. C. Gordon, J. Raman Spectrosc., 2007, 38, 1533. 20. G. Dal Sasso, M. Lebon, I. Angelini, L. Maritan, D. Usai and G. Artioli, Palaeogeogr., Palaeoclimatol., Palaeoecol., 2016, 463, 168. 21. G. H. Langejans, J. Archaeol. Sci., 2010, 37, 971. 22. M. Lombard and L. Wadley, in Archaeological Science Under a Microscope: Studies in Residue and Ancient DNA Analysis in Honour of Thomas H. Loy, ed. M. Haslam, G. Robertson, A. Crowther, S. Nugent and L. Kirkwood, ANU Press, 2009, p. 11.

Published on 26 October 2018 on https://pubs.rsc.org | doi:10.1039/9781788013475-00097

Chapter 8

Biological Materials of Significance to Cultural Heritage Elizabeth A. Carter* Sydney Analytical – Vibrational Spectroscopy Facility and the School of Chemistry, University of Sydney, NSW 2006, Australia *E-mail: [email protected]

8.1  Introduction The earliest application of Raman spectroscopy to cultural heritage samples was for the analysis of ancient inorganic pigments by Guineau in 1984.1 Biological samples are inherently fluorescent and for this reason are very challenging to investigate but the development of FT-Raman spectrometers in 1986.2 using near-infrared laser excitation, allowed for the collection of spectra from biological tissues with minimal fluorescence. Prof. Howell G. M. Edwards and his extensive group of students, researchers and collaborators laid the foundations for the analysis of biological samples of significance to cultural heritage having studied a diverse range of samples. This chapter provides an overview that is focused on the analysis of human specimens and attempts to provide an update of the elegantly written chapter by Prof. Edwards produced in the first edition of this book published in 2005.3

  Raman Spectroscopy in Archaeology and Art History Volume 2 Edited by Peter Vandenabeele and Howell Edwards © The Royal Society of Chemistry 2019 Published by the Royal Society of Chemistry, www.rsc.org

97

View Online

98

Chapter 8

8.2  Human Tissue Published on 26 October 2018 on https://pubs.rsc.org | doi:10.1039/9781788013475-00097

8.2.1  Keratin Proteins Keratin is the most abundant structural protein in epithelial cells, which are the cells that line the surface of the body. These proteins are insoluble, durable and tough, and are composed of polymeric constituents with a high cysteine content and a complex hierarchical structure. Keratin proteins are the major components of animals' hard-outer layers such as wool, horns, claws, nails, beaks and feathers, which provide insulation, protection and are used for defence. Keratin can be classified on the basis of its sulphur content, most of which is contained in the disulphide bonds of cysteine residues. The aforementioned structures are classified as “hard” keratin proteins because the sulphur concentration is greater than 3%. The outermost layer of skin, the stratum corneum, is considered “soft” as it contains less than 3% sulphur. X-ray diffraction provides further categorisation into α-keratin (α-pattern and amorphous) and β-keratin (β-pattern and feather-pattern). The α- and β-keratin protein conformations can be differentiated by their molecular structures (see Figure 8.1A and B)4 as further discussed in Section 8.2.3. α-keratin proteins consist of two polypeptide chains that wind around each other to form a right-handed helix stabilised by hydrogen bonds. Two double-stranded helices coil around each other to produce a left-handed coiled coil. β-keratin proteins are comprised of β-strands laterally packed in a parallel or antiparallel manner with the chains held together by intermolecular hydrogen bonds. The hydrogen bonds stabilise the pleated sheet structure and the planarity of the peptide bond forces the β-sheet to be pleated.

8.2.2  Morphological Structure 8.2.2.1 Hair Fibres Hair fibres are composed of three morphologically and chemically different layers, see Figure 8.1C. The cuticle is the outermost layer which is formed by overlapping cells that produce a serrated edge that points towards the hair fibre tip.5 The cuticle encapsulates the cortex, the major structural component, which contains cortical cells and the cell membrane complex. The macrofibrils are the major portion of the cortical cells and consists of intermediate filaments (previously called microfibrils) and the matrix. The intermediate filaments are low in cystine (∼6%) and are embedded in a cystine rich matrix (∼21%). The cell membrane complex binds the cuticle and cortical cells together and is a non-keratinous protein with a low cystine content (∼2%). The medulla is not always present, or its structure can be highly variable, generally it comprises only a minor percentage of the hair fibre mass.6

View Online

99

Published on 26 October 2018 on https://pubs.rsc.org | doi:10.1039/9781788013475-00097

Biological Materials of Significance to Cultural Heritage

Figure 8.1  Molecular  structure of (A) α-keratin and (B) β-keratin.57 Schematic dia-

grams of keratin containing biological materials including (C) hair, (D) skin. Copyright N. Sotoudeh (Mucca Design).

View Online

100

Chapter 8

Published on 26 October 2018 on https://pubs.rsc.org | doi:10.1039/9781788013475-00097

8.2.2.2 Skin Human skin is a complex heterogeneous tissue composed of a number of morphologically and chemically distinct layers including the epidermis, dermis and subcutaneous tissue. Two important functions of skin are to act as a permeability barrier to keep water in and prevent harmful agents such as chemicals and micro-organisms from entering the body; and to act as a regulator of body temperature. Figure 8.1D presents a diagrammatic representation of the basic organisation of the various layers of skin.7 The epidermis is a continuous keratinising stratified epithelium that varies in thickness over most of the body, particularly the load bearing parts of the body such as the palms of hands or the soles of feet, where it may be as thick as 1.5 mm and the eyelids where it is less than 0.1 mm.8 One essential role of the epidermis is to generate the stratum corneum, the outermost layer of skin that provides the main permeability barrier to percutaneous absorption for most exogenous chemicals. The stratum corneum typically consists of 10 to 15 layers of flattened, anucleated keratinised cells (corneocytes) embedded in a lipoidal matrix; the structure has been likened to a brick wall, in which the proteinaceous cells are the “bricks” embedded in a “mortar” of specialised lipids.9 The dermis, which lies below the epidermis, is composed of collagen, elastin and reticular fibres, which are embedded in a glycosaminoglycan matrix. Collagen and elastin are proteins that permit skin to easily stretch yet retain its shape.

8.2.3  Characteristic Raman Spectra of Keratin Proteins Figure 8.2 presents the Raman spectra of a variety of keratin proteins and some characteristic features have been marked as they will be referred to throughout the chapter. The region from 3200 to 2700 cm−1 comprises of a number of overlapping bands attributed to symmetric νs(CH) and asymmetric νas(CH) stretching modes arising from the CH, CH2 and CH3 groups of lipids and proteins. Figure 8.2D presents the spectrum of the lipid containing stratum corneum, the contribution of the lipid CH groups is very evident with intense bands at 2882 and 2851 cm−1, which are assigned to ν(CH2) and νas(CH2) modes, respectively. The 1800–400 cm−1 region is dominated by the Amide bands, that originate from the peptide bond, and CH bending modes, which arise from a combination of lipids and proteins, as well as bands from aromatic amino acids such as phenylalanine, tyrosine and tryptophan. The predominant secondary structure present in most proteins is the α-helix, however, there are a number of other protein conformations present including the β-pleated sheet, random coil, and amorphous form. The positions of the Amide bands are characteristic for various secondary structures and are used in conjunction with other bands, such as the C–C skeletal backbone mode at ∼935 cm−1, for secondary structure identification.10 Figure 8.2 is an excellent example of the spectral differences that can be observed in the

View Online

Published on 26 October 2018 on https://pubs.rsc.org | doi:10.1039/9781788013475-00097

Biological Materials of Significance to Cultural Heritage

101

Figure 8.2  Raman  spectra collected from keratin containing biological materials

of interest including (A) wool, (B) nail, (C) feather and (D) Stratum corneum. Spectra (1064 nm, 2000 scans, 4 cm−1, 200 mW) have been normalised to the CH bending mode at ∼1450 cm−1 and have been offset for clarity. The spectrum collected from the feather has been baseline corrected.

line shape, width and position of the Amide I band of keratin proteins. For instance, the Amide I band of the β-pleated feather keratin (Figure 8.2C) is observed at ∼1667 cm−1. In comparison, this same band is centered at ∼1651 cm−1 in the other spectra as all of these proteins are predominately α-helical. Also, one should note that the Raman spectra collected from the stratum corneum (Figure 8.2D) which is regarded to be a “soft” keratin protein has no disulphide band (ν(S–S)) but the remaining spectra collected from the “hard” keratin proteins i.e., wool, nail and feather (Figure 8.2A–C), have a band at ∼514 cm−1 attributed to disulphide bonds.

8.2.4  Mummified Remains The preservation of human and animal bodies can provide a wealth of information about historical and technological developments. Mummi­ fied remains provide information about disease, diet, medical treatment, genetics, mummification techniques, religious customs and the culture and habits of our ancestors.11,12 There are three classes of mummification (I) natural preservation due to suitable climactic conditions, i.e., Ötzi13 or the Qilakitsoq14 mummies (see section 8.2.4.1 and 8.2.4.2);

View Online

Published on 26 October 2018 on https://pubs.rsc.org | doi:10.1039/9781788013475-00097

102

Chapter 8

(II) exploitation of natural preservation e.g., Incan children sacrificed in a ritual known as capacocha who were given coca and alcohol, which would have sedated the children prior to their death;15 (III) artificial preservation e.g., embalming.16 Mummification began in ancient Egypt in the Pre-Dynastic period (4800–3100 BCE) where the environmental conditions of the dry and hot desert sands were used to naturally desiccate the bodies. The Egyptians were thought to believe that the dead would live on in the next world and that their bodies needed to be preserved to enable the immortal spirit to return to the corpse. It has been speculated that the introduction of artificial preservation was to provide a means of preserving the lifelike form and features of the deceased.11 Early attempts at mummification were unsuccessful until the first major advance in the early fourth Dynasty (∼2613–2494 BCE), which was the evisceration of the abdominal and thoracic cavities. The innovative application of various resins and oils in the New Kingdom period (∼1550–1077 BCE) led to improved tissue preservation and helped to mask the odours produced due to putrefaction and the mummification process. After cleansing, the body was dehydrated in a naturally occurring salt called natron. There is conflicting literature about the length of time that the body was left in natron with the general consensus being seventy days.11,17 However, recent work has suggested that the entire mummification process from death to burial took 70 days with the body embalmed in natron between 30 and 40 days.18

8.2.4.1 Ötzi The Iceman, or Ötzi, was discovered by German tourists walking in the Tyrolean Ötztaler Alps in 1991 and was the first mummified sample to be investigated using Raman spectroscopy. Radiocarbon dating of skin and bone established that Ötzi was between 5100 to 5300 years old and is the oldest and best preserved mummified human body ever discovered. The body was found buried in a hollow under a glacier and was essentially freeze dried preventing putrefaction; this provided a unique opportunity for the analysis of mummified skin that had occurred without the use of exogenous chemicals. A comparative analysis of the Iceman skin and a modern day freeze-dried sample was performed using a combination of scanning and transmission electron microscopies together with Raman spectroscopy (1064 nm, 4000 scans, 20 mW).13 Scanning electron microscopy (SEM) images revealed the Iceman skin to have an outer layer of compressed stratum corneum cells and the second layer a laminated sheet-like structure attributed to the dermis. However, the transmission electron micrographs did not reveal a distinctive stratum corneum structure when compared with the modern day freeze-dried sample. This was proposed to be due to sampling issues that occurred during tissue sectioning. Raman spectroscopy confirmed the presence of two distinct skin layers in the Iceman sample. Raman spectra of the

View Online

Published on 26 October 2018 on https://pubs.rsc.org | doi:10.1039/9781788013475-00097

Biological Materials of Significance to Cultural Heritage

103

ancient and modern skin samples clearly indicated that the Iceman skin contained lipids with the position of the various ν(CH) bands found to be very similar between the spectra of the different samples, however, it was noted that there was a reduction in the intensity and line width of these bands in spectra collected from the Iceman sample. Further spectral evidence confirming the presence of lipids were bands at 1440 and 1300 cm−1, attributed to δ(CH) modes. The profile of these lipid bands was notable different in the Raman spectra of the Iceman sample compared to the modern-day equivalent. The absence of bands at 3060 and 1590 cm−1, assigned to ν(CH) and ν(C=C) modes were attributed to oxidation of the olefinic bonds of lipids. In 2010, Janko et al.19 used a combination of Raman spectroscopy and atomic force microscopy (AFM) to investigate the structural preservation of the Iceman's mummified skin. Skin samples from the right hand, the back near the vertebra and near a wound at the back of the Iceman were collected. AFM revealed networks of extremely well-preserved collagen fibrils. Wound tissue was investigated to establish if the collagen had decomposed or had been altered due to insect or micro-organisms infestation, which would be expected within a wound, but no degradation was observed. These findings were confirmed by Raman spectroscopic measurements (532 nm, 3 or 1 cm−1, 240 s, 1.0 mW), which revealed that the molecular structure of the mummified collagen was extremely well preserved. AFM nanoindentation was used to assess the collagen fibrils elasticity and these measurements indicated that there were small changes in the mechanical behaviour of the fibrils. The authors concluded that a loss of interstitial water due to dehydration resulted in a more densely packed fibril structure and promoted the formation of additional cross-links within the collagen. The study results illustrated that the preservation of the collagen ultrastructure was due to mummification by freeze drying and highlighted the importance of dehydration in this process.

8.2.4.2 Qilakitsoq Mummies The Qilakitsoq mummies from Greenland date from 1475 CE (±50 years) and are the oldest preserved bodies in the Arctic region. Eight mummies were found in two graves and skin samples from a 4-year-old boy and three females believed to be aged 20, 30 and 50 years old were collected for Raman spectroscopic analysis.14 The spectra (1064 nm, 1000 scans, 20 mW, 100 µm spot size) collected from these 500-year-old samples were comparatively similar to that of the ∼5200-year-old Ötzi samples, with the authors suggesting that the changes in molecular structure took place in a relatively short time frame after mummification. Gniadecka et al.14 proposed that low temperatures and air humidity together with a protective shelter against the elements promoted natural mummification and prevented the decaying processes, which requires water and ambient temperatures above 4 °C.

View Online

104

Chapter 8

Published on 26 October 2018 on https://pubs.rsc.org | doi:10.1039/9781788013475-00097

8.2.4.3 Chiribayan Mummies A later study by Gniadecka et al.12 in 1999 allowed for a comparison of Raman data collected from the above mentioned Ötzi and Qilakitsoq samples together with samples collected from the Chiribayan mummies of Peru. The Chiribaya Alta region of the Peruvian desert provided an interesting and contrasting environment for preservation. The arid environment, a nitraterich soil and the cultural practices of the Chiribaya people permitted the preservation of a variety of organic material including plants, mummified humans and animals. The 1000-year-old bodies were exhumed from burial pits, many of them deep and narrow, lined with stones and then covered with larger stones. Once the mummy bundle and offerings had been removed from the pit it was reported that the preservation was astonishing and the skin, tendon, organs, nail and hair were intact without the aid of any artificial processing.20 Gniadecka and co-authors12 were provided with an opportunity to study these samples with Raman spectroscopy (1064 nm, 1000 scans, 20 mW). An interesting observation was that the majority of the bodies were light brown in colour but some were very darkly pigmented leading to the hypothesis that these bodies had been artificially mummified. Data collected from the Chiribayan mummies, the naturally mummified Ötzi and the Qilakitsoq samples, was compared to that from contemporary skin samples (n = 4) that had been freeze dried for six days (n = 2) or kept within a moist environment at 4 °C (n = 2).21 Spectral analysis revealed that all of the samples exhibited signs of protein degradation, with specific attention drawn to the reduced intensities of the Amide I and III bands. The similarity between the 500, 1000 and 5200-year-old skin samples lead the authors to suggest that the change in molecular structure took place in a short time frame, most likely between death and the completion of the natural mummification process. Recently, it has been reported that natural mummification for adults takes 6–12 months and several months for children and potentially this is the time frame in which these molecular changes occur.22 The darkly pigmented Peruvian mummies were thought have undergone artificial mummification, but analysis revealed that they were similar to the Qilakitsoq mummies. However, striking differences were observed in the spectra of the lightly pigmented Chiribayan samples with a marked increase in the intensity of a number lipid modes, observed at 2882, 2856 and ∼1300 cm−1, compared to the spectra of the other mummified samples. It was suggested that the origin of these bands could be the embalming material, which led to better sample preservation. Further examination of the spectra revealed that the Amide I band of these samples was more intense than the other mummies, supporting the idea that the lightly pigmented Chiribayan samples had been embalmed. This was the first time Raman spectroscopy was used to confirm that mummification had been achieved using an artificial process.

View Online

Biological Materials of Significance to Cultural Heritage

105

Published on 26 October 2018 on https://pubs.rsc.org | doi:10.1039/9781788013475-00097

23

Later research by Pabst et al. was undertaken to examine a unique Chiribayan mummy who was found with two different types of tattoos. On the hands, arms and lower left leg, decorative tattoos displaying different animals and symbolic ciphers were found. On the neck and upper part of the back were circular tattoos of various diameters, partly overlapping and asymmetrically distributed. It was postulated that the circular tattoos were therapeutic and a combination of analytical techniques including light microscopy, transmission electron microscopy (TEM), energy-dispersive X-ray spectrometry (EDXS) and Raman spectroscopy were used to investigate the shape, size, composition and distribution of dye particles sampled from both tattoo sets.23 Raman spectra were collected with 633 and 785 nm excitation lines using varying laser powers and acquisition times, neither of these parameters were reported. The samples were prone to fluorescence using either excitation line and this was said to be indicative of the presence of organic material. The data, not shown, was described as having weak peaks, which were attributed to amorphous carbon. The combined findings from all the techniques suggested that the tattoos on the extremities were decorative in nature and the circular tattoos, which would have been hidden due to clothing and hair, were therapeutic in nature and located close to acupuncture points.

8.2.4.4 Khnum-Nakht and Nekht-Ankh In 1906, the “Tomb of the Two Brothers”, Khnum-Nakht and Nekht-Ankh, was discovered at Rifeh in Upper Egypt. The Two Brothers were from the XIIth Dynasty (1991–1783 BCE) and were found at the finest intact nonroyal tomb ever found from that era. The excavation was led by Prof. William Flinders Petrie (later Sir William Flinders Petrie) who wrote to the Manchester Museum and offered the contents of the burial site for a £500 contribution to his next excavation; within a few weeks £570 19 s was raised.24 In 1908, Dr. Margaret Murray, the first Egyptologist at the Manchester Museum, unwrapped the bodies of the Two Brothers to a capacity-filled lecture theatre in Manchester University. Alongside Dr. Murray were specialists in textile studies, medicine and chemistry and this unique multi-disciplinary team carried out a full-scale scientific investigation of the two mummies. The bones of Nekht-Ankh were found to be in position and intact but not so the body. The remains were moist, and the bandages were wet. However, the facial skin was reported to be perfectly preserved and hair remained on the head and the sides of the face. The hair was dark brown and turning grey and about ¾ of an inch in length. The nails of the fingers and toes were also present. The difference in the condition of Khnum-Nekht compared to Nehkt-Ankh was striking, with the body of Khnum-Nekht found to be absolutely dry as were the bandages he was wrapped in. Where the skin

View Online

Published on 26 October 2018 on https://pubs.rsc.org | doi:10.1039/9781788013475-00097

106

Chapter 8

remained, it was white covered in little holes and was described as having the texture of vellum. The tendons looked like sticks and the flesh was a fine light-powder.24 In 2003, Petersen et al.25 were the first researchers to use Raman microspectroscopy for the analysis of mummified skin. Raman spectra (1064 nm, 2000 scans, 8 cm−1, 20 mW, ×20 objective) were measured from four skin samples collected from different areas of Nekht-Ankh to determine the extent of preservation achieved when using an artificial mummification process. The collected spectra were categorised into three groups based on protein content (low, intermediate and well-preserved) and spectral similarity within the fingerprint region i.e., 1800 to 900 cm−1. Nekht-Ankh was embalmed with natron, a natural mineral containing sodium carbonate (NaCO3), sodium bicarbonate (NaHCO3) with small quantities of sodium sulphate (Na2SO4) and sodium chloride (NaCl) as impurities. Raman spectra indicated that the proteins and lipids were well-preserved in some sample regions illustrating the effectiveness of natron for artificial preservation. However, in some instances a higher degree of degradation was observed, and this was in areas where sodium sulphate was detected. This was the only chemical remaining from the embalming process that was identified by spectroscopy. The well-preserved skin spectra of the Nekht-Ankh mummy were very similar to that of the Qilakitsoq child mummy illustrating that the artificial process was generally effective in a hot climate.

8.2.5  Hair In 1999, Wilson et al.,26 with knowledge gained from the work with the Ötzi and Qilakitsoq mummies, used FT-Raman spectroscopy to investigate ancient and degraded samples of human terminal scalp hair. Bulk (2000 scans, 8 cm−1) and single (18 000 scans, 4 cm−1, ×40 objective) fibres were analysed and despite long collection times for data acquisition from single fibres no spectral changes indicative of degradation due to extended laser irradiation were observed. A defocused laser beam was used for darker samples due to the potential of sampling heating and fluorescence. The age span of the hair samples was roughly 4000 years with the oldest sample from ∼2050 BCE and the youngest from 1993 CE. Many of the samples were contaminated with adherent soil deposits and a preparative washing step prior to spectroscopic analysis was considered. One sample was left overnight in a 50 : 50 mixture of methylated spirits and distilled water to establish the effect of washing. No significant difference was observed in the Raman spectra collected from a washed and unwashed sample. It was decided that the potential effect of leaching solubilised products and the overall deleterious effects on the embrittled samples was not worth the risk of sample damage. Raman spectra collected from all of the samples showed evidence of degradation characterised by changes in band widths and intensities. The most significant changes were a decrease in the intensity of the Amide I

View Online

Biological Materials of Significance to Cultural Heritage

Published on 26 October 2018 on https://pubs.rsc.org | doi:10.1039/9781788013475-00097

−1

−1

107 −1

(∼1650 cm ), Amide III (∼1451 cm ) and δ(CH) (∼1350 cm ) bands with the exception of three spectra where the Amide I and III bands were completely absent. An increase in the intensity of a ν(C=C) band was reported with the position of the band varying over a range from 1606 to 1578 cm−1. A new feature observed at 1340 cm−1 was attributed to oxidative change and was supported by the absence/reduced intensities of the vibrational modes associated with the disulphide bond i.e. the ν(S–S) bands at 540, 525, 510 cm−1 and the ν(C–S) bands found within the ranges of 745–700 and 670–630 cm−1. Some unusual features were observed in the spectra of hair samples from lead-lined coffins and cave sites that were attributed to the presence of lead carbonate (1047 cm−1) and calcium carbonate (1086 cm−1), respectively. A cross-sectioned hair fibre from a lead-lined coffin was investigated with Raman microscopy and results confirmed that lead carbonate had penetrated into the fibre. The introduction of contaminants was proposed to result from the hair fibre porosity increasing as the structural morphology degraded. Microscopic examination of all the samples revealed a widespread fungal attack although it was not possible to distinguish if this was due to the burial site environment or post-excavation contamination – highlighting the need for appropriate sample packing and storage. A contrasting study several years later provided an opportunity to investigate two historical hair samples, 150 and 300 years old, that had not been subjected to a harsh burial environment.27 The National Railway Museum in York (UK) provided a bundle of light brown and grey hair strands attributed to Robert Stephenson (1803–1859), who was one of the foremost civil and mechanical engineers of his time. Stephenson was held in high esteem by business, science and the public based on his work on the development of the railway network and locomotive technology in Britain.28 A second sample was provided by a private collector and was attributed to Sir Isaac Newton (1643–1727). Newton was one of the foremost scientific intellects of all times. A mathematician and physicist, he has been regarded to be the founding exemplar of modern physical science.29 Raman microspectroscopic studies were undertaken using a non-dispersive (1064 nm, 4000 scans, 4 cm−1,