University of Evora ARCHMAT (ERASMUS MUNDUS MASTER in Archaeological Materials Science)
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University of Evora ARCHMAT (ERASMUS MUNDUS MASTER IN ARCHaeological MATerials Science) A multi-analytical protocol combining EDXRF, SEM+EDS, μXRD and Monte Carlo simulations applied to analyse non-destructively Portuguese corroded copper coins E. Güncem Diktaş, 36190 Nick Schiavon, University of Evora (Supervisor) Antonio Brunetti, Università degli Studi di Sassari (Co-Supervisor) José Mirão, University of Evora (Co-Supervisor) Évora, October 2017 i University of Evora ARCHMAT (ERASMUS MUNDUS MASTER IN ARCHaeological MATerials Science) Um protocolo multi-analítico que combina as simulações EDXRF, SEM + EDS, μXRD e Monte Carlo aplicadas para analisar não destrutivas as de moedas de cobre portuguesas corroídas Güncem Diktaş, 36190 Nick Schiavon, University of Evora (Supervisor) Antonio Brunetti, Università degli Studi di Sassari (Co-Supervisor) José Mirão, University of Evora (Co-Supervisor) Évora, October 2017 ii ii i TABLE OF CONTENTS ABSTRACT ........................................................................................................................................ v RESUMO .......................................................................................................................................... vi ACKNOWLEDGEMENTS ..................................................................................................... vii 1. INTRODUCTION ................................................................................................................1 1.1. COINS AS HISTORIC ARTEFACTS ........................................................................................ 1 1.1.2. A BRIEF HISTORY OF COINAGE ......................................................................................... 3 1.1.2 NUMISMATICS IN PORTUGAL ....................................................................................... 4 1.2. HISTORICAL BACKGROUND OF THE COINS ................................................................ 4 1.3. CORROSION .................................................................................................................... 9 1.3.1. COPPER CORROSION IN DIFFERENT ENVIRONMENTS .................................... 18 1.3.2. BURIED COPPER CORROSION IN DIFFERENT ENVIRONMENTS ...................... 22 2. MATERIALS AND METHODS ................................................................................................ 25 2.1. MATERIALS ......................................................................................................................... 25 2.2. METHODOLOGY ................................................................................................................. 28 2.2.1. X-RAY FLUORESCENCE ANALYSIS ........................................................................... 28 2.2.2. X-RAY DIFFRACTOMETER TECHNIQUE AND μXRD .................................................. 29 2.2.3. SCANNING ELECTRON MICROSCOPE ................................................................ 29 2.2.4. MONTE CARLO SIMULATION ................................................................................ 29 2.2.5. MECHANICAL CLEANING OF THE COPPER COINS ............................................ 32 3. RESULTS AND DISCUSSION ................................................................................................ 34 3.1. μXRD ................................................................................................................................... 34 3.2. SEM-EDS ............................................................................................................................. 44 3.3. MC SIMULATION ....................................................................................................... 55 3.4. EDXRF ................................................................................................................................. 60 4. FINAL REMARKS AND FURTHER WORKS ................................................................................. 69 5. REFERENCES ........................................................................................................................... 71 ANNEX ........................................................................................................................................... 79 WORKING PRINCIPLES OF APPLIED ANALYTICAL TECHNIQUES ................................................... 79 1. X-RAY FLUORESCENCE ANALYSIS ........................................................................................... 80 iii 2. X-RAY DIFFRACTOMETER TECHNIQUE AND μXRD ................................................................. 81 2.1. QUALITATIVE PHASE ANALYSIS WITH X – RAYS DIFFRACTION (XRD) ...................... 82 3. SCANNING ELECTRON MICROSCOPE ............................................................................... 83 4. MONTE CARLO SIMULATION ............................................................................................... 89 APPENDIX .................................................................................................................................... 105 iv ABSTRACT Performing quantitative analyses on archaeological and cultural heritage metallic artefacts is challenging due to their complex multi-layered internal structure. “Layers” may include a) Original metal and/or alloy substrate (gold, silver, bronze etc.) b) Surface patinas enriched in corrosion products sulphides, oxides and/or chlorides compounds c) Protective treatments applied in past conservation interventions d) Soil derived incrustations from archaeological burial environment. To obtain compositional data on the metal substrate, usually these layers have to be removed but this not always possible due to the inherent fragility of the corroded artefacts as it is the case in particular with copper objects such as coins. The setting up of a non-destructive protocol is therefore important. In this study, a protocol combining SEM-EDS, μXRD, EDXRF and Monte Carlo simulations has been tested on a series of Portuguese coins from the 12th to the 19th centuries found at Largo das Olárias and Travessa do Jordão in Lisbon. 1. Analyze non-destructively the corrosion patterns and patinas developed on the surface Portuguese Copper coins from a Lisbon archaeological site (Largo das Olarias) SEM+EDS, μXRD and portable EDXRF 2. Apply the mineralogical and chemical data obtained during the analytical sessions to run Monte Carlo simulations of EDXRF spectra 3. Assess the feasibility of the combined non-destructive protocol in obtaining a reliable quantitative estimation of the metal substrate composition without the need to remove the surface corrosion patinas. Keywords: SEM-EDS, μXRD, EDXRF, Monte Carlo, Copper, Coins, Corrosion v RESUMO Realizar análises quantitativas em artefactos metálicos arqueológicos de património cultural é um desafio devido à sua estrutura interna com múltiplas camadas. Essas ‘’Camadas’’ podem incluir: a) Substrato original de metal e / ou liga (ouro, prata, bronze etc.) b) Patinas de superfície enriquecidas em produtos de corrosão compostos de sulfetos, óxidos e / ou cloretos c) Tratamentos de protecção aplicados em intervenções de conservação passadas d) Incrustações derivadas do solo do ambiente de enterro arqueológico. Para obter dados de composição sobre o substrato metálico, geralmente essas camadas devem ser removidas, porém isso nem sempre é possível devido à fragilidade inerente aos artefactos corroídos, como é o caso em particular de objectos de cobre como as moedas. A criação de um protocolo não destrutivo é, portanto, importante. Neste estudo, um protocolo que combina as simulações SEM-EDS, μXRD, EDXRF e Monte Carlo foi testado numa série de moedas portuguesas dos séculos XII ao XIX encontradas num Largo das Olárias e Travessa do Jordão em Lisboa. 1. Analisar de forma não destrutiva os padrões de corrosão e patinas desenvolvidas na superfície de moedas de cobre portuguesas de um sítio arqueológico de Lisboa SEM + EDS, μXRD e EDXRF portátil. 2. Aplicar os dados mineralógicos e químicos obtidos durante as sessões analíticas para executar simulações Monte Carlo dos espectros EDXRF. 3. Avaliar a viabilidade do protocolo não destrutivo combinado na obtenção de uma estimativa quantitativa confiável da composição do substrato metálico sem a necessidade de remover as patinas de corrosão superficial. Palavras-chave: SEM-EDS, μXRD, EDXRF, Monte Carlo, Cobre, Moeda, Corrosão vi ACKNOWLEDGEMENTS I wish to express the deepest gratitude to my supervisor professor Nick Schiavon and my co- supervisors Antonio Brunetti and José Mirão for their guidance, advice, criticism and encouragements throughout this research. I really would like to express my gratefulness to Professor Andre Teixeira and Tiago Gil Curado from the University of Lisbon for their kind support and provision of the samples. I would also like to thank everyone in the HERCULES Lab for their assistance and my fellow ARCHMAT students. Finally, special thanks to my mother who always supported and encouraged me, to my father who whenever I called tried to make me smile, to my friends for, maybe not physically, being there for me. vii 1. INTRODUCTION 1.1. COINS AS HISTORIC ARTEFACTS The conservation and valorisation of cultural heritage is of fundamental importance for our society, since it is witness to the artistic and industrial legacies of human societies. The information that can be gathered from such materials is a valuable source to understanding the past. A large component of this consists of material cultural