Results and Data Analysis
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A SCIENTIFIC AND ARCHAEOLOGICAL INVESTIGATION OF PREHISTORIC GLASSES FROM ITALY. by Andrew C. Towle, BA. MA Thesis submitted to the University of Nottingham for the degree of Doctor of Philosophy, January 2002. CONTENTS CHAPTER 1: INTRODUCTION 1 1.1 Project Origins 1 1.2 Sample Collection 1 1.3 selection of analytical techniques 5 1.4 The investigation of glass technology 6 1.5 Technological aspects of glass beads 7 1.6 Objectives of the project 8 CHAPTER 2: THE EVIDENCE FOR GLASS PRODUCTION IN PREHISTORIC NORTHERN ITALY, AND ASSUMPTIONS UNDERPINNING ITS STUDY 10 2.1 Evidence for early glass production in prehistoric Italy: the Middle to Final Bronze Age 10 2.2 Characteristic glass forms from prehistoric Italy: The Early Iron Age and Etruscan periods 17 2.3 Theoretical assumptions underpinning the research 22 2.4 The relationship between technology and society 28 2.5 Summary 37 CHAPTER 3: THE ARCHAEOMETRY OF ANCIENT GLASS 39 3.1 Introduction 39 3.2 Physical and Chemical Properties of Glass 39 3.3 Why are glasses complex materials? 44 3.4 Related Materials 45 3.4.1 Faience 45 3.4.2 Slag 47 3.4.3 Glazes 47 3.5 Earliest glass 48 3.6 Sources of Information on glass technology 49 3.6.1 Texts 49 3.6.2 Development of modern glass industries 55 3.6.3 Direct study of ancient materials. 55 3.6.4 Experimental work 56 3.7 Interpreting compositional analyses of glass 57 3.7.1 Silica 59 3.7.2 Soda 66 3.7.3 Potash 73 3.7.4 Magnesia 77 3.7.5 Alumina 80 3.7.6 Calcium oxide 83 3.7.7 Phosphorous pentoxide 86 3.7.8 Copper oxide 87 3.7.9 Lead oxide 92 3.7.10 Chlorine 96 3.7.11 Chromium oxide 97 3.7.12 Tin oxide 97 3.7.13 Bismuth oxide 99 3.7.14 Nickel oxide 100 3.7.15 Manganese oxide 100 3.7.16 Antimony compounds 103 3.7.17 Silver oxide 105 3.7.18 Gold 106 3.7.19 Arsenic 107 3.7.20 Cobalt oxide 108 3.7.21 Titanium oxide 115 3.7.22 Sulfur 115 3.7.23 Iron oxide 116 3.7.24 Barium oxide 119 3.7.25 Zinc oxide 120 3.8 Conclusions 120 CHAPTER 4: ANALYTICAL PROCEDURES 122 4.1. Introduction 122 4.2 X-Ray Fluorescence Analysis. 123 4.2.1. Principles of the Technique: X-ray generation 124 4.2.2 Interaction with the sample 126 4.2.3 Scattering 126 4.2.4 Primary Absorption 127 4.2.5 Fluorescence 128 4.2.6 Secondary absorption and escape depth 128 4.2.7 Enhancement 129 4.2.8 Auger Process and fluorescent yield 129 4.2.9 Detection of characteristic X-rays: energy dispersive systems 130 4.2.10 Qualification and Quantification of Results 132 4.2.11 Resolution 132 4.2.12 Identification 132 4.2.13 Background 133 4.2.14 Intensity 133 4.2.15 Calibration 133 4.2.16 Wavelength Dispersive Systems 134 4.2.17 Detection in wavelength dispersive systems 135 4.2.18 Energy Dispersive and Wavelength Dispersive Systems 136 4.3 Energy Dispersive X-Ray MicroAnalysis (EDXMA) 137 4.3.1 Imaging. 137 4.3.2 X-ray generation. 138 4.3.3 Interaction with the sample 139 4.3.4 Detection 140 4.3.5 Qualification and Quantification of results 140 4.4 Electron Microprobe Analysis 140 4.5 X-ray Diffraction 142 4.6 Operating Conditions Employed 144 4.7 Experiments to establish ideal instrument and operating conditions for the analysis of ancient glasses I: XRF 144 4.7.1 X-ray tube potential 149 4.7.2 Relationship between peak:background ratio and accelerating voltage 150 4.7.3 Beam current: Relationship between peak:background ratio and beam current 151 4.7.4 Beam and the count rate 153 4.7.5 Primary X-ray beam diameter 156 4.7.6 Counting time 158 4.7.7 Background files 160 4.7.8 Accuracy and Precision of XRF results 164 4.7.9 Problems encountered applying XRF to archaeological specimens 168 4.7.10 Surface preparation 168 4.7.11 Further archaeological samples: a Faliscan bead from the Ashmolean Museum 174 4.7.12 Surface geometry 176 4.8 Experiments to establish ideal instrument and operating conditions for the analysis of ancient glasses II: Electron Microprobe Analysis 179 4.8.1 Sample preparation 179 4.8.2 EMP of archaeological samples 182 4.8.3 Discussion of the errors 183 4.8.4 Comparison of the data quality between XRF and EMP 184 4.9 Non-Quantitative Methods 187 4.9.1 Energy Dispersive X-ray Micro Analysis (EDXMA) 188 4.9.2 X-Ray Diffraction 189 4.10 Conclusions 190 CHAPTER 5: RESULTS AND DATA ANALYSIS 191 5.1 Introduction 191 5.2 Treatment of the data 192 5.3 Characterisation of glasses from Final Bronze Age Sites 194 5.3.1 Montagnana 194 5.3.2 Frattesina 206 5.3.3 Mariconda 212 5.3.4 Discussion of the Bronze Age material 221 5.4 Etruscan Material 230 5.4.1 Discussion of glasses from Etruscan contexts 245 5.5 7th Century BC Beads from Pozzouli and Cumae 247 5.5.1 Pozzouli 247 5.5.2 Cumae 257 5.5.3 Discussion of 7th Century BC glasses from Pozzuoli and Cumae 262 5.6 Glass from the Este Culture 262 5.6.1 Casa di Recovero 263 5.6.2 Benvenuti 270 5.6.3 Rebato 278 5.6.4 Alfonsi 280 5.6.5 Muletti Prosdocimi 282 5.6.6. Discussion of the Este glasses 284 5.7 Co Garizoni 285 5.8 Canale Bianco 290 5.9 Ca’Cima 298 5.10 Faliscan 301 5.11 Unprovenanced items 302 5.12 Integration of data across sites: Global perspectives of the data 306 5.12.1 Statistical analysis of the entire data set 306 5.12.2. Discussion of artefacts types across site boundaries: Brooch Slider decorations 314 5.12.3 Discussion of artefacts types across site boundaries: Spindle Whorls 317 5.12.4 Discussion of artefacts types across site boundaries: Eye-decorated beads 320 5.12.5 Discussion of artefact types across site boundaries: Punic head bead 323 5.13 Summary 325 CHAPTER 6: GLASS PRODUCTION AND EXCHANGE IN PREHISTORIC NORTHERN ITALY 327 6.1 Introduction 327 6.2 Traditional perspectives of Italian prehistory 328 6.3 The final Bronze Age: the evidence for localised production at Frattesina, Mariconda and Montagnana 330 6.4 The evidence for regional production and exotic imports from the Early Iron Age to the Etruscans 346 6.5 Further considerations on Trade and Exchange 348 6.6 Conclusions for this Chapter 351 CHAPTER 7: CONCLUSIONS 355 7.1 Analytical Techniques 355 7.2 Experimental work 356 7.3 Final Bronze Age 358 7.4 Iron Age and Etruscan 359 7.5 The scientific analysis of glass and technical choices 360 7.6 In conclusion 361 REFERENCES 364 APPENDIX 1: COMPOSITIONAL DATA 441 APPENDIX 2: SAMPLE CATALOGUE 461 APPENDIX 3: PLATES 537 Andrew C. Towle A SCIENTIFIC AND ARCHAEOLOGICAL INVESTIGATION OF PREHISTORIC GLASSES FROM ITALY. ABSTRACT: keywords: Ancient glass, Italy, Final Bronze Age, Proto-Villanovan, Early Iron Age, Etruscan, X-ray fluorescence, electron microprobe, scanning electron microscope Ancient glasses are invariably complex materials, in which the specific chemical composition and microstructure capture aspects of their technologies. The chemical characterisation of glasses in specific archaeological contexts has given useful insight into the peculiarities of diverse glass-making technologies. In addition such studies generate more general information upon an important range of phenomenon, including the pyrotechnological milieu, empirical knowledge of sophisticated chemistry, organisation of production, access to significant raw materials and long-distance trade. This study examines a wide selection of glass artefacts recovered from archaeological contexts in Northern and Central Italy from approximately 1200 BC to 200 BC. The earliest material is from the Final Bronze Age, and extends the characterisation of an established glass type, which is unique to Europe and distinct from the contemporary technologies of the Eastern Mediterranean. Using a combination of X-ray fluorescence analysis, electron microprobe and scanning electron microscopy glass artefacts from a thousand-year period from the same region are investigated. The shifting technologies permit the discussion of localised production and importation of glass from elsewhere. The chemical analysis reveals a complex picture of glass production, which defies the expected pattern, and there is evidence for new compositional types, which may yet prove to be diagnostic of highly localised production. The changing compositions are discussed in relation to the broader archaeological context. dedicated to Charles Drury Acknowledgements: I am grateful for the help and advice of a large number of people during the course of this project. I would particularly like to thank my supervisor Professor Julian Henderson for his encouragement, support and friendship throughout this study, and also for introducing me to the joys of archaeology in Syria with the Raqqa Project. Without the assistance of a number of colleagues in Italy, the project would have stalled at an early stage, and I would like to thank the following individuals for helping arrange access to material and providing additional references: Dr Armando De Guido of the Department of Archaeology, Padua University, Dr Simonetta Bonomi, Director of Adria National Museum, Dott. Giavanna Gambacurta of Padua University and Dott. Luigi Malnati, Superintendent of Archaeology for the Veneto Region. In addition I would like to thank Dr Paulo Bellintani for discussion of some of the results and providing copies of unpublished work on Prehistoric glass in Northern Italy.