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Durham E-Theses Iron Age and Roman copper alloys from northern Britain. Dungworth, David Barry How to cite: Dungworth, David Barry (1995) Iron Age and Roman copper alloys from northern Britain., Durham theses, Durham University. Available at Durham E-Theses Online: http://etheses.dur.ac.uk/1024/ Use policy The full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that: • a full bibliographic reference is made to the original source • a link is made to the metadata record in Durham E-Theses • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders. Please consult the full Durham E-Theses policy for further details. Academic Support Oce, Durham University, University Oce, Old Elvet, Durham DH1 3HP e-mail: [email protected] Tel: +44 0191 334 6107 http://etheses.dur.ac.uk IRON AGE AND ROMAN COPPER ALLOYS FROM NORTHERN BRITAIN David Barry Dungworth The copyright of this thesis rests with the author. No quotation from it should be published without his prior written consent and information derived from it should be acknowledged. Thesis submitted for the Degree of Doctor of Philosophy University of Durham Department of Archaeology 1995 1 4 JUN 1995 ABSTRACT IRON AGE AND ROMAN COPPER ALLOYS FROM NORTHERN BRITAIN David Barry Dungworth This thesis presents the chemical analysis of over 1500 Iron Age and Roman copper alloys. Patterns evident from these analyses have enabled the nature of alloys to be reliably characterised. Iron Age alloys are almost exclusively of one type only - a tin bronze which often contains a small amount of arsenic (up to 1%). This alloy is quite distinctive when compared to the range of alloys used in the Roman period (brass, bronze and gunmetal, all with varying amounts of lead). The contrast between Iron Age and Roman alloys allows a reconsideration of many 'Celtic' items. It is now clear that the majority of 'Celtic' metalwork which survives dates to the end of the Iron Age or the Roman period (despite the traditional equation of the Iron Age with 'Celtic' material). The most successful means of representing the range of Roman alloys used has been the three dimensional plot. This examines the relationship between two elements (in this case zinc and tin) and shows the relative frequency of the different alloy types. This 3-D plot also illustrates some general features of Roman alloying and possible recycling. There are a number of peaks in the distribution of zinc and tin contents that represent specific alloy types which were commonly produced. The largest peak relates to the commonest alloy: bronze. The second peak relates to brass and the third to copper. All the remaining analyses fall into a diffuse area between the bronze and the brass peaks, and these are referred to by the modern term gunmetal. It is clear that copper alloys were recycled and that some care was taken over the ways in which this occurred. The lack of low zinc brasses shows that this alloy was rarely recycled on its own. If brass was recycled then it was always mixed with some bronze. The proportions of bronze and brass that were mixed varied widely as there is no distinct peak within the distribution of the zinc and tin contents of gunmetals. The thesis uses this overall view of Roman copper metallurgy (and that derived from previous work) to examine changes in alloy production and use. The results (interpreted in the light of metallurgical theory and practice, and of wider archaeological theory and data) challenge many of the traditional accounts of chronological and cultural change, and of the deposition processes operating in the Roman period. Page ii Contents Page Page Number Title Page List of Contents List of Figures iv List of Tables vii Abbreviations vii Declaration viii Acknowledgements ix CHAPTER 1 INTRODUCTION 1 CHAPTER 2 PREVIOUS WORK & PRESENT METHODOLOGY 6 Introduction 6 Previous Analyses of lion Age and 6 Roman Copper Alloys Present Methodology 12 Analytical Method 20 Methods for Presenting and Describing Results 23 Summary 29 CHAPTER 3 ARCHAEOLOGICAL BACKGROUND 30 Introduction 30 Ron Age in northern Britain 31 Roman Period in northern Britain 37 Deposition and the Archaeological record 42 Summary 44 CHAPTER 4 MODES OF PRODUCTION 45 Introduction 45 Prehistoric Production 46 Production in the Roman World 55 Production in Roman Britain 63 Summary 65 CHAPTER 5 IRON AGE ALLOYS 66 Introduction 66 Origins of Iron Age copper metallurgy 66 lion Age 68 'Celtic' artefacts 81 Late lion Age 87 Summary 90 CHAPTER 6 ROMAN ALLOYS 91 Introduction 91 Selection of samples 91 Alloying in the Roman Period 92 Page iii Comparison with Previous Analyses 100 Trace elements 101 Summary 104 CHAPTER 7 ALLOYS AND TYPOLOGY 105 Introduction 105 Brooches 106 Other personal ornaments 114 Household objects 116 Military fittings 120 Summary 124 CHAPTER 8 ALLOYS AND RECYCLING 125 Introduction 125 Production of alloys 125 Recycling Models 130 Remelting Thermodynamics: Theory 131 Remelting Thermodynamics: Experiments 133 Remelting thermodynamics: Conclusions 136 CHAPTER 9 CHRONOLOGICAL ASPECTS OF ALLOY USE 137 Introduction 137 Caley's 'zinc decline' 137 The 'zinc decline' re-examined 139 Chronological changes in Roman alloys 142 Summary 145 CHAPTER 10 CULTURAL ASPECTS OF ALLOY USE 146 Introduction 146 The use of brass in prehistoric and Roman Europe 146 Brass as an 'index of Romanisation' 147 Structured deposition and alloys 149 Problems of inter-site comparisons 150 Summary 157 CHAPTER 11 CONCLUSIONS 159 Summary of main results 159 Brass production 160 Historical and Archaeological Time 162 Cultural Change 164 Future Research 166 BIBLIOGRAPHY 167 APPENDIX 1 ANALYTICAL METHOD 189 APPENDIX 2 ESTIMATION OF ANALYTICAL ERRORS 201 APPENDIX 3 LIST OF SITES 209 APPENDIX 4 LIST OF ARTEFACT TYPES 225 APPENDIX 5 LIST OF ANALYSES 241 Page iv List of Figures Figure 2:1 Map of northern Britain showing the principal sites investigated. Figure 2:2 Barchart showing the date of the samples analysed. Figure 2:3 Barchart showing the types of site from which the samples were taken. Figure 2:4 Barchart showing the categories of objects analysed. Figure 2:5 Barchart showing the lead composition of Roman statues (after Craddock 1975: 159, figure 2). Figure 2:6 Scatter plot showing the correlation between zinc and tin in Roman alloys (after Craddock 1975: 222, figure 5). Figure 2:7 Ternary diagram showing the composition of Dolphin brooches (after Bayley 1992: figure 10.19). Figure 2:8 3-D surface chart showing the zinc and tin contents of all Roman samples analysed for this thesis. Figure 2:9 2-D chart of zinc and tin contents showing the boundaries of the four alloy types (bronze, brass, gunmetal and copper). Figure 5:1 Barchart showing the tin content of Iron Age copper alloys (from northern Britain). Figure 5:2 Barchart showing the tin content of a range of Iron Age copper alloys (previously published results). Sources: Barnes 1985; Cowell 1990; Craddock 1986; Northover 1984a; 1987; 1991a; 1991b. Figure 5:3 Barchart showing the tin content of cast copper alloys (from northern Britain). Figure 5:4 Barchart showing the tin content of wrought copper alloys (from northern Britain). Figure 5:5 Barchart showing the lead content of Iron Age copper alloys (from northern Britain). Figure 5:6 Barchart showing the zinc content of Iron Age copper alloys (from northern Britain). Figure 5:7 Barehart showing the arsenic content of Iron Age copper alloys (from northern Britain). Figure 5:8 Barchart showing the arsenic content of a range of Iron Age copper alloys (previously published results). Sources: Barnes 1985; Cowell 1990; Craddock 1986; Northover 1984a; 1987; 1991a; 1991b). Figure 5:9 Barchart showing the iron content of Iron Age copper alloys (from northern Britain. Figure 5:10 Barchart showing the iron content of a Roman copper alloys. Figure 5:11 Barchart showing the cobalt content of lion Age copper alloys (from northern Britain). Figure 5:12 Barchart showing the cobalt content of a range of Iron Age copper alloys (previously published results). Sources: Barnes 1985; Cowell 1990; Craddock 1986; Northover 1984a; 1987; 1991a; 1991b. Figure 5:13 Barchart showing the nickel content of Iron Age copper alloys (from northern Britain). Figure 5:14 Barchart showing the nickel content of a range of Iron Age copper alloys (previously published results). Sources: Barnes 1985; Cowell 1990; Craddock 1986; Northover 1984a; 1987; 1991a; 1991b). Page v Figure 5:15 Scatter plot of zinc and tin content of 'Celtic' metalwork (from northern Britain). Figure 5:16 Barehart showing the different alloys used for 'Celtic' metalwork from northern Britain). Figure 5:17 Scatter plot of zinc and tin content of 'Celtic' swords (from northern Britain). Figure 5:18 Melsonby hoard: scatter plot showing zinc and tin content. Figure 5:19 Melsonby hoard: enlarged scatter plot showing zinc and tin content. Figure 5:20 Barchart showing the different alloys used for Late Iron Age (metalwork from northern Britain). Figure 6:1 Barchart showing the zinc content of Roman copper alloys from northern Britain. Figure 6:2 Barchart showing the tin content of Roman copper alloys from northern Britain. Figure 6:3 Barchart showing the lead content of Roman copper alloys from northern Britain. Figure 6:4 Smoothed 3-D surface chart showing the zinc and tin contents of Roman copper alloys from northern Britain. Figure 6:5 2-D chart of zinc and tin contents showing the boundaries of the four alloy types (bronze, brass, gunmetal and copper).