Durham E-Theses Iron Age and Roman copper alloys from northern Britain.

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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/
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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).
Figure 6:6 Barchart showing the proportions of the different Roman alloy types
analysed.
Figure 6:7 3-D surface chart showing the zinc and tin contents of unleaded Roman
copper alloys from northern Britain.
Figure 6:8 3-D surface chart showing the zinc and tin contents of leaded Roman
copper alloys from northern Britain.
Figure 6:9 Barchart showing the proportions of alloy types for leaded and
unleaded alloys.
Figure 6:10 Barchart showing the iron content of Roman copper alloys from
northern Britain.
Figure 6:11. Scatter chart showing zinc and iron contents of Roman alloys.
Figure 6:12 Barchart showing the nickel content of Roman copper alloys from
northern Britain.
Figure 6:13 Barchart showing the arsenic content of Roman copper alloys from
northern Britain.
Figure 7:1 Barchart showing the alloy types used for different categories of
artefact.
Figure 7:2 Illustration of some of the brooches analysed.
Figure 7:3 Scatter plot showing the lead and zinc content of Trumpet brooches.
Figure 7:4 Scatter plot showing the zinc and lead content of Headstud brooches.
Figure 7:5 Scatter plot showing the zinc and tin content of Dragonesque brooches.
Figure 7:6 Illustration of some of the ligulae analysed.
Figure 7:7 Scatter plot showing the zinc and lead content of ligulae.
Figure 7:8 Barchart showing the tin content of Roman mirrors and other high tin
alloys.
Page vi
Figure 8:1 Ellingham diagram: Gibb's Free Energy for the formation of metal
oxides (data from: Reed 1971; Kubaschewski & Alcock 1979).
Figure 8:2 Vapour pressure diagram (data from Kubaschewski & Alcock 1979).
Figure 8:3 Scatter plot showing the relative loss of zinc during remelting.
Figure 8:4 Barchart of alloy type found in objects and waste at Brougham
Figure 9:1 Scatter plot of zinc content of Roman brass coins against date of issue.
Source: Caley 1964; Carter 1966; Cope 1974; Riederer 1974; Carter &
Buttrey 1977; Carradice & Cowell 1987; Etienne & Rachet 1984.
Figure 9:2 Bar chart showing the average zinc content of Roman brass coins for
each emperor.
Figure 9:3 Chart showing the data in figure 9:1 fitted to a function.
Figure 9:4 Chart showing the 'zinc decline' that would be expected.
Figure 9:5 Barchart showing chronological changes in the types of Roman alloys
used.
Figure 9:6 Barchart showing chronological changes in the proportions of leaded
Roman alloys used.
Figure 9:7 Barchart showing the chronological changes in the provenance of
Roman samples.
Figure 10:1 Barchart showing the proportions of alloy types used on a range of
Roman sites.
Figure 10:2 Barchart showing the proportions of alloy types found in 'indigenous
contexts'.
Figure 10:3 Barchart showing the date of samples from a range of different sites.
Figure 10:4 Barchart showing the proportions of alloy types used in forts.
Figure 10:5 Barchart showing the proportions of alloy types used in vici.
Figure 10:6 Barchart showing the proportions of alloy types used in towns.
Figure 10:7 Barchart showing the proportions of third century alloy types used at
Brougham and elsewhere.
Figure 10:8 Barchart showing the proportions of alloy types used in larger rural
settlements.
Figure 10:9 Barchart showing the proportions of alloy types used in villas.
Figure 10:10 Barchart showing the proportions of different object categories from
different sites in northern Britain
Page vii
List of Tables
Table 5:1 Composition of late Bronze Age/early Iron Age alloys.
Table 5:2 Distribution of analysed Iron Age finds in northern Britain.
Table 5:3 Proportions of leaded and unleaded alloys.
Table 5:4 Melsonby Hoard: assigning previously uncertain items to sets.
Table 5:5 Distribution of analysed late Iron Age finds in northern Britain.
Table 6:1 Provenance and date of all Roman objects analysed.
Table 6:2 Method of fabrication.
Table 6:3 Average composition of cast and wrought alloys.
Table 8:1 Zinc levels in a bronze melted in a crucible previously used for brass
casting.
Table 9:1 Composition of some late sestertii and dupondii analysed for this thesis.
Abbreviations
AAS Atomic Absorption Spectroscopy
BMC British Museum Coin Catalogue
cps Counts Per Second
EDXRF Energy Dispersive X-ray Fluorescence
EMPA Electron Micro-Probe Analyser
nd not detected (see Appendices 1 and 5)
ND Not Determined (see Appendices 1 and 5)
OES Optical Emission Spectroscopy
MC Roman Imperial Coinage
XRF X-ray Fluorescence
Page viii
Declaration:
No part of this work has been submitted as part of a degree by myself at this or any
other University.
Statement of Copyright
© The copyright of this thesis rests with the author. No quotation from it should be
published without written consent and information derived from it should be
acknowledged.
Appendix 2 was written in conjunction with Peter Craig, Department of Mathematics,
University of Durham.