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Characterization of Bronze Casting in Insula 56, in Roman Aventicum

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Characterization of Bronze Casting in Insula 56, in Roman Aventicum CHARACTERIZATION OF BRONZE CASTING IN INSULA 56, IN ROMAN AVENTICUM by JESSICA WHEAT COOK (Under the Direction of Ervan Garrison) ABSTRACT This study characterizes metallurgical wastes (slag) recovered from a bronze workshop during excavations in 1997-1998 at the Roman provincial city of Aventicum, located in western Switzerland, then Germania Superior. Previous research has identified the workshop as one devoted to the production of large leaded bronze statuary. The slag assemblage analyzed in this study is unusual due to the absence of ceramic crucible fragments normally associated with the production of copper alloys. Instead, this workshop is hypothesized to have used iron crucibles. Electron Microprobe Analysis (EMPA) and X-Ray Diffraction (XRD) were used to analyze the chemical composition of the slags in contrast to previous bulk analysis studies. Modern metal casting methods were observed for analogues. The data show that the slag reached temperatures between 1350°-1400° C and chemical components indicated the use of sand and lime fluxes. Evidence of high temperatures is proposed as one chemical fingerprint that can be used to re-assess slag for the presence of iron crucibles in other Roman bronze workshops. INDEX WORDS: Aventicum, Classical Bronzes, EMPA, XRD, Roman Metallurgy CHARACTERIZATION OF BRONZE CASTING IN INSULA 56, IN ROMAN AVENTICUM by JESSICA WHEAT COOK AB History, Anthropology, The University of Georgia, 2003 A Thesis Submitted to the Graduate Faculty of The University of Georgia in Partial Fulfillment of the Requirements for the Degree MASTER OF SCIENCE ATHENS, GEORGIA 2008 © 2008 Jessica Wheat Cook All Rights Reserved CHARACTERIZATION OF BRONZE CASTING IN INSULA 56, IN ROMAN AVENTICUM by JESSICA WHEAT COOK Major Professor: Ervan Garrison Committee: Samuel Swanson Douglas Crowe Electronic Version Approved: Maureen Grasso Dean of the Graduate School The University of Georgia May 2008 iv ACKNOWLEDGMENTS The author wishes to thank Drs. Ervan Garrison, Douglas Crowe, and Samuel Swanson their guidance and patience. It is not easy to make a scientist out of someone with a background in history and anthropology, no matter how eager the student. I also would like to thank Dr. Vincent Serneels of the University of Fribourg, Switzerland, for providing me with not only the materials for analysis but also a generous amount of good faith in an American graduate student. Professors RG Brown III and James “Jimbo” Buonaccorsi made it possible for me to actually engage in metal casting instead of merely studying from the relative safety of a laboratory. Finally, I would like to thank my friends and colleagues among the graduate students in the Geology Department at UGA. I am grateful beyond words for your support and encouragement during my time here. This work is dedicated to the memory of my late father, Bobby Lee Cook, Jr., who first sparked my curiosity for the mysteries of history and pre-history. This work was driven not only by my own intellectual curiosity, but also by my dedication to my son Patrick Aidan Fell, whose eagerness to explore his world inspires my own. Finally, the completion of this manuscript would have been a far more miserable process without the help and support of my husband, Nathan. v TABLE OF CONTENTS Page ACKNOWLEDGEMENTS..........................................................................................................................iv LIST OF TABLES...........................................................................................................................................vii LIST OF FIGURES .........................................................................................................................................ix INTRODUCTION ...........................................................................................................................................1 Previous Work..........................................................................................................................4 Current Hypothesis .................................................................................................................6 Study Objectives ......................................................................................................................6 Copper Slag and Copper Alloys............................................................................................7 Copper Alloys in Western Switzerland: From La Tene to the Gallo-Roman World .............................................................. 10 Copper Alloy Statuary in Aventicum ................................................................................ 12 Techniques Used................................................................................................................... 14 METHODS...................................................................................................................................................... 16 Electron Microprobe Analysis (EMPA)........................................................................... 17 X-Ray Diffraction (XRD) ................................................................................................... 19 Modern Metal Casting Observations ................................................................................ 20 RESULTS ....................................................................................................................................................... 21 Rough Sorting of Sample Types by Hand Sample ......................................................... 21 Images with EDS spectra.................................................................................................... 24 Electron Dispersive Spectrometry Data........................................................................... 39 vi Wavelength Dispersive Spectrometry Data..................................................................... 42 X-Ray Diffraction (XRD) ................................................................................................... 60 Modern Metal Casting Work.............................................................................................. 62 DISCUSSION.................................................................................................................................................. 67 CONCLUSIONS............................................................................................................................................ 77 REFERENCES............................................................................................................................................... 79 APPENDICES................................................................................................................................................ 83 A: Stratigraphic profiles....................................................................................................... 83 B: Accession........................................................................................................................... 86 C: Photographic and Image data........................................................................................ 88 D: WDS data.......................................................................................................................... 97 E: Statistics........................................................................................................................... 113 vii LIST OF TABLES Page Table 1: Oxide standards used for oxide analyses .......................................................................... 18 Table 2: Element standards used in WDS analysis of metal........................................................ 18 Table 3: Hand sample results and descriptions................................................................................ 22 Table 4: Phases suggested by EDS within the slag groundmass and ceramic......................... 41 Table 5: Components detected in the metal inclusions within the samples ............................. 42 Table 6: Normalized data for ceramic, minus fayalite analysis................................................... 43 Table 7: Normalized data for metals .................................................................................................. 43 Table 8: WDS data for slag groundmass, normalized.................................................................... 47 Table 9: Correlation coefficients for WDS data, groundmass points only............................... 59 Table 10: XRD results by d-spacing for AVS722, ceramic portion. ......................................... 61 Table 11: XRD results by d-spacing for AVS722, vitrified portion. ......................................... 61 Table 12: Average weight percentages, metals ............................................................................... 67 Table 13:Normalized Element Weight Percent Alloy Components........................................... 69 Table 14: Oxide Standards.................................................................................................................... 85 Table 15 : Element Standards............................................................................................................... 85 Table 16: Non-normalized data for ceramic portion of AVS722 .................................................. 97 Table 17: Normalized data for ceramic portion of AVS722........................................................ 97 Table 18: Non-normalized
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