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Investigation of the Manufacturing Technology of Complex Copper Alloy Late Roman Coins (240 AD to 395 AD) Using Archaeometallurgy Techniques

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Abstract

Coinage in the Late Roman Period suffered from severe debasement. From approximately 40% in 240 AD, the silver content dropped to 20% in 250 AD, and by 260 AD, the fineness of the silver denomination had been reduced to just 5% Ag. For the production of these “silver” coins, copper-based quaternary copper–tin–lead–silver alloys were used. Their surface was covered by thin silver plating which was worn off easily during the circulation and use of the coins. Later, the same method was used for a new coin, the nummus, introduced by Diocletian, in his monetary reform (AD 293/4). During the fourth century, the method continued to be in use for the production of debased nummi and other silvered copper alloy coins. Previous analyses of these coins did not solve key technological issues and, in particular, the deployment of quaternary alloys for their production. For the purposes of this project, the British Museum’s Department of Coins and Medals kindly allowed further examination of coins from Cope’s archive, utilizing a range of analytical techniques. This paper presents the outcomes of the metallographic examination of 179 late Roman coins from this archive. As part of this work, a series of experiments were also undertaken to replicate the alloys used in the production of the Roman coins and provide samples to research their microstructure. The examination of the metallographic structures of the quaternary alloys showed that they were similar to the microstructures of the Roman coins demonstrating that some of the coins were in as-cast condition. EPMA and SEM examination of the quaternary alloys confirmed that the structure was as described in the metallographic examination and the distribution of Ag and Pb in the alloy was uniform.

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Acknowledgements

This work was part of the author’s doctorate research The manufacturing and plating technology used in the production of mid-3rd/4th century AD Roman coins – An analytical study, submitted to the Archaeological Science Department, University of Bradford, 2004 . The author is grateful to her PhD supervisor Dr Gerry McDonnell for his wealth of knowledge on ancient metallurgy and the valuable guidance, comments and encouragement he generously provided during the project and beyond. The author would like also to acknowledge the Hellenic Republic, State Scholarship's Foundation (S.S.F.) for funding this research project and the British Museum Department of Coins and Medals and Department of Scientific Research, for allowing access to Cope's Archive. Furthermore, the Department of Earth Sciences, University of Manchester and NERC for the permission to use the electron microprobe facility and Mr. Dave Plant for performing the analyses

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Correspondence to Constantina Vlachou-Mogire.

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This invited article is part of a special topical issue of the journal Metallography, Microstructure, and Analysis on Archaeometallurgy. The issue was organized by Dr. Patricia Carrizo, National Technological University–Mendoza Regional, and Dr. Omid Oudbashi, Art University of Isfahan and The Metropolitan Museum of Art, on behalf of the ASM International Archaeometallurgy Committee.

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Vlachou-Mogire, C. Investigation of the Manufacturing Technology of Complex Copper Alloy Late Roman Coins (240 AD to 395 AD) Using Archaeometallurgy Techniques. Metallogr. Microstruct. Anal. 12, 202–218 (2023). https://doi.org/10.1007/s13632-023-00954-2

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