George, NE
(2019)
The Manufacture of Official Roman Silver Coinage and Blanks Between AD193 and AD270.
PhD thesis, University of Liverpool.
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Abstract
This thesis addresses the lack of microstructural data for Roman silver coins which has impeded our understanding of the methods used in their manufacture. In particular, many questions remain about the silvering technologies used to conceal the debased nature of Roman silver minted in the third century AD. Previous investigations into Roman silver coinage have focused on determining episodes of debasement by identifying the fineness and weights of different issues and precise elemental profiles can now be achieved using minimally destructive techniques. Comparatively, few studies have looked at the methods used to manufacture the coins. Destructive microstructural analysis is often necessary to establish the minting technologies employed by ancient moneyers. Since ancient coins are precious objects with both intrinsic and cultural value, they are often subject to strict sampling regulations. The limited access to coins for destructive analysis is the main reason for the shortage of microstructural data for Roman silver coins. For this investigation, a group of 36 Roman silver coins, minted between AD193 and AD270, were investigated using optical microscopy (OM) and scanning electron microscopy (SEM). Complementary elemental data were acquired using energy dispersive spectroscopy (EDS) and mass plasma atomic emission spectroscopy (MP-AES). Experiments were carried out to explore specific aspects of the minting process related to the different potential silvering technologies. The blanks created in the experimental castings provided microstructural data, acquired under controlled conditions, which were then compared to the ancient examples. The study revealed that silver-copper alloy blanks were artificially enriched using repetitive cycles of oxidation and blanching. Inverse segregation of the silver-rich eutectic phase was found to play no role in artificially enriching the surfaces of silver-copper alloy blanks. The investigation found that the surfaces of later quaternary alloy blanks introduced sometime between Valerian and Gallienus joint reign (AD253-260) and Gallienus sole reign (AD260-268), were artificially enhanced by a direct form of enrichment. The exudation of these white-metals creates a white-metal coating. A comparison of the ancient quaternary alloy coins and the experimental blanks revealed many shared microstructural features characteristic of direct enrichment. The evidence put forward in this thesis delivers an answer to this long-standing question. The application of heat to a cast quaternary alloy blank promotes segregation of the silver, tin and lead to the surface.
| Item Type: | Thesis (PhD) |
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| Divisions: | Faculty of Humanities and Social Sciences > School of Histories, Languages and Cultures |
| Depositing User: | Symplectic Admin |
| Date Deposited: | 07 Jan 2020 11:31 |
| Last Modified: | 19 Jan 2023 00:21 |
| DOI: | 10.17638/03060449 |
| Supervisors: |
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| URI: | https://livrepository.liverpool.ac.uk/id/eprint/3060449 |
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