Abstract
A set of ancient Antoninianus silver coins, dating back between 249 and 274 A.D. and minted in Rome, Galliae, Orient and Ticinum, have been characterized. We use, for the first time, a combination of nano-invasive (focused ion beam-field emission scanning electron microscopy-X-ray microanalysis (FIB-FESEM-EDX), voltammetry of microparticles (VIMP)) and destructive techniques (scanning electron microscopy (SEM-EDX) and electron microprobe analysis (EMPA)) along with non-invasive, i.e., micro-Raman spectroscopy. The results revealed that, contrary to the extended belief, a complex Ag-Cu-Pb-Sn alloy was used. The use of alloys was common in the flourishing years of the Roman Empire. In the prosperous periods, Romans produced Ag-Cu alloys with relatively high silver content for the manufacture of both the external layers and inner nucleus of coins. This study also revealed that, although surface silvering processes were applied in different periods of crisis under the reign of Antoninii, even during crisis, Romans produced Antoninianus of high quality. Moreover, a first attempt to improve the silvering procedure using Hg-Ag amalgam has been identified.
Highlights
Studies about coinage have proved to be a valuable tool for a better understanding of the technological aspects, helping archaeologists for numismatic analysis[1,2] as well as useful for conservation and restoration of metal artefacts[3,4,5], aiming to preserve these objects from further damage
A severe debasement of mint and political affairs lead to productions of coins similar to argentiferous bronze coins until the beginning of the reign of Diocletian, who in 294 A.D. reintroduced an high quality of silver coinage[9]
The results obtained in the set of cross-sectioned coins enabled to distinguish two main groups on the basis of their microstructure, chemical composition and the degree of corrosion, in agreement with that observed using FIB-FESEM-EDX and complementary techniques
Summary
Studies about coinage have proved to be a valuable tool for a better understanding of the technological aspects, helping archaeologists for numismatic analysis[1,2] as well as useful for conservation and restoration of metal artefacts[3,4,5], aiming to preserve these objects from further damage. The first imperial silver coinage was of a great production, with high content of Ag. a severe debasement of mint and political affairs lead to productions of coins similar to argentiferous bronze coins until the beginning of the reign of Diocletian, who in 294 A.D. reintroduced an high quality of silver coinage[9]. The Antoninianus denomination was a silver-rich coin (up to 80% of Ag), but gradually was devalued becoming a bronze coin with a very low content of silver (about 2–3% of Ag). Historians referred[10] that Caracalla minted this denomination with a medium content of Ag around 50%. This content decreased progressively, reaching the lowest values (about or less than 5%) under the reigns of Gallienus and Aurelianus (270–275 A.D.) as consequence of a economic crisis[9].
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