Experimental investigation of silvering in late Roman coinage
- PDF / 206,367 Bytes
- 9 Pages / 612 x 792 pts (letter) Page_size
- 77 Downloads / 163 Views
Experimental investigation of silvering in late Roman coinage
C. Vlachou, J.G. McDonnell, R.C. Janaway Department of Archaeological Sciences, University of Bradford, BD7 1DP, UK. ABSTRACT Roman Coinage suffered from severe debasement during the 3rd century AD. By 250 AD., the production of complex copper alloy (Cu-Sn-Pb-Ag) coins with a silvered surface, became common practice. The same method continued to be applied during the 4th century AD for the production of a new denomination introduced by Diocletian in 293/4 AD. Previous analyses of these coins did not solve key technological issues and in particular, the silvering process. The British Museum kindly allowed further research at Bradford to examine coins from Cope’s Archive in more detail, utilizing XRF, SEM-EDS metallography, LA-ICP-MS and EPMA. Metallographic and SEM examination of 128 coins, revealed that the silver layer was very difficult to trace because its thickness was a few microns and in some cases it was present under the corrosion layer. Results derived from the LA-ICP-MS and EPMA analyses have demonstrated, for the first time, the presence of Hg in the surface layers of these coins. A review of ancient sources and historic literature indicated possible methods which might have been used for the production of the plating. A programme of plating experiments was undertaken to examine a number of variables in the process, such as amalgam preparation, and heating cycles. Results from the experimental work are presented. ITRODUCTION
Coinage in the Late Roman Period suffered from severe debasement. By 250 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). The nummus was meant to have been coined to the same standard in all the Imperial mints. It was the first time that a uniform coinage circulated throughout the Roman world and huge numbers of new coins had to be produced to cover the needs of its estimated 60 million people[1]. For a few years the economic system was quite stable, but by Constantius Chlorus’ death in Britain (July 306 AD), serious political problems had arisen which caused considerable tensions between the East and the West. These political problems had an immediate impact on the monetary system. Nummi’s weight was gradually reduced from 10 gr. to only 3 gr. and during the rest of the 4th century A.D., nummi continued to circulate in very debased form [2]. The main aim of this research is to investigate the method used for almost 100 years (250 – 350 AD) for the production of Roman coins. These data will contribute to: • characterise the plating technology used in large scale production of coins • assess the uniformity of manufacturing technology of an Empire-wide co
Data Loading...
