Some Metallurgical Aspects of Ancient Silver Coins Discovered in Romania (Original and Imitations) Provenance, Destination and Commercial Networks

For coins, chemical differences that occur during preparation of alloys will affect the elemental composition and could be used for the identification of technologies and workshops and also to distinguish between originals and counterfeits. We illustrate with the case of Geto-Dacian coins (Thassos and Macedonian - Phillip II, Alexander the Greek and Phillip III 'barbarized' tetradrachms) and with Greek Apollonia and Dyrrhachium silver drachmas emitted by these old cities for Pompejus. To analyze the chemical composition of these coins, we used two methods: Am-241 and Pu-238 gamma sources based X-Ray Fluorescence (XRF) and in vacuum 3 MeV protons Particle Induced X-ray Emission (PIXE). Some special measurements on the edge of some coins (to identify plated exemplaires) were done using the ATOMKI Debrecen Van de Graaf 2 MeV protons microprobe. Concerning the Geto-Dacian coins, we observed there is a reduction of the fineness in time that is specific to almost every coin issue and tin concentration in coins increased in time (this could suggest that bronze was used in alloying silver coins instead of copper). For quality control, many coins present attempts made on their edge to verify the real silver content in the bulk using a knife. Some historical and economical considerations about the adulterations during silver coining process are presented