Microchemical investigations of historical coins

Microchemical investigations were carried out on ancient silver coins originated from the same country but of different historical periods between the fifth and the second centuries B.C. Energy-Dispersive X-ray microanalysis in a Scanning Electron Microscope (SEM-EDX) was employed to obtain qualitative and semi-quantitative information about the chemical composition of these coins. SEM-EDX analyses employ an electron beam of 20 keV, which interacts with the sample leading to the emission of characteristic X-rays, to determine elements present in the surface patina, closely related to the sample preservation. In the X-ray photoelectron spectroscopy (XPS) analysis a monochromatic Al Kα radiation (1486.6 eV) interacts with the sample and photoelectrons are detected as secondary radiation, to investigate about coins elemental composition. Moreover a beam of Ar + ions with an energy of 3 keV was used for the sputtering procedure in order to perform depth profile measurements, from the surface (patina composition) down to deeper layers. Useful information about production, chronological period and utilization places of coins are obtained to support a correct dating of these samples.