Physicochemical characterization of ancient copper alloys using electron microscopy and X-ray diffraction

This study presents a comparative archaeometallurgical analysis of copper coins from the Kushana (30-310 CE) and Gupta (240-550 CE) empires using Field-Emission Scanning Electron Microscopy with Energy-Dispersive X-ray Spectroscopy (FESEM-EDS) and X-ray Diffraction (XRD). Five coins were examined to assess alloy composition, microstructure, and corrosion behavior. Kushana coins exhibit lower copper purity (47.57-57.49 wt%) with elevated Fe, Si, Ca, S, and Cl, may reflect limited refining and the use of polymetallic ores, leading to heterogeneous corrosion dominated by Cu 2 O and silicate phases. Surface EDS analyses show higher copper concentrations in Gupta coins (67.80-74.74 wt%) with minor silver additions (0.75-3.32 wt%), suggesting differences in ore selection and metallurgical practices. Their surfaces show relatively compact, oxide-dominated corrosion assemblages. EDS analysis was conducted on corroded coin surfaces, the reported elemental compositions represent surface signatures inclusive of corrosion products and soil-derived contaminants, rather than original bulk alloy purity. The results suggest possible differences in surface compositional characteristics and corrosion behavior between the analyzed Kushana and Gupta specimens. The non-destructive nature of the combined FESEM-EDS and XRD approach makes it particularly suitable for the physicochemical investigation of rare heritage objects.