Surface Elemental Characterization of Indian Punch-Marked Coins of 600 to 200 BCE Era

Abstract

In the present work, X-ray diffraction [XRD] and x-ray photoelectron spectroscopic [XPS] techniques are used for surface elemental analysis and chemical composition of nine series of imperial punch-marked coins [PMC] of 600 to 200 BCE stored in the Numismatic Society of India at BHU, Varanasi. These coins were selected based on the Gupta-Hardakar classification system of the Mahajanpada and Janpada periods. PMCs are considered the oldest coins in India. They are among the most common coinages globally and are frequently found in hoards. XRD results show four prominent diffraction peaks, whereas XPS spectral analysis of these nine series of imperial punch-marked coins at different surface positions shows a non-uniform distribution revealed by the elemental analysis, which shows different element percentages in each coin. In XPS, Silver is found in dominant, along with copper, lead and a few other elements in very low percentages and gold in Janpada PMC only. In XRD, silver is found in the crystal fcc phase at the surface of PMCs. XPS data shows that the percentage of silver found decreases with the increase of lead and copper in the varying series. The results show a high degree of metallurgical understanding and alloying techniques between the sixth and third centuries BCE. It also demonstrates that the coins were issued at different times when technology was advancing. Numerous issues were raised by the decreasing silver content, including the state of the economy, the growth in coin demand for exchange, and the preservation of weight standards.