Minerals and Metals in Ancient India v1.c28.s7.t5.6

v1.c28.s7.t5.6

Metallographic examination provides further insight to the steps which might have been taken to make these coins. Bharadwaj (1979: 107-22) studied the Taxilian silver coins (reported in our Table 17.3) and the AD 900 Rājghāt silver coin just now reported. The presence of lead globules (and sulphur) in the coins indicated that argentiferous galena must have been the principal ore from which the metal was extracted. In the Rājghāt coin, bismuth was present; this being insoluble in copper and silver, spread as a thin film along the grain boundaries and caused embrittlement and crack in the micro-structure. The punch-marked coins from Taxila showed dendrites of silver and eutectic mixture of silver and copper; this implies an essentially cast structure, slowly cooled before being die-punched. The grains appeared to be equiaxed. On the edges, grains were elongated and distorted, the micro-constituents were curved around the punch-marks. (Bhardwaj, 1979: 110 and 113-22)