History of Technology in India, Vol. I: From Antiquity to c. 1200 A.D. v1.c14.s4.3

v1.c14.s4.3

3 The Arthaśāstra refers to the purification of impure silver by adding lead to the extent of one-fourth of the weight of the silver (II; 10, 13) and apparently by heating the total mass of metal. In another place the same text recommends that impure silver should be heated four times in a crucible of bone (i.e. made of a mixture of clay and bone dust?), four times with equal amount of lead (in a pot of clay), four times in a dry crucible, three times in a pot-sherd and twice in cowdung and then it should be made bright with Indus-earth (II, 13, 49). According to Pliny, silver ore “cannot be smelted except when combined with lead or with the vein of lead, called galena. The lead ore, is usually found running near veins of silver ore. When submitted to the process of firing, part of the ore precipitates as lead while the silver floats on the surface, like oil in water” (NAH, XXXIII, 31, 95). For the purification of crude gold the Arthaśāstra indicates the use of lead and heating of the mass by cow-dung fire (II, 13, 9). The sufficiency in the degree of purification was to be attested to by an equation of the quality of the colour of two lines drawn on a touchstone, one by a piece of pure gold and the other by a part of the material (varṇikā) already heated for attaining fineness (II, 13, 17).