An Encyclopaedia of Indian Archaeology v1.c21.s9.t1.21

v1.c21.s9.t1.21

The occurrence of slag is an evidence of local smelting. Its analyses are instructive in that they reveal the contemporary smelting practices, nature of the ores used, percentage of the metal extracted, use of flux and the temperature available. The analyses of (1) copper slag from AHAR² (Chalcolithic), (2) copper slag from RAJGHAT⁴, Pd I (early historical), (3) iron slag (from the same site and level), and (4) slag from KUPGAL (ash mound) are as follows per cent: loss on ignition—in (1) and (2) nil, in (3) 3·14, in (4) 10·5 (by difference); SiO₂—in (1) 38·16, in (2) 39·17, in (3) 16·32, in (4) 62·00; Fe₂O₃/FeO—in (1) 45·32, in (2) 38·72, in (3) 74·43, in (4) 11·00 (combined with Al₂O₃); Al₂O₃—in (1) 5·96, in (2) 12·02, in (3) 4·25, in (4) see above; CaO—in (1) nil, in (2) 5·39, in (3) 1·20, in (4) 8·00; MgO—in (1) 3·02, in (2) 0·62, in (3) 0·45, in (4) nil; MnO₂—in (1) 0·89, in (2), (3) and (4) nil; CuO—in (1) 0·91, in (2) 1·05, in (3) and (4) nil; Ni, in (1), (3) and (4) nil, in (2) trace; SO₃—in (1) 4·14, in (2) 0·20, in (3) and (4) nil; P₂O₅—in 1 and (2) nil, in (3) trace, in (4) 2·5; TiO₂—in (1), (2) and (4) nil, in (3) trace; K₂O—in (1), (2) and (3) nil, in (4) 5·00; C—in (1), (2) and (3) nil, in (4) 1·00. Thus in (1) and (2) chalcopyrite is the main copper ore used and either the ore contained good percentage of silica or silica was added as flux. About 1% of the metal is left in the slag which shows that extraction was fairly good. In (3) very rich ore was used but as much as 74% of the ore was left unsmelted. It implies that iron technology was not yet fully evolved and the requisite temperature was not available. The so-called slag reported from the ash mounds is not of iron but is the product of continual burning of cowdung.