History of Technology in India, Vol. I: From Antiquity to c. 1200 A.D. v1.c17.s4.t1: The Issue of Ore-Artifact Correlation
History of Technology in India, Vol. I: From Antiquity to c. 1200 A.D. v1.c17.s4.t1
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The Issue of Ore-Artifact Correlation
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In pursuing the laudable objective of establishing that the metals were produced indigenously in ancient India, our archaeologists have sought correlation between the artifacts and ores in the subcontinent in terms of trace metal impurities. Most of the enthusiastic investigators ignored the cautionary remarks of Thomson (1958) pointing out the hazards in ore-correlations, and occasionally reported 'positive correlation'.
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We have pointed out (Biswas, A.K. et al, 1990: 50-51) that the correlation depends upon: (a) the type of ore, oxide or sulphide or silicate, the nature of impurities, (b) the precise conditions of smelting, such as temperature, nature of fuel, flux etc., and several other factors.
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The ore types may very even within a region of small area. Hegde (1968) failed to detect the impurity elements of Cr, Co, Ni, Bi and Mo (present in the Devnimori silver coin) in the nearby Zawar argentiferous galena ore and concluded that the silver was 'imported'. Shekar (1983) however found them in the Ambamata deposit only a hundred kilometres away!
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So far as the occurrence of metallic artifacts in the ancient sites are concerned, the existence or absence of mines in the neighbourhood areas in the modern age hardly establishes any truth. On the one hand, the currently known mines might have been unknown to the ancient people, and on the other, some small near-surface reserves might have been thoroughly exploited by the ancient miners, so that we do not know them at present. Certain impurities such as arsenic might have been eliminated through certain simple pre-smelting operations such as roasting. Thus we are not sure whether arsenic-free copper ingots of Lothal were made at Oman as claimed by S.R. Rao (1979 & 1985) or made out of Indian arsenic-bearing ore after a pre-smelting roast.
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Having stated the hazards of the ore-metal correlation, let us report some of the 'positive correlations' obtained by our archaeo-metallurgists. Friedman et al (1966) claimed that with regard to copper artifacts, the elements of Ag, As, Bi, Fe, Sb and Pb were the most important metallic impurities in relating the metal back to the original type of ore. Following this argument, Agrawal (1971, 1984) suggested that Chanhu-daro celt and Mohenjo-daro spearhead were made from Khetri chalcopyrite ore, since all the three materials contained trace impurities of Sb, Pb, but not Fe and As.
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Hegde (1969) compared the artifacts from Ahar with the chalcopyrite ore from Khetri, and the similarities led him to conclude that 'copper metal of the Ahar artifacts was probably smelted from the ore of the Aravalli region'. The slag dumps and neighbouring mines indeed suggest that copper was made at Ahar indigenously, but Hegde's argument is unsound. 'The Aravalli region' alluded to by Hegde corresponds to a vast area and ores of more than one type; it is hard to believe that chalcopyrite ore was brought all the way from Khetri to Ahar over a distance of hundreds of kilometres while there were ores in the vicinity.
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Hegde (1985, 1989) has himself modified his earlier view and suggested that the Ahar artifacts were possibly made from the nearby region of the Aravalli which constitutes of not-too-hard tremolite-chlorite schists rather than the far-off Khetri ore embedded in quartzite rocks, hard and less easily extractable. While impurity patterns of the ores in different parts of the Aravalli 'may be similar' (the previously stated Ahar-Khetri correlation now loses much of its significance), the lead isotope ratios markedly differ in the north-eastern, central, and south- western parts of Aravalli (Hegde, 1985). Efforts are in progress to correlate metal artifacts and specific ore deposits through lead isotope ratio analysis.
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Further cautioning is necessary in this regard. The ancient smelting process, which is not definitely known at present, would certainly have considerable effect of the trace element profile as proven by smelting experiments (Tylecote et al, 1977). Lead isotope correlation between ore and artifact has been successful in one case (Gale et al, 1982). Reporting failure in another case, Craddock (1985: 59) has rightly questioned that lead in the artifact could come not only from the copper ore (as presumed) but also from the flux and deliberate addition of lead during smelting.
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We do not discourage attempts for ore-artifact correlation, but these must be supplemented with additional evidences for (a) mines of antiquity, (b) outfits for smelting, furnaces and crucible, (c) heaps of slag and slag-ore correlation regarding the non-metallic phases, and (d) a reasonably large number of artifacts at different stages of manufacture and of composition and properties varying within narrow limits (Biswas, A.K. et al, 1990: 51). Fortunately, several such evidences for indigenous metallurgy in India have been obtained from Mehargarh, Ganeshwar-Jodhpura, Lothal, Ahar, Khetri (for copper), Chanhu-daro and Lothal (for beads and seals), Atranjikhera, Ujjain (for iron), Zawar (zinc, lead and silver) etc.