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Minerals and Metals in Ancient India v1.c18.s4: Copper in the Historical Period

Minerals and Metals in Ancient India v1.c18.s4

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Copper in the Historical Period

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The silver sheets of Gungeria make one wonder whether the Gungeria culture had some link with the *Mahājanapada* tradition and the early Historical period, when punch-marked coins were introduced and the copper plates used to be made for inscriptions and land donations. One of the earliest copper plates is the Sohagura copper alloy plate from Gorakhpur district in the Uttar Pradesh in which the Mauryan inscription is in Brāhmī characters; this tradition continued in the post-Christian era. Bhardwaj (1979) analysed a piece of a copper sheet, obtained from Rajghat, Varanasi dated 600-400 BC, and found this to be 95.45 per cent copper, containing 1.75 per cent CaO, 0.96 per cent iron, 0.25 As, 0.15 Ni.

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The 600-400 BC Samples from Rajghat were made of unalloyed copper whereas 400-200 BC samples from the same site contained tin. A bronze fragment assayed 13.99 per cent tin, copper bangle 1.82 per cent, and an uninscribed rectangular coin 7.83 per cent tin. The impurity analyses of the artefacts and ore (the presence in both of Ni, Co, Mo, and very low frequency of Pb, As, Sb) suggested that the Rajghat copper artefacts were probably derived from Bihar ore. (Bhardwaj, 1979) It is apparent that during the Historical Period, the Harappan tradition of tin-alloying of copper was revived in the Eastern India; Kausa-mbi 500 BC bronze assayed 19.13 per cent tin, Sonepur Pd II bronze 32.42 per cent tin and so on. This was possible due to discovery and exploitation of the tin ore mines from the Hazaribagh area and/or some import of tin from Malayasia.

Some Ancient Copper Mines

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There is the likelihood that copper smelting started in the mining area of Singhbhum positively by the time of Copper Hoard Culture (1100-800 BC), and continued uninterrupted during the Historical Period. Bhardwaj (1979: 191-99) listed 19 ancient mines of Rajasthan, 11 of Uttar Pradesh and 12 of Bihar which include the famous Bara-gunda (= twelve pits) mine of Hazaribagh district having extensive old workings over a length of 1200 metres and slag heaps having 0.08 to 13.04 per cent copper, the Surda and Mosabani mines of Singhbhum district etc. Unfortunately, the organic residues in these ancient mines have not been preserved for C-14 bio-dating. (Kerr-Cross, 1950; Dunn, 1965)

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Some of the Indian copper ore mines with early C-14 datings are: Dariba (Rajpura) in Udaipur, Rajasthan, 1260 ± 160 BC continued up to 250 ± 100 BC, Ambamata (Banaskantha, Gujarat), 160 BC onwards to the post-Christian era, Bandlomattu Hill, (Guntur, Andhra Pradesh) AD 50 onwards to AD 1215, Ingaldahal (Chitradurga, Karnataka) AD 220 etc. (Chakrabarti, 1986: 188-96)

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S.R. Rao (1987) has suggested that Ingaldahal mining area supplied copper not only in the Historical era but also to the megalith-builders of the Chitradurga region around 500 BC, and even earlier around 1200 BC to produce Chalcolithic Period bronze artefacts of Brahmagiri which is not far away from Ingaldahal. Similarly, Kalyadi mine in Arsikere region of Karnataka has been claimed to have supplied copper ore to the megalith folk of the fifth century BC. Kallur copper swords (1200-1000 BC) were possibly made utilising the near-by copper oxide deposits. Thus, it is evident that the Peninsular Chalcolithic Culture and the Copper Hoard Culture, spreading to the Gaṅgā-Yamunā Doab, developed local copper mines to produce regional varieties of copper artefacts, till the Maurya era brought about a synthesis.

Copper Slag and Artefacts from Rājghāṭ

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Analysis of the Rājghāṭ copper slag showed that it was chiefly iron silicate with 5.39 per cent calcium oxide, whereas the Ahar slag did not contain any calcium oxide. Evidently, lime was used as a flux, a new innovation in India, and this is also shown in the CaO content (1-2.5 %) in the copper artefacts of Rajghat. (Bhardwaj, 1979) Presence of 1 per cent + copper oxide in the metallic phase shows that the molten copper was not properly ‘green poled’ or dexoidised.

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Metallographic examination showed that the copper sheet of Rājghāṭ had globular alternate banding of Cu-CuO eutectic. Annealing twins provided the evidence of heat-treatment having been done. Bronze coins had segregated Cu-rich Zone and Sn-rich grain boundary, proving that it was a cast structure. Very good coining and embossing were revealed in some Pre-Christian era Taxila coins which had glassy elongated slag streaks and fine equi-axed grains; these were evidently hot-worked, then cold-worked, and finally annealed. (Bhardwaj, 1979: 81)