Minerals and Metals in Ancient India v1.c15.s4: Copper in Ahar
Minerals and Metals in Ancient India v1.c15.s4
- Language
- English
Copper in Ahar
v1.c15.s4.1
The use of copper in Ahar, which was a major chalcolithic centre, is attested by the unearthing of the following objects:
v1.c15.s4.2
Six circular rings (Period I and II) of diameter 15-20 mm and thickness 2-5 mm; three bangles (Period Ia and Ib); knife blades; Kohl sticks; four celts (Phase Ib) length 13 cm width 8-12 cms, maximum thickness 5 mm, thinner than those reported from Jorwe, Nevasa etc.; several unidentified objects; four socketless flat copper axes of dimensions similar to the celts; 1 mm thick sheet etc.
v1.c15.s4.3
Hegde undertook detailed analysis of one axe and the metal sheet made of copper. (Hegde In Sankalia, Deo and Ansari, 1969: 225-28) The axe and the sheet assayed in terms of copper 90.92 and 96.28 per cent respectively, Fe 6.48 and 1.22, Pb 1.62 and 1.64, Ni 0.31 and 0.26, Mn 0.23 and 0.31 per cent repectively. Both the samples contained detectable traces of Zn, Co, As, Bi and S.
v1.c15.s4.4
Spectrographic analysis was made of the above two samples and a copper ore from Khetri in the northern Rajasthan. Hegde found that (a) the following elements were detectable in all the three samples: Cu, Pb, Ni, Co, Bi, Fe, Mn, Zn, Al, Cr, Mo, Ti, Mg, Gd, P, Ca, As, Sb; (b) the following elements were not detectable in any sample: Sn, Au, Ag; and (c) while W and V were present in the ore, these were not detectable in the metal samples. The impurity patterns (a) and (b) led Hegde to suggest that “the copper metal of the artefacts recovered from Ahar was probably smelted from the chalcopyrite ore of the Aravalli region”. (Hegde In Excavations at Ahar, Sankalia, Deo and Ansari, 1969: 226)
v1.c15.s4.5
However, Aravalli region extends through hundreds of kilometers, and there is no reason why the Aharians had to bring copper ore from far away Khetri in north Rajasthan. The high lead content (1.62-1.64%) in the artefact suggests that the Aharians might have tapped copper-lead ore from some neighbouring deposits in south Rajasthan.
v1.c15.s4.6
During the excavation of Period I levels at Ahar, heaps of slag-like material were recovered from more than one trench at three different depths. Evidently the copper-smelting industry at Ahar was extensive. The analysis of the slag is as follows: SiO₂ 35.2-38.2 per cent, Fe₂O₃ + FeO 43.9-48.3, MgO 2.4-3.6, Al₂O₃ 5.3-7.8, MnO₂ 1.2-2.3, CuO 0.7-0.9 and SO₃ 3.6-6.1 per cent Evidently, complete removal of sulphur and recovery of copper were not possible. Copper ore from Khetri indicated 16.7 per cent silica in its composition, which is less than half of the percentage of silica in the slag. So Hegde presumed that the copper ore was fluxed with silica during smelting in the chalcolithic period at Ahar.
v1.c15.s4.7
It is unfortunate that Hegde did not conduct phase studies on the ancient slag. The modern Khetri Copper Plant produces slag which contains phases such as magnetite Fe₃O₄ and copper ferrites such as CuFeO₂, Cu₆Fe₃O₇ and some free copper oxide. (Sharma and Shekhawat, 1984) Similar phase studies on the ancient slag would have shown whether (a) such a slag could be derived from Khetri copper ore containing specific gangue materials, and (b) if so, what temperature and other physico-chemical conditions might have been employed.
v1.c15.s4.8
Iron content in the Ahar axe was high: 6.48 per cent, but in the copper sheet we find much lower value viz., 1.22 per cent iron, which means that removal of iron from copper was substantial. Considering that chalcopyrite ore of Khetri contains as high as 4 per cent arsenic and Ahar artefacts contain only traces, it is possible that the crushed ore might have been heated to a high temperature such as 500°C to remove arsenic. Lothal copper artefacts also contain negligible quantity of arsenic and for this we do not have to agree with S.R. Rao (1979 and 1985) that the ingot was imported from Oman. Lothal artisans might have learnt like the Aharians the technology of removal of arsenic from copper ore.
v1.c15.s4.9
Metallographic examination of the Ahar axe showed casting fins and rough uneven corrugated surface finish, which suggest that the artefact was cast in a crude sand mould. There are globules of cuprous oxide and lead which does not form solid solution with copper. The metal sample is porous; the porosity must have resulted due to inadequate ventilation during casting and entrapment of the evolved gases. Presence of dendrites and coring indicated slow cooling after casting and the fact that the sample was not work-hardened.
v1.c15.s4.10
Aharians do not seem to have used tin and other alloying elements to produce bronze etc. Their techniques of casting, forging and fabrication were certainly inferior to those of the earlier Harappans or later Navdatolians. On the other hand, Aharians were, like the artisans of Ganeshwar-Jodhpura, the prime producers of copper and probably their target was to produce crude ingots for further processing elsewhere. It may be noted that the Banas culture in the neighbouring site of Kayatha revealed copper artefacts of better finish and quality.