Minerals and Metals in Ancient India v1.c20.s4: Iron Metallurgy at Dhatwa
Minerals and Metals in Ancient India v1.c20.s4
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Iron Metallurgy at Dhatwa
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Dhatwa in the district Surat on the south bank of the Tapti (Tapi) had a chalcolithic occupation up to tenth century BC showing wares and beads of terracotta, semi-precious stones, shell, microliths of carnelian, jasper, chalcedony and chert. (Mehta, 1975) The iron-using people settling in the area during the early historical period fifth century BC, might have had some link with the Ujjain culture.
v1.c20.s4.2
The existence of an iron-smelting industry in the past is evident from the heaps of iron metallurgical tap slag and pieces of iron ore. The quantity of slag heaps in three layers was of the order of several thousand quintals.
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Among the iron objects recovered were a hoe with a flat underside, upturned butt and pointed end, and fragments of chisels, knives and nails. The major offence weapons were absent. The smiths probably catered mainly for the needs of the agricultural communities. (Hegde, 1973a)
v1.c20.s4.4
A large quantity of pieces of deep red hematite and light red limonite was found on the site. It is possible that the surface limonite deposits in the nearby area (one 2 km south, the other 2 km east of the site) were exploited, and this material (Fe₂O₃, n H₂O) containing 43-45 per cent Fe₂O₃ was roasted to partially remove the water of hydration and produce the deep red variety of hematite containing half the amount of water (LOI 8.1%) and 52.5 per cent Fe₂O₃.
v1.c20.s4.5
Probably wood charcoal was used as fuel. The slag assayed around 50 per cent Fe₂O₃, 22 per cent silica (bound as silicate), and this indicated high wastage of iron in the slag. Two metal samples, one cut from the hoe and the other cut from a fragment of a knife were analysed; these were remarkably pure and assayed 99.76 and 99.84 per cent iron. The metal cut from the hoe was found to be much harder near the upper and lower surface of the implement (123 and 117 D.P.N. respectively), whereas the hardness varied from 99 to 107 D.P.N. in the interior of the metal. Microscopic examination of the polished internal surface of the metal revealed a laminated structure.
Reconstruction of the Techniques
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After roasting, the ore was probably crushed into small pieces, mixed with charcoal and probably fed into a kind of small clay-lined crucible-shaped shaft furnace into which air was forced with the help of bellows. At Kumbhariya, a village near Ambaji in north Gujarat, such primitive smelting furnaces belonging to the medieval period have been found. (Hegde, 1973a: 420) On the top of the furnace, excess fuel was heaped to conserve the reducing condition within.
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The small bloom that resulted was taken out of the furnace, heated to redness in an open hearth, and forged on an anvil in front of the hearth. In the forging process, the adhering slag separated out, and simultaneously the surface of the metal was carburised and case-hardened. The bloom was beaten into a thin strip of metal, and these strips were later forge-welded together to build up a laminated sheet which was further forged to shape it into a suitable object.
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Photomicrograph of the Dhatwa iron hoe actually revealed laminated structure, the lines of lateral forge-welding and the use of lamination technique which had started in Komaranhalli and Tadakanhalli. (Hegde, 1973b: 402-4) Such techniques persisted till recent past amongst the iron-making tribal communities such as the Agarias and Loharias.
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The iron-making tradition of Dhatwa persisted in other areas of Gujarat. During the beginning of the Christian era, there was a habitation of iron-smelters at Shamlaji in the district of Sabarkantha, who utilised the nearby ore and smelted iron in crucibles fitted with tuyeres for blowing. (Ghosh, 1989, Vol. 2: 406)
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Periplus informs us that during the first century AD, Indian iron and steel used to be exported from Ariaca (Gulf of Cambay area).