An Encyclopaedia of Indian Archaeology v1.c21.s7: 16.7 Furnaces
An Encyclopaedia of Indian Archaeology v1.c21.s7
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16.7 Furnaces
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So far neither in exploration nor in excavation has any furnace been found which can be said to have been used for smelting metal during the Chalcolithic period [4.14]. But copper 'bun' ingots have been found at the Harappa [4.9] site of LOTHAL and a number of copper and bronze objects have been recovered from excavations at all Harappa sites and many a Chalcolithic site. A number of these objects from sites in Punjab, Rajasthan, Gujarat, Madhya Pradesh and Maharashtra have been subjected to detailed metallurgical analysis. AHAR² yielded within the strata of the Chalcolithic period copper objects along with slag [16.9.4]—a waste product of the coppersmelting industry. [For a Megalithic, 4.17.6, furnace see NAIKUND.] Analysis of the slag throws useful light on the ancient Indian copper-smelting and metal-working technology.
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Fig. 52. Furnace (pottery kiln from Mohenjo-daro)
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While 1200°C is adequate for the smelting of copper it is inadequate for the effective smelting of iron, which requires a temperature of 1535°C and a strong reducing environment. It appears that in ancient Indian metallurgy the same type of furnace that was used for smelting copper was also used for smelting iron in which the slag was tapped. Remains of such type of furnace with evidence of their use for smelting both copper and iron metals have recently been discovered at Kumbhariya, a village near Ambaji in n. Gujarat. This large metalworking site has been dated to the 10th-11th century A.D. These furnaces are all broken at the bottom. They have slag adhering inside them. Analysis of this slag shows that some of them were used for smelting copper and the others for smelting iron. They are small in size, shaped like a crucible and made of clay. They are all forced-draught, slag-tapping furnaces. The diameter near their mouth varies from 15 to 20 cm, the thickness of their clay wall from 3 to 4 cm and the diameter of their tuyere from 4 to 5 cm.
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The use of this type of small, crucible-shaped, clay-lined, forced-draught furnace, which probably began in the Chalcolithic period in India, has continued to the present day. [For furnaces of the historical period see UJJAIN, NĀLANDĀ.] Many metal-working tribes like the Loharia and Agaria use it for smelting iron. They charge the furnace with crushed haematite and charcoal (2 to 3 cm cube), which they push into the furnace in small quantities at a time from the top as required according to the colour of the flame. About 20 kg of ore and 20 kg of charcoal are added in about four hours and finally topped with excess charcoal. When the charge is smelted the flame becomes luminous; the bellows are stopped and the slag outlet opened. A spongy bloom of wrought iron, about 1 kg in weight, is formed at the bottom of the furnace. It is taken out by breaking the furnace. It is repeatedly heated to redness in an open hearth and forged on an anvil in front of the hearth to separate out the adhering slag. Simultaneously the surface of the metal is carburized and case-hardened. It is further forged to shape the metal into desired objects.
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Elwin, V., 1942, *Agaria*, Calcutta. Hegde, K.T.M., 1965, "Chalcolithic Period Copper Metallurgy in India", unpublished thesis, Baroda; 1965, in *Excavations at Ahar*, Poona; 1973, in *Man*, 8, 3, pp. 416-21. Mehta, R.N., 1969, in *Swadhyaya*, 5, 2, pp. 31-5 (for Kumbhariya). Tylecote, R. F., 1965, in *Jour. Iron & Steel Inst.* 669, pp. 340-8.—K.T M. HEGDE