Minerals and Metals in Ancient India v1.c27.s1.t2: The Later-Day Evidences
Minerals and Metals in Ancient India v1.c27.s1.t2
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The Later-Day Evidences
v1.c27.s1.t2.1
Bronson records that the evidences of wootz being made in India come from much later medieval periods. Wrought iron, made from direct reduction of magnetite, used to be heated with wood or organic materials in closed crucibles over charcoal fire, maintained at high temperature by blowing air.
v1.c27.s1.t2.2
Bronson (1986: 39-46) has compiled the information on the various processes of making wootz in pre-modern India, studied by the previous scholars. (Buchanan 1807; Heyne 1814; Voysey 1832; Heath 1839; Schwartz, 1901; Coomaraswamy 1956; Rao *et al.*, 1970 etc.) The common denominator of most of the processes was to heat the charge of iron and vegetable matter in a sealed crucible. Voysey (1832: 247) observed a process at Golconda (Hyderabad) in which low-carbon and high-carbon iron smaples were fused together. Additional carbon could have come from rice husk in the crucible wall.
v1.c27.s1.t2.3
Coomaraswamy (1956) reported a Ceylonese steel or wootz assaying 1.97 per cent carbon. Verhoeven (1987a) wondered whether wootz was first made in the 2.5-3.5 per cent carbon range and then de-carburized. He favoured the other notion that most wootz had lower as cast carbon level of 1.6 per cent, which meant that the crucible temperature was at least in the 1400-1450°C temperature range. Rao *et al.* (1970: 16) detected cristobalite in the fired crucible proving that the crucible must have been heated over 1470°C at least for a short duration. Such a temperature could be reached in a bellows-blown charcoal fire. The ingots were probably in nearly molten condition, although the distinct carbon concentration profile in some samples suggested solid state diffusion rather than mixing of carbon. Smith (1960: 23) published the cross-section of a nineteenth-century wootz ingot (1.34 % carbon) showing the dendritically-induced microsegregation of the impurity elements: P (0.1 %), Mn (0.06 %), Si (0.04 %) and S (0.02 %). The Oriental Damascus dagger and sword samples contain 0.1 to 0.25 per cent phosphorus. Verhoeven and Jones (1987b) have shown that the high phosphorus impurity levels of Damascus steels could have controlled the mechanism of cementite formation. The formation of primary cementite between austenite dendrites during solidification could lead to the Damask pattern of the final sword.