An Encyclopaedia of Indian Archaeology v1.c21.s9.21

v1.c21.s9.21

In the post-Christian period iron technology excelled in forging enormous masses of iron into huge pillars and large beams showing high resistance to corrosion. The classical example is the famous 4th-century iron pillar at Mehrauli in Delhi. Its dimensions are: length 7·20 m, above ground 6·70 m, underground 0·50 m, upper diameter 0·30 m; lower diameter 0·40 m the total estimated weight is over 6096 kg. Its percentage chemical composition is: iron 99·768; carbon, 0·23; silicon, 0·026; phosphorus, 0·180; manganese, nil; sulphur, trace; and nitrogen, 0.0065. The specific gravity is 7·747 and the metal is wrought iron. The pillar is believed to be made by successively forge-welding blooms of wrought iron. The corrosion resistance of this pillar has been an enigma to scientists. It is generally ascribed to: (1) the purity of iron, high phosphorus, low sulphur and absence of manganese; (2) cinder coating formed on the surface and better conditions in the surface roughness; (3) better forge-welding; and (4) drier and uncontaminated atmospheric conditions (Ghosh, 1963). [The rustlessness of the pillar has been exaggerated. While the body of the pillar is smooth, an excavation of its rough underground portion in 1961 showed that that portion was thickly covered with rust and other corrosion products. So was also the socket at its top, to hold a capital or emblem. *IAR—1961-2*, 149.]