History of Technology in India, Vol. I: From Antiquity to c. 1200 A.D. v1.c13.s2.t4.165

v1.c13.s2.t4.165

The crucibles used in this process had a conical or pear shape and they were very skillfully prepared from a refractory material capable of sustaining such treatment. *Fig. 37* shows a picture of conical crucible preserved in the National Museum of Madras, and also a sketch of the same is shown in *Fig 38*. These crucibles were prepared from a range of compositions based on their end use and these have been mentioned in the ancient Ayurvedic texts *Rasa Ratna Samuccaya* and *Suśruta Samhitā*. The crucibles used for making Wootz steel generally prepared from a mixture of some silicious clay or Caoline mixed with rice husk and iron oxide sand. On firing of these crucibles in reducing atmosphere at first at 400-500°C and then at 1100-1200°C, the rice husk got charred depositing carbon and adding SiO2 to the clay. Recently Lowe et al. (1990) have analysed and studied the composition as well as structure of many such used crucibles collected from the steel melting sites of the Hyderabad region and confirmed the excellent refractoriness of these crucibles. The structure of these crucibles was found to be consisting of SiO2 phase present in a matrix of Mullite (M.P. 1800°C), some graphite particles and small prills of iron, produced by the reduction FeO present in the crucible.