History of Chemistry in Ancient and Medieval India, Incorporating the History of Hindu Chemistry by Acharya Prafulla Chandra Ray c15.s1.79

c15.s1.79

General specimens of pottery found at Arıkamedu are glazed, showing the characteristic crackled surface or 'crazing'. The coating of glaze, as pointed out by the archæological survey chemist, does not, however, stand out as a dıstınct layer, and the glazed effect is only superficial. The specimens were probably salt-glazed. Moist salt was very likely thrown into the kiln, when the fuel was almost burnt out. A few potsherds confined to the pre-Arretine and the lowest Arretine layers show a black slip with a striking metallic lustre The particles of the black film were found by the archæological chemist to be magnetic, which on analysis proved to be magnetic oxide of iron. The same chemist also found fine particles of carbon inside the pores of the sherd. It was concluded by him that a slip of ferruginous clay was applied to the ware and it was heated at a moderate temperature in a smoky fire. A polished, bright-red slip is occasionally found at Arıkamedu in potteries of all periods and has been identified as haematite.