History of Technology in India, Vol. I: From Antiquity to c. 1200 A.D. v1.c13.s2.t3.20

v1.c13.s2.t3.20

As discussed earlier PbS after roasting gets converted into PbO and this can be easily reduced at 500°C to molten lead. The process used in ancient India at Zawar was most probably ‘Ore Hearth Process’ where the roasting and reduction of rich Galena is carried out in an open pit furnace. Fig.5 shows a sketch of such a furnace as reported by Raistrick (1927) and referred by Tylecote (1976). In such a furnace temperature as high as 1000°C can be easily obtained under natural draft and the reduced metal flows out and gets collected in the front pit. At this temperature Ag₂S also gets decomposed, reduced and forms an alloy with molten lead. The details of this process has been mentioned by Sevryukov (1975).