History of Technology in India, Vol. I: From Antiquity to c. 1200 A.D. v1.c15.s7.7

v1.c15.s7.7

According to K.T.M. Hedge, the mirror-like polish of the NBP ware “was produced by an application of liquid clay, quite similar to that employed for manufacturing the body of ware, but which in addition to levigation was carefully further shifted and cleaned for the purpose of reducing heavier particles like felspar, quartz and limestone present in the clay by means of suspending and stirring the clay in water. This clear clay liquid was then peptized by the addition of an alkali containing material” (Hedge, 1962, pp.159-161; 1966, p.623). The clay solution thus prepared and treated with a little alkali gives a black shiny slip when fired in reducing conditions.