History of Chemistry in Ancient and Medieval India, Incorporating the History of Hindu Chemistry by Acharya Prafulla Chandra Ray c12.58

c12.58

In the case of a few other bodies, an impression of a canvas-like material has been found on the surface below the glaze. It is suggested that this served as a backing to hold together the ingredients of the paste constituting the body of the ware, preparatory to glazing. The canvas-like material was subsequently burnt away in the kiln. The glaze has, however, been found to penetrate well into the paste forming a hard but somewhat brittle material. It is also likely, as assumed by Sana Ullah, that the glazing was carried out in a second firing as at present. The prevailing colours of the faience glaze of the Indus Valley wares are bluish green or greenish blue, although indigo blue, apple green, maroon, black and colourless examples have been found. The blue shades owe their colour to copper oxide, while green contains iron oxide in addition. The black or dark maroon glaze contains an excess of manganese oxide.