History of Chemistry in Ancient and Medieval India, Incorporating the History of Hindu Chemistry by Acharya Prafulla Chandra Ray c12.27

c12.27

The prevailing colours of the brick, pottery and miscellaneous terra-cotta objects found in such abundance at the Indus Valley sites are light red or salmon. Black or grey are rather rare. Sana Ullah (archæological chemist), in his analysis of these products, remarks that the colours are due to the presence of iron compounds in the clay, which develop a red shade in the oxidising atmosphere of the kiln, while black or grey products are obtained when a reducing or smoking atmosphere prevails in the course of burning. Analysis further shows that the slip of bright red colour sometimes found covering the pottery body is due to ferric oxide; and the black or chocolate designs, that are found painted on the body, owe their colour to oxides of manganese. This establishes an identity of the colouring agents used by the Indus Valley people with those used to-day by the Indian potters. Much of the ancient technique seems to have been handed down to the present time without alteration. The potters in India today prepare the red slip by levigating red ochre or *Multani matti* (a yellow ochreous earth) with water. For black or chocolate shades he employs a manganiferous hæmatite. The manganese oxides, frequently associated with ferric oxide, give a pure black colour when rich in manganese; when the proportion of iron in the mixture preponderates, a chocolate colour develops