History of Chemistry in Ancient and Medieval India, Incorporating the History of Hindu Chemistry by Acharya Prafulla Chandra Ray c15.s1.41

c15.s1.41

M. Sanaullah, the archæological chemist gives an account of their composition and of the process involved in their making on the basis of his analysis. The black colour is attributed by him to the presence of ferrous oxide (about 13 per cent). The original slip was evidently a highly ferruginous body consisting possibly of a finely levigated mixture of clay and red ochre. This was ground in water and applied to the surface of the vessel before firing. The black colour was developed by the action of reducing gases formed in the kiln. The polishing might have been done before or after the firing. The coating is not a siliceous glaze