History of Chemistry in Ancient and Medieval India, Incorporating the History of Hindu Chemistry by Acharya Prafulla Chandra Ray c12.41

c12.41

The microscopic examination of faience objects at Mohenjo-daro reveals a compact granular structure, composed of angular quartz grains They are bound together with a transparent cement. A chemical analysis of these objects also shows that silica is the chief constituent (Table I), forming about ninety per cent of the total amount. It may, therefore, be inferred that the composition of the original paste was finely crushed quartz or pure white sand, a glassy flux and, if necessary, a colouring matter. The moulded object had to be dried and fired in order to bring about the fusion of the flux Curiously enough, analysis shows absence of clay which might have given coherence and plasticity to the paste for working and moulding. It is suggested by some authorities that probably silicate of soda, which forms a highly viscous solution with water, was used as a constituent of the paste. This served to impart the desired property to the wet paste. The practice of preparing an alkaline silicate by the fusion of soda with sand was well known to the ancient peoples who practised the art of glazing. The hollow objects were possibly moulded on cores of sand, which was held in some fabric and raked out after firing. Impressions of the fabric as well as remains of the sandy core, have been detected in several specimens