History of Technology in India, Vol. I: From Antiquity to c. 1200 A.D. v1.c29.s2.t3.3

v1.c29.s2.t3.3

*Nature of clay:* The soil used for fabrication of bricks consists mainly of clay along with natural impurities of the soil as quartz, mica, feldspar, calcite, kaolinite, depending upon the basic material from which the soil is formed. Main criterion for the mud to be useful for moulding bricks is its plasticity. Pure clay is very plastic and natural impurities affect its plasticity. The nature of the minerals, shape and size of the grains, presence of soluble salts and organic material influence the suitability of the soil for bricks. Plasticity can be increased by adding selected clay and can be decreased by adding quartz, sand, slag, organic material like husk of rice, or chopped straw. The composition of the brick varies according to the region.