Ball clay: Ball clay is used in the body for improving workability and conferring strength to the unfired articles. Carbonaceous ball clays are usually incorporated where the production process is carried over through casting method. The colloidal carbonaceous matter helps in the production of stable casting slips. Normally to have a better body, blended ball clays are usually preferred.
China clay: China clay is added to earthenware bodies to improve the colour and also to reduce to some extent the large drying shrinkage. China clay lacks plasticity and strength.
Silica: This is used as a refractory constituent in the body to reduce the drying and firing shrinkage and to help the article to retain its shape. On combining with fluxing materials, it forms glassy substances which on cooling hold the article together and give it fired strength. Silica also controls the expansion co-efficient of the body so as to make it compatible with that of the glaze. Normally silica is used in the form of dry ground powder or wet ground liquid.
To be continued……………………
