The ball clay burns to a light grey or light buff in colour. It becomes very dense when fired to about 1300oC. The shrinkage of ball clay is very high - sometimes goes upto 20% during firing and hence it is impossible to use ball clay alone in sanitaryware making. Ball clays are usually used as an admixture to other clays to secure increased plasticity and workability.
In manufacturing the traditional ceramic white wares, ball clay is an indispensable raw material as an addition to the body to overcome the non plastic properties of kaolin. However if whiteness of the body is main criteria, we cannot use ball clay more than 15% in the body. Ball clays contain very high percentage of carbonaceous material. This carbon burns off during firing and does not affect the final firing colour of the clay. However the presence of carbon increases the plasticity of the body.
to be contd…….
