Since kaolin is a primary clay it is relatively free from mineral impurities such as iron however the clay substance is usually mingled with rock fragments which must be removed by some method of purification. Kaolin is a highly refractory clay and has a melting point above 1800oc . Kaolin is difficult to shape into objects because of its poor plasticity. In practice therefore kaolin is seldom used by itself.
To increase its workability and to lower the kiln temperature other materials are added to it. The shrinkage of kaolin is very low because of its relatively coarse grain structure. There are some secondary kaolins which tend to be darker in burning however they are more plastic than the pure kaolins.
To be contd…………….
