In any clay, in addition to the very fine particle size there will be some portion of larger size particles also. In primary clay such as most kaolins there is so much coarse material of unaltered feldspar and quartz or other mineral grains which has to be necessarily removed by washing process.
Apart from other mineral impurities clay usually contains some organic matter as impurities. Even though the organic matter burns out and disappears in firing its presence has an important effect on the physical behaviour of the material before firing. Clay is most of the times formed in situations where
organic matter becomes associated with it. This organic matter leaves a residue of carbon in the clay. Carbonaceous matter in clay may also be caused by bacterial action in the damp clay itself.
To be continued……………
