Kaoline


The general properties of clays have been discussed in the chapter “Clays – General”.
There are some specific properties which are important from the point of view of industrial
use of china clay. These properties of pure marketable grade china clay are as follows.
1. Whiteness: Both the raw and fired colours of china clay are white. The normal
content of the colouring matter Fe2O3 is only 0.6-1.3 per cent. The colouring
parameter ‘L’ value is as high as 90 -96 (cf., the value of fresh TiO2, which is the
bench mark for whiteness, is 98-100).
2. Brightness: The brightness of calibrated china clay (i.e. even-sized fine grains) as
measured in terms of reflectance from blue light (wave length 457 microns) is 80-87
(cf., the value of fresh TiO2, which is the bench mark for brightness, is 97-98).

3. Fusion point of china clay is 17850C.
4. Dry shrinkage (at 110oC) is 14% (max), total fired shrinkage (at 1350oC) is 18%
(max).
5. Its plasticity is very low (almost non-plastic).
6. Its specific gravity is 2.6.
7. It is soft and can be pulverized to a fine size of less than one micron. At this size, the
particles quickly disperse in water and remain in suspension for a long time.
8. Chemically, it is inert and non-toxic, but its oil absorption is fairly high (25-45%).
9. It is electrically non-conductor.
10. Its refractive index is 1.56.
These properties are standards in a marketable grade beneficial to china clay. There may,
however, be variations in the contents of certain chemical impurities and in a few of the
physical parameters, which are especially specified by user industries.