Several clays in commercial use consist largely
of kaolinite, a hydrated aluminum silicate. Large deposits
of this mineral occur in China; Czechoslovakia; Cornwall,
England; and several states of the United States. Various
grades of kaolin clays may be distinguished. White kaolin
clays are fine in particle size, soft, nonabrasive, and
chemically inert over a wide pH range. Their largest
consumer is the paper industry, which uses them as a
coating to make paper smoother, whiter, and more printable,
and as a filler to enhance opacity and ink receptivity.
Ball clays are usually much darker because they contain
more organic carbonaceous material. These fine grained
refractory bond clays have excellent plasticity and
strength, and they fire to a light cream to white color.
For these reasons, ball clays are used in ceramics.