Materials used in the manufacture of Ceramics
China Clay
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China Clay |
China clay is kaolinised feldspar - they are highly
valued for their whiteness, hence their use in bone
china.
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Kaolin - what it is:
The chief constituent of kaolin is the clay mineral kaolinite, a hydrous aluminium silicate, Al4Si4O10(OH)8, formed by the decomposition of aluminium silicates, particularly feldspar.
Kaolin - where it is found:
Kaolin is now mined primarily in Malaysia and in Cornwall, England. China clays were first discovered in England in the 1740s. In England the china clays are found near St Austell, on western flanks of Dartmoor and on the western and southern parts of Bodmin Moor. The quarrying technique is unusual. High pressure hoses are directed at the wall of the clay pits. The fine clay forms a slurry and is washed down. Most of the impurities are left behind.
Kaolin - how it is used:
China clays have poor plasticity so they are often used in conjunction with additives - usually ball clay and bentonite. As a general rule china clays are quicker to cast than sedimentary clays. They are highly valued for their whiteness, hence their use in bone china. Shrinkage of clays fired at 1300ºC is about 12%.
CHINESE ORIGINS
Kaolin (Chinese kauling, "high ridge"), or china clay, a pure, soft, white clay of variable but usually low plasticity that retains its white colour when fired.
The name derives from the hill—in Jiangxi Province, south-eastern China—from which the clay was first obtained. It was the Chinese who, in the 7th and 8th centuries AD, first developed the techniques for using kaolin to make porcelain. Europeans began importing Chinese porcelain in the 14th century, but it was not until the early 18th century that they were able to reproduce its much-prized hardness, whiteness, and translucency for themselves.
questions / comments? email Steve Birks steveb@netcentral.co.uk