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Calcine - Reduce to calcium carbonate. To purify a substance by subjecting it to high temperatures.

Calcium carbonate - A white insoluble solid. Occurs naturally as chalk, limestone, marble and calcite. It is used as flux in glazes.

Caliper (or Calliper) - A measuring device resembling a compass. Internal calipers measure internal diameters or apertures and external calipers measure outside diameters or overall sizes. External calipers look like a jockey (without his horse) and inside calipers look like a girl in a tight skirt.

Cast - To produce shapes by pouring fluid clay into moulds. The 'negative' moulds are usually of plaster of Paris, and made from a 'positive' so that when they wear out, new ones can be made.

Calcine - Reduce to calcium carbonate. To purify a substance by subjecting it to high temperatures.

Celadon - A grey-green glaze, usually pale in colour, of Chinese origin.

Cheese-hard or leather-hard - Clay that has dried to the point where it is stiff enough to retain its shape but wet enough for further work to be done on it.

China Porcelain - The first porcelain imported into Europe was from China.

China clay Kaolin A white clay made from pegmatite found in Cornwall.

China stone Pegmatite - A feldspar.

Chrome oxide - Used to produce yellow or green colours in glazes.

Chuck - Tube-like form to hold a pot upside-down on the wheel for trimming the foot.

Chun - A pale blue glaze used on stoneware.

Clay - A mixture of water an powder from decomposed feldspar. Clay is the potter's basic material. When moist it is soft and plastic; when fired becomes permanently hard.

Climbing kiln - A multi-chamber kiln with each successive chamber at a higher level than the last. This type of kiln is of oriental origin and was popularized in Britain by Bernard Leach and his students.

Cobalt oxide - Used to produce a blue colour in glazes

Coiling - Rolled clay in flat form or with a rounded section that welds to itself when fired to make a solid form.

Cone - Cones are test pieces inserted in the kiln to indicate to the potter when a certain temperature has been reached. They are made of various glaze materials of known melting point. Two examples of cones are Seger cones, named after Hermann August Seger, and Orton cones, manufactured by the Orton Ceramic Foundation in the USA.

Copper oxide - Used to produce green colours in glazes. When used in a reducing atmosphere it produces a red colour.

CPA - The Craft Potters' Association. An organization to promote the work of British potters.

Crackle - Cracks in the glaze formed intentionally as a decorative feature. (See also - Crazing)

Crawling Shrinkage or retraction of the glaze during firing, causing exposed areas of body.

Crazing A fine network of cracks in the glaze usually caused by uneven contraction and expansion of the body and the glaze during changes of temperature. In some pottery this is a design feature rather than a fault (See - Crackle), but in earthenware pots the cracks can allow moisture to penetrate to the porous body leading to further damage.