Pinching

Coiling Ceramics definition


Absorbency

The ability of porous materials to attract a liquid (water) into its air spaces. In the production of pottery this is useful for the application of glaze to bisque ware in preparation for the glaze firing. The absorption rate of finished pieces (after firing) should be of concern to the consumer. Pieces with lower absorption rates tend to be more durable. See also .

Bisque

This term may also be seen as bisc, biscuit, bisqueware, bisquefired, biscuit. Refers to both a preparation firing process and the pottery piece that has undergone the firing. The firing is to a temperature that brings about a physical and chemical change to clay. Atomically attached molecules of water are driven off the individual clay particles and they are fused together transforming them into one piece. This intermediate step in glazed ceramics gives bisque ware the ability to absorb water of the glaze solution causing the glaze materials to adhere to the piece while it maintains its shape. Considered to be in the "low-fire" range, some pieces are never fired above this and are therefore usually less durable. See also .

Black core

Occurs during the firing process when carbon inside the clay body has not been sufficiently eliminated. All clays contain some carbonaceous matter, which oxidizes during firing at approximately 1400 F producing carbon dioxide that escapes from the claybody. If the presence of oxygen is insufficient in the kiln atmosphere, the carbon cannot be eliminated from the clay and it is left in a weaker state. This tends to occur more during a "reduction" firing where oxygen in the kiln atmosphere is reduced. See also.

Blackhard

A stage in the drying of a piece of pottery where it is no longer malleable, but it has not yet dried out completely. The moisture content still in the piece gives is a dark tone. See also, , , .

Bone china

A clay body created 18th century Britain as an attempt to duplicate the translucent ability of Oriental Porcelain, whose formula was kept secret form Europe. This claybody is difficult to work with on a potter’s wheel and is most conducive to slip-casting or press-molding. The names is derived from the fact it is an attempt to reproduce porcelain from China using Bone Ash as a primary ingredient. It is still in use today and, because of its durability, it is considered an excellent claybody for use in dinnerware. See also.

Burnishing

A process by which leatherhard or blackhard clay is made smooth by rubbing it with a hard smooth object like a stone, spoon or piece of glass. This procedure gives the piece a polished look. Burnished pots are usually unglazed but sometimes fine slips are applied to add to the decorating. Burnishing not only adds a glossy surface, it also contributes to the durability of the clay by making it more resistant to water absorption. See also, .

Casting slip

A cream-like mixture of clay and water used in the process of producing ceramic objects by means of pouring the slip into a porous mould. Water is drawn from the slip and into the mould, leaving a thin shell of soft but non-liquid clay around the inner surface of the form. When the slip achieves the proper thickness, the excess liquid is poured out and the remaining slip is left to dry completely. It is...



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