Kilnworks home »

Glossary of studio pottery terms used through this site

Bisque: Ceramic: Clay: Dipping: Earthenware: Firing: Glaze: Kiln: Leather Hard: Matured Bisque: Salt Glaze: Slip: Throwing: Turning:



Bisque:

Clay that has been fired but not glazed. Prefiring also makes the tableware easier to handle. Glaze is then applied and it is fired again. 'Low' bisque firing is typical for pottery and ceramics while vitrified bisque is done for bone china and some types of stoneware. Low bisque is fired as high as possible to burn away all carbonaceous matter, yet low enough to provide enough absorbency to make glaze application easy. Glazes have special additives to make them gel and stick to the ware.

Ceramic:

Any man-made solid produced by the fusion of mineral substances in a kiln. The term 'pottery' is used to refer to those individuals who fabricate their own ware using plastic clays of all types and at all temperatures ranges.

Clay:

The decomposition of granite through the process of Kaolinisation creates clay. Clay is a mineral with a plate (platelet) like structure; it is these plates (about 0.5 microns across) which, when lubricated with water, slide against one another to form the plastic mass we know as Clay.

'Primary' clays are those found close to the area of Kaolinisation and hence the purest (China Clays). Secondary clays are those moved by water away from the site of Kaolinisation and get progressively more plastic and less pure (Ball Clays, fire clays, Earthenware and marls).

Dipping:

The process of dipping ware into glazes.

Earthenware:

A low fired form of pottery (porous clay bodies) which are fired to maturity at approx. 1100°C.

Firing:

The process which changes clay into ceramic. Up to 600°C the chemically bonded water in Clay is driven off. This irreversibly changes the chemistry of the clay into pottery.

Glaze:

A thin 'glassy' layer formed on the surface of fired ceramic. Glazes are a finely ground mixture of mineral and man-made powders tuned to melt and flow at a specific temperature. Many clays will melt well at high temperatures and thus qualify as 'slip' glaze.

Glazes are often classified to designate type within a specific type of ceramic ware. Glaze has a random molecular structure which is the result of fast cooling, so crystals do not develop (the exception being Crystalline Glazes). For example; Granite cools slowly (geologically speaking) so we can easily see the crystals in polished granite, glaze cools quickly so the molecules do not have a chance to crystallise. Its high viscosity means it does not run off the pot.

Kiln:

Basically an insulated box which is heated and 'fires' clay and glazed objects to maturity. The maximum operating temperature for most pottery kilns is about 1300°C although many wood fired kilns may be fired up to 1350°C.

Leather Hard:

A stage in the drying process of clay when the material is pliable but strong enough to handle. It is the ideal time for Trimming and for the addition of handles and spouts.

Matured Bisque:

A bisque that has been fired at the proper rate of heating and cooling to produce an even state of hardness throughout.

Salt Glaze:

Salt firing is a process where unglazed ware is fired to high temperatures and salt fumes are introduced into the kiln chamber (normally by a spray in the burner ports). The sodium in the salt combines with the silica and alumina in the clay to form a glaze. The glaze is characterised by a pitted orange peel surface (although magnesium based slips may result in a smoother surface). The typical colours resulting from salt glaze are oranges, browns and blues. Notable exponents of the salt glaze technique are Walter Keeler and Michael Casson.

Slip:

A clay with enough water added to become a 'cream' like consistency, it is used to join slabbed forms and handles and spouts to the body of the vessel while leather hard, but before the bisque firing.

Throwing:

A delicate balance which defies gravity and centrifugal force as clay is coaxed up by hand from the spinning turntable. A process ideally suited to forming Cups, Vases and Jugs.

Turning:

Certain forms made on the potters wheel will not support themselves unless excess clay is left at the base. The solution to this problem is turning (done at the leather hard stage). The pot is inverted onto a potters wheel and a metal cutting tool is applied to the bottom of the pot until the desired finish is achieved.

tableware

outlets

inspiration

workshop

Kilnworks