Clay Glossary
Clay Glossary
Pottery jargon can be confusing to the beginner. Use our glossary to discover the meaning of any terms you may come across.
Alumina Aluminium oxide. It is used to bed bone china in the biscuit firing. A fine white powder with a high fusing temperature. Top
Antiquing A method of applying colour, then wiping it back to highlight or accentuate the surface detail. Top
Ash Glaze A glaze made with ground ash, usually wood ash and sometimes mixed with other materials. Top
Banding Wheel A turntable used for applying lateral decoration to a pot. Top
Bat A flat disk that sits on the wheel. Used for heavy pieces that would be difficult to separate from the wheel. Top
Bisque ware (or biscuit) Pottery that has been given a preliminary firing to render them hard enough for further work, such as decoration and glazing. The higher the temperature of the bisque firing, the harder the pot will be, resulting in reduced reaction between glaze and body in the final firing. Top
Bisque firing The first firing of pottery, to mature the clay and give it permanence. In this firing, pots can be stacked or touching, as there is no glaze to stick them to each other. Top
Blunge Mix water with clay. Top
Blunger Machine for mixing water with clay to create slip. The clay is fed into a hopper and goes through rotating blades to mix it with the water. Top
Body The substance from which a pot is made. A particular mix of clay, such as stoneware or earthenware body. Top
Bone China A china made white and translucent by the addition of calcined animal bone (bone ash) to the body. Top
Burnish To smooth the surface of a pot to a polish by rubbing with a hard object. Top
Calcine To purify a substance by subjecting it to high temperatures to drive out water or carbon gases. Top
Caliper A measuring device resembling a pair of compasses. Internal calipers measure internal diameters and external calipers measure outside diameters. Top
Casting To produce shapes by pouring liquid clay into porous moulds to build up a layer of clay. Top
China Porcelain. Top
Chuck Hollow, tube-like form for holding a pot upside-down on the wheel during trimming. Top
Coiling Making pots or other objects using coils of clay. Roll out coils of clay with the palms of your hands before coiling the clay round into a pot shape. The coils can then be smoothed out using a scraper or rib tool to produce a flat surface to the pot. Top
Cone Cones of ceramic material inserted in the kiln which melt at a known point. Used to indicate to the potter when a certain temperature has been reached. Modern kilns have programmers which detect when certain temperatures are reached, negating the use of these cones, however many potters still refer to the cone system when choosing the firing temperature. Top
Crawling Movement of the glaze during firing, causing exposed areas of clay body. Usually due to dust or grease on the surface. Top
Crazing A fine network of cracks in the glaze usually caused by contraction of the glaze during firing. In some pottery such as Raku this is a design feature, but in earthenware pots the cracks can allow unwanted moisture to penetrate to the porous body. Top
Damper A crude device - usually a refractory clay brick - used to block the flue of a kiln. Top
Decal Imagery or text, printed onto a transfer paper, used to decorate pottery or glass. Top
Dipping Applying glaze by immersion. Top
Earthenware Pottery fired to a relatively low temperature. Earthenware is porous if left unglazed so must be glazed if it is to hold food or liquid. Usually fired at low temperatures. Top
Enamel Low temperature fired (low-fired) coloured glazes. Top
Engobe Fluid clay used for decoration. This term is usually used to describe coloured slips. Top
Fettling The removal of unwanted blemishes or seams with a sponge or knife from nearly dry pottery, prior to glazing and firing. Top
Firing To heat pots in a kiln to a set temperature to mature the glaze or clay. Top
Firing Range The temperatures between which a clay or glaze matures or fuses. Top
Flatware Plates, saucers, trays, etc. Top
Flux A substance mixed with a body or glaze to help it melt readily to promote fusion. Top
Foot The base of a pot. Top
Frit A vitreous composition used in glazes and enamels. Top
Glaze A glass-like substance used to decorate the surface of pottery. Top
Glaze Firing The second firing of a pot after the glaze is applied. Top
Greenware Unfired pottery. Top
Grog Gritty material added to clay to add texture, lessen warping and improve resistance to thermal shock. It is usually ground, fired clay. Top
Handbuilding To make pottery without a potter’s wheel. Using clay slabs, moulded clay, clay coils or otherwise manipulating the clay by hand. Top
Impress To stamp or roll a pattern into leather-hard clay with a tool. Top
Incise To carve a pattern into the raw clay with a sharp tool. Top
Kidney See Rib Top
Kiln The oven in which pottery is fired. Kilns can be fuelled by wood, oil, gas or electricity. Top
Kiln Furniture Items made of refractory material used in the kiln to support the pots. E.g. Shelves, posts, etc. Top
Kiln Wash Shelf separator brushed onto kiln furniture to prevent glaze from sticking to them during firing. Top
Kneading See Wedging Top
Leather-hard (Sometimes known as cheese-hard). Clay that is stiff but still slightly damp. Hard enough to retain its shape but wet enough for further work to be done on it (e.g. joining or stamping). Top
Maturing Temperature The temperature at which a clay body reaches its optimum hardness or a glaze is fully fused into the clay body. Top
Mould A former made from plaster into which clay can be pressed or slip cast to take on the mould shape. Top
Nesting Stacking pots on a kiln for bisque firing. In this firing unglazed pots can be stacked without fear of them sticking. Top
On-glaze Enamels. A form of decoration applied on top of a fired glazed, then fired again. Top
Overglaze Decoration A decoration applied over an already glazed finish, such as decals or enamels. Top
Oxidation Firing pottery in a kiln with a sufficient supply of oxygen so that combustion is complete. Top
Peephole Small hole in the kiln for the potter to see inside during firing without the kiln losing too much heat. Top
Pinching A handbuilding method using your thumb and fingers to pinch a cup or pot shape from a ball of clay. Hold the clay ball in one hand and push the thumb of your other hand into the top of the ball. Using your thumb and fingers in a pinching motion, squeeze the clay as you rotate it with the other hand to gradually make a bowl shape. Top
Pinholing Small dots of unglazed or depressed areas in the glaze surface. Usually unwanted, pinholing occurs when gases in the glaze and clay bubble up to the surface. The bubbles pop and a 'hole' appears, which doesn't fuse over. Top
Porcelain Fine, high-fired clay body. It is white and translucent when fired. Top
Prop (or Post) Refractory pillar shape onto which a kiln shelf is placed when firing. Top
Pugmill A machine for wedging clay. It mixes and extrudes clay. Top
Pyrometer An instrument for measuring the very high temperatures in a kiln. Top
Raku Japanese earthenware firing technique where pots are placed into a hot kiln, and removed when still red hot, creating a crazed effect in the glaze. Top
Reducing Atmosphere When there is insufficient oxygen in the kiln for the flame to burn out its carbon content. This affects the resulting clay and glaze colours. Top
Refractory Ceramic material capable of withstanding very high temperatures. Kiln bricks and furniture are usually made from refractory material. Top
Rib Wooden, metal or plastic shaping tools used in forming and smoothing pots. Sometimes known as a kidney. Top
Saggar A box used to protect pottery from flames and gases while it is being fired in a (non-electric) kiln. Top
Sgraffito The technique of cutting or scratching through a coating of slip to reveal the different coloured body beneath. Top
Slab Building A handbuilding technique where pottery is made using slabs of clay. Create the slabs by either pushing the clay out flat with the heel of your hand, beat them out with the side of your fist, roll them out with a rolling pin or cut slabs from a cube of clay with a wire. Slabs should be joined when leather-hard using slip and soft clay. Top
Slip Liquid clay used for decorating, joining and for casting. Top
Slip Trailing Decorating with slip by trailing it onto a pot through a fine nozzle. Top
Slipware Slip decorated earthenware pottery. Top
Soak Keeping a steady temperature in the kiln, usually at the end of a firing to enhance the glaze finish. Top
Sprig Press-moulded decorative piece of clay, applied to pot when it is leather hard. Top
Stoneware Vitrified clay, fired at high temperature, which is inherently non-porous, unlike earthenware. Stoneware is also more durable than earthenware. Top
Terracotta Red earthenware. Red due to the iron content in the clay. Top
Thermal Shock Sudden expansion or contraction of the clay due to sudden temperature change. Causing weakness or damage to the pottery. Top
Throwing Making pottery using a potters' wheel. Clay is thrown onto the centre of the revolving wheel and the potter shapes it by hand. Top
Underglaze Colour applied to greenware or bisque before covering with a transparent glaze. Top
Vitrification When clay particles fuse to a glass-like state (during firing). Top
Wax-resist Wax applied to a pot as a barrier to slip or glaze. Used to create a decorative effect. Top
Wedging Preparing clay body by kneading and mixing it to an even consistency. Top
Wheel A revolving wheel onto which clay is thrown and shaped. Usually powered by electricity or the potter’s foot. Top
Wire Length of cheesewire with a handle at each end. Used for cutting clay. Top