Glossary of Terms
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Ash glaze- A glaze made with varying proportions of wood or vegetation-derived ash, sometimes together with clay, feldspars and other minerals. Different ashes impart their own distinctive colors and textures to glazes.

Ball Clay- A plastic secondary clay, stands high temperature and fires off-white.

Biscuit or bisque- Ware which is fired to a state hard enough to facilitate handling in glazing. In many cases it also makes some decorative techniques simpler to achieve.

Body- The substance from which the work is finally made; rarely just a clay, usually a balanced blend of clays, feldspars, quartz (silica) and other non-plastic 'opening' ingredients like sand or grog which together form a satisfactory combination for working and firing.

Bone china- An English for of porcelain originally made to compete with Oriental true hard-paste porcelain. The body consists of 40-50% calcined ox bones, which lowers the vitrification point and produces whiteness and translucency.

Borax- A powerful flux in many glazes and frits; calcined borax, not ordinary borax is usually used because of its high water content.

Burnishing- Compacting the surface of a pot or slip coating on a pot to give a polished finish. Hard smooth objects like pebbles or spoons are used.

Calcine- To heat to red heat or more, after which the material is usually crushed ready for use.

Calcium Carbonate- Whiting, chalk, limestone and some marbles. All make approximately the same kind of middle-and high-temperature fluxes.

Cast- To make shapes by pouring liquid clay (slip) into molds usually made from plaster of Paris.

Celadon- A name given to a whole range of stoneware and porcelain glazes ranging in color from light grey-green to deep olive-green, produced by small amounts of iron in a reduction atmosphere.

Chun- A thick high-fired opalescent glaze first made by the Chinese; beautiful light blues can be obtained without the use of cobalt, but when reduced iron is present in small amounts.

Coiling- To form pottery by the use of rolls of clay welded together.

Cone- Small conical object made of compressed graduated glaze materials with a known melting point, used to indicate temperature reached in a kiln at a given point.

Crackle- A more or less controlled crazing of glaze for decorative effect: oxides are sometimes rubbed in to enhance the pattern.

Crawling- When the fired glaze retracts to expose the bare body.

Crazing- The cracking of the glaze in fine lines caused by uneven tension between glaze and body during cooling. The process is sometimes long delayed. It is considered a defect in earthenwares because they are porous and the vessel will not then hold liquid.

Delft- Dutch and English earthenware, coated with a lead glaze opacified with tin oxide. Metal oxides are painted on the glaze before firing to give the characteristic colors, such as blue (cobalt), green (copper), browny-mauve (manganese) and yellow (antimoniate of lead). Also known as maiolica and faience, it first made its appearance in the Middle East.

Dunting- The breaking or cracking of pots while cooling after firing-caused by cold air getting into the kiln.

Earthenware- One of the three main types of pottery, the others being stoneware and porcelain. It is opaque, relatively soft, and porous unless covered with an uncrazed glaze. The firing temperature can be as low as 800 ºC, as with some African pottery, or as high as 1200 ºC before it starts to vitrify, and technically becomes stoneware.

Egyptian Paste- A body first used in ancient Egypt to make jewelry and small models. The soluble fluxing ingredient, soda, was mixed in with the other substances (mainly quartz and copper carbonate) so that it migrated outwards as the water evaporated leaving a glazed surface. The copper carbonate gave the typical Egyptian turquoise green but other carbonates such as manganese and cobalt can be used for other brilliant colors. The work is fired to about 950 ºC.

Enamels- Low-temperature colored glazes used on top of already fired high-temperature glazes.

Engobes- Another word for a slip, often used for slip coating on coarse bodies and slips especially compounded for use on biscuited bodies.

Eutectic- The lowest melting point of two or more substances.

Faience- French earthenware. See Delft.

Feathering- A method of decorating by drawing the tip of a feather across lines of wet slip to give a characteristic pattern.

Fettle- To finish the surface of leather-hard or dry clay by removing unwanted marks especially seams made by casting molds.

Flux- Any substance that lowers the melting point of a ceramic body, glaze or color. Glazes are usually named after the chief flux used in a particular mixture, eg: dolomite glaze, talc glaze, etc.

Frit- A material used in glazes and on-glaze enamels usually on low-temperature ware. Frits are made by heating, shattering and grinding certain substances together whereby soluble or toxic substances can be made safely usable.

Fusibility- The ability to melt; a fusible glaze would be one that melted to a smooth glassy finish or surface.

Galena- Lead sulphide used as a glaze, for example on English medieval earthenware pots.

Gilding- Overglaze gilding is fired on to an already-fired glaze surface at about 800ºC. Flux, gold in various forms, a little gum arabic. are mixed together-after the firing the gold may have to be burnished; silver can be used in this way.

Glaze- An impervious vitreous coating on pottery, usually produced by the fusion of silica with alumina by means of a flux. It can range in both visual and tactile quality from a dull, rough, matte surface to a very smooth and shiny one.

Greenware- Unfired pottery.

Grog- Fired, crushed and ground clay added to modify a clay body. You can buy grog in certain mesh sizes such as 30 to 60 for handbuilding or 60 to dust for finer work.

Gum arabic and tragacanth- Natural gums mixed in to help glazes and oxides to stay on the pot while it dries and then fires.

Handbuilding- To make pots or other forms by any method other than throwing on a wheel or mechanical process; usually refers to pinching, coiling and slabbing techniques.

Jiggering and Jolleying- A mechanical method of making repetition shapes, usually simple shapes such as plates and cups on the wheel with plaster molds and profiles.

Leather-hard- Clay when it is stiff but still damp enough to be joined to other pieces with slip, or have handles, lugs, knobs, etc., joined to it; also called cheese-hard.

Levigation- Method of refining clay by floatation in water: allowing the heavier particles to settle and the smaller particles to be taken off, the process being repeated until the finest particles are separated out.

Lustre- A film-like coating of metal or metallic oxide applied to the already-fired glazed surface, and fused onto it in a second firing at the low temperature of 600-800 ºC.

Lute- To join leather-hard clay surfaces together, with slip or slurry.

Maturing temperature- The point at which a clay can be said to have fired to its correct strength or a glaze to have properly fused or melted.

Oxidation- Firing a kiln with an oxidizing atmosphere, one which has an adequate supply of air, to enable metals in clays and glazes to give their oxide colors, greens from copper and honey colors from iron. Electric kilns give oxidizing firing unless a reducing agent is introduced.

Porcelain- True oriental porcelain, also known as hard-paste, contains china clay, feldspar and silica; it is fired at about 1300 ºC or higher, is translucent when thin, usually white and extremely hard. In the West, various bodies eg soft-paste porcelain and bone china, were made in imitation of true porcelain.

Press-mold or press- To make shapes by pressing sheets of clay, patted, rolled or cut from blocks, into or onto molds normally made of biscuited clay or plaster of Paris. Handles and spouts, as well as dishes and pots made from one or more molds, are made in this way.

Pulling- (handles) Plastic clay is stroked with water by hand to shape handles, either directly on the pot from a lump stuck on the side, or by pulling (shaping) a rudimentary handle which is completed later, once attached to the pot.

Raku- Low-fired earthenware, glazed with lead or alkaline glazes; traditionally made in Japan for the tea ceremony. The pots are taken from the still-firing kiln and plunged into water, sometimes having been previously dropped into vegetation to reduce the metal oxides and so give different color results.

Raw glazing- Glazing unfired pots, the biscuit firing is omitted and the glazes must contain enough clay in them to stay on the pots as they shrink during the single-firing.

Reduction- Firing a kiln with a reducing atmosphere; the condition in a kiln if not enough air is supplied to burn completely the carbon particles and compounds in the flame, giving a smoky atmosphere. This process causes coppers to turn red, small amounts of iron to go green, and in higher firings, iron pyrites in the clay to give a characteristic speckled look.

Refractory- Resistant to heat, capable of standing high temperatures in the range of 1300 ºC plus.

Sgraffito- A decorating technique. A layer of slip is scratched through to reveal a different color of clay or body beneath.

Slabbing- A hand-building technique involving sheets of clay which can be rolled round other forms, or cut and jointed as in woodwork to make hard-edged forms.

Slip- Liquid clay, often used with added metal oxides for coloring, or other materials to make it more, or less, vitreous. Pots can be dipped in slip or it can be poured, painted or trailed on to the surface.

Soak- To hold the temperature in a kiln steady for some time.

Soft-paste- Imitation porcelain. The body was a glass frit fired at around
1000ºC.

Stoneware- Pottery which is opaque, hard and usually vitreous or non-porous, fired above
1200 ºC.

Temmoku- The Japanese name given to the glaze first produced in China. It usually contains at least 7% or 8% iron oxide to give a lustrous brown-black that breaks to orange-red where the glaze thins on edges and throwing rings.

Throwing- Using the momentum of the potter's wheel to draw plastic clay into various circular forms.

Tooth- Roughness or coarseness in a clay, a little can aid throwing, and counteract warping in handbuilding.

Turning- Trimming pottery upside down on the wheel while it is leather-hard to remove excess clay and to form a foot-ring on the base of the pot.

Vitrify- To fire or heat to a glassy state.

Volatilize- To change into a vapor, oxides such as copper that do this at high temperatures are often deposited elsewhere in the kiln, on shelves or other pots.

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