To heat a material to a temperature high enough to drive off all chemically combined water.

CaO—3B₂O₃ traditional important LT alkaline flux, but is no longer being mined. Replace with Ferro 3134 for LT glazes, commercial Gerstley borate substitutes for HT glazes. Test all substitutes.  

CaCO₃ alkaline earth, contributing calcium oxide to glaze powerful AT flux major HT flux for glazes gives strong durable glass. Sometimes used in low-fire clay bodies to extend firing range and give greater fired strength.

Ca₃(PO₄)₂ HT flux opacifier in LT glazes translucence in HT glazes (from colloidal phosphorus globules) and especially in bone china (from supercharged glassy-phase). Toxic in inhalation. 

CaSiO₃ used in partial replacement of silica and whiting in HT bodies, improves thermal shock resistance. In some cases, it is used in place of whiting to eliminate L.O.I. Toxic in inhalation.

Adjustable tool for measuring inside/outside diameters, as in making lids.

Kiln where kiln floor and often the door are mounted on a car that may be rolled in and out of kiln on tracks. Sometimes has two cars, with doors in both ends of the kiln.

Firing defect where excessively fast bisque-firing and/or excessive early reduction retard out gassing, causing carbon and sulfur to be trapped within clay body. May cause discoloration of glaze, and as clay vitrifies and becomes thermoplastic, trapped carbon and sulfur may expand, causing bloating. 

Refractory red stoneware clay, used to obtain rich red and brown colors in high-fire clay bodies.

Usually purposeful effect where carbon is trapped within surface of the glaze, giving smoky shaded areas, especially in shino glazes. Encouraged by slightly early body reduction; can be promoted in high-fire by brushing saturated soda ash solution over glaze.

Serious affliction of the wrist resulting from excessive and/or stressful repetitive-motion activity such as hand wedging clay. See pug mill.

Short for cast able refractory a refractory mix that can be cast into molds to form kiln parts.

A parabolic kiln arch requiring no buttressing or steel frame; laid out by hanging a chain from two points and marking the resulting curve.

Classic East Asian transparent or translucent glaze with small percentages of iron and/or copper and/or chrome, giving range of soft greens, blue-greens, and gray-greens. Most desirable Chinese celadon's often contain minute air-bubble inclusions, giving slight opalescence.

Critical step in throwing, occurring during and after wheel wedging, whereby the clay mass is formed into a symmetrical lump before penetrating and raising walls.

Ceramic insulating material composed of spun kaolin fiber available in blanket form, braided tape, rigid board, and tubular flue liners. Highest insulating rating of standard refractories, but can release carcinogenic fibers.

CaCO₃ alkaline earth, contributing calcium oxide to glaze powerful AT flux major HT flux for glazes gives strong durable glass. Sometimes used in low-fire clay bodies to extend firing range and give greater fired strength.

Very soft, pliable animal skin when wet works well to smooth wet clay surfaces.

A quantity of chemical material, usually salt or soda, which is inserted or injected into a hot kiln during vapor-glazing processes.

Inserting or injecting a charge of chemical material into a kiln during vapor-glazing processes.

Water in molecular combination within clay and glaze materials, which is driven off during the water-smoking period of the firing.

Al₂O₃—2SiO₂—2H₂O Primary clay that fires pure white, very refractory, coarse particle size, low plasticity, high-temperature major component of porcelain and some white ware bodies.  See EPK, Grolleg, Helmer, Tile-6.

Very low temperature (cone 018) glaze colors applied over a previously fired higher-temperature glaze. Allow greater detail, brighter colors than other ceramic glaze effects, but are vulnerable to surface abrasion.

European pottery, eighteenth century and later, featuring decoration inspired by imported Chinese Ming Dynasty wares.

Cr₂O₃ standard vivid green colorant often softened with a little iron or manganese. Very refractory. With tin produces pink. May go gray-brown in reduction. Highly toxic in inhalation and ingestion.

On the wheel, a temporary wet-clay form or reusable bisque-fired form upon which wares may be inverted for trimming.

A pale gray-blue feldspathic stoneware glaze featuring opalescence due to inclusions of phosphorous and/or other materials.

Widely occurring aluminum silicate mineral resulting from natural decomposition of feldspar and granite. Composed of microscopic disk-shaped platelates that give clay its slippery, plastic quality.

Clay mixture formulated of clays and other ceramic raw materials to give desired working characteristics.

Any one of a variety of East Asian kiln designs featuring single or multiple chambers that climb up a slope, creating adequate draft often with little or no chimney. See anagama, noborigama, tube kiln.

In a fuel kiln, atmosphere that is slightly reducing, but still allows increase in temperature. See reduction firing.

Wheel-thrown form that is closed off completely and then altered to form a vessel or sculptural component.

Carboxymethylcellulose (CMC) an organic gum used as a suspension/adhesion agent in glazes. Normally, a small amount of gum is added to a quart or so of warm water and left overnight. Once dissolved, this solution may be added in small doses to glazes, slips, and engobes to improve application performance.  See gum additives.

Co₃O₄ calcined cobalt carbonate twice as powerful coarser than carbonate, and may give mottling in glaze. Works well for under glaze brushwork, with few crawling problems. Toxic in inhalation and ingestion.

A measurement of a materials tendency to expand when heated and contract when cooled. The higher the coefficient of expansion, the lower the thermal shock resistance. In firing dissimilar materials in contact with one another the coefficient of expansion must be matched. See thermal expansion.

Small stamp wheel with raised pattern around the rim, which when rolled along a plastic clay surface leaves a band of relief pattern. Usually formed with damp or dry clay and bisque-fired.

Ceramic forming method utilizing ropelike coils of plastic clay, assembled in successive courses to build up wall of vessel or sculpture.

CaO—3B₂O₃ traditional important LT alkaline flux, but is no longer being mined. Replace with Ferro 3134 for LT glazes, commercial Gerstley borate substitutes for HT glazes. Test all substitutes.

Process of reducing the upper diameter of a thrown form by working the walls of the rotating form inwards with fingers or rib, as in a bottle shape.

Gaseous, liquid, or solid materials that remain suspended within glaze melt without dissolving into melt, and which often coagulate to form visible particles. An example is copper in a copper-red glaze if firing is too fast, minute copper globules will not coagulate into visible masses, and glaze will be clear.

Slip of a composition that affects color of glazes placed over it. Can result from coloring oxides, color modifiers, or textural qualities that influence color.

Decoration where a toothed instrument is dragged over a soft clay surface, sometimes through a layer of slip.

Reaction initiated when fuel reaches kindling temperature, at which point oxidation of hydrocarbon gases releases heat, sustaining and accelerating reaction.

In wheel throwing, the act of hand or finger pressure on the clay, resulting in lower moisture content and a denser structure. Lack of compression in bottoms of pots can result in S-cracks.

See pyrometric cones.

Industrial tunnel car kilns or rolling-hearth kilns in which wares are slowly moved through a kiln that continuously remains at maturing temperature.

A glaze designed to crawl as glaze materials shrink during drying or during early red heat, producing alligator skin or beaded effect. See crawling.

Upwards rise of warm air currents due to the transference of heat.

The profile or schedule of temperature change in the cooling of a kiln. See firing ramp.

CuCO₃ a major glaze colorant to produce greens in LT and HT, copper reds in HT reduction, and greens and metallic effects in raku. Toxic in inhalation and ingestion.

CuO alternate source of copper, coarser particle size, twice as powerful as copper carbonate. Toxic in inhalation and ingestion.

Popular mid-range and high-fire glazes featuring very small percentage of copper that, under correct light reducing conditions, gathers into colloidal particles of red copper oxide, producing bright rich red and red-purple colors. For good copper reds, start reduction at cone 012 or 010, and maintain partial up to maturation, with oxidation cleanup at end but no glaze reduction.

CuSO₄ color source for saggar firing and pit-firing. Soluble, and highly toxic in absorption, ingestion, and inhalation.

2MgO—2Al ₂O₃—5SiO₂ magnesium/aluminum silicate clay mineral, used to make grog for refractory products promotes formation of mullite.

K₂O/Na₂O/CaO—Al₂O₃—10SiO₂ HT feldspathic alkaline flux containing calcium and potassium, but more refractory than potash feldspars. Substitution eight parts potash feldspar, two parts silica, one part kaolin. Toxic in inhalation.

K₂O/Na₂O/CaO—Al₂O₃—10SiO₂ HT feldspathic alkaline flux containing calcium and potassium, but more refractory than potash feldspars. Substitution eight parts potash feldspar, two parts silica, one part kaolin. Toxic in inhalation.

Adjustable wooden forms used in casting plaster molds.

See crazing.

A glaze designed to craze for decorative effect. Appropriate primarily for nonfunctional objects and surfaces, as crazing is a flaw and weakens wares.

Glaze fault where glaze recedes away from an area in the firing, leaving bare clay. Usually caused by dusty, dirty, or oily surface beneath glaze or by excessively powdery glaze. In some cases results from very high L.O.I. in glaze materials, causing high glaze-shrinkage and resulting cracking during firing. Used intentionally in controlled crawl and beading glazes.

Very fine surface cracks in fired glaze surface technically a fault in glazed wares, but often sought after, especially in raku.

Crystalline form of silica, which can form in clay and glaze above 2200°F; has very high coefficient of expansion, producing low thermal shock resistance. Promoted by excessive free silica in clay and/or glaze, by repeated firing, and/or by excessive soaking or slow firing/cooling at high temperatures.

Fuel-burning kiln, usually downdraft, where heat enters at floor level at one side of ware chamber and exits at floor level at opposite side of chamber.

Na₃AlF₆ small amounts promote crackle effects, larger amounts become very volatile with silica and may cause blistering. Used for special effect crater glazes. Toxic in inhalation.

Solid material characterized by regular repeating geometric molecular structure or lattice, with specific melting point, as compared to glass, an amorphous, non crystalline material that softens over broad temperature range. See glass super-cooled liquid.

Glazes in which significant macro crystalline structure forms in surface of low-alumina glaze seeded with zinc or titanium. Crystalline glazes feature large, visible crystal development, vs. microcrystalline effects, as in matt glazes and saturated-iron glazes.

Technique where a design is outlined in oxide-tinted wax resist, and the intervening spaces coated with glazes. Finished results show areas of glaze divided by dark unglazed lines.

Crushed window or bottle glass, occasionally used as a glaze material.

K₂O—Al₂O₃—6SiO₂ a common potash feldspar HT alkaline flux. See feldspar. Close match to G-200. Toxic in inhalation.

First stage in kiln evolution beyond bonfire, consisting of cylindrical clay wall containing fire and wares, covered with layer of shards.