A refractory clay enclosure in which wares are fired. Originally developed to protect wares from ash-slagging and flame-flashing in wood firings. In contemporary use, with clean-burning gas firings, process used in exactly opposite way. See saggar firing.

Contemporary firing process in which wares are placed within refractory saggars, along with chemicals and combustibles, in order to achieve certain surface effects.

Vapor-glazing process where salt (sodium chloride) is introduced into kiln firebox at high temperature. Salt vaporizes, and sodium vapor combines with silica in clay surface, forming extremely hard sodium-silicate glaze. See soda firing.

NaCl table salt, rock salt used in salt-firing. Skin irritant.

Granular silica. Major grit besides grog used to give clay bodies structure for throwing and hand building, high shrinkage in HT clay bodies, but gives smoother fired surface than grog. Toxic in inhalation.

See kaki.

Cosmetic smoking process where unglazed wares are buried in sawdust in a brick enclosure or a perforated steel drum. Sawdust is ignited at the top and allowed to smoulder down over a period of hours. Often mistakenly referred to as pit-firing, but does not achieve true firing temperatures, and wares must be bisque-fired first.

Cosmetic smoking process where unglazed wares are buried in sawdust in a brick enclosure or a perforated steel drum. Sawdust is ignited at the top and allowed to smoulder down over a period of hours. Often mistakenly referred to as pit-firing, but does not achieve true firing temperatures, and wares must be bisque-fired first.

Process of incising surface of wet or leather-hard clay in crosshatch pattern before applying slurry and joining pieces.

S-shaped cracks that occasionally appear in the bottoms of wheel-thrown pots, resulting from inadequate compression of the bottom and/or excessive water left in bottom. Occur most often in fine-grain gritless clay bodies, especially thrown off the hump.

In fuel-burning kilns, air that enters after initial combustion and feeds flames as they leave primary combustion source. In gas kiln, secondary air enters burner port around burner tip. In wood kiln, secondary air enters above grates in conventional firebox, and below grates or hobs in Bourry-box. See primary air.

Clays that have been transported away from their point of geologic origins by wind or water. Finer particle-size gives greater plasticity ball clays, stoneware clays, fireclays, etc.

Kaolins that have been transported some distance from the parent rock and are still very pure, but much more plastic than primary kaolins.

Clays that have been transported away from their point of geologic origins by wind or water. Finer particle-size gives greater plasticity ball clays, stoneware clays, fireclays, etc.

A formula generated by glaze calculation, which lists all glaze oxides present in separate columns for fluxes, refractories, and glass-formers.

Firing in a sloped tube kiln or noborigama, where as each chamber or zone reaches maturity, the fire is moved up to the next, and each one preheats subsequent chambers or zones.

To place wares in a kiln. Or, in a loaded kiln, the entire structure of shelves, furniture, and wares.

Process of loading a kiln, or technically, of placing the set. See set.

Decorating technique achieved by scratching or carving through a layer of slip or glaze (helps to apply wax-resist over glaze before carving) before firing to expose contrasting clay body beneath.

A broken fragment of pottery.

Classic Japanese glaze ranging from gray to white to orange, often containing spodumene or other source of lithium, and/or Nephtline Syenite. The orange color is achieved with thinner glaze coating when fluxes in the glaze activate iron content in the clay body. In the West, many potters seek shinos that break from off-white to orange, often with carbon-trapping effects. Carbon trapping can be accentuated with a brush coat of saturated soda ash solution.

Serious and dangerous glaze defect where excessive glaze compression causes small razor-sharp chips of glaze to pop off along outer edges, corners, and rims. All wares showing shivering must be destroyed. Cure is to slightly increase flux and/or decrease silica in glaze.

Clay with insufficient plasticity ends to fragment during forming.

Permanent contraction of the clay in both drying and firing stages. Overall may be as much as 18%.

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.

A container with fine-mesh wire screen in the bottom, available in different mesh sizes, used for straining slips and glazes.

The process of working a glaze or slip through a wire-mesh sieve to strain out impurities and to break up clumped raw materials.

SiO₂ The primary glass-former in clay and glazes vitrification, fluidity, transparency/opacity controlled by adding fluxes and/or refractories. Highly toxic in inhalation.

SiC -- Extremely refractory material used to form kiln shelves. Highly resistant to corrosive atmospheres, and therefore suitable for salt, soda, and wood firing. Silicon carbide kiln shelves conduct electricity and should never be used in electric kilns. Occasionally used in powdered form as local reducing agent in oxidation firings, used in very small quantities for localized reduction of copper reds Slarger amounts for frothing glazes. Toxic in inhalation.

SiO₂The primary glass-former in clay and glazes vitrification, fluidity, transparency/opacity controlled by adding fluxes and/or refractories. Highly toxic in inhalation.

Process of glaze-firing glazed green ware without a bisque-firing.

In heating clays and glazes, a solid-state reaction where particles stick together permanently, and mass can be considered fired. With increasing temperature, fluxes and glass-formers begin to interact, increasing the strength of bond between refractory particles, still leaving open, porous structure, as in bisque-fired and low-fired wares, which are sintered but not vitrified.

Special angled bricks used to support the first course of arch bricks on either side of a sprung arch.

A mechanized but usually manually operated device for rolling out large uniform slabs of clay.

The process of returning dry unfired clay to a slip by soaking in water.

The process of returning dry unfired clay to a slip by soaking in water.

Clay suspended in water, usually the consistency of thick cream. May be colored and used to decorate surfaces, or may be cast into plaster molds to create ceramic forms.

The creation of ceramic forms by casting slip in plaster molds.

A naturally occurring clay that contains a high enough component of flux to form a glaze at high-fire temperatures.

A glaze with slip-clay or earthenware clay contributing the primary flux.

Decorating technique where resist materials are applied to prevent slip from adhering to some areas.

Application of decoration to wet or leather-hard clay by flowing on lines of slip with a fine pointed dispenser, such as a rubber syringe.

  Process of creating ceramic wares with a slump-mold. Firing defect where glassy-phase begins to dissolve sintered structure in clay, causing it to sag and deform.

Very thick clay slip, often used for joining clay pieces after scoring surfaces.

Very thick clay slip, often used for joining clay pieces after scoring surfaces.

During firing or cooling ramp, the act of holding kiln at steady temperature for a period of time to allow proper formation or maturation of certain clay and glaze effects.

A specialized hard brick shape, half the width of a standard brick. Useful for posts in salt and wood firings

3MgO—4SiO₂—H₂O HT alkaline earth flux in glaze, promotes smooth buttery surfaces, partial opacity similar composition to clay, but in LT clay bodies gives low shrinkage and high thermal shock resistance, as in standard 50/50 talc/ball clay white ware body. Highly toxic in inhalation and ingestion.

Na₂CO₃soluble source of soda, used as deflocculant, or to supply soda in vapor-glazing process. Source of flux in Egyptian paste recipes. Brush solution over hi-fire glaze to increase carbon trapping. Highly toxic in inhalation and ingestion. Skin irritant. See magic water under sodium silicate.

Na₂O—Al₂O₃—6SiO₂ feldspars contributing sodium (and potassium), primarily as a HT flux includes Kona F-4, NC-4 and Nephtline Syenite. Toxic in inhalation.

Vapor-glazing process touted as modern-day nontoxic replacement for salt firing. Gives slightly less gloss and orange-peel. Instead of salt, soda ash (sodium carbonate) in water solution is sprayed into kiln at maturing temperature, and sodium vapor combines with silica in clay to form sodium-silicate glaze. Recent research indicates that effluent gases are highly corrosive and no more benign (or destructive) than salt-firing fumes. See salt firing.

Na₃—AlF₆ 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.

Na₂CO₃ soluble source of soda, used as deflocculant, or to supply soda in vapor-glazing process. Source of flux in Egyptian paste recipes. Brush solution over hi-fire glaze to increase carbon trapping. Highly toxic in inhalation and ingestion. Skin irritant. See magic water under sodium silicate.

NaCl table salt, rock salt used in salt-firing. Skin irritant.

Na₂SiO₃ comes as a liquid used as a deflocculant in slips, as an air-setting binder for LT refractories. Lana Wilson (and many clay artists/artisans) promotes its use in magic water for use in place of slurry for joining wet or soft leather-hard ceramic forms. Add 1.5% sodium silicate and 1.5% soda ash by weight to a measure of water. Toxic in ingestion. Skin irritant.

Na₂O—2B₂O₃—10H₂O a major LT alkaline flux, available in granular or powdered form. Gives smooth finish, bright colors. Water soluble, so is often used in fritted form. In excessive amounts creates brittle glass and can cause blistering and pin holing. Available in granular and powdered form. Sometimes used with salt or soda in vapor glazing to lower firing temperature and/or achieve a smoother, shinier surface. Toxic in inhalation and ingestion.

Traditional European term for a dense, white clay body that fires at lower temperature and was the precursor to true porcelain.

See insulating firebrick.

Range of soluble metallic salts like bismuth subnitrate, silver nitrate, copper sulfate, cobalt sulfate, ferric chloride, and stannous chloride, used to create fumed luster effects on glazed wares and to create surface effects on unglazed saggar-fired wares. Most are water soluble and highly toxic.

A liquid mix where the components are fully dissolved (as in a water/soda ash solution for vapor-glazing), where materials will not settle out via gravity.

An agent that acts to accelerate the dissolution of a more resistant material. In glaze maturation, the flux-glass-former combination acts as a solvent on alumina.

Defect in repeatedly fired clay materials where outer layers shrink and peel away most often occurs in kiln hot-face when refractories are repeatedly fired beyond their rated temperature.

The weight or density of a liquid measured in proportion to that of water. A glaze with a specific gravity of 1.2 is 1.2 times as dense as water per unit of measure. See hydrometer.

A specialized hard brick, half the thickness of a standard brick.

Li₂O—Al₂O₃—4SiO₂ lithium feldspar powerful HT alkaline flux promotes copper blues good for thermal-shock bodies and matching glazes. Toxic in inhalation.

A repair medium for bone-dry green ware, made of equal parts vinegar and corn syrup mixed with dry powdered clay body to the desired consistency.

Open-front enclosure with an exhaust fan at the rear, designed to draw off all overspray and other toxic dust or fumes.

Application of liquid slip, engobe, glaze, or stain, using mechanized spray equipment. Gives smooth glaze coating, but with less glaze pooling in recesses.

Surface decorating technique in which small coils or balls of clay are affixed to the damp or leather-hard surface, usually with a layer of slip.

Kiln arch representing less than 180 degrees of curvature, and requiring buttressing to support outward thrust of the arch.

See peephole.

See refractories.

Commercial ceramic colorants that have been fritted in order to eliminate solubility problems and give greater stability in firing and truer color before firing. Mixture of ceramic stains or pure coloring oxides (sometimes with a little flux) in water suspension, which can for over glaze brushwork, or as a patina on unglazed clay.

Stable fritted ceramic colorants available in wide range of colors, suitable for coloring clays, slips, engobes, and glazes. Most are stable up to cone 5, many to cone 10. Can be mixed with 25—50% Ferro 3134 frit for Majolica over glaze decoration. Most stains are ground glass and are highly toxic in inhalation.

Soluble metallic salt fuming agent to create mother-of-pearl luster on glazed surfaces. Introduced in cooling ramp at dull red heat, it will affect everything in kiln. Highly toxic in inhalation and ingestion. Fumes are especially toxic.

3MgO—4SiO₂—H₂O HT alkaline earth flux in glaze, promotes smooth buttery surfaces, partial opacity similar composition to clay, but in LT clay bodies gives low shrinkage and high thermal shock resistance, as in standard 50/50 talc/ball clay white ware body. Highly toxic in inhalation and ingestion.

Term often applied to all kiln posts, but more correctly referring to specialized refractory furniture pieces equipped with ceramic or metallic points designed to support fully glazed wares during firing.

High-fired vitreous ware, literally as hard and durable as stone. Matures from 2200-2400° F. (cone 511).

Naturally occurring refractory clays with adequate fluxes to fire in stoneware temperature range.

SrCO₃ alkaline earth, HT flux, similar to barium, slightly more powerful gives semi matt surfaces. Nontoxic in balanced glaze. Substitute.75 parts strontium to one part barium.

A material that, in its solid form, maintains the amorphous physical structure of a liquid rather than the ordered structure of a crystalline material. A crystalline material softens or solidifies at a specific freezing point, whereas a super-cooled liquid like glass remains amorphous, softening or solidifying gradually over a broad temperature range.

Zircon opacifier. See zirconium silicate. Toxic in inhalation.