Glossary

Please check below for a glossary of materials we sell. Note: AT = all temperature, LT = low temperature, HT = high temperature.

ALBANY SLIP CLAY

Traditional dark brown slip-clay used as liner-glaze in high-fired Early American wares. No longer being mined – use Alberta slip.

ALBERTA SLIP CLAY

substitute for Albany slip. Highly fluxed with iron – true slip clay – will form glaze at HT.

ALUMINA HYDRATE

Al(OH)3 – Alumina source, rarely used in claybodies or glazes, because all needed alumina comes from clay and feldspar. Used primarily for shelf-wash and wadding – better adhesion and suspension than aluminum oxide (Al2O3). Small additions increase viscosity of glaze melt. Should not be used as matting agent in functional glazes – produces immature glaze.

BALL CLAY

OM4- Al2O3.2SiO2.2H2O – fine particle-size secondary clay, extremely plastic – primary plasticizing clay in most claybodies – in large quantities promotes high shrinkage.

BARIUM CARBONATE

BaCO3 – alkaline earth – active HT flux, but also promotes matt glaze surface. Unsafe for low-fire functional glazes. Controversial in HT functional glazes, but toxicity problems from balanced HT glaze not proven. Often used as additive in claybodies in very small percentages to render sulfates insoluble, reducing scumming. Toxic in inhalation and ingestion.

BENTONITE

Al2O3.5SIO2.7H2O – montmorillonitic clay formed from decomposition of airborne volcanic ash – finest particle-size of all clays – plasticizer (3-times as powerful as ball clay), suspension agent, should be used in quantities no more than 3% of dry materials weight.

BONE ASH; CALCIUM PHOSPHATE

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).

CHROME OXIDE

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.

CMC GUM

Carboxymethylcellulose – 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.

COBALT CARBONATE

CoCO3 – standard blue colorant for slips and glazes – very powerful – 5% will give dark blue in glaze or slip. Will cause crawling is used raw for underglaze brushwork. Toxic in inhallation and ingestion.

COBALT OXIDE

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

COLEMANITE

see GERSTLEY BORATE.

COPPER CARBONATE

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 inhallation and ingestion.

COPPER OXIDE, BLACK; CUPRIC OXIDE

CuO – alternate source of copper, coarser particle size, twice as powerful as copper carbonate. Toxic in inhallation and jestion.

COPPER OXIDE, RED; CUPROUS

Cu2O – alternate source of copper, may help promote copper reds in LT and HT glazes. Rarely used, because has no affinity for water, and floats back to surface, but a few drops of detergent will break surface tension. Toxic in inhallation and jestion.

CORNWALL STONE; CORNISH STONE

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.

CRYOLITE; SODIUM ALUMINUM FLUORIDE

Na3.AlF6 – small amounts promote crackle effects, larger amounts become very volatile with silica, and may cause blistering. Used for special effect crater glazes.

CUSTER FELDSPAR

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

DOLOMITE; CALCIUM/MAGNESIUM CARBONATE

MgCO3.CaCO3 – HT alkaline earth flux, promotes hard, durable surfaces and re-crystallization/matting in glazes. Often added to claybodies to give longer firing range, and can promote more durable low-fire bodies.

EPK; EDGAR PLASTIC KAOLIN

Al2O3.2SiO2.2H2O – pure white kaolin, less plastic than Tile-6 kaolin, frequently used in glazes.

EPK, CALCINED

Al2O3.2SiO2 – used in place of regular kaolin to adjust raw fit (reduce glaze drying-shrinkage) in glazes and engobes.

FELDSPAR

HT alkaline fluxes – insoluble aluminum silicates of potassium, sodium, calcium, and/or lithium – inexpensive flux for clay and glaze. Substitution of soda spar for potash spar can lower vitrification by 100 degrees. Toxic in inhalation. See CUSTER, G-200, KONA F-4, SPODUMENE, NEPHYLENE SYENITE.

FIRE CLAY

very refractory clay, for sculpture and raku bodies. Tremendous variation between different brands.

FLINT

see SILICA. Highly toxic in inhalation.

FRIT

fluxes which have been melted to a glass, cooled and ground, in order to stabilize soluble and/or toxic components during handling of unfired material. All frits are ground glass, and are toxic in inhalation.

FERRO 3124

high-alumina calcium-borate frit, gives greater strength in LT claybodies.

FERRO 3134

Calcium-borate frit often used as substitute for gerstley borate in low-fire glazes when greater reliability and/or long-term insolubility and/or greater transparency are desired. Makes good cone 04 transparent glaze by itself.

FERRO 3110 and 3195

Both very similar to 3134 – run tests to determine which works best for your needs.

G-200

K2O.Al2O3.6SiO2 – common potash feldspar, HT alkaline flux – close match to Custer. Toxic in inhalation.

GERSTLEY BORATE; COLEMANITE; CALCIUM BORATE

2CaO.3B2O3 – major LT alkaline flux – often gives slight opalescence in glaze – for greater transparency and long-term stability substitute Ferro 3134 or other Gerstley borate substitute.

GLOMAX

calcined kaolin. See EPK, CALCINED.

GOLDART

Buff stoneware clay, produced by Cedar Heights Clay Company.

GROLLEG KAOLIN

Al2O3.2SiO2.2H2O – English kaolin, more costly than other choices, but gives whiter porcelain. Less plastic than TILE-6. Best kaolin for translucent bone china.

HAWTHORN BOND

Refractory stoneware clay or fireclay, used in stoneware claybodies.

HELMER KAOLIN

Al2O3.2SiO2.2H2O – Kaolin which works especially well as flashing slip for salt, soda, and wood firing, especially since Avery Kaolin is no longer being mined.

ILMENITE

An iron ore with significant titanium – most often used in granular form to produce dark specks in clay or glaze. Higher iron concentration than in rutile.

IRON OXIDE, RED, FERRIC

Fe2O3 – powdered rust – refractory red in oxidation, converts to black iron (flux) in reduction and/or high-fire. Low quantities in clear glaze produces celadon-green – high quantities produce temmoku black or saturated iron red – powerful flux. More than 5% in a glaze significantly increases fluxing in reduction.

IRON OXIDE, BLACK, FERROUS

FeO – reduced form of iron oxide – gives same results as red iron in the firing, dependent on oxidation/reduction.

IRON OXIDE, YELLOW

see YELLOW OCHRE

KAOLIN; CHINA CLAY

Al2O3.2SiO2.2H2O – very refractory white primary clay – essential ingredient of porcelain and whiteware – less plastic than most other clays. See EPK, GROLLEG, HELMER, TILE-6.

KONA F-4 FELDSPAR

Na2O.Al2O3.6SiO2 – a common soda feldspar – powerful HT alkaline flux. Toxic in inhalation. Sub Minspar or G-200

KYANITE

3Al2O3.2SiO2 – aluminum silicate used in place of alumina and silica to promote formation of mullite crystals, increase thermal shock resistance. Coarse-ground used as grog in refractory bodies for kiln-furniture.

LITHIUM CARBONATE

Li2CO3 – powerful AT alkaline flux, especially with soda or potash feldspars. Promotes hardness and re-crystallization in LT glazes. Forms low-temperature eutectic with silica.

LIZELLA CLAY

High-iron (4%) stoneware clay – substitute for OCMULGEE , which is no longer being mined.

MAGNESIUM CARBONATE

MgCO3 – alkaline earth – HT flux, promotes matness and opacity in LT glazes, smooth, hard, buttery surface in HT glazes – promotes purples or pinks with cobalt. High L.O.I., used to promote controlled crawl glaze effects.

MANGANESE DIOXIDE

MnO2 – flexible colorant – with alkaline fluxes gives purple and red colors – by itself gives soft yellow-brown – with cobalt gives black. Used with iron to color basalt bodies. Concentrations of more than 5% may promote blistering. Toxic in inhalation and ingestion.

MICA

K2O.3Al2O3.6SiO2 – an aluminosilicate with a fine sheet-lattice structure, closely related to clay and feldspar, and often found as minute iridescent flakes in some clays.

MOLOCHITE

Porcelain grog – source of grit for pure white claybodies.

MULLITE

substitute for Albany slip. Highly fluxed with iron – true slip clay – will form glaze at HT.

NEPHELINE SYENITE

K2O.3Na2O.4Al2O3.9SiO2 – a common feldspathic flux, high in both soda and potash, used in claybodies and glazes. Less silica than soda feldspars, and therefore more powerful. Increases firing range of low-fire and midrange glazes. Toxic in inhalation.

NICKEL OXIDE, BLACK

Ni2O3 – reduces to GREEN NICKEL OXIDE early in firing, and produces similar effects.

NICKEL OXIDE, GREEN

NiO – colorant or modifier – can give blues, tan, browns, greens, grays, dependent on fluxes present. Often used to mute the effects of cobalt, copper, and other colorants.

OM-4

(Old Mine #4) – a well known Kentucky BALL CLAY.

PETALITE

Li2O.Al2O3.8SiO2 – lithium feldspar – HT alkaline flux – good for reducing thermal expansion, increasing thermal-shock resistance claybodies.

REDART

Brick-red earthenware clay, produced by Cedar Heights Clay Company.

RUTILE

Titanium ore, used as source of TITANIUM DIOXIDE, contains iron, other trace minerals – gives tan color, promotes crystallization giving mottled multi-color effects in some HT glazes, or in overglaze stain (very refractory, use sparingly). Gives rich mottled medium blue in some HT glazes. Dark rutile contains higher percentage of iron.

SILICA; SILICON DIOXIDE; FLINT ; QUARTZ

SiO2 – main glass-former – vitrification, fluidity, transparency/opacity controlled by adding fluxes and/or refractories. Highly toxic in inhalation.

SODA FELDSPAR

Na2O.Al2O3.6SiO2 – feldspars contributing sodium (and potassium), primarily as a HT flux – includes KONA F-4, NC-4 and NEPHYLINE SYENITE. Toxic in inhalation.

SODIUM CARBONATE

see SODA ASH.

SPODUMENE

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

STAINS – MASON, HARSHAW, PEMBCO, FERRO, ETC.

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 Maiolica overglaze decoration. Most stains are ground glass, and are highly toxic in inhalation.

STRONTIUM CARBONATE

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

SUPERPAX

Zircon opacifier. See ZIRCONIUM SILICATE. Toxic in inhalation.

TALC; MAGNESIUM SILICATE; STEATITE; SOAPSTONE

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

TILE-6 KAOLIN

Al2O3.2SiO2.2H2O – air-floated secondary kaolin – broader particle distribution than primary kaolins, greater plasticity, green strength.

TIN OXIDE

SnO2 – most powerful opacifier, but expensive – inert dispersoid in glaze melt – 5-7% will produce opaque white in a clear glaze.

TITANIUM DIOXIDE

TiO2 – matting/opacifying agent. Promotes crystal growth, visual texture in glazes.

VEEGUM-CER

Combination of VEEGUM-T and carboxymethylcellulose gum, used as a suspension and adhesion agent in glazes. Product of H. T. Vanderbilt Company.

VEEGUM-T

Suspension agent/plasticizer similar to BENTONITE and MACALOID. Up to 2% of dry materials weight as plasticizer in high-kaolin claybodies, and up to ½ of 1% of dry materials weight as suspension agent, brushing medium in glazes and slips. Mix with water before adding other ingredients. Product of H. T. Vanderbilt Company.

VOLCANIC ASH; PUMICE

HT alkaline flux, similar in composition to potash feldspar, but higher in silica, with at least 1% iron. May be substituted for 7 parts potash spar, 3 parts flint. Toxic in inhalation.

WHITING; CALCIUM CARBONATE; LIMESTONE; MARBLE; CHALK

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 claybodies to extend firing range and give greater fired strength.

WOLLASTONITE; CALCIUM SILICATE

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 inhallation.

XX-SAGGER

A plastic refractory stoneware clay, often used in sculpture and raku bodies.

YELLOW OCHRE

High-iron yellow clay mineral, used as colorant in glazes and slips, converts to red iron oxide in oxidation or black iron oxide in reduction and/or high-fire.

ZINC OXIDE

ZnO – HT flux which promotes brilliant glossy surfaces. In some glazes can encourage opacity. With titanium in low-alumina glaze can encourage macrocrystalline growth (crystalline glazes). Volatizes in high-fire reduction. Toxic in inhallation.

ZIRCONIUM SILICATE

ZrSiO4 – zircon opacifier – inert dispersoid in glaze melt – low-cost substitute for tin oxide – use double the recipe weight of tin. Includes ZIRCOPAX, OPAX, SUPERPAX, ULTROX. All are toxic in inhalation.

ZIRCOPAX

Zircon opacifier, no longer being manufactured. See ZIRCONIUM SILICATE. Toxic in inhalation.

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