Clay and Chemical Names and Uses:
Alumina Hydrate Al (OH)3 The preferred source of alumina in glazes. Useful as a kiln wash ingredient. Produces matt glazes.
Alumina Oxide Al2O3 Responsible for the mattness or brilliance of glazes. Prevents devitrification and adds strength. Insoluble in water and melts at 3550° F. Addition of too much alumina can cause dry, under-fired appearance
Antimony Oxide Sb2O3 This is sometimes used as an opacifier in older glaze formulations. It was primarily used to produce Naples Yellow when combined with lead oxide. Toxic.
Ball Clay, OM#4 (Old Mine #4) The "universal" ball clay which can usually be substituted for most any ball clay in a formula, although some glazes might be sensitive to changes. Considered a plastic, light burning ingredient in clay formula.
Barium Carbonate BaCo3 Main source of barium oxide in glazes. It is an active flux and will help in producing matt finishes. It may also be used to stop scumming in clay bodies when added in small amounts. Suspected toxic leacher. Also know as witherite.
Bentonite Al2O3.4Sio2.H2O A plastic montmorillonite clay containing colloidal matter which, in very small amounts, lends plasticity to a clay body. It is never used alone due to its high shrinkage rate and its tendency to cause swelling. Bentonite may also be used as a suspending agent in glazes.
Barnard Blackbird Slip A naturally occuring clay colorant or decorating slip. Similar in nature to Albany Slip.
Bone Ash Ca3 (PO4)2 A natural source of phosphate. Bone Ash is also used to give texture in low fire glazes.
Borax, Granular Na2O 2B2O3 10H20 A soluble, low temperature flux which lowers the fusion point of glazes and promotes a smooth melt. Gives bright colors with most oxides. A source of sodium and boric oxide in glazes.
Boric Acid, Granular B2O3 2H20 Used as a flux to increase gloss and elasticity of glazes. Acts as both a glass former and a flux. Improves the fit between the glaze and clay body. Tends to be soluble in water.
Calcium Carbonate CaCO3 Also known as whiting. This is the most common source of calcium oxide in glazes.
Chrome Oxide (Green) Cr2O3 Used in glazes to produce various shades green. The maximum percentage for use in glaze is 5%. Combined with cobalt it can give a peacock color. Mixed with tin oxide, pinks are possible.
CMC Sodium CarboxyMethlCellulose. An organic vegetable gum that is used as a binder, thickener and suspending agent. Use .25 - 2%. If added dry to the glaze batch, sieve after wetting several times. Usually mixed with water, blended very well and then put into the wet glaze. This is a gelling substance.
Cobalt Carbonate CoCO3 A pink powder, used as a glaze colorant and for brushed oxide decoration. Produces various shades of blue and, where manganese is present can give a purple color. Better suited to oxidation. Use from 1 - 3%. May be doubled to equal the strength of cobalt oxide.
Cobalt Oxide (Black) Co3O4 A very stable oxide which is a black powder. In small amounts it produces very strong blues. Used as a glaze colorant and for brushed decoration. Source of old time "flow-blue" decorations. Use .25 - 1%. This is the most powerful colorant and a very active flux. Well suited to reduction.
Colemanite See Gerstley Borate.
Copper Carbonate CuCO3 A light green powder used as a colorant. It may produce green, blue-green or copper red. To convert a copper oxide formula to copper carbonate, multiply the carbonate by 1.5.
Copper Oxide (Black) CuO The first glaze colorant known. It is a strong flux and will produce fluid glazes. Can produce copper reds under reduction. Usually not preferred over copper carbonate. Use 2 - 5%.
Copper Oxide (Red) Cu2O Will revert to CuO on firing and is interchangeable. Use a few drops of liquid soap detergent like "Ivory" to dissperse the powder into the glaze batch. Can produce copper reds under reduction. Use 2 - 5%.
Cornwall Stone (English Cornish) A complex spar used in clay bodies to add strength while firing. Also used in engobe formulae because of its adhesive properties during and after firing. With the addition of a suitable flux, Cornwall Stone can be used as a glaze. Has a light green color in raw form and is almost iron-free. Defluorinated.
Cryolite Na3AlF6 Sodium aluminum fluoride. Source of sodium in glazes, some glazes will pit or pinhole because of the fluorine content. An active flux in most glazes that will produce crater effects.
Dolomite CaMg(CO3)2 Dolomite is useful as a source of calcium and magnesium. It can be used as a high temperature flux and also to promote crystallizing. Produces "dolomite matts".
Feldspar, NC4, Soda Na2O Al2O3 6Sio2 A soda spar used widely in both clays and glazes. More active than most potash spars.
Feldspar, G-200, Potash K2O Al2O3 6Sio2 This is a potash feldspar. It is a material that is extremely low in impurities which makes it highly suited to pure white glazes and as a flux in porcelain clay bodies.
Flint, SiO2 (silica)(quartz) Glass former in glaze and clay. Predominate ingredient in many glazes, this chemical will usually be the controlling factor for most glazes fitting properly.
Fire Clay, High temperatre (refractory) clay usually added to clays to raise their maturing temperature and give the body "tooth" (texture).
Flourspar CaF2 Flourspar has a lower fluxing temperature than other calcia compounds. It can be used as a substitute for whiting to promote more fusible glazes. Can be destructive to kiln furniture after long-term use because of fuming.
Foundry Hill Cream, New. A creamy colored ball clay.
Frit F-280 (3110) (P311) (H90) (GF-134) A high soda-silica, low borate frit. Melts at 1400°
Frit F-19 (3124) (P311) (H14) Soda-Calcium-Borate. Melts at 1600° F
Frit F-12 (3134) (P54) (H399) High calcium, low potash borate, low silica. Melts at 1450° F.
Frit FZ-25 (3269) (3819) (P25) (H259) Soda-Borate-Zinc with a little Flou-rine. Melts at 1320°-1420° F.
Gerstley Borate 2CaO3 B2O3 5H20 A sodium/calcium/borate compound used as a low temperature flux which helps to prevent crazing. Can act somewhat as an opacifier. Also can be used as a substitute for calcium in glazes where a pink or red is desired. In most cases can be substituted for Colemanite. NOTE: The Gerstley Borate mine was closed by US Borax. The remaining material will not be around long. We recommend using glazes that do not contain GB or using one of the substitutes available now available.
Goldart Clay Light tan, air-floated stoneware clay suitable for light finring, high temp clays. Low sulfer.
Grolleg Clay Kaolin mined in England. The main ingredient in "True English" style porcelains.
Grog Refractory brick which is crushed to various mesh size and added to throwing and sculpture bodies to increase working strength and to reduce the amount of shrinkage. Also aids in drying for large pieces of unusual thickness.
Gum (CMC) See CMC.
Iron Chromate FeCrO4 Produces dark colors in engobes and underglazes. Can also be added with manganese stains to clay bodies as a colorant. Fugitive above cone 04.
Iron Oxide (Black) Fe3O4 Ferrous Oxide. Produces various shades of brown or green when used as a glaze colorant or decorative oxide. In high fire matt glazes, iron oxide and titanium can produce reddish glazes.
Iron Oxide (Red) Fe2O3 Ferric Oxide. Basically the same as black iron oxide except not quite as concentrated. 82-86% natural and synthetic iron oxides. Makes an excellent decorating wash.
Kaolin, EPK. Al2O3.2SiO2.2H2O. A plastic kaolin mined in Edgar, Florida. Suitable for both glaze and clay formula. May be substituted for any china clay.
Kyanite, 3Al2.O3.2SiO2. Substance used as a refractory filler that greatly increases thermal shock in clay bodies such as Raku clays.
Lithium Carbonate Li2 CO3 Used as a flux. It is a source of lithia which is a strong high temperature flux. Lithium carbonate improves the brightness of glazes and increases the firing range. Also reduces thermal expansion.
Manganese Carbonate MnCO3 A very weak coloring agent. In an alkaline glaze, a blue-purple or plum color can be obtained. Manganese carbonate is more useful as a flux.
Manganese Dioxide MnO2 A black powder which will produce brown, purple or black tones to clay bodies and glazes, depending on composition. Manganese carbonate may be substituted by using 1.5 times the carbonate.
Manganese Dioxide (Granular) A colorant to give specks to clay bodies and low fire glazes. It tends to over flux after cone 8.
Molochite. White firing porcelain grog suitable for use in any white clay body.
Nepheline Syenite K2O.3Na2O.4Al2O3.9SiO2 A very active soda spar. Helpfull in reducing crazing when added to clay bodies. This substance usually settles into a hard mass in the bottom of the glaze bucket, use any suspender to help lift it.
Nickel Carbonate (Green) NiCO3 Produces nickel oxide which is a colorant that yields a variety of browns, blues, grays and yellows depending on the presence of various other materials. Nickel Oxide is stronger.
Nickel Oxide (Black) NiO A black powder which produces browns, grays, blues and yellows. Can also tone down more intense colorants such as copper and cobalt. Its limit as a colorant is 3%. Black and green nickel are interchangeable.
Ochre A natural iron-based colorant used in clays and glazes that produces tans and pale yellow tones.
Plastic Vitrox. 1RO.1.69Al2O3.14.64Sio2. A complex type of material similar to potash feldspar and Cornwall stone.
Potassium Carbonate K2CO3 Also known as Pearl Ash. It is a strong flux and can be used as a color modifier in glazes. Can change copper greens into yellow-greens or bright blue.
Pumice Also known as Volcanic Ash. Frequently used as a feldspar substitute in glazes.
Redart Clay, A low temperature, air-floated clay that produces red to brown clays. May be used as a colorant in high temp clays.
Rutile (Ceramic Grade) TiO2 A titanium dioxide colorant which contains a small amount of iron and vanadium. Will produce tans and mottle other colorants..
Silica Sio2, Also known as flint or quartz. Glass former. In a glaze it will raise the maturing temperature and increase the hardness of the glaze. It will lower a glaze thermal expansion, but will increase it in a clay body.
Silicon Carbide SiC,(FFF) An artificial reduction agent used in oxidation which produces a localized reduction on the glaze. Add in 0.5 percent to alkaline glazes.
Soda Carbonate Na2CO3 Soda Ash. This is an active flux which also serves an important function as a deflocculant for slip casting bodies. Increases strength and workability, reduces shrinkage. As a glaze deflocculant, you should add 3 gm for every 100 gm dry ingredient.
Sodium Silicate (Wet) Sodium Silicate is a major deflocculant in slip casting and in glazes that settle. NOTE: Read directions carefully. Adding too much can cause the opposite effect. Can sometimes be combined with Soda Ash.
Spodumene. Li2O.Al2O3.4Sio2 An important source of Lithia and an active flux. This ingredient helps promote unusual copper blues. Can be added as a replacement for feldspar in some clay bodies to reduce shrinkage and maturing temps.
Strontium Carbonate SrCo3. Source of strontium oxide in glaze formula.
Superpax ZrSiO4 Zircon opacifier, used in a wide variety of applications. Effective in controlling texture, craze resistance and color stability.
Talc 3MgO 4SiO2 H20 A flux for low temperature, white clay bodies and low and high fire glazes. Gives a slight opacity to a glaze.
Tin Oxide SnO2 The most effective opacifier to produce even, opaque, glossy glazes. The normal content of tin oxide in a glaze is between 5 and 10%. The results obtained are consistent. A dull matt glaze can result when used in excess. Excess may also result in crawling glaze. Will pick up pink flashes if chromium oxide is present in other glazed items in the same kiln. *
Titanium Dioxide TiO2 The best opacifier for white matt glazes, usually will cause the most effect on other colorants. 10% is the maximum content limit. Useful in forming crystalline glazes. *
Umber (Burnt) A hydrated ferric oxide with manganese dioxide. It is used as a decorative element to produce a reddish-brown color. Also can be added to clay bodies to make the color darker.
Vanadium V2O5 A weak yellow colorant that is usually combined with tin oxide to give a yellow color capable of firing to higher temps. Use up to 10%.
Vee-Gum T A macaloid-type gum suspension for glazes. Also used as a surface hardener. It is an extremely plastic, hydrous magnesium silicate used to give plasticity to non-plastic white-ware and refractories.
Volcanic Ash Also known as Pumice. Frequently used as a feldspar substitute in glazes.
Whiting (Calcium Carbonate) CaCO3 This is the most common source of calcium oxide in glazes. It is a major high temperature flux which gives durability and hardness to a glaze.
Wollastonite CaSio3 A natural calcium silicate used to reduce shrinkage in clay bodies and glazes during firing. Can replace silica and whiting. It will reduce firing shrinkage and also improve heat shock in clays and glazes.
Zinc Oxide ZnO, Calcined (Ceramic Grade) A high temperature flux. It increases the maturing range of glazes and produces bright colors and promotes a high gloss finish with reduced expansion. Also may be used to give opacity to glazes.
Zircopax ZrO2 SiO4 The original Zirconium opacifier. Used mostly where semi-opaqueness is desired.