New Mexico Clay Chemicals and Minerals Descriptions (list from the 1980's)

(We do not carry all of these listed.)

ALUMINA HYDRATE

Preferred over the calcined form in a glaze for adhesive and suspension qualities. Commonly used as a kiln wash in salt fire operations and as an aid in reducing crazing.

ALUMINA OXIDE

Used in glazes to achieve matte finish. Prevents devitification and increases strength. Too much alumina causes a dry and underfired appearance. Insoluble in water.

BARIUM CARBONATE

The main source of barium in glazes. Insoluble in water and quite resistant to fusing when used raw, this material assists in the formation of matte finishes and in neutralizing sulfates in clay bodies. Toxic.

BENTONITE

A swelling montomorillonite of volcanic origin that fuses at about 2400 F. More effective than ball clay as a body plasticizer but shrinkage may be severe. Also addition of up to 3% helps suspend a glaze.

BICARBONATE OF SODA

Soda ash is the form more commonly used as a glaze flux. Used in cobalt sulfate stains and as a major ingredient for Egyptian paste.

BONE ASH

Formerly calcined and ground animal bone, now a synthetic, it is an important phosphate source. Most commonly associated with bone china it lowers firing temperatures and increases translucency.

BORAX

Next to lead, the major low fire flux. Very soluble in water it is most often used in fritted form. Promotes smooth melting bright colors with oxides. Keep dry.

BORAX, Granular

Same as Borax, powdered, but in coarse size.

BORIC ACID

Although a neutral oxide, it functions more as a flux. Unlike silica, an acid, boron lowers expansion and increases elasticity (fit) of a glaze. Soluble in water it also increases gloss in a glaze.

C.M.C.

Powder (carboxymethyl-cellulose) Used to increase glaze adherence, as a glaze mediun, or to impart strength to a cast of pressed body. .3%

CALCIUM BORATE

(See Gerstley Borate)

CALCIUM CARBONATE

(See Whiting)

CALCIUM FLUORIDE

(See Fluorspar)

CHINA CLAY

(See Kaolins)

CHROME OXIDE, Green

A very strong coloring oxide used in glazes and stains to produce greens at high temperatures. Low temperature reds in high-lead, low-alumina glaze. Reduction blackens color. May jump from pot to pot in high fire.

COBALT CARBONATE

A very strong coloring oxide used in glazes and stains to produce blues. Disperses well for even color. Combined with magnesium a purple is possible. Little goes a long way.

COBALT OXIDE

Stronger than carbonate form, but may not disperse as readily, causing speckles.

COPPER CARBONATE

A major green colorant in glazes. The carbonate form is preferred to the oxide (soluble in water, but is more toxic) in producing blue-greens or copper reds in reduction.

COPPER OXIDE, Black (cupric)

Used whenever Copper Oxide is required, but unspecified as to red or black. Coppers tend to volitize (jump from pot to pot) at high temperatures.

CORNISH STONE

(See Cornwall Stone)

CORNWALL STONE

(Cornish Stone) Has characteristics between a kaolin and a feldspar. Used to achieve a smaller concentration of alkali flux in a glaze. This results in less shrink, minimizing glaze defects. Combined with a flux it is itself a glaze.

CROCUS MARTIS

(See Iron Oxides)

CRYOLITE

A sodium-aluminum fluoride primarily used as a flux and opacifier for enamels and glasses. Fluorine gas may bubble through glaze causing pinholing, but in small % is used to flux low fire glazes color is desired.

DEXTRINE, Yellow

A binder for glazes. (See notes on binder usage under Gum Arabic)

DOLOMITE

A double carbonate of magnesia. A cheap source of calcia and magnesia flux into a glaze. May be used to replace whiting in cases where lighter glaze color is desired.

EPSOM SALTS

(See Magnesium Sulfate)

FELDSPAR-KONA, F-4 (soda)

A soda feldspar used in glazes and clay bodies if a soda flux is wanted.

FELDSPAR-CUSTER

A potash feldspar with a mid-range soda/potash ratio. It is, therefore, a good substitute for Eureka, Oxford, Clinchfield, and Keystone Feldspars.

FERRIC/FERROUS, Oxide

(See Iron Oxide)

FLINT, 200 mesh

(Silica) Fine silica used in glaze work.

FLUORSPAR

(Calcium Fluoride) Fluorspar fluxes at a lower temperature than other calcia compounds. Limited use as glaze flux, but with copper oxide some unusual blue-greens can develop.

GERSTLEY BORATE

A natural borate similar to but not interchangeable with Colemanite on a 1 to 1 basis. If substituting Colemanite for Gerstley use1/2 as much Colemanite as Gerstley and add 1% CaCO3 . If substituting Gerstley for Colemanite use twice as much Gerstley.

HEMATITE

(See Iron Oxide, Red)

ILLMENITE, Granular

This is the mineral source of titanium and its compounds . Used to produce dark specks in glaze.

ILLMENITE, Milled, Powder

Same as above in powdered form.

IRON CHROMATE

Used in combination with manganese and zinc compounds for underglaze (engobe) browns or with cobalt for black. Fugitive, burns off, if used alone above cone 04.

IRON OXIDE, Black (Ferrous)

May be used in glaze formulations and in most cases gives the same color as Iron Oxide Red. With titanium in a high-fire glaze can give a matte red.

IRON OXIDE, Magnetic (ferrous/ferric)

(See Magnetite)

IRON OXIDE, Red (ferric)

Known as Hematite. Red Iron Oxide is the stable form of iron and no matter what form is added to a glaze or clay, firing converts it into Fe2O3. Iron is both a colorant and a flux. We stock two strengths of Iron Oxide Red listed below.

IRON OXIDE, Red

(Clay Body) 86% Fe

IRON OXIDE, Red

(Glaze Body) 99% Fe

IRON OXIDE, Yellow

(hydrated ferric) Similar to irons above, but tends to give lighter colors in the buff to cream range.

KRYOLITH

(See Cryolite)

LEAD BISILICATE

A lead fritted with silica to reduce lead release (solubility) of lead. Used as a flux in low-fire glazes.

LEAD CARBONATE, White

White Lead is a low-fire flux used to achieve flawless glossy glazes. A dangerous (poison) material, we recommend using lead only in fritted (see Lead Bisilicate above) and in the studio. TOXIC.

LEAD CHROMATE, Yellow

Used in much the same way as White Lead, this yellow powder produces opaque glazes in the coral-red range. TOXIC.

LEAD MONOSILICATE

A frit made of lead and silicate eliminate the toxic effects of the lead compounds.

LEAD MONOXIDE

(See Litharge)

LEAD OXIDE

(See Red Lead and Litharge)

LEPIDOLITE

Also known as Lithium Mica. Contains 3 to 6% lithia. A flux in high-temperature glazes, it tends to brighten colors and lower thermal expansion. Also as a body ingredient for "flameware".

LITHARGE

(Lead Monoxide) One of the two types of Lead Oxide use in ceramics. (See Red Lead) Contains impurities and has larger particles than Red Lead, but the same. TOXIC.

LITHIUM CARBONATE

A common source of slightly soluble lithia. A high-temperature flux, it can be used in place of lead in medium-fire ranges. Low thermal expansion, it also improves brightness.

LITHOLITE No. 400

(sub. for Lepidolite) Was developed to replace Lepidloite in formulations and can be used successfully in both body and glaze.

MANGANESE DIOXIDE, Powdered.

Used as a colorant, but also a powerful flux. For plum color use in an alkaline glaze.

MANGANESE DIOXIDE, Granular

Same as above in granular form to provide specks of dark brown or black to clay bodies and glazes.

MAROON BASE

(See Pink Oxide)

MAGNESIUM CARBONATE

An insoluble magnesia source. Used as a high-temperature flux, or even an opacifier in some glazes.

MAGNESIUM SULFATE

Primarily used in glazes to retard settling of frits. 1% dissolved in hot water will be sufficient and have no effects on glaze.

NEPHELINE SYENITE

Roughly similar to a feldspar, it can be used like a soda-spar to reduce crazing when added to a clay and inducing crazing when added to a glaze.

NICKEL CARBONATE

Source of Nickel Oxide which produces a range of browns, blues, grays, and yellows. Highly refractory, it tends to opacify. Use a little more to replace Nickel Oxide in a glaze.

NICKEL OXIDE, Black.

Both Black and Green Nickel serve almost solely as a colorant. Depending on flux and ratio of alumina a wide variety of colors is possible.

NICKEL OXIDE, Green.

Basically the same uses as Black (above). In addition, 5 to 10% results in formation of crystalline structure.

OCHRE, Yellow.

An earth substance (clay containing varying amounts of red iron and manganese oxides) used as a luster pigment.

OPAX

A standard commercially produced opacifier. Maintains color stability and aids in craze resistance. Weaker but cheaper than tin.

PEARL ASH

(See Potassium Carbonate)

PETALITE

Used to reduce thermal expansion and increase shock resistance. Similar to lepidolite. Availability has been shaky; substitute 55 to 60% Spodumene and 45 to 50% Pyrophillite.

PINK OXIDE

Also known as Maroon Base. A prepared ceramic pigment made by calcining chromium in the presence of tin. Produced reds, but in oxidation only.

PLASTER

 #1 Pottery. For mold making. Also good for bats, drying trays, (for slip tempering clays) and wedging tables.

POTASSIUM CARBONATE

Used to modify color effects and as a flux. Changes usual: Copper Oxide glaze color from green to yellow-green to bright blue. Soluble.

POTASSIUM DICHROMATE

(Dichromate of Potash) Used in glazes as a green colorant. Produces pink and red stains when calcinated with tin (see Pink Oxide). Preferred form because of more chrome per weight. Soluble. TOXIC.

PUMICE

Volcanic Ash. Used in much the same way as feldspar but less desirable in glazes.

PYROPHLLITE

A naturally hydrated aluminum silicate; it decreases thermal expansion and crazing. A nonplasitc, its clay body uses are limited.

RED LEAD

(Lead Oxide) Known also as Minium. One of two forms of Lead Oxide used in ceramics. (See Litharge) A better flux than Litharge. Produces a smooth, bright glaze. Caution: TOXIC.

RUTILE

An impure oxide of titanium it also carries small amounts of iron and vanadium. Used as a tan colorant. Has wide use when mixed with other colorants.

RUTILE, Granular.

Same as above to produce large spots.

SILICA, 200 mesh.

Also known as flint, it increases durability and chip resistance. In a glaze, the addition of flint decreases its thermal expansion; in a body it increases it.

SILICA SAND, 60 mesh.

A 95% pure, sharp angle grind silica sand with less than .02% iron oxide. Good for opening clay bodies.

SILIA SAND, 30 mesh

Same as above, gives clay body even more "tooth".

SILICON CARBIDE, FFF

Added to the glaze, it aids in reduction and promotes reds in copper reduction glazes.

SODA ASH

(Sodium Carbonate) A very active flux, but because of solubility more commonly used in fritted form. Serves as a deffloculant and also reduces shrinkage from wet to dry.

SODIUM BICARBONATE

(See Bicarbonate of Soda)

SODIUM CARBONATE

(See Soda Ash)

SODIUM SILICATE, "N" Brand

This liquid is the major deffloculant in slip casting clays. It minimizes shrinkage and adds to green strength.

SPODUMENE

Important source of lithia. Used to replace a portion of the feldspar in a body it reduces maturation and shrinkage. Common ingredient of "flameware".

STANNIC OXIDE

(See Tin Oxide)

TALC

A flux for low and high fire glazes. Gives slight opacity and acts like magnesium in large amounts. Often a body flux in low fire.

TIN OXIDE

Also known as Stannic Oxide. The best, most effective opacifier. 5 to 7% produces a completely white, opaque glaze, Remains suspended well but too much produces a dull finish.

TITANIUM DIOXIDE

A major opacifier when used either alone or in a frit. Like rutile, an impure form of titanium containing iron, when used in quantity it will produce a semi-matte surface.

TITANIUM OXIDE

More correctly Titanium Dioxide above.

UMBER, BURNT

A naturally hydrated iron and manganese earth compound similar to ochre. Produces reddish-brown color.

VANADIUM PENTOXIDE

Rather a weak yellow colorant when used alone. When fritted with tin and yellow, color strengthens. Has a long firing range (06-14) undamaged by reduction.

VOLCANIC ASH

(See Pumice)

WALLASTONITE

A natural calcium silicate. A replacement for silica and whiting compliment in a glaze, it reduces shrinkage and improves heat shock. Used in both bodies and glazes.

WAX RESIST

A high solids (50%), smooth flowing, easy to handle wax with a melting point of 125 F. Disperse with warm water. Stable for several months if protected from freezing.

WHITING

(Calcium Carbonate) The major high-fire flux. Benefits bodies where a limited amount will lower vitrification temperature and reduce porosity. Gives durable hardness to a glaze.

ZINC OXIDE

In general, zinc increases the maturing range of a glaze, promotes higher gloss, brightens colors and reduces expansion. Used extensively in once fired Bristol Glazes (see Nelson) and crystalline glazes.

ZIRCONIUM OXIDE

Not quite as refractory as milled Zircon, it is used to prepare a number of zirconium fritted opacifiers.

ZIRCOPAX

The original zirconium silicate glaze opacifier.

FERRO FRITS:

Frits are glaze materials which have been melted, cooled and ground into a powder which is then added to a glaze formula for the purpose of rendering insoluble any soluble material present.

MELTING POINT

3110-- HIGH CALCIUM/SODIUM, LOW ALUMINA 1400*F

3124-- SODA-CALCIUM-BORATE 1600*F

3134-- CALCIUM BORATE, LOW SILICA, NO ALUMINA 1450*F

3195-- VERY FLUID, HIGH CALCIUM BORATE 1500*F

3269-- SODA-BORATE-ZINC

3819 --

FERRO EQUIVALENT FRITS

NOTE: * NMCLAY STOCKS FERRO BRAND.

 

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