Suspension agent plasticizer similar to Bentonite and Veegum T. Up to 2% of dry-materials weight as plasticizer in high-kaolin clay bodies. Up to 1/2 of 1% of dry-materials weight as suspension agent, brushing medium in glazes, and slips. Mix with water before adding other ingredients.

Glaze effect featuring large patches of crystal development on glaze surface, as compared to microcrystalline effects. See crystalline glazes.

MgCO₃ alkaline earth HT flux, promotes mattness 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.

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.

MgSO₄ water soluble, rarely used as magnesium source in glazes. Most often used as flocculant for slips and glazes. Often added to porcelain and porcelaineous stoneware bodies (1/2 of 1% of dry materials weight) to counteract deflocculating alkalinity released by kaolins or fluxes.

Earthenware, generally terracotta, with opaque white glaze and colored over glaze decoration, not to be confused with majolica.

Historic English style of brightly glazed earthenware vessels made in the form of vegetables, animals, etc., not to be confused with majolica.

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. Fumes from firing are especially toxic.

Primitive gauge for measuring water column inches, consisting of a U-shaped glass tube partially filled with water, with the pressure source connected to one end. See water column inches.

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.

Glaze featuring a dull, non glossy surface.

Firing point at which a clay body or glaze reaches its desired condition of color, hardness, density, etc.

During drying and firing of clay, the phenomenon whereby a clay piece will remember  the way it was formed and will often shrink specifically according to the forming method. If not accommodated, memory can aggravate a variety of drying and firing faults.

K₂O—3Al₂O₂—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.

Crystal effects dependent on tiny crystals in the glaze surface, as compared to macro crystalline effects.

Glaze-firing range usually including cone 4 to cone 7, very popular with electric kilns.

East Asian method of creating an inlaid effect by applying contrasting slip into a design incised in leather-hard clay. When the slip stiffens, the excess is scraped off.

Glaze materials that are added to a base glaze to modify surface qualities such as color, gloss, mattness, opacity, crystal development, etc.

In making plaster molds, compounds that are applied to all surfaces except damp clay, in order to prevent plaster from sticking. Liquid hand soap works great. Paint it on and let it dry before pouring plaster. Never use oil-base release compounds on plaster molds for press-molding or slip-casting.

A group of atoms chemically bonded together to form a compound.

Clays such as Bentonite, resulting from the breakdown of airborne volcanic ash. The finest particle size of all clays. Very high shrinkage, and generally used only as an additive to clay bodies or glazes. See Bentonite.

In some wood kilns, a small air-port and passage that admits air directly beneath the coal bed.

MATERIAL SAFETY DATA SHEET, available from your supplier, giving toxicity information on each of the ceramic materials you use.

A fuel-burning kiln in which flames and combustion gases are ducted through sealed refractory flues within the ware chamber, heating the wares while maintaining a clean oxidizing atmosphere.

   3Al₂O₃—2SiO₂ calcined Kyanite, but is also found naturally. Very desirable interlocking needlelike aluminum silicate crystals form above 1800° F and greatly add to the strength of high-fired vitrified clay bodies and glazes. In well-formulated high-fired wares, clay-glaze interface is extremely strong partially due to interlocking mullite crystals.

Wares where more than one glaze firing is required to achieve particular surface effects, as in lusters and china paints.