Forming technique where a soft leather-hard form may be shaped and thinned with a wood or bisqued clay paddle on the outside and a rounded anvil of wood, stone, or bisqued clay applying corresponding pressure on the inside.

Technique of shaping a soft or medium leather-hard piece by gently hitting with a wooden paddle (sometimes textured) to create flat facets or to resolve irregularities in the surface.

Technique popularized by Rosette Gault, utilizing a clay body or slip containing paper pulp, which reduces shrinkage in drying stage, and encourages extremely strong joinery, allowing unconventional joinery such as wet to dry.

Decoration technique where strips of moist or adhesive paper are adhered to the surface to resist application of slip or glaze.

In a fuel kiln, atmosphere that is slightly reducing, but still allows increase in temperature. See reduction firing.

Paste-on-paste decoration in which sculptural relief decoration is built up with contrasting slip on surface of leather-hard ware.

An overall thin wash of glaze or oxide stain, allowing the color and texture of the clay body to show through.

K₂CO₃-HT alkaline potash flux, but soluble. Occasionally used as AT color modifier to soften effects of coloring oxides.

Small hoes in kiln door or wall, allowing viewing of cones, flames, wares, and or atmosphere during firing.

A kiln that is loaded cold, brought to temperature, cooled and unloaded. See continuous kiln.

A table listing all of the chemical elements (those substances that can theoretically be reduced to individual atoms), with the smallest and simplest across the top and the heaviest and most complex at the bottom and grouped by similar physical/chemical characteristics.

Porous expanded granular silica, useful in making insulating refractories.

Li₂O—Al₂O₃—8SiO₂ lithium feldspar HT alkaline flux good for reducing thermal expansion, increasing thermal-shock resistance. Toxic in inhalation.

Feldspathic rock, similar to Cornwall stone, found in China. Traditional Chinese flux for HT glazes and clay bodies.

Hand building method where clay objects are formed by pinching repeatedly between thumb and fingers or between fingers of one hand and palm of opposing hand.

Glaze defect characterized by fine pinholes in the surface often caused by pinholes already present in dry unfired glaze coating. Can also be caused by burst bubbles in glaze surface that are not given opportunity to heal  at end of firing.

Al₂O₃—2SiO₂—2H₂O plastic secondary kaolin wider particle distribution gives greater plasticity, green strength.

A type of bonfire-firing where wares are buried in sawdust in a pit in the ground and a bonfire is built on top, so that the fire and coals slowly burn away the sawdust and fire the wares. Not to be confused with sawdust smoking.

CaSO₄—2H₂O hydrated calcium sulfate, manufactured from gypsum, which will set to a hard solid after being mixed properly with water. Used for making molds for pressing or casting ceramic forms.

K₂O/Na₂O/CaO—Al₂O₃—10SiO₂ a plastic high-potash feldspathic clay, similar in structure to Cornwall stone used in place of potash feldspar in some porcelain bodies to increase plasticity. Toxic in inhalation

Quality of moldable flexibility in damp clay superior plasticity depends on smaller clay particle size, slight acidity, less non plastic additives, aging of damp clay body, adequate water content, and or addition of accessory plasticizers, such as Veegum T or Macaloid.

Materials added to some clay bodies, especially those high in kaolins, to increase plasticity and dry strength includes Bentonite, Macaloid, Veegum-T.

Flat, thin crystals that make up clay. When wet they become sticky and slippery, creating the phenomenon we call plasticity.

As compared to burnishing, the act of creating a shiny surface on terra sigillata (or any clay or slip) by rubbing with soft cloth, a soft brush, or a piece of plastic film.

High-fired vitreous clay body containing kaolin, silica, fluxes, and often ball clay to increase plasticity, with total clay component not more than 50%. Usually pure white or eggshell in color; some porcelains may fire translucent where thin.

White-firing stoneware clay bodies closely related to porcelain.

Calcium silicate aluminates air-setting cement, often added in small quantities to homemade cast able refractor mix in order to introduce air-setting qualities. Toxic in inhalation

See raku.

See G-200; Custer feldspar.

K₂CO₃-HT alkaline potash flux, but soluble. Occasionally used as AT color modifier to soften effects of coloring oxides.

K₂Cr₂O₇ Occasionally used as acid-green colorant in raku glazes, but is highly toxic in absorption, ingestion, and inhalation.

A long wooden tool with a knob on the end, often covered with chamois, which is inserted in a bottle or jug on the wheel after the top has been necked in and is used to broaden and refine the shape.

Machine with a horizontally spinning wheel head upon which potters form and trim clay vessels by hand.

Any burner in which a mechanical blower or other pressurized air source entrains the primary air for combustion.

Forming of multiples by pressing plastic clay into a plaster press-mold.

A mold, usually plaster, into which moist clay is pressed to crease multiples.

In a fuel-burning kiln, air that feeds initial combustion; in a wood-burning kiln, air that feeds base of flames; in a gas kiln air that enters back end of burner tube in an atmospheric burner, or via blower in a power burner. See secondary air.

Clays that remains at the site of the parent rock, without being transported by wind or water tend to be free of contaminants but coarse particle size and therefore low plasticity. Includes the purest kaolins.

A machine similar to an oversized meat grinder, used to homogenize plastic clay bodies. Deairing pug mill has vacuum pump attachment, effectively removes all air from clay, eliminating need for hand wedging. See carpal tunnel syndrome.

Fine volcanic particulate expelled from surface vents in a volcanic eruption. 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.

A manufactured pyrophyllite product, promotes plasticity more than other pyrophyllite products. Product of the H.T. Vanderbilt Company.

Temperature gauge connected to a thermocouple, which indicates temperature within kiln. Pyrometers provide good general reference, but only respond to temperature, whereas clay and glazes (and cones) are affected by temperature, duration, and atmosphere of firing. See pyrometric cones.

Small slender pyramidal-shaped indicators made of ceramic material formulated to bend at a specific temperature standard method for determining maturing temperature of firing. Like clay and glazes, cones respond to temperature, duration, and atmosphere of firing far more accurately than mechanical measurement.

Al₂O₃—4SiO₂—H₂O used in HT clay bodies (20% or less) to reduce thermal expansion, increase thermal shock resistance, reduce shrinkage, give stronger vitreous bodies. May reduce plasticity.

Flexibility of clay or glaze when heated sufficiently, as a result of developing glassy-phase.

A manufactured pyrophyllite product, made by the Resco Company.