S-shaped cracks that occasionally appear in the bottoms of wheel-thrown pots, resulting from inadequate compression of the bottom and/or excessive water left in bottom.
Source:
Clay: A Studio Handbook
Rutile
Titanium ore, used as source of titanium dioxide, contains iron, other trace minerals—gives tan color, promotes crystallization giving mottled multicolor 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.
Source:
Clay: A Studio Handbook
Rolled Edge
Beveled edge obtained by rolling the outer edge of the foot of a soft leather-hard pot at an angle against a hard, flat surface.
Source:
Clay: A Studio Handbook
Rib
Wide, flat handheld tool used to shape, smooth, and/or scrape clay surfaces; usually wood, rubber, plastic, or metal, either rigid or flexible, with straight, curved, or profiled edge.
Source:
Clay: A Studio Handbook
Resist
Material used in glazing and decorating that can be applied to surface to prevent adhesion of slip or glaze.
Source:
Clay: A Studio Handbook
Residual Ash
In a wood kiln, the surface effects created by fly-ash settling upon the wares. Effect is maximized by turbulence in firebox, considerable draft through kiln, and/or active stirring of the coal bed. In short wood firings ash doesn’t have time to melt, and leaves a rough, crusty surface.
Source:
Clay: A Studio Handbook
Refractories
Any materials highly resistant to the effects of heat. In kiln construction, high-temperature insulating materials, such as firebrick, ceramic fiber, etc. In clay and glaze chemistry, the neutrals or stabilizers that are resistant to melting and that combine with the fluxes (bases) and glass-formers (acids). Primary refractory material in ceramics is alumina, most often introduced in the form of clay (aluminum silicate).
Source:
Clay: A Studio Handbook
Reduction Cooling
In a fuel kiln, maintaining slight reduction atmosphere during cooling cycle, from maturing temperature down to approximately 1400° F, in order to minimize reoxidation of clay and/or glazes.
Source:
Clay: A Studio Handbook
Reduction
Chemical reaction in which oxygen atoms are removed from a compound.
Source:
Clay: A Studio Handbook
Reduce
To induce reduction.
Source:
Clay: A Studio Handbook
Red Iron Oxide
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.
Source:
Clay: A Studio Handbook
Ramp
Profile of the firing of a kiln, including speed, duration, soaking periods, etc. of both the heating and cooling cycle, as in firing ramp and cooling ramp.
Source:
Clay: A Studio Handbook
Pyroplastic
Flexibility of clay or glaze when heated sufficiently, as a result of developing glassy-phase.
Source:
Clay: A Studio Handbook
Pyrophyllite
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.
Source:
Clay: A Studio Handbook
Pugmill
A machine similar to an oversized meat grinder, used to homogenize plastic clay bodies. Deairing pugmills have a vacuum pump attachment, which effectively removes all air from clay, eliminating need for hand wedging.
Source:
Clay: A Studio Handbook
Primary Air
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.
Source:
Clay: A Studio Handbook
Press Mold
A mold, usually plaster, into which moist clay is pressed to crease multiples
Source:
Clay: A Studio Handbook
Pottery Wheel (Potter’s Wheel/Potters Wheel)
Machine with a horizontally spinning wheel head upon which potters form and trim clay vessels by hand.
Source:
Clay: A Studio Handbook
Pottery Bat
A pottery bat is a pottery throwing accessory that enables freshly thrown work to be removed from the throwing wheel without the damage or warpage that can occur from touching the pot directly. Pottery bats also make it possible to return a piece to exact center to work on later.
Throwing bats can be made from most any rigid material, but wood, wood composites, plastics, and plaster are the most common. Except for plastic, these materials are all porous so pots will release from them easily as they absorb water from the clay. If the material is not porous (e.g., plastic) the pot must be wired off before it sets up too much, or it will crack as it shrinks.
Some of the materials that pottery bats are made from include:
Duron® (aka Masonite® or tempered hardboard), a resin impregnated hardboard that’s water resistant and smooth on both sides.
Medex®, a fiber board material made with a formaldehyde-free adhesive that’s waterproof yet porous
Plastics of several different types (nonporous and waterproof, so they require wiring off pots)
Plywood (must be exterior- or marine-grade to avoid delaminating)
Plaster, one of the traditional materials for bats and one of the best for porosity
Hydro-Stone, a USG product containing cement and crystalline silica, is similar to plaster but 8 to 10 times stronger
Most wheel manufacturers pre-drill wheel heads with bat-pin holes that hold 3/8-inch (or 10-mm) bat pins on 10-inch centers. Most bat makers produce bats that fit this standard. While pottery bats can be stuck to the wheel head with clay or pottery slip, bat pins allow the user to quickly add and remove bats with ease.
Source:
Clay: A Studio Handbook
Potassium Dichromate
K2Cr2O7—Occasionally used as acid-green colorant in raku glazes, but is highly toxic in absorption, ingestion, and inhalation.
S-shaped cracks that occasionally appear in the bottoms of wheel-thrown pots, resulting from inadequate compression of the bottom and/or excessive water left in bottom.
Source: Clay: A Studio Handbook
Titanium ore, used as source of titanium dioxide, contains iron, other trace minerals—gives tan color, promotes crystallization giving mottled multicolor 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.
Source: Clay: A Studio Handbook
Beveled edge obtained by rolling the outer edge of the foot of a soft leather-hard pot at an angle against a hard, flat surface.
Source: Clay: A Studio Handbook
Wide, flat handheld tool used to shape, smooth, and/or scrape clay surfaces; usually wood, rubber, plastic, or metal, either rigid or flexible, with straight, curved, or profiled edge.
Source: Clay: A Studio Handbook
Material used in glazing and decorating that can be applied to surface to prevent adhesion of slip or glaze.
Source: Clay: A Studio Handbook
In a wood kiln, the surface effects created by fly-ash settling upon the wares. Effect is maximized by turbulence in firebox, considerable draft through kiln, and/or active stirring of the coal bed. In short wood firings ash doesn’t have time to melt, and leaves a rough, crusty surface.
Source: Clay: A Studio Handbook
Any materials highly resistant to the effects of heat. In kiln construction, high-temperature insulating materials, such as firebrick, ceramic fiber, etc. In clay and glaze chemistry, the neutrals or stabilizers that are resistant to melting and that combine with the fluxes (bases) and glass-formers (acids). Primary refractory material in ceramics is alumina, most often introduced in the form of clay (aluminum silicate).
Source: Clay: A Studio Handbook
In a fuel kiln, maintaining slight reduction atmosphere during cooling cycle, from maturing temperature down to approximately 1400° F, in order to minimize reoxidation of clay and/or glazes.
Source: Clay: A Studio Handbook
Chemical reaction in which oxygen atoms are removed from a compound.
Source: Clay: A Studio Handbook
To induce reduction.
Source: Clay: A Studio Handbook
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.
Source: Clay: A Studio Handbook
Profile of the firing of a kiln, including speed, duration, soaking periods, etc. of both the heating and cooling cycle, as in firing ramp and cooling ramp.
Source: Clay: A Studio Handbook
Flexibility of clay or glaze when heated sufficiently, as a result of developing glassy-phase.
Source: Clay: A Studio Handbook
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.
Source: Clay: A Studio Handbook
A machine similar to an oversized meat grinder, used to homogenize plastic clay bodies. Deairing pugmills have a vacuum pump attachment, which effectively removes all air from clay, eliminating need for hand wedging.
Source: Clay: A Studio Handbook
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.
Source: Clay: A Studio Handbook
Source: Clay: A Studio Handbook
Machine with a horizontally spinning wheel head upon which potters form and trim clay vessels by hand.
Source: Clay: A Studio Handbook
A pottery bat is a pottery throwing accessory that enables freshly thrown work to be removed from the throwing wheel without the damage or warpage that can occur from touching the pot directly. Pottery bats also make it possible to return a piece to exact center to work on later.
Throwing bats can be made from most any rigid material, but wood, wood composites, plastics, and plaster are the most common. Except for plastic, these materials are all porous so pots will release from them easily as they absorb water from the clay. If the material is not porous (e.g., plastic) the pot must be wired off before it sets up too much, or it will crack as it shrinks.
Some of the materials that pottery bats are made from include:
- Duron® (aka Masonite® or tempered hardboard), a resin impregnated hardboard that’s water resistant and smooth on both sides.
- Medex®, a fiber board material made with a formaldehyde-free adhesive that’s waterproof yet porous
- Plastics of several different types (nonporous and waterproof, so they require wiring off pots)
- Plywood (must be exterior- or marine-grade to avoid delaminating)
- Plaster, one of the traditional materials for bats and one of the best for porosity
- Hydro-Stone, a USG product containing cement and crystalline silica, is similar to plaster but 8 to 10 times stronger
Most wheel manufacturers pre-drill wheel heads with bat-pin holes that hold 3/8-inch (or 10-mm) bat pins on 10-inch centers. Most bat makers produce bats that fit this standard. While pottery bats can be stuck to the wheel head with clay or pottery slip, bat pins allow the user to quickly add and remove bats with ease.Source: Clay: A Studio Handbook
K2Cr2O7—Occasionally used as acid-green colorant in raku glazes, but is highly toxic in absorption, ingestion, and inhalation.
Source: Clay: A Studio Handbook