Crystal effects dependent on tiny crystals in the glaze surface, as compared to macrocrystalline effects.
Source:
Clay: A Studio Handbook
Mica
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.
Source:
Clay: A Studio Handbook
Memory
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.
Source:
Clay: A Studio Handbook
Matte Glaze
Glaze featuring a dull, nonglossy surface.
Source:
Clay: A Studio Handbook
Manganese Dioxide
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.
Source:
Clay: A Studio Handbook
Majolica
Trade name for an historic English style of brightly glazed earthenware vessels made in the form of vegetables, animals, etc. Not to be confused with maiolica, which is defined as earthenware with opaque white glaze (traditionally a lead glaze made opaque white with the addition of tin oxide) and colored overglaze decoration.
Source:
Clay: A Studio Handbook
Maiolica
Earthenware, generally terra cotta, with opaque white glaze (traditionally a lead glaze made opaque white with the addition of tin oxide) and colored overglaze decoration. Originated from Islamic/Moorish techniques used on the Spanish island of Mallorca, which exported these wares throughout the Mediterranean in the 15th and 16th centuries. The technique was adopted by Italy during the Renaissance, which is when the term maiolica was introduced to describe these brightly decorated wares. Not to be confused with majolica, which is a trade name for an historic English style of brightly glazed earthenware vessels made in the forms of vegetables, animals, etc.
Source:
Clay: A Studio Handbook
Macrocrystalline
Glaze effect featuring large patches of crystal development on glaze surface, as compared to microcrystalline effects.
Source:
Clay: A Studio Handbook
Macaloid
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.
Source:
Clay: A Studio Handbook
Lye
Potassium hydroxide or sodium hydroxide. Caustic alkaline soluble that leaches out of wood ashes when they are soaked in water. Occasionally used as a flux additive in terra sigillata, as in the black slip on Classical Greek wares. Toxic in liquid state, and may cause burns.
Source:
Clay: A Studio Handbook
Low Mid Range
Firing range usually including cone 01 to cone 3, underused in studio ceramics, useful for functional earthenware, refractory sculpture bodies, and outdoor terra cotta work
Source:
Clay: A Studio Handbook
Low Fire
Low-temperature firing range, usually below cone 02 (2048° F), used for most bisque-firing and for glaze-firing terra cotta and whiteware.
Source:
Clay: A Studio Handbook
Lithium Carbonate
Li2CO3—powerful AT alkaline flux, especially with soda or potash feldspars. Promotes hardness and recrystallization in LT glazes. Forms low-temperature eutectic with silica. Toxic in inhalation.
Source:
Clay: A Studio Handbook
Lepidolite
Lithium feldspar—HT alkaline flux—used for thermal shock bodies and matching glazes. Contains fluorine, with associated problems. Toxic in inhalation.
Source:
Clay: A Studio Handbook
Leather Hard
Condition of clay in which it has stiffened but is still damp. Point at which pieces are joined and most surface modification and trimming are done. Soft leather-hard ideal for forming, joining, thick slip-decorating. Medium leather-hard good for thin slip- decorating, joining, incising, carving, piercing. Hard leather-hard good for thin slip- decorating, carving, scraping.
Source:
Clay: A Studio Handbook
Kyanite
3Al2O3×2SiO2—aluminum silicate used in place of alumina and silica to promote formation of mullite crystals, increase thermal shock resistance. Coarse-ground used as grog in refractory bodies for kiln furniture.
Source:
Clay: A Studio Handbook
Kona F 4 Feldspar
Na2O×Al2O3×6SiO2—a common soda feldspar—powerful HT alkaline flux. Toxic in inhalation.
Source:
Clay: A Studio Handbook
Kingman Feldspar
Potash spar no longer mined. Substitute Custer or G-200.
Source:
Clay: A Studio Handbook
Kiln Wash
Kiln wash is a refractory slip coating applied to the top surface of a kiln shelf to protect it from glaze runs, drips and other accidents that occur in red hot kilns, like pots that tip over, bloating or melting clay bodies, etc. It is also used to protect shelves from volatiles in atmospheric kilns like wood ash, or sodium oxide in salt and soda kilns.
There are many kiln wash recipes to choose from and it’s important to find the recipe that works best with your firing practices. What works well at one firing range or atmosphere, may not be well suited for another.
A good wash requires materials that have very high melting points and that, when combined, do not create eutectics that cause melting. Kiln wash is used in the full range of ceramics firing from cone 022 to cone 14. The type needed varies for each specific situation because some potters work in electric kilns at low-fire temperatures, while others work with fuel-fired kilns at very high temperatures.
A common recipe for gas and electric oxidation or reduction kilns is 50% kaolin and 50% silica (flint). However, that mixture must never be used in salt, soda, and wood firing. For those processes, use 40% kaolin, 10% ball clay, and 50% alumina hydrate.
Mix kiln wash to a thick creamy consistency and apply with a wide brush or paint roller. In some cases you may wish to build up successive coats, especially in any situation where significant glaze runs are fairly common.
In all cases, avoid getting your wash on the edges of the shelves where it can flake off in the firing and fall on glaze wares below.
Kiln wash is a refractory slip coating applied to the top surface of a kiln shelf to protect it from glaze runs, drips and other accidents that occur in red hot kilns, like pots that tip over, bloating or melting clay bodies, etc. It is also used to protect shelves from volatiles in atmospheric kilns like wood ash, or sodium oxide in salt and soda kilns.
Source:
Clay: A Studio Handbook
Kiln Stilts
Term often applied to all kiln posts, but more correctly referring to specialized refractory furniture pieces equipped with ceramic or metallic points designed to support fully glazed wares during firing.
Crystal effects dependent on tiny crystals in the glaze surface, as compared to macrocrystalline effects.
Source: Clay: A Studio Handbook
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.
Source: Clay: A Studio Handbook
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.
Source: Clay: A Studio Handbook
Glaze featuring a dull, nonglossy surface.
Source: Clay: A Studio Handbook
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.
Source: Clay: A Studio Handbook
Trade name for an historic English style of brightly glazed earthenware vessels made in the form of vegetables, animals, etc. Not to be confused with maiolica, which is defined as earthenware with opaque white glaze (traditionally a lead glaze made opaque white with the addition of tin oxide) and colored overglaze decoration.
Source: Clay: A Studio Handbook
Earthenware, generally terra cotta, with opaque white glaze (traditionally a lead glaze made opaque white with the addition of tin oxide) and colored overglaze decoration. Originated from Islamic/Moorish techniques used on the Spanish island of Mallorca, which exported these wares throughout the Mediterranean in the 15th and 16th centuries. The technique was adopted by Italy during the Renaissance, which is when the term maiolica was introduced to describe these brightly decorated wares. Not to be confused with majolica, which is a trade name for an historic English style of brightly glazed earthenware vessels made in the forms of vegetables, animals, etc.
Source: Clay: A Studio Handbook
Glaze effect featuring large patches of crystal development on glaze surface, as compared to microcrystalline effects.
Source: Clay: A Studio Handbook
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.
Source: Clay: A Studio Handbook
Potassium hydroxide or sodium hydroxide. Caustic alkaline soluble that leaches out of wood ashes when they are soaked in water. Occasionally used as a flux additive in terra sigillata, as in the black slip on Classical Greek wares. Toxic in liquid state, and may cause burns.
Source: Clay: A Studio Handbook
Source: Clay: A Studio Handbook
Low-temperature firing range, usually below cone 02 (2048° F), used for most bisque-firing and for glaze-firing terra cotta and whiteware.
Source: Clay: A Studio Handbook
Li2CO3—powerful AT alkaline flux, especially with soda or potash feldspars. Promotes hardness and recrystallization in LT glazes. Forms low-temperature eutectic with silica. Toxic in inhalation.
Source: Clay: A Studio Handbook
Lithium feldspar—HT alkaline flux—used for thermal shock bodies and matching glazes. Contains fluorine, with associated problems. Toxic in inhalation.
Source: Clay: A Studio Handbook
Condition of clay in which it has stiffened but is still damp. Point at which pieces are joined and most surface modification and trimming are done. Soft leather-hard ideal for forming, joining, thick slip-decorating. Medium leather-hard good for thin slip- decorating, joining, incising, carving, piercing. Hard leather-hard good for thin slip- decorating, carving, scraping.
Source: Clay: A Studio Handbook
3Al2O3×2SiO2—aluminum silicate used in place of alumina and silica to promote formation of mullite crystals, increase thermal shock resistance. Coarse-ground used as grog in refractory bodies for kiln furniture.
Source: Clay: A Studio Handbook
Na2O×Al2O3×6SiO2—a common soda feldspar—powerful HT alkaline flux. Toxic in inhalation.
Source: Clay: A Studio Handbook
Potash spar no longer mined. Substitute Custer or G-200.
Source: Clay: A Studio Handbook
Kiln wash is a refractory slip coating applied to the top surface of a kiln shelf to protect it from glaze runs, drips and other accidents that occur in red hot kilns, like pots that tip over, bloating or melting clay bodies, etc. It is also used to protect shelves from volatiles in atmospheric kilns like wood ash, or sodium oxide in salt and soda kilns.
There are many kiln wash recipes to choose from and it’s important to find the recipe that works best with your firing practices. What works well at one firing range or atmosphere, may not be well suited for another.
A good wash requires materials that have very high melting points and that, when combined, do not create eutectics that cause melting. Kiln wash is used in the full range of ceramics firing from cone 022 to cone 14. The type needed varies for each specific situation because some potters work in electric kilns at low-fire temperatures, while others work with fuel-fired kilns at very high temperatures.
A common recipe for gas and electric oxidation or reduction kilns is 50% kaolin and 50% silica (flint). However, that mixture must never be used in salt, soda, and wood firing. For those processes, use 40% kaolin, 10% ball clay, and 50% alumina hydrate.
Mix kiln wash to a thick creamy consistency and apply with a wide brush or paint roller. In some cases you may wish to build up successive coats, especially in any situation where significant glaze runs are fairly common.
In all cases, avoid getting your wash on the edges of the shelves where it can flake off in the firing and fall on glaze wares below.
Kiln wash is a refractory slip coating applied to the top surface of a kiln shelf to protect it from glaze runs, drips and other accidents that occur in red hot kilns, like pots that tip over, bloating or melting clay bodies, etc. It is also used to protect shelves from volatiles in atmospheric kilns like wood ash, or sodium oxide in salt and soda kilns.
Source: Clay: A Studio Handbook
Term often applied to all kiln posts, but more correctly referring to specialized refractory furniture pieces equipped with ceramic or metallic points designed to support fully glazed wares during firing.
Source: Clay: A Studio Handbook