Clay Bodies
earthenware Pottery with a porous and permeable body after firing which is waterproofed, if necessary, by a covering glaze.

Because of its colors and workability, earthenware is used for the widest range of working methods: throwing, hand building, pressing, and slip-casting.
Egyptian paste A prepared self-glazing clay body that contains water soluble fluxes that move to the surface as the clay dries. During firing, the fluxes combine with silica and alumina in the clay to create a thin layer of glaze on the surface. Egyptian paste has low workability, and ceramists who use it often employ press mold forming or slip casting techniques. It was developed in pre-dynastic Egypt for the production of beads and vessels, and is presently still used almost exclusively for decorative wares such as beads, small dishes and vessels, and frames.
engobe A liquid clay slip which has lower clay content than other slips and is colored with metallic earth oxides or glaze stains. It is applied to wet or leather-hard ware for decoration.

Engobes and slips do not flow in the fire, therefore they can be used for complex, graphic images.
grogged Ground up fired clay particles, used as a filler in making a clay body. Grog serves to subdue the sticky quality of highly plastic natural clays. It also helps reduce clay shrinkage, warping, cracks, and heat shock. In addition, it strengthens the clay body and makes complex construction less risky.
low-fire clay Low-fire bodies are fired at temperatures between 1700-2000 F.
Low-fire clay has good workability and will not shrink, warp, or sag. They, however, are less durable and can absorb liquids.

Low-fire clay is divided into two types: white and buff firing and darker-colored bodies. The white bodies are composed of half clay and half melter (often talc). Dark-colored bodies have a high clay content; their color derives from the iron-bearing clays used their clay bodies.
porcelain Porcelain clay is white and very hard, and, unless it is very thin, it is the strongest of all clay bodies. The body can be either translucent or opaque when fired, depending on the thickness or composition of the clay. Porcelain bodies are not easy to throw or handle as they have a critical moisture range and can easily be too soft or too dry. Prepared porcelain bodies can be bought from a supplier, but many potters mix their own.
stoneware A hard, strong and vitrified ware, usually fired above 2192 F, in which the body and glaze mature at the same time and form an integrated body-glaze layer.

Stoneware clays are especially appropriate for functional ware because they stand up well to constant use and frequent cleaning.
terra cotta Red-colored earthenware that is generally low-fired and unglazed.

The word comes from the Italian and means simply fired earth. Terra cotta is associated with pottery and architectural work.
terra sigillata An extraordinary fine-ground clay suspension in water that shines when applied as a coating. It is always fired at low temperatures to preserve the shine.

Terra sigillata is best applied to greenware. It can be applied by brushing, spraying, dipping, and pouring. Terra sigillata is often used with sgraffito imagery on greenware pieces, a technique used by the ancient Greek vase painters.


Processes
altered A wheel thrown piece is often altered after the throwing process to give it diversity. Thrown forms can have subtle modifications or significant alterations; for example, parts can be added to or subtracted from the form, or the shape of the piece can be changed. The resulting form has characteristics of both throwing and hand building.
burnished The process of polishing with a smooth stone or tool on leather-hard clay or slip to make a surface sheen; the surface will not stay shiny if fired at temperatures above 2000 F.
carved Carving is one of the techniques used to create surface imagery. Flat, angled tools or other implements are used for carving.
coil built Method of hand-building hollow forms by rolling and attaching ropes of soft clay together.
collage A technique of making an image from various materials or objects which are affixed to a surface.
extruded Method used to change the shape of clay by forcing it, mechanically or by hand, through an auger or other form.
hand built Techniques that do not use the potter's wheel or molds. These include pinching clay, coil building, forming, and slab building.
impressions Imagery created by pressing into the clay with objects like stamps, coins, shells, wood, leaves, bone, and textile fabrics.
incised Surface decoration made by cutting, using a beveled tool to scratch into wet or leather-hard clay. When the article is glazed, the depth of the incision gives a subtle quality and variation of color as well as design.
inlaid Surface decoration created by filling a recess or impression in a clay surface with another plastic clay or slip. When both are leather-hard or bone dry, the surface is carefully scraped to leave a sharp outline between the two colored clays.
pierced A technique for creating pattern in which holes are cut through the clay wall.
polished A technique used to create a smooth surface finish on fired ceramics using abrasive paper.
press molded A forming technique in which plastic clay slabs are pressed onto, against, and into plaster molds or other forms. As the clay stiffens, it retains the shape of the mold.
sandblasted Process of cleaning or treating a piece with a jet of sand driven by compressed air or steam.
slab built Method of hand-building forms. Clay is beaten or rolled out into flat slabs, trimmed into various shapes, and joined together with slip to produce the desired form. Slab construction is ideal for large scale; it is a faster method than other hand-building methods like pinching or coiling. Slabs for large work can be laid over combustible cores or sand-stuffed pillows.
slip cast Process used to build mold-formed pieces. A clay slurry is poured into a plaster mold. As the clay next to the mold begins to dry, a clay wall is formed in the shape of the mold and any excess clay slurry is poured out. Once dry, the remaining clay is removed from the mold and finished and fired.

Slip-casting is economical and allows for easy duplication of complex forms and decoration from the same mold.
stenciled Stenciling is a process used to apply complex surface imagery with slips and engobes.
wheel thrown Process of forming pieces from solid lumps of clay into hollow forms on a revolving potter's wheel.


Surface Treatments
Albany slip A slip glaze made from Albany clay which produces rich yellows, blacks and browns over a wide range of temperatures. Albany clay is mined in the vicinity of Albany, New York, and is natural clay containing sufficient fluxes to melt and function as a glaze. It was first developed when the early American potters followed the European practice of refining the clay to make a glaze.
decals Ceramic pigments photo-screened or pattern-screened onto flexible decal paper for transfer to bisque or over glaze. Decals can be bought or made.
lead glaze Lead glazes produce a wide range of colors and bright, shiny surfaces. They are reliable, easy to control, colorful and durable enough for most purposes. However, lead is toxic and should not be used on vessels that hold or serve food. Lead's toxicity can be controlled somewhat but not eliminated.

The invention of lead glazes around 1000 B.C. was a milestone in ceramics history because practical glazed ware became possible for the first time. Since then, most of the glazed earthenware in all parts of the world has been glazed with lead.
low-fire glazes Most low-fire glazes can be divided into two distinct groups--alkaline or lead. Both result in smooth, glossy surfaces and are often characterized by bright, shiny colors.
luster glaze Glaze with a brilliant, iridescent metallic film on glaze, formed from certain metallic salts at a specific temperature in a reduced atmosphere, usually on the cooling side of the firing cycle.
majolica glazes An opaque glaze with a smooth, glossy surface, and generally white in color produced by its significant tin content. This serves as a base for colored stain or overglaze decoration which is applied to the unfired base coat.

Historically, majolica refers to the decorated tin-glazed earthenware from the island of Majorca which was imported to Italy in the 15th century.
oxides Mined metallic oxides and scientifically prepared stains or enamels can be used to give color to ceramics. They will vary in strength and stability.
slip An homogenous mixture of clay and water. Slips are used for coating clays to give color and a smooth textured surface. There is also a process for forming pots from slip.


Firing Methods
dung-fired Low-firing technique using dung (animal excrement) as a fuel.

Dung can also be used as insulation during pit firing.
high-fire Firing temperature range of 2232 F to 2400 F. High-fire produces durable clay bodies with rich, stable glazes. However, as the temperature rises, the color range becomes more limited.
low-fire Firing temperature of 1940 F to 2014 F. Low-fire produces vivid colors and graphic glaze imagery though low-fire clay bodies are less durable and can absorb liquids.
oxidation fired The presence or lack of oxygen in a kiln chamber during firing has a significant effect on the appearance of the ware. A piece which has been oxidation fired has been fired in a kiln chamber that retained an ample supply of oxygen therefore allowing the oxygen to combine completely with the glaze and metals in the clay.
pit fired Firing wares in a pit that has been laced with combustible materials such as straw, paper, rags, sawdust, or twigs. The pit could be a pit in the ground, a formed pit using bricks or other materials, or some type of container.
raku fired Raku is a quick-firing technique that produces wares with brilliant, crackled glazed surfaces and dark bodies. Raku firing requires a special low-fire kiln, and can be used only on wares and glazes specifically designed to withstand abrupt heating followed by rapid cooling.
reduction fired The presence or lack of oxygen in a kiln chamber during firing has a significant effect on the appearance of the ware. A piece which has been reduction fired has been fired in a kiln chamber with a restricted supply of oxygen. This restriction of oxygen causes the kiln fuel to give off carbon monoxide which in turn produces significant color changes. Copper in reduction is oxblood red, in oxidation firing green; iron in reduction firing is celadon, in oxidation amber yellow, or brown.
salt fired Rock salt is thrown into the fire at the maturing temperature of the clay until an "orange-peel" clear glaze appears on the ware.
sawdust fired A simple system of firing in which pots are set in sawdust within a brick or metal lidded box. Pockets of oxidation and reduction firing are caused which produce interesting decoration especially on burnished red clays. Many potters now use this process to produce interesting coloration and also some reduction to lustre of copper and silver salts on previously biscuited pieces.
soda fired Soda fired is similar to salt fired except that soda can be added to the fire at any temperature. Soda encourages bright colors and does not produce the pockmarked surface of salt glazing.
wood fired

A kiln using wood as the fuel for bisquing and glazing. The advantage of wood-burning kilns is the unique effects that wood and its ashes have on the surfaces of both unglazed and glazed wares.

The wood must be absolutely dry, and must be prepared and stored at least a year in advance.

 

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