Coil method One of the oldest ways of forming pottery. Long strands of clay which are laid on top of each other and joined through blending coil to coil. Coil pieces can be almost any shape and any size.
Crackle glaze Minute decorative cracks in the glaze that are often accentuated by rubbed-in coloring material.
Crazing The fine network of small cracks that occurs on glazes. The Japanese encourage crazing and will stain cracks with concentrated tea.
Earthenware A low-fire clay. Porous and not waterproof. To be functional, it needs to be glazed.
Firing Clay is hardened by heating it to a high temperature, fusing the clay particles. Primitive pottery is usually fired on the ground or in pits with whatever flammable material is available. Kilns allow a more efficient use of materials and more control over the atmosphere during a firing. The two basic atmospheres, oxidation and reduction, affect the color of the final piece. Glaze A coating of material applied to ceramics before firing that forms a glass-like surface.
Glazes can be colored, opaque, translucent or matte.
Kiln The furnace in which ceramics are fired. Kilns can be electric, natural gas, wood, coal, fuel oil or propane. Materials used to heat the kiln can affect the work: wood ash can build up on the surfaces of a piece and form a glaze at high temperatures. Some potters introduce chemicals into the kiln to influence the effects of the firing. Famed ceramist Beatrice Wood achieved a lustre effect by throwing moth balls into the kiln.
Oxidation (Compare to Reduction) A firing atmosphere with ample oxygen. An electric kiln always gives an oxidizing fire. In a wood or gas firing, the mixture of fuel and air is perfectly adjusted to give a clean burn. Acoma whiteware is fired in oxidation.
Oxides Metal oxides can be mixed with water and applied to the surface of clay. By varying the amount of material applied and rubbed off, the potter can achieve effects similar to stained wood. The most common stain is iron oxide (rust).
Pinch Pots Starting with a ball of clay the potter opens a hole into the ball and forms a bowl shape through a combination of stroking and pinching the clay. Many coil-built pieces are constructed on top of a pinched bottom.
Porcelain True porcelain was being made in China and Korea around 960 AD. Porcelain is a combination of kaolin (a pure, white, primary clay), silica and feldspar. A unique aspect of porcelain is that it can be worked as clay, but when fired properly reaches a state similar to glass. Primary qualities of porcelain are translucency and whiteness. In the 17th Century, English potters invented Bone China to compete with the porcelain being imported into Europe.
Raku Pottery is fired normally but removed when it is red hot and the glaze is molten. It is then usually placed in a bed of combustible materials and covered, creating intense reduction resulting in irregular surfaces and colors.
Reduction (Compare to Oxidation) A firing atmosphere with inadequate oxygen and large amounts of carbon (smoke or unburned fuel). What would have been copper oxide in an oxidation atmosphere will be pure copper in reduction. Reduction allowed the Chinese to develop the sangue de beouf red glazes and gives Raku its metallic finishes. In Indian pottery, Maria's black pieces are the result of heavy reduction; the same piece in oxidation would be a terra cotta color.
Slab Built Clay slabs are cut to shape and joined together using scoring and wet clay called slip. Slabs can be draped over or into forms, rolled around cylinders or built-up into geometric forms. Large forms are difficult because of stresses on the seams and because the slab naturally sags. Some potters get around this by working fibers into the clay body. The fibers burn out during the firing, leaving a network of tiny holes.
Slip A fine, liquid form of clay applied to the surface of a vessel prior to firing. Slip fills in pores and gives uniform color.
Stoneware A high-fire clay. Stoneware is waterproof even without glaze; the resulting ware is sturdier than earthenware.
Terra cotta A brownish-orange earthenware clay body commonly used for ceramic sculpture.
Wheel thrown The term throw comes from Old English meaning spin. A piece of clay is placed on a potter's wheel head which spins. The clay is shaped by compression while it is in motion. Often the potter will use several thrown shapes together to form one piece (a teapot can be constructed from three or four thrown forms).