Pottery and Ceramics

There are many discussions about the definitions of pottery, porcelain, earthenware, ceramics and china. For those of you who wish to understand the process of production or manufacture and the materials, we have defined the basics and provided the resources to get you started or help you develop new techniques or ideas for your craft.

Ceramics means the art of making any article of clay, as in its original and true meaning. Americans use the word to cover all the silicate industries where the burning process is essential in production. Pottery or Earthenware is opaque, somewhat porous, non-vitrified ware. Porcelain is clear ware with a body which is non-porous, non-absorbent, or vitrified. To be true porcelain, a piece should show the shadow of your hand when held before light. When a piece of porcelain is struck, there is a clear, bell-like tone. China is another name of porcelain, so used because true porcelain was first made in China. Bone China is a form of porcelain that contains bone ash, made from calcined cattle bones, for added translucency and whiteness. Today, China has become a generic term for almost any dinnerware.

The creation process starts with Clay. There are different kinds of clay and other minerals are added to impart desired qualities to the finished product. Clay and these other materials are mixed with water to make Slip. Then the impurities are removed, the water pressed out, the clay is dried, the air expelled. Now the clay is ready to be shaped. This is called Forming. The making of a piece of clay into an object.

There are several common methods. Casting is where the slip is poured into plaster molds. The plaster draws moisture out of the clay so the ware can be handled when it is unmolded, commonly called greenware. Throwing is forming a piece of ware by hand, on a potter's wheel. Jiggering is a process for making plates and other fairly flat items. The clay is placed on a form that represents the top of the piece, pressed down and spun. A template representing the outline of the underside of the piece is placed against the clay and finishes the shaping.

The term Body is usually used when referring to the color and composition of the clay. Keep in mind that the color of a piece of ware can be in the body or on it. Bisque ware (also biscuit ware) is any clay ware that has been hardened through a first firing. Embossed ware has a raised or molded decoration produced either in the mold or formed separately and applied before the first firing. Sprig is a molded piece of clay applied to the greenware with slip.

Slip trailing is another decoration method. Slip (a liquid clay) is applied to the greenware through a tube or nozzle, much like icing a cake. The Gadroon Edge is an in-the-mold decoration, usually found on the edge or rim of an item, that resembles a braided rope. Pate-sur-Pate (French) was first employed in China during the eighteenth century. It is the successive application of semi-fluid clay to build up a design in slight relief.

The base clay is often the determining factor for how a ware is named. Redware is made from a clay with a high amount of ferrous oxide, which gives the body its red color and usually has a lead glaze. Terra Cotta (from the Italian meaning "cooked earth") is a hard, semi-fired, absorbent clay used for both decorative and construction products. The colors can range from grayish to dark reddish-orange, light ot medium reddish-brown, or strong brown to brownish or deep orange.

Yellowware the body color varies in hue from ecru to mustard and is made from a naturally occurring clay. White ware is pottery or porcelain with a white body, so called to distinguish it from Redware or Yellowware. White Granite has ground stone used in the body. The color varies from creamy white to bluish or grayish-white. The process makes the ware harder and stronger than earthenware. White Granite is also referred to as White Ironstone, Pearl China, Pearl Granite, Porcelain Granite, Flintware and Opaque China all commercial names intended to inspire confidence in the strength of the ware.

Stoneware is made from some clays which have some impurities in them so that they burn to a dark color. Will stand a relatively high temperature and burn to a dense hard body, as hard and non-porous as china, but lacking the light color, delicacy, and translucency. They are usually covered with a salt or lead glaze. Vitrified is a glass-like, non-porous ware which has been fired at a higher temperature than earthenware and contains silica, which makes a body non-absorbent.

The Kiln is an oven-like structure for firing the greenware, glazes and decorations. These are not fired together, as each requires different firing temperatures. The Glost Kiln is used for firing glazed pieces, decal-decorated pieces, the firing is not as hot as the bisque firing nor as long. The Firing is a process of heat treatment of clay based products for the purpose of securring resistance and permanency of product, it is also called burning.

Art Pottery and Ceramics are ornamental ware either hand decorated by the artist or glazed with a special controlled effect. In the strictest sense, pottery and ceramics made and decorated by hand. Where casting is used the mold was made by the artisan. Various techniques of glazing for the finishing design will cause very different results and is a matter of choice to the artisan.

The Under Glaze is used if designs or colors are put on the bisque before it is glazed. Print and paint is where the outline of a design is printed on bisque and filled in with color by hand. It is a popular decorating method, giving the artist wide creativity in design and color.

Glaze is a mixture of mineral substances, either transparent or colored, which will melt and harden on the surface of the clay body during the glost-firing process. The purpose is to cover the ware to make a porous body nonporous, secure greater permanency or to beautify an object.

Overglaze, when decorations are applied to the ware after the glost-firing, they are known as overglaze decorations. The colors are apt to be brighter and sharper. You can identify overglaze decorations by running your finger over the ware from the background to the decorations. If you feel a change in texture, it is an overglaze.

Engobe is a white or colored slip used as an intermediate layer between the body of an article and the glaze. Sometimes a white engobe is used over colored clays so that the ware appears to be made of white clay.

Matte Glaze is a flat, non-gloss finish, sometimes rough. Crackle also Craquelle is a glaze that intentionally has minute cracks in the surface finish which are caused by the uneven contraction of glaze and body. It gives a ware an interesting finished texture. Lead Glaze contains lead oxide and creates a very shiny finish.

Salt Glaze is created by throwing salt into the kiln where it vaporizes and combines with the silica in the body of the ware, producing a shiny glaze. Dipping is a process of covering a bisque body with a glaze by immersion in the liquid, either by hand or machine.

Decorating the ware can be accomplished by adding decals, lines, designs, decorative highlights or banding. Gilding is the application of precious metals such as gold or platinum (which represents silver).

Lining is a decorative process where a thin line of gold, silver or a color is applied to the ware by hand. If a wide line is applied it is called Banding. A decoration is achieved by scratching through a surface of slip or glaze to the body underneath, it is called Sgrafitto. The surface beneath is often a different color and sometimes a Sgrafitto design is filled in with a color.

Parian is unglazed porcelain (bisque ware) intended to resemble marble. Sponge Ware is where the color is applied with a sponge or rag in a random or precise pattern.

An artisan has unlimited methods of applied decoration to any ware they create. Many create a design or method that is unique to represent their own style and creativity.

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