Calcined alumina, can enhance the fired properties of a body. Chamotte, also called grog, is fired clay which it is crushed, and sometimes then milled. Helps attenuate drying shrinkage. Bone ash, produced by the calcination of animal bone. A key raw material for bone china. Frit, produced made by quenching and breaking up a glass of a specific composition. Can be used at low additions in some bodies, but common uses include as components of a glaze or enamel, or for the body of fritware, when it usually mixed with larger quantities of quartz sand. Various others at low levels of addition such as dolomite, limestone, talc and wollastonite. Production The production of pottery includes the following stages: Preparing the clay body. Shaping Drying Firing Glazing and decorating. (this can be undertaken prior to firing. Also, additional firing stages after decoration may be needed.) Shaping Before being shaped, clay must be prepared. This may include kneading to ensure an even moisture content throughout the body. Air trapped within the clay body needs to be removed, or de-aired, and can be accomplished either by a machine called a vacuum pug or manually by wedging. Wedging can also help produce an even moisture content. Once a clay body has been kneaded and de-aired or wedged, it is shaped by a variety of techniques, which include: Drying Prior to firing the water in an article needs to be removed. A number of different stages, or conditions of the article, can be identified: Greenware refers to unfired objects. At sufficient moisture content, bodies at this stage are in their most plastic form (as they are soft and malleable, and hence can be easily deformed by handling). Leather-hard refers to a clay body that has been dried partially. At this stage the clay object has approximately 15% moisture content. Clay bodies at this stage are very firm and only slightly pliable. Trimming and handle attachment often occurs at the leather-hard state. Bone-dry refers to clay bodies when they reach a moisture content at or near 0%. At that moisture content, the item is ready to be fired. Additionally, the piece is extremely fragile at this stage and must be handled with care. Firing Firing produces permanent and irreversible changes in the body. It is only after firing that the article or material is pottery. In lower-fired pottery, the changes include sintering, the fusing together of