A Pottery Glossary for Beginners
Bat: Thin slab of wood, plaster, or plastic used to support pottery forms during throwing, attached to the head of the potter's wheel by clay body or "bat pins"
Bisque: This term may also be seen as bisc, biscuit, bisqueware, bisquefired, biscuit. Refers to both a preparation firing process and the pottery piece that has undergone the firing. The firing is to a temperature that brings about a physical and chemical change to clay. Atomically attached molecules of water are driven off the individual clay particles and they are fused together transforming them into one piece. This intermediate step in glazed ceramics gives bisque ware the ability to absorb water of the glaze solution causing the glaze materials to adhere to the piece while it maintains its shape. Considered to be in the "low-fire" range, some pieces are never fired above this and are therefore usually less durable.
Bone Dry: The final stage of greenware dried to a completely dry state and ready to be fired. In this stage, the clay is very fragile, non-plastic and porous. Approximately 45-65% of moisture is retained within the clay body.
Chuck: On the wheel, a temporary wet-clay form or reusable bisque-fired form upon which wares may be inverted for trimming.
Greenware: A stage in the production of pottery where a vessel and been from and is going through the drying process necessary before it can be safely fired. There several sub-stages in greenware.
Earthenware: A type of claybody usually associated with low-fired ceramics. Earthenware tends to be more porous than higher fired clays. The relatively low physical hardness of both the clay and the glaze tend to make earthenware less durable then higher fired claybodies and less appropriate a choice for functional pieces.
Leatherhard: A stage in the drying process when a clay object can be carefully handled without danger of the shape being deformed, but the clay is still pliable enough so alterations can be made if desired. Many ceramic artists take great advantage of this relatively short period of time to add personal and unique characteristics to their creations. It is also the stage when attachments, such as handles, are added to wheel-thrown pieces.
Oxidation: In pottery this refers to a process that takes place during the firing stage of production. Oxygen in the air is allowed to enter the kiln to combine with elements in the clay and glaze. This is particularly important so that carbon and sulfur naturally occurring in clay can be "burned off". This takes place between temperatures of 1300 F and 2100 F. While all pottery firings go through a stage of oxidation, when it is allowed to continue throughout the entire process, it is called an "oxidation firing". An opposite effect is known as a "reduction firing".
Reduction: Refers to a glaze firing process or a glaze mixture that is best enhanced when going through this type of firing. What is actually being reduced is the quantity of oxygen that is chemically bonded to any metal oxides in the clay or glaze mixture. To bring about the removal of oxygen molecules, when the kiln temperature reaches the melting point of the glazes used the kiln atmosphere is "flooded" with combustible material, such as gas or wood, thus causing the fire to pull oxygen from the pieces being fired. The duration of the stage varies, but it can be as long as an hour or more. The removal of iron oxide in clay causes a "fluxing" (melting) action thus creating a stronger bond between clay and glaze. In the glaze mixture, reduction brings about a wide array of colors depending on the combination of materials used in the glaze. In general, reduction fired glazes tend to have what is considered warmer tones than those of oxidation glazes. Both have the potential for beautifully produced pieces.
Shrinkage: An irreversible reduction in the size/volume of a ceramic piece or glaze which is caused during the drying and firing process. This differs from expansion and contraction, which occurs naturally as a piece heats and cools. All pieces usually undergo a small amount of shrinkage. It takes a lot of experience and skill to select and work with the right types of clays and glazes so that shrinkage does not deform or otherwise damage a finished piece.
Slump Mold: A typically shallow frame or mold into which a slab of clay is allowed to fall or settle in order to form a vessel. These can be frames with no bottom.
Stoneware: A strong, hard, vitrified ware, usually high-fired above 2,200 F, in which the claybody and glaze mature at the same temperature, forming an integrated clay-glaze layer. This high-firing process brings the clay to a point of maximum solidification without danger of distortion, creating pieces very suitable for kitchenware and other functional pieces.
Underglaze: Decoration applied to biscuit pottery and covered with a glaze.
Wax Resist: Used as a masking medium for application to areas on which no glaze is required.
Wedging: A manual process of preparing clay for use by a potter. Similar to kneading dough, wedging accomplishes three things: a) it removes air pockets present within the clay mass, b) it helps to align the individual clay particles making the process of throwing slightly easier and the clay stronger, and c) it is a final mixing process that tends to even out water concentrations in the clay as well as homogenize the various ingredients in the clay mixture.
