Bat (or Throwing Bat) - a piece of varying material (plastic, wood, metal, etc.) to separate the clay from the wheel head in order to throw multiple pieces.
Biscuit/Bisque - Round 1 of firing is over, the piece is fired but not glazed
Calipers - A pair of compasses made of plastic, metal or boxwood – used for checking and comparing measurements of pottery e.g. when fitting lids, when producing sets of similar dimensions.
Casting - Forming pottery by pouring slip into a porous mold, usually made from potters plaster.
Casting Slip - A very fluid slip of high specific gravity, obtained by deflocculation and used for forming ware using the casting process.
Ceramic - Derived from the Greek ‘Keramos’ meaning ‘earthen vessel’. Today it applies to a whole range of products, i.e. bricks, tiles, pipes, porcelain, china, pottery, etc.
Chittering - A series of small irregularities on the outer edge or rim of pottery ware. Mainly caused by incorrect fettling.
Crawling - Movement of glaze over the body surface during the gloss firing stage, due to dust or grease on the surface or over application of the glaze or excessive colloidal material in the glaze.
Crazing - A network of cracks in the glaze caused by tensile stresses greater than the glaze is able to withstand. These may result from mis-match of the glaze with the body.
Cutting Wires - Wire attached to wooden or plastic holders at both ends to ensure firm, straight cutting of clay.
Dipping - The application of a glaze by immersion and then allowing the excess to drain off.
Earthenware - A moderately porous pottery body that is fired to a temperature somewhat below that required to produce a vitreous article. Typically 1060 to 1100 C
Extrusion - The process of forcing clay through an aperture or die. e.g. through a pugmill.
Glaze - A thin glassy layer formed on the surface of a ceramic article by the exposure of the glaze coated article to a high temperature. Glaze is usually applied in the form of a suspension of ground glaze in a liquid medium, to the clay or biscuit surface of the article.
Glaze/Body Fit - The relationship between thermal expansion of body and glaze. Ideally the glaze should have a lower thermal expansion than the clay body, so that on contraction the body puts the glaze into compression. This avoids crazing of the glaze due to tensile stresses in it.
Glaze Stain - Coloring agent added to a glaze.
Greenware - Unfired clay ware.
Grog - Ceramic material which has been heated to a high temperature to burn off moisture and other gasses therefore is predominantly inert. This is then ground to a required grain size to add to a body formulation.
Kiln - Pottery oven or furnace in which ceramic products are fired. May be fired by wood, coal, sawdust, electricity or gas.
Leather Hard - Partially dried clay ware. The ideal stage for turning, fettling, sponging, etc.
Needle Tool - Used for trimming, carving and piercing clay, as well as measuring the thickness of bases while throwing and unglogging glaze holes.
Pin Holes - A glaze or body fault resulting from trapped air erupting through the body or glaze during maturation in the kiln.
Pugging - The mixing, blending, de-airing and extrusion of plastic clay bodies.
Rib - ceramic tools made of plastic, wood, metal and rubber and are used to smooth clay while turning with a wheel.
Slip - The suspension of a clay body in water, used for casting ware in molds. Deflocculants are added to keep the clay in suspension.
Stoneware - A ceramic body containing a naturally vitrifying clay e.g. a stoneware clay or a suitable ball clay. Sometimes a non-plastic constituent and a flux are added. See clay chart for vitrification temperatures.
Thermal Conductivity - The rate at which heat passes through a material as measured by its rise in temperature.
Thermal Shock - Thermal shock is the way in which some materials are prone to damage by stresses set up due to differences in temperature in different parts of the article.
Throwing - The technique of forming pottery on the potter’s wheel. A ball of prepared clay is thrown on the wheel and it is centered and shaped with the hands.
Underglaze - Decorative colors applied to ware before the application of glaze.
Vitrification - The progressive fusion of a material or body during the firing process. As vitrification proceeds the proportion of glassy bond increases and the apparent porosity of the fired product becomes progressively lower.
Wedging - A method of de-airing and dispersing moisture uniformly by hand in a piece of clay. The lump of clay is repeatedly thrown hard onto the work bench, turned over and occasionally cut through and re-joined. ex. Spiral wedging, Rams Head wedging
