CERAMICS VOCABULARY LIST Pea Ridge High School Pea Ridge, AR Teacher- Anya Bruhin abruhin@prs.k12.ar.us Ceramics - Objects made of clay fired sufficiently high in temperature for a chemical change to take place in the clay body, usually over 1550 degrees F. The word comes from the Greek keramos meaning clay. Clay A product of the geologic weathering of the surface of the earth. Residual clays are brittle and were once rock that has dissolved within the earth over a very long time. Sedimentary clays are the most plastic and are blown by the wind. They mix with organic matter as they gather in moving water and collect in lakes and rivers. Ex. Stoneware, Porcelain, Earthenware. Stoneware - Gray, reddish or tan clay that has been high fired (cones 5 to 10.) Earthenware A brittle, low fire clay that is usually red or orange. Fat Clay Clay with a high plasticity. Plasticity Refers to the quality of clay that allows it to be easily manipulated and still maintain its shape. Bentonite increases this quality. Feldspar A white crystal found in granite comprising of silica, alumina and a flux in the form of sodium, potassium, or calcium. Feldspar is the matrix of all clay. Bentonite - The most plastic material known to man comes from volcanic ash and is added to clay to make it more plastic or flexible. Grog Clay that has been fired to dehydration and ground into powder. Added to clay bodies to reduce shrinkage and add strength. Kaolin Pure high firing residual clay. China Clay High fire clay made from a mixture of Kaolin and Porcelain. Porcelain The highest firing sedimentary clay. A refinement of stoneware made from china clay, feldspar and quartz.
Foot The base of the vessel. Also, the edge of the base that keeps the bottom of the vessel off the table top. Lip Top edge of a ceramic vessel. Shard Piece of broken pottery. CERAMIC CONSTRUCTION TECHNIQUES Coiling - 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 or size. Pinching - 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. Slab Building - Clay slabs are rolled or thrown and cut to shape and joined together using scoring and wet clay called slip. Draping - Slabs are rolled or thrown and draped over a mold only long enough for the shape to set. Casting - Casting may be done in two ways: A. slabs are laid or pressed inside a plaster or other mold and pop out when dry. B. slip is poured into a plaster mold tilting until the surface is covered. The slip adheres evenly to the entire surface and excess is poured out. The clay dries and pops out of the mold. Carving - A chunk of clay is modeled by using tools to cut away portions of the clay body. This process is best done with clay is not too soft as pushing on it will displace the clay. Scoring and Slipping- This is the process by which a piece of clay is joined with another. Score the clay by scratching the surface of both pieces to be joined. Then add slip to both pieces and mush together until slip oozes from the crack. Paddling Gently beating the clay to strengthen walls and joints and/or creating texture. Helps refine the shape of the clay.
Burnishing- Rubbing leatherhard clay with a smooth (metal or plastic) object to create a shiny smooth surface. Throwing Refers to the creation of clay vessels on the potter s wheel. Fettling The process of removing seams from casted pieces. TOOLS Armature- something to support clay while it is being formed, such as newspaper or a drape mold Bat- a round, flat top, plate or bowl shaped object on which pottery is built. Bats can be made of Plaster-of-Paris, wood, or plastic. Native Americans called the flat rocks they used as bats Pokies. Caliper- measuring tools for checking symmetry and fitting lids to pots Canvas- thick material draped over pieces of wood used as work surfaces and transporting pieces Clay paddles- stick (or spoon) for paddling clay for evenness Drape molds- molds of plaster for draping a slab of clay until leather hard Extruder- tool that uses lever system to force clay through holes to create certain shapes, especially when coil building. Fettling knife- Flexible flat knife used for scraping and shaping clay. Hardwood tools- boxwood tools with a variety of end shapes for modeling clay Loop tools- tools with ribbons of wire for shaping and trimming Plaster-of-Paris Partially dehydrated calcium sulfate (gypsum.) Used in bats, wedging, and molds. Pulls moisture out of clay.
Ribs- shaped pieces of wood, metal, or rubber for shaping, smoothing, or scraping clay Rolling pins- for rolling out slabs Turntable (banding wheel) - decorating or sculpting wheel for turning work while forming Wedging table- surface for kneading moist clay to eliminate air bubbles and produce a uniform texture Wire cutter- thin gauge wire between two small pieces of wood for cutting clay from a block Pug Mill A machine that mixes dry clay with water. It grinds and mixes plastic clay until it is firm. STAGES OF CLAY Leather hard - A damp condition of the clay when it is too firm to bend yet soft enough to be carved. A time in the drying process when it becomes impossible to add more clay to the vessel or sculpture. Plastic stage - clay is easily manipulated and bent. Greenware (bone dry stage) - Unfired clay ready or nearly ready for firing. No visible moisture - no dampness to touch clay, should not feel cold. The clay has hidden moisture inside (chemically combined water) that must be allowed to evaporate during the first hour of firing. Bisqueware - Clay that has been fired once, usually at a low temperature. Vitrify - A glassy, non-porous state caused by heat or fusion (what happens when glaze is added then fired.)
COLORING AND DECORATING CLAY 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). Engobe - A white or colored thin layer of liquid clay used to decorate a bisque pot. It may or may not be glazed over. 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. Incised - These decorations are surface designs cut into the clay. Mishima - (inlaid clay) contrasting colored slip is inlayed into incised lines. This can be done using wax resist - incising then applying slip. OR slip may be applied to incised lines and sanded off the raised body. Sgraffito - This comes the Italian word meaning "scratched through" and is done by incising or cutting a design through a colored slip coating to reveal the clay body. Luster Refers to the amount of shine on a burnished or glazed vessel. FIRING CLAY 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. Bisque Fire Firing of clay until it is fully dehydrated and the chemically combined water has been driven out. Fired usually around cones 04, 05, 06.
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. Kiln Wash - A mixture of china clay and flint in water solution used to coat kiln shelves to protect them from dripping glaze. Cones (Pyrometric) small pyramids of glaze materials which bend and melt to indicate the degree of heat attained in the kiln Flux Lowers maturing temperature of clay (helps clay melt.) Examples: Borax, Cargonite and Lead Kiln Shelves - The shelves inside a kiln that ceramic greenware is stacked on in the kiln. The shelves must be coated with kiln wash to prevent glazed pottery from sticking to the shelf. Shelf Supports (or props) - Thick posts used to hold shelves in a kiln. Stilt - A triangular support for clay pieces that helps prevent glaze from melting on to shelves during a firing. Elements - Coils of high temperature resistance wire that convert electricity to heat. Maturing Point - Time and temperature needed to completely fire a glaze or clay object to the "vitrified" state. 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.
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 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. 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. GLAZING Glaze - A coating of material applied to ceramics before firing that forms a glasslike surface. Glazes can be colored, opaque, translucent, or matte and render the vessel waterproof. Glaze Fire Firing the clay vessels in a kiln until the glaze has matured. A cycle during which glaze materials are heated sufficiently to melt and form a glass-like surface. Matte glaze - Dull-surfaced glazes, lusterless and non shiny. Crackle - Minute decorative cracks in the glaze that are often accentuated by rubbed-in coloring material. This is caused by the glaze shrinking more than the clay during cooling. Dipping A method of glazing by immersing bisqueware in a container of glaze. Dry footing - Glaze is removed from the bottom of a piece before firing, making stilting unnecessary. This is typically done using wax to resist the glaze on the bottom of the piece. Crazing - The fine network of small cracks that occurs on glazes. The Japanese encourage crazing and will stain cracks with concentrated tea.