GLOSSARY FOR CERAMICS

Balance – A state of equilibrium, equality in amount, weight, value, or importance between two things or parts of an object. The pleasing harmony of various elements in a design, painting, musical composition, etc.

Bisque, Biscuit – Fired ware that has not been glazed.  We bisque fire to cone 06, 1830 degrees.

Bisque fire – The first firing, without glaze.

Bone dry – Completely dry clay ware, ready for bisque firing.

Burnishing – Polishing with a smooth stone or tool on leather hard clay or slip to make a surface sheen by mechanically compressing the clay particles.  The ware is usually bonfired or low fired (the surface will not stay shiny at temperatures above 2000 degrees F); the traditional process used in North and South American Indian pottery.

Contrast – A difference between two things being compared. The effect of a striking difference between two tones, shapes, or textures/surfaces.

Coil – A piece of clay rolled like a rope, used in making clay forms.

Cones – Pyrometric cones are pyramids made of clay and glaze constituents that soften and bend at specific temperatures.  Cones are placed in the kiln during firing as a guide, and to indicate the final heat; numbers coded to their softening point classifies them.

Extruder – A device that forces clay through a die, creating a consistent cross section throughout the length of clay.  Used to make coils, handles, wall shapes, tubes.

Firing – (1) Heating in a kiln to the required temperature for clay or glaze. (2) Bonfiring in a pit or on the ground. We use electric kilns and a gas fired downdraft kiln.

Glaze – Glassy melted coating developed by chemicals and heat on a clay or metal surface; technically, an impervious silicate coating formed by the fusion of inorganic materials.  Glaze has a similar oxide composition to glass, but also includes a binder.  Glaze provides decoration and color, prevents penetration of liquids or acids, and yields a matt or glossy, easily cleaned, functional surface.

Glaze firing – The final firing, with glaze.

Greenware – Finished leather hard or bone-dry clay pieces not yet fired; raw ware.

Incising - Carving lines with a tool or knife into a clay surface.

Leather hard - clay that has dried enough to be handled without becoming distorted, but which contains sufficient moisture to permit joins to be made and slips applied without cracking.  Incising, carving, and stamping are most conveniently done at this stage, because the clay cuts cleanly and does not stick to the tool.  Thrown forms are usually trimmed at the leather hard state.

Kiln – A furnace of refractory clay bricks for firing clay ware.

Metaphor – Something used to represent something else; emblem; symbol.

Oxidation – Firing with a full supply of oxygen.  Electric kilns fire in oxidation.

Pinching – Moving and shaping clay, usually with the fingers.

Plastic – The quality of clay which allows it to be manipulated into different shapes without cracking or breaking, its workability. Clay with a water content of 25 – 30% is usually elastic enough to be considered plastic.  Some clays are more plastic than others; ball clay is more plastic than kaolin.  Most commercial clays are combinations of various clays used for their particular qualities, together making the most useful composite.

Pontifex – Literally, path-maker or bridge.  See metaphor.

Proportion – The comparative relationship between parts, things, or elements with respect to size, amount, degree, etc.; ratio, (height/width).

Reduction – Firing with reduced oxygen in the kiln.  Reduction is the result of incompletely burned fuel in the kiln and chemically affects clay and glazes.

Sagger – (1) Refractory container in which pottery is stacked during firing for protection from direct flame or atmosphere. (2) A container for holding fuming materials such as metal oxides, chemical salts, and organic substances, that will act on the ware in the saggar during the fire.

Sgraffito - Incising through a layer of slip to reveal the clay underneath. This is best done when the slip is leather hard.

Slip – (1) Clay that has been thinned with water to a smooth consistency suitable for painting or trailing with a rubber bulb on leather hard clay.  Some slips are colored with the addition metallic oxides.  Colored slips affect the final glaze color.  (2) Clay that has been thinned with water and used as an aid in joining leather hard pieces; slabs, handles, etc.

Space – The distance, expanse, or area between, over, within, etc. things.

Stain – Oxide and water, used to color bisque ware and for brush work on glazes.

Stoneware – All ceramic ware fired between 2,100 and 2,300 degrees F.

Stamping - Pressing a design into clay, best done when the clay is softer than leather hard.

Stiff – The state of clay between plastic and leather hard.  This is a good time to smooth the surface, join pieces, add texture, or stamp.

Terra Sigillata – An extraordinary fine ground clay suspension in water that shines when applied as a coating and fired at low temperature (the molecular structure changes at high fire, destroying the sheen).

Wedging – A method of kneading clay to make it homogenous.