Ceramics
syllabus
vocabulary
glazes
oxides
clay
safety and fees
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VOCABULARY
absorbency - the ability of a material to soak up water
Albany slip - a natural clay containing sufficient fluxes to melt and function as a glaze alumina (AL2 O3) - a major ingredient found in all clays and glazes; imparts greater strength and higher firing temperatures to the body and glaze
bag wall - a baffle wall in a kiln, separating the chamber from the combustion area
ball clay - an extremely fine-grained, plastic, sedimentary clay
bat - a disk or slab of plaster of paris on which pottery is formed or dried; it is also used to remove excess moisture from plastic clay
bentonite - an extremely plastic clay, formed by decomposed volcanic ash and glaze
bisque or biscuit - unglazed ware fired to a temperature sufficient to harden but not mature the body
blowing (bloating) - the bursting or warping of pots in a kiln caused by a too-rapid temperature rise; the water content of the clay turns into steam and forces the body to distort or expand and explode
calcine - to heat a ceramic material or mixture to the temperature necessary to drive off the chemical water, carbon dioxide, and other volitile gases
celadon - a glaze characterized by a soft gray-green color that results from firing iron oxide in a reduction atmosphere chemical water - water (H2O) chemically combined in the glaze and body compounds; At approximately 842 degrees F. during the firing cycle, this water will begin to leave the body and glaze as water vapor. Little shrinkage occurs at this point, although there is a loss in weight.
clay - a decomposed granite-type rock; To be classed as a clay the decomposed rock must have fine particles so that it will be plastic. They are classified into various types, such as ball clays, fire clays and slip clays. Pure clay is expressed chemically as: AL2O3 2SiO2 2H2O.
coiling - a hand method of forming pottery by building up the walls with ropelike rolls of clay and then smoothing over the joints
crackle glaze - a glaze containing minute cracks in the surface caused in cooling by the different rates at which the body and the glaze contract after firing
crawling - The separation of a glaze coating from the clay body during the firing caused by too heavy application. This results in exposed areas of unglazed clay.
crazing - an undesirable and excessive crackle in the glaze, which penetrates through the glaze to the clay body
dipping - glazing pottery by immersing it in a large pan or vat of glaze
dryfoot - to clean the bottom of a glazed piece before firing
dunting - cracking of fired ware in a cooling kiln as a result of opening the flues and cooling too rapidly
earthenware - low-fire pottery (below cone 03), usually red or tan in color, with an absorbency of from 5 to 20 percent
engobe - a prepared slip that is halfway between a glaze and a clay; usually applied to damp ware although may be used on bisque ware
escape the best part was pulling down the shades stuffing the doorbell with rags putting the phone in the refrigerator and going to bed for 3 or 4 days. and the next best part was nobody ever missed me. -Charles Bukowski
fire box - combustion chamber of a gas, oil, or wood-fired kiln, usually directly below the kiln chamber
flux - lowest-melting compound in a glaze, such as lead, borax, soda ash, or lime, and including the potash or soda contained in the feldspar; The flux combines easily with silica and thereby helps higher-melting alumina-silica compounds to form a glass.
foot - the ring-like base of a ceramic piece, usually formed by tooling the excess clay
glaze - a liquid suspension of finely ground minerals that is applied by brushing, pouring, or spraying on the surface of a bisque-fired ceramic ware; Glaze ingredients will melt together to form a glassy surface coating.
glaze fire - a firing cycle to the temperature at which the glaze materials will melt together to form a glasslike surface coating
greenware - pottery that has not been bisque fired
grog - hard fired clay that has been crushed or ground to various particle sizes; It is used to open up a raku body or to reduce shrinkage in such ceramic products as sculpture and architectural terra cotta tiles, which have drying and shrinkage problems. Finely crushed grog is also used in throwing bodies to help the clay stand up.
kaolin - pure clay, also known as china clay; It is used in glass and porcelain bodies and fires to a pure white.
kiln - a furnace made of refractory clay materials for firing ceramic products
kiln furniture - refactory shelves and posts upon which ceramic ware is placed while being fired in the kiln
kiln wash - a protective coating of refactory materials applied to the surface of the shelves and the kiln floor to prevent excess glaze from fusing the ware to the shelves
leather hard - the condition of the raw ware when most of the moisture has left the body but when it is still plastic enough to be carved or joined
mat glaze - a dull surface with no gloss but pleasant to the touch, not to be confused with a incompletely fired glaze
maturity - the temperature or time at which a clay or clay body develops the desirable characteristics of maximum nonporosity and hardness; or the point at which the glaze ingredients enter into complete fusion, developing a strong body with the body, a stable structure, maximum resistance to abrasion, and a pleasant surface texture
muffle - a lining, made of refactory materials, forming the kiln chamber, around which the hot gases pass from the firebox to the chimney; the purpose is to protect the ware from the direct flames of the fire and the resulting combustion impurities
muffle kiln - a kiln with muffle features as opposed to a kiln using saggers
neutral kiln - a fire that is neither oxidizing nor reducing
overglaze - decoration applied with overglaze colors on glazed and fired ware; Firing of the overglaze decoration is at a lower temperature than the glaze firing.
oxidizing fire - a fire during which the kiln chamber retains an ample supply of oxygen; This means that the combustion in the firebox must be perfectly adjusted. An electric kiln always gives an oxidizing fire.
porcelain (hard) - a hard, nonabsorbent clay body that is white and translucent; In both types of porcelain the bisque is low-fired and the glaze is very high-fired (generally cones 14-16).
porcelain (Chinese) - a hard, nonabsorbent clay body, white or gray in color, that rings when struck
pyrometer - an instrument of measuring heat at high temperatures
pyrometric cones - small triangular cones (1 1/8" & 2 5/8" in height) made of ceramic materials that are composed to bend and melt at specific temperatures, thus enabling the potter to determine when the firing is complete
raku - glazed, groggy earthenware originated in Japan and associated with the tea ceremony
reduction fire - a firing using insuffient oxygen; carbon monoxide thus formed unites with oxygen from the body and glaze to form carbon dioxide, producing color changes in coloring oxides
refractory - the quality of resisting the effects of high temperatures; also materials, high in alumina and silica, that are used for making kiln insulation, muffles and kiln furniture
salt glaze - a glaze developed by throwing salt into a hot kiln; the salt vaporizes and combines with the silica in the body to form sodium silicate, a hard, glassy glaze
shard - a broken fragment of pottery
short - descriptive of a body or clay lacking in plasticity
silica - flint (SiO2) produced in the United States by grinding almost pure flint sand
single fire - a firing cycle in which the normal bisque and glaze firings are combined
slab construction - a handbuilding method in which forms are created by joining flat pieces of clay; the pieces are thinned and flattened with a rolling pin or slab roller
slip clay - a clay such as Albany or Michigan containing sufficient fluxes to function as a glaze with little or no additions
stain - sometimes a single coloring oxide, but usually a combination of oxides plus alumina, flint and a fluxing compound; the purpose is to form a stable coloring agent not likely to be altered by the action of the glaze or heat
stilt - a ceramic tripod upon which glazed ware is placed in the kiln
stoneware - a high-fire ware (above cone 6) with slight or no absorbency; it is usually gray in color but may be tan or slightly reddish
terra cotta - an earthenware body generally red in color and containing grog; it is the common body type used for ceramic sculpture
throwing - forming plastic clay on potter's wheel
turning or tooling - trimming the walls and foot of a pot on the wheel while the clay is leather-hard
water smoking - the initial phase of the firing cycle up to a dull red heat (1000 degrees to 1100 degrees F./ 537 degrees to 594 degrees C.) ; depending upon the thickness of the ware, this may take from two or three hours for thin pottery, up to twelve hours for sculpture; the heat rise must be gradual to allow atmospheric and chemical water to escape
wax resist - a method of decorating pottery by brushing on a design with a hot melted wax emulsion; this will prevent an applied stain or glaze from adhering to the decorated portions
wedging - kneading plastic clay with the fingers and heels of the hands in a rocking spiral motion which forces out trapped air pockets and develops a uniform texture