Ceramics

Primary Clay

Clay found at the original site where it was formed by decomposing rock

Secondary Clay

Clay that has been transported from its original site by water, air or ice and deposited in layers elsewhere

Earthenware

Clay that hardens at a low temperature but remains porous (able to absorb moisture). Earthenware is a

secondary clay.

Porosity

The capacity of a clay body to absorb moisture

Preparing Clay

Before making anything with clay, whether by hand or on the pottery wheel, the clay must be wedged so that it can survive the firing process. Pottery will explode in the kiln if air bubbles or impurities are in the clay or if certain areas are drier than others. In order to remove any air bubbles and evenly distribute water throughout the clay, it must be repetitively kneaded.

Plasticity

The quality of clay that allows it to be easily manipulated and still maintain

its shape

Leather hard

The condition of unfired clay when most of the moisture has evaporated

leaving it still soft enough to be carved into or joined to other pieces.

Clay should be leather hard when building with slabs of clay

Bone dry

The condition of unfired clay when it is as dry as possible prior to firing

Wedging

Mixing and de-airing clay by cutting it diagonally and slamming the pieces

together.

Kneading

Working clay on a surface with the palms of the hands in order to remove

air from it and obtain a uniform consistency

Clay Building Techniques

Coil building

Slab building

Coil

A rope-like roll of clay used in hand building

Slurry/Slip

A creamy mixture of clay and water often used as a glue to bond two

pieces of clay together

Viscosity

The property of a liquid to resist movement. (Water has a low viscosity while syrup has a high

viscosity.) Slurry should have a viscosity similar to that of pudding to be used for gluing pieces of clay

together.

Clay Modeling Tools

Clockwise from bottom left: wood rib, sponge, ribbon tool,

loop tool, needlepoint tool, wood modeling tool, wire clay

cutter, steel rib

Rib

A hand held tool made of hard material used for shaping ceramic

pieces and compressing clay particles

Kiln

A furnace, built of refractory (resistant to heat and melting)

material, for firing ceramic ware

Firing

The heating of clay or glaze to a specific temperature

Greenware

Unfired clay pieces

Bisquit or Bisqueware

Clay pieces which have been fired once and are unglazed

Kilns and Firing

•Kilns are used to fire pottery•Pottery is considered to be in the greenware stage until it is fired •After its first firing, it is bisqueware

•Bisqueware can be covered with coats

of glaze and fired again numerous times

Warping

Distortion of a clay shape cause by uneven stresses during shaping,

drying or firing

Cone Firing

Pyrometric cones are devices that gauge heatwork (the combined effect of both time and temperature) when firing materials inside a kiln. Cones range from 022 (the coolest) to 42 (the

hottest). Earthenware clay is fired around 1900 degrees Fahrenheit, or between cone 06 and

cone 04.

Cone

Small, pyramid-shaped forms of ceramic materials made to bend and

melt at specific temperatures and gauge the temperature of the kiln

Pyrometric Cones

Guide Cone: One cone number below your goalFire Cone: The cone number you wish to achieve

Guard Cone: One cone higher than your goal

Glaze Techniques

Glazes can be applied with any technique imaginable. The most

common applications are painting, dipping, or spraying.

Glaze

A glass-like coating that is bonded to a surface through heat

Vitreous

Glass-like; hard, dense, and non-absorbent

Glaze Firing

A second kiln firing after the initial bisque firing in which glaze materials are heated sufficiently to melt and form a glass-like coating over ceramic pieces when cooled

Key Termspottery that has been fired but not yet glazed

ceramic ware made of porous clay fired at low heat

pottery that has not been fired

stage in the drying process of clay where all shrinkage has occurred

clay that has been saturated with water to create a thick liquid

process of cutting grooves into a piece of clay where another scored piece will be attached

method of de-airing and dispersing moisture uniformly by hand in a piece of clay

devices that gauge heatwork (the combined effect of both time and temperature) when firing materials inside a kiln

Bisqueware

Earthenware

Greenware

Leather hard

Slurry

Scoring

Kneading

Cone