Ceramics. Primary Clay Clay found at the original site where it was formed by decomposing rock...
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Transcript of Ceramics. Primary Clay Clay found at the original site where it was formed by decomposing rock...
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