Find impurities like counting bears, needle tools, exacto knives when kneading
Once the clay is prepared, you can begin creating your piece. There are three methods of construction. The first is handbuilding, which is simply using your hands to squeeze, push or pull the clay. The other two are coil building and slab building. Coil building involves rolling the clay out into ropes and layering them on top of each other. Slab building involves rolling out the clay into flat slabs with a rolling pin or a slab rolling machine. Coils can just be stacked on top of each other, but slabs have to be attached through a process called slipping and scoring. Here you can see the sculptor using a red-based clay called earthenware, which is a porous clay that is fired at a low temperature.
After you have finished your piece, you can allow it to dry out gradually. Once your piece has become stiff and is no longer shrinking, it is considered leather hard. Greenware, however, cannot be fired until it is bone dry to assure that there is not enough water within the clay to boil in the kiln and cause your piece to explode. The initial firing is called the bisque fire, and pottery is called bisqueware after its first firing. Bisqueware is ready to be glazed and fired again.
The temperature at which you should fire your piece is determined by cones. Cones are devices that guage heatwork (the combined effect of time and temperature) in the kiln. Cones were originally created for gas kilns that had peep holes where you could look into the kiln and see if the cones had melted. An easy way to understand the Pyrometric cone chart is to think of the zeros as negatives. So –22 is colder than –5 and –5 is colder than 13.
Glazing is often the coolest part of making a piece. Glazes can be applied any way you can think of. You can paint the glaze on with a paintbrush, dunk your piece in a bucket of glaze, spray glaze on with an airbrush, or even spin it on the pottery wheel and drizzle the glaze over it.
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.
Bisquit or Bisqueware Clay pieces which have been fired once and are unglazed
Kilns and Firing <ul><li>Kilns are used to fire pottery </li></ul><ul><li>Pottery is considered to be in the greenware stage until it is fired </li></ul><ul><li>After its first firing, it is bisqueware </li></ul><ul><li>Bisqueware can be covered with coats of glaze and fired again numerous times </li></ul>
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 goal Fire 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 <ul><li>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 </li></ul>
Key Terms pottery 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