This is clay in its raw, natural state when dug up from the ground. The color and working properties depend on the location where it is found and the minerals and impurities present in the clay. Raw clay is difficult to work with and may break when dried or fired in the kiln due to impurities. Various additives are used to make the clay malleable (plastic) and safe to fire.

Clay is mixed and “pugged” (de-aired) in a special machine to produce “plastic” or prepared clay ready for use. *Knightdale High Art Department is one among a very few number of schools in North Carolina to own and operate a mixer/pugmill

Wet or Plastic clay (prepared) has been processed to remove most air bubbles and impurities. Water and various additives have been included to make it more malleable, fire more evenly, etc. It is called “plastic” because this is the stage where it is easiest to manipulate. The clay we use is called Earthenware. It is a low fire clay. Earthenware clay can be white, red, buff or other colors Click on image to view video

Overworking your wet clay: Excessive folding, cutting into it, poking fingers in it, etc.) will dry out the clay and cause cracks. Worse, it will create air pockets. When the clay is placed in the kiln and heated the air will expand and result in an explosion that destroys the piece.

Prepared clay that has been soaked in water is called Slip. It can be quite runny or a thicker consistency like mayonnaise or yogurt, depending on the need. Slip can be poured into molds to make hollow forms or used as glue to bind two pieces of moist clay together. Slip can also be used to paint designs on moist or leather hard clay Click on image to view video

When clay has dried to a point where it holds its form but maintains a degree of moisture so that it feels and works like a piece of leather it is called leather hard. Although it's still semi moist it is strong enough to support itself and keep its shape when pressure is applied. This is the stage where designs can be carved or a handle added.

Green ware is when clay is completely air dried. And since Green ware is basically dried mud any contact with water will return it to its plastic or slip stage. This stage is also when a clay piece is most fragile; the slightest pressure or vibration can easily damage the piece. Clay must pass through this drying stage before it can be put in the kiln for its initial bisque firing. Any excess moisture left in a piece will expand into steam in the kiln and destroy the work.

Up to this point your clay piece is basically dried mud. Any contact with water will return it to its plastic or slip stage.

Bisque ware is clay that has undergone a first firing in a kiln. A kiln is a high temperature oven that can reach up to 2600 degrees. After about 660 degrees the heat begins to evaporate the last molecules of water. When the kiln temperature reaches the maturing point of the clay (about 900 degrees) it transforms it into ceramic material. At this stage it can no longer be affected by water nor changed in any way. However, it is still porous and will not hold water for very long. Bisque is the preparatory stage for glazing. Click on image to view video

Once your piece has been bisque fired it needs to be colored using water colors for a subtle, interesting look. Remember that once watercolor is applied it stains the porous bisque body and cannot be removed

Once your piece has been bisque fired it needs to be glazed and fired again to enable it to hold liquids. Unlike paint, glazes cannot be mixed to create secondary colors. Glazes are chemical/mineral formulae that mature at a specific temperature to create a glassy coating in the desired color. Mixing them corrupts the formula and creates unpredictable results. Click on image to view video

Modern digital kilns do not use these cones but we still use the terminology to determine firing temperatures. And some potters still prefer to use pyrometric cones rather than rely on a digital thermometer. Cones are ceramic based and melt at a specific temperature. Cones of varying temperature levels are packed together and placed inside the kiln near a viewing portal. The potter watches the cones and as the correct temperature cone begins to bend he shuts off the kiln.

Ceramic glazes are designed to mature at a specific temperature or cone number. Cones range from a cooler cone 022 to a very hot cone 10. We bisque fire our earthenware clay at cone 04 and glaze fire at cone 05. Therefore, the bisque fire is a bit hotter than the glaze fire. This assures that all moisture and carbon have been burned out of the clay body before we add the glaze. CONFUSED? Just think of it in terms of a thermometer where 4 degrees (cone 4) is warmer than minus 4 degrees (cone 04)