Clay and Glazes

Clay is composed of very fine particles of minerals which are broken down from rocks in the earth's crust.  Earthenware is a porous clay which matures at a lower temperature than stoneware and porcelain clay.  Pieces go "clunk" when you snap them with your finger.  Because the glaze sits on top of the clay, rather than chemically interfacing with it, earthenware dishes tend to chip easily.  Glazes scratch relatively easily and colors are brighter and more varied than glazes which fire at higher temperatures.  Earthenware clay may be any color, including red, terra cotta, white, and cream.   

Stoneware clay may be either mid-fire or high fire, depending on its maturing temperature.  It is much less porous than earthenware and more resistant to scratching and chipping, due to the higher maturing temperature of the clay and bonding with the glaze during the final firing.  Although glaze colors tend to be less bright than those in the low-fired range, wonderful effects may be achieved through interaction with the clay and with other glazes.  Finished pieces have a melodic ring when snapped with the finger.  Stoneware clay comes in a wide variety of colors, including red, brown, buff, gray, white, and others.

Porcelain is a special type of stoneware clay, which results in white or off-white ware, occasionally having a translucent quality.  It fires to mid or high fire ranges.  The glaze-clay interaction is even greater in porcelain than in stoneware clay, resulting in ware of superior strength.

Glazes are composed of raw materials, such as feldspars, whiting, and silica, which are mined from the earth's crust.  Glaze colors come from a variety of oxides, such as iron, chrome, and cobalt.  Stains are colorants in which the oxides have been especially prepared to be stable.   

My clay of choice is a mid-fire porcelain which fires from cream to slightly off white in color and produces very strong, chip-resistant ware.  However, for other applications, particularly pit and saggar fired ware, I lean toward earthenware or stoneware clay.  White satin glaze is my first choice for pots on which a design will be hand brushed.  Huckleberry and floral designs are often accented with a colored glaze dripping down from the rim.  For most other functional ware, a combination of glazes adds color, beauty, and interest.  

The Process      Throwing      Trimming      Firing