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 comes in red, such as terra cotta, white or cream, and other shades.   

          Stoneware clay may be either midfire or high fire, depending on its maturing temperature.  Stoneware is much less porous than earthenware and more resistant to scratching and chipping.  This is due to the higher maturing temperature of the clay and bonding of the glaze with the clay during the final firing.  Wonderful effects in the glaze may be seen due to this interaction, but glaze colors tend to be less bright than in lower fired clays.  Finished pieces have a melodic ring when snapped with the finger.  Stoneware clay comes in a wide variety of colors:  red, brown, buff, gray, white, and others.

          Porcelain is a special type of stoneware clay, which results in white or off-white ware often 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 midfire porcelain which fires to slightly off white and produces very strong chip resistant ware.  However, I also occasionally use stoneware and earthenware clays.  My preferred glazes are transparent, translucent, or white glazes which enhance the light color of the porcelain and also make a nice canvas for the colored designs I brush on.  In addition, I use a number of colored glazes as accents for my pieces.