Types of Clays

ost clay bodies that you will come into contact with are secondary clays that have been adjusted, or completely formulated clay bodies. In the formulated clays, the natural ingredients such as kaolins, ball clays, bentonites and other ingredients are mixed up to create a clay body of a particular type, e.g. a white earthenware. You can make your own clay bodies according to available recipes, experiment with your own variations or just buy a commercially manufactured clay from a potters supply shop.

Clay Bodies

• Earthenware
  This is the most common type of clay. Terra-cotta is one type of earthenware that is relatively coarse and red in color. Other earthenware bodies may be finer and have various colors, ranging from white to gray, buff and red. Earthenware clays are usually fired between 1700o F (927o C) - 2100o F (1150o C). At this temperature the clay body is still porous and needs to be glazed, e.g. if it is to be used as dinnerware.
• Raku
  Raku bodies originated in Japan around the 16th C. They were commonly used in the Japanese Tea Ceremony. They are a type of 'rough' earthenware that harden at lower temperatures and must withstand the thermal shock of a Raku firing. To this end, they often contain a large amount of fire clay and grog (clay sand).
• Mid-Fire
  Mid-fire clays are a type of hybrid earthenware/stoneware clay that matures in between the two temperature ranges. This means that it is possible to get the qualities of the higher fired stoneware, while saving money and fuel in the firing. Mid-fire clays typically mature around 2100o F (1150o C) - 2265o F (1240o C)
• Stoneware
  Stoneware clays are fired up to 2370o F (1300o C), where they become quite hard and vitreous. Colors range from off white to gray and dark brown. There are also various degrees of roughness or fineness, depending on the formulation. This the hardest, most durable type of clay.
• Porcelain
  Porcelain is a totally manufactured clay. While it is not synthetic as such, various natural ingredients are refined and mixed up according to formulas. A good porcelain must be very white, vitreous, translucent while at the same time being plastic enough to work with. Porcelain is fired from 2335o F (1280o C) to 2550o F (1400o C).

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