May 16, 2011

Tips to Classify Clay

For the purposes of the hobbyist, it might be advantageous to classify clays according to their ultimate purposes. This article will help you how to classify clays.

First, there is pottery clay. Probably the two kinds most used are gray stoneware and terra-cotta clay. Both will produce good plastic, workable pottery clay. The stoneware clay fires a light buff and permits the use of lighter and more brilliant colors in glazing. The terra-cotta clay fires a reddish-brown and consequently darkens all glaze colors. This should be considered when choosing clay for a project. If both types of pottery clay can be obtained, they will increase the possibilities available in decoration and colors. Terra cotta is especially suited to sculpture, and is best left unglazed as the warm color and matte surface produce an effective appearance.

Next is sculpture clay, particularly desirable for this purpose because it is stronger, more rigid, and can take more stress and strain than other clays. It contains an addition of grog. Sculpture clay can be bought prepared or made by mixing grog about 20% by weight with either of the pottery clays.

Finally, there is jewelry clay. The requirements for jewelry clay are quite different from those for pottery or sculpture clay. As the object to be made is smaller in volume, the details must be finer and sharper, the colors on the finished piece should be more vivid, and the firing temperature need not be as high. Therefore, fine-grained white clay, with a high percentage of flint, is recommended because it gives brilliance to the glaze colors and fires at a low temperature.

Preparing and Storing Clay
Whenever possible, it is simpler to buy clay in a moist state, but it can be purchased in dry powder form and mixed as needed. This will require several days, depending on the atmosphere and the temperature of the room in which the clay is mixed.

To prepare clay from the dry powder: The powder should be spread in a sink, tub or flat pan and mixed with water to the consistency of thick molasses. All lumps should be removed by stirring. Allow water to evaporate until the clay reaches a slushy state, and then spread it on plaster bats to dry. Turn and press the mass before a crust develops on either side. When it passes beyond the sticky state to a soft firmness, remove it from the bats, wedge and store it.

Clays are of many kind, it uses are of different types, depending on the types and quality of model to be make. From the above article you can know what type of clay will match your model.
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