1. The Origin of Clays - The term clay is applied to natural earth deposits that possess and display the singular property of plasticity. Clay is the product of the ageing and decomposition of granite, feldspars, an pegmatite's, which have been subjected to the actions of water wind, glaciers, and plate tectonic movements over millions of years, plus the chemical action of the water, carbon dioxide, humic acids, and less commonly, sulfur and fluoride gases, aide by elevated temperatures.

2. Two categories of clay- Primary or residual Less plasticity, less fine grain Remain in original location Secondary or sedimentary More plasticity, finer Transported from original location Found near water beds

3. Once clay is extracted from the deposits, they are exposed to the elements for several years. One of the processes that gives clay its plasticity is aging. The next step is grinding. The clay is fed through mills, where it is crushed, then mixed with water and set aside. Various sifting processes are undergone and finally mechanically wedged then wrapped in plastic.

4. Clay is one of the oldest materials Geologists classify clay into two groups, residual (primary), or sedimentary (secondary). Sedimentary clays are used in pottery because they are looser and malleable. top, clockwise: Raku, Red earthenware, White earthenware, Buff stoneware, White stoneware, and Porcelain

5. These clays are made of various types of clays and contain a high proportion of alumina and silica. One of these are terra- cotta clay. This clay is high in iron oxide content which gives this clay its color; it is considered a low temperature clay. Sculptural clays are resistant to high temperatures.

6. White Earthenware is difficult to distinguish from white stoneware or porcelain after a bisque firing because they all fire to the same color. These are very plastic, porous bodies with a characteristic grayish color in their raw state, although after firing they are white. White earthenware is often used to produce slip-cast forms, dishes, small sculptures and wall tiles.

7. Stoneware We will be working with stoneware. Stoneware is grayish white, opaque, vitrified clay body. This clay is a high- temperature clay. It is sensitive to thermal shock, so they must be heated and cooled very slowly in order to avoid sudden thermal changes, especially in the case of larger, thick pieces.

8. Porcelain Porcelain bodies are white. One of their main characteristics is that they contain only small amounts of impurities from colorants such as iron oxide and titanium dioxide. Porcelain can be used for utilitarian pieces and sculpture.

9. Plasticity- is the capacity of clay to absorb water, or to formed without cracking or rupturing and to retain its shape. Size and shape of clay particles Electrical attraction Carbonaceous matter and bacteria Water Aging If the clay absorbs too mush water, it will become a slip and lose its plasticity.

10. COLORED CLAYSWHITE CLAYS POROUSVITRIFIEDPOROUSVITRIFIED TERRA COTA SCULPTURAL CLAY COLORED CLAY CONE 6 WHITE STONWARE CONE 6 DARK STONEWARE WHITE EARTHINWARE CONE 10 WHITE EARTHENWARE PORCELAIN 1742°F–1992°F2282°F–2336°F1796°F–1972°F2282°F–2372°F

11. Hardness Raw refractory materials lack a plastic quality and thus have greatly reduced potential for being formed. It is difficult to make any object from them with causing cracking or warping. The plasticity of clay body may be diminished by the addition of non-plastic raw materials – these reduce plasticity, shrinkage, and drying time. Among the most important ones are silica, feldspar, and grog.

12. Porosity Porosity is the ability of clay bodies to absorb water after firing. The higher the firing temperature, the lower the porosity of the body. Porosity is common to all pieces fired at low temperatures, a fact that also affects glaze application.

13. Shrinkage The water that surrounds the clay particles and that makes the clay workable is water of plasticity; it makes up 20 to 35 % of the weight of the wet clay. When the water evaporates, the particles of clay move closer together, and the entire pieces shrinks. The smaller the particles, the greater the shrinkage, and thus the greater the risk that the piece with become distorted or cracked. The final size of the work will be slightly smaller because it loses all of this water. Terra cotta will shrink 6 – 8%, porcelain, 10 – 15%.