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The most significant ceramic material is CLAY! A Ceramic product is made from a nonmetallic mineral through the process of firing or exposing it to extreme heat. Clay is fired in a kiln.

Pottery is a small consumer of clay. Most clay is used in the manufacturing of industrial products.

“It is through pottery that a great deal of human history has been recorded and documented.” 3,000 BCE Egypt 12,000 BCE Japan 1,600 BCE Crete 800 AD South America 1,200 AD Mexico 2006 USA 1,400 AD China 500 BCE Greece

About 75% of the earths surface is clay or will be clay after weathering. Clay may be abundant, however it takes a lot of work to make it suitable for sculpture or pottery. Clay naturally contains rocks, pebbles, sand, twigs, branches, or other earthly matter. All of these impurities have to be sifted out before the clay can be used. Once the clay is clean, water is added and the clay is kneaded and wedged into a workable form.

Over 100 MILLION tons of clay are mined in the U.S. annually !!

1. Plasticity - Plasticity is the ability of clay to hold its form while maintaining its ability to be manipulated into shapes and forms. - It is determined by the size and shape of particles of clay called platelets. - The smaller and smoother the platelets the easier the clay is to push around. - Bentonite is too plastic. As a result from its slippery and wet nature it cannot be used by itself to make pottery.

The “water of plasticity” affects the clays ability to be plastic. Too much water and the clay is goopy. Not enough water and the clay becomes powder like. Organic matter such as dry leaves, roots, and grass How can you change plasticity?

2. Porosity - Porosity is how porous the clay is. - If clay is too plastic (platelets are closely squeezed together) water can’t evaporate evenly from all parts of the ware and therefore the ware cracks. - Clay must be porous enough to allow the water to evaporate evenly from all parts of the sculpture. - To change porosity: add silica sand or grog (ground fired clay).

3. Vitrification - “Vitrification is the process of becoming glass like” or hard. - It is the ability of clay to hold its shape and not melt during the firing process. - Vitrification varies between clay types. - If the clay is fired at too high of a temperature, it will begin to melt.

Review the “Uses and Sources of Clay” and the “Properties of Clay” NOTES and VOCAB from your reading.

Earthenware, Stoneware, and Porcelain -the three general types of clay characterized by their plasticity, porosity, and their ability to vitrify.

Earthenware is usually a red clay because it contains a lot of iron. (However, ours is gray) It is fired at a low temperature (1900°F) because it can only partly vitrify before it melts. Because it cannot be fully vitrified, earthenware remains porous and needs to be glazed in order to seal the pores.

Stoneware clays are light yellow or grey in color. Depending when the potter turns off the kiln stoneware can be semi-vitreous or vitreous. It is fired at a medium temperature (2100°F °F) When stoneware is semi-vitreous it can still absorb a tiny amount of water. When stoneware is vitreous it becomes very hard and brittle and will absorb almost no water.

Porcelain is white in color. It is fired at a high temperature (2250°F °F) Unlike earthenware and stoneware porcelain-type is usually a non-plastic clay type and therefore is difficult to work with.

 One part alumina AI 2 O 3  Two parts silica SiO 2  Two parts water H 2 O  Clay in its plastic form has two types of water: the water of plasticity and chemical water.  The water of plasticity is ADDED to clay’s basic formula to manipulate its plasticity  Chemical water is part of clay’s basic formula and is present in clay until it has been fired.

Clay comes from a mineral called feldspar which can be found in the rocks like granite, gabbro, and gniess. Centuries of weathering from rain and snow fall cause the rocks to break apart until it becomes a fine dust which usually erodes and settles at the bottom of lakes or swamps. It is at this point that, over LONG periods of time, this feldspar sediment evolves into clay.

During geological weathering not only is the feldspar being broken down, it is also being mixed with other minerals such as iron, magnesium, and titanium. Therefore, no two clays are exactly alike. Their unique journeys give them different properties, however, all clay contains the basic formula: alumina, silica, and chemical water.

Please review the “Types of Clay” and “How Clay is Formed: The Basic Formula” sections from your reading.

Clay Categories:

Primary Clay, also called “residual clay”, is the purest type of clay. It was created by decomposition of feldspar close to the location where the rock originated. Because the clay comes from a stone that collapsed on the spot, the particles were not able to grind each other down. Therefore, primary clay is difficult to work with (they are not plastic). Kaolin is the most common and valuable of the primary clays. It was first used by the Chinese to make porcelain. Later Chinese porcelain was duplicated by the Europeans and they named it china clay. Secondary Clay, also called “sedimentary clay”, is far more common than primary clays. With the help of nature, it was transported a great distance from its original location. Because of this, the clay particles had the chance to be ground down until they were fine and smooth. The small particle size gives the secondary clays more plasticity, which makes them easier to work with then primary clays. Ball clays, earthenware, stoneware, and fire clay are all types of secondary clay.

Ball Clays are found in swamps. They contain an abundance of organic matter and are therefore very plastic and slippery. Earthenware is the most common type of clay throughout the world. It was used by primitive cultures because it was easy to work with and easy to fire. Fire Clays are used to make fire brick because it resists heat and melting. Fire brick is used to make kilns, kiln furniture, and furnaces for melting metal or glass. Fire Clays are fired on the high end of the heat spectrum (2700 °F). Stoneware is similar to fire clay however it is more plastic and fired at a range of 2100°F and 2350°F

Adobe used for bricks and it is not fired. Terra cotta very coarse and used for large sculpture. Bentonite extremely plastic and used as a plasticizer All of the above are seldom used by potters

m The progression of building pottery and using clay

Ancient Potting Techniques

Prepared Clay Bodies are modified clays usually manufactured by a supplier. There are three categories of prepared clay bodies: Earthenware Stoneware China/Porcelain The differences in these clay bodies are the differences in the three essential properties of clay: Plasticity Porosity Vitrification

Earthenware occurs naturally as a red or brown clay and can be used without adjustments. However, earthenware clay bodies are altered to fit the particular way they are to be used. White earthenware (which is often the clay of choice in schools) seldom occurs naturally and almost always has to be manufactured. Earthenware can be fired at lower temperatures which is what makes them so popular among artists and educators. Earthenware clay and clay bodies are low fire, non- vitreous, and soft.

Stoneware can be used just as it is found and without any adjustments. Studio potters typically prefer stoneware for the following reasons: The clays are usually plastic They are easily thrown They are great for hand building Stoneware fires to a hard vitreous mass and does not need to be glazed other than for design purposes.

Review the “Clay Categories” and the “Clay Mixtures, Prepared Clay, Clay Bodies” sections from your reading.