CLAY A ceramic product is made from nonmetallic mineral by exposing it to extreme heat.

Pottery is a small consumer of clay Pottery is a small consumer of clay. Most clay is used in the manufacture of industrial products like plumbing fixtures, roofing and drainage tiles, firebricks, spark plugs, electrical insulators, rocket nose cones, nuclear reactor parts, tools for cutting metal and even toothpaste.

Any substance will melt at some temperature Any substance will melt at some temperature. Most materials tend to become soft and deform before they melt. The ability of clay to hold its shape and not sag or slump in the primary melting stages sets it apart from other materials.

Types of Clay Indigenous Earthenware Stoneware Porcelain A fragment of broken pottery, especially one found in an archaeological excavation.

Basic Clay Formula Al²O³+ 2SiO²+ 2H²O One part Alumina Two parts Silica Two parts Water

Alumina and Silica are oxides Alumina and Silica are oxides. Each is a combination of oxygen and one other element (aluminum and silicon) Water… its not always wet. Chemical water has two perfect little molecules that have attached themselves to one molecule of alumina and two molecules of silica. It happens like magic but takes millions of years and hasn’t been duplicated by scientists.

Something has to be added to clay to make it both slippery and sticky Something has to be added to clay to make it both slippery and sticky. That’s (real) water. It is essential.

For the most part, geologists look for clay, not potters For the most part, geologists look for clay, not potters. Clay is mined with heavy machinery then taken to factories for sifting and packaging. Over 100 million tons of clay are mined in the US each year.

Indigenous Clay Naturally occurring clay made by the earth (We don’t use indigenous clay in school)

“Weathering” Before clay was clay, it was a rock- a granite type rock called feldspar. This rock spent centuries being rained and snowed upon. Water turned to ice in its cracks and split it to pieces. Glaciers smashed it smaller. Streams washed it around and ground it even smaller. The wind carried it to dust. Finally, it picked up the chemical water while just lying around in the bottom of swamps or lakes. It went through all this and became clay.

Most indigenous clay contains too much iron, alkaline impurities or too much foreign matter (rocks, twigs, bugs) to be used without some work.

Earthenware Most common clay, easy to use, preferred for school students kiln temps 1200-1900° (considered low temperature) Earthenware is predominantly a red clay (has lots of iron) but can be white. Pit-fired red earthenware dates back to 29,000BC.

Stoneware Used mostly for the Potters wheel (kiln temps 1800-2300) Stoneware clay is usually buff or gray colored. At 2350° f, the clay becomes harder than steel but more brittle.

Stoneware clay has a rough texture because of “grog” in the mix Stoneware clay has a rough texture because of “grog” in the mix. These fine-ground, fired clay particles give strength to clay when it is being thrown on the potters wheel.

Porcelain Used by professional potters (kiln temp 2250-2600) Porcelain is a non-plastic clay body and is difficult to handle. (plasticity described in slide 26)

(other) Adobe clay not fired, used for bricks

(other) Terra Cotta clay a course clay for large sculpture

(other) Fire Clay Fire Clay is used to make firebrick (other) Fire Clay Fire Clay is used to make firebrick. Firebrick is used to build kilns or furnaces. It resists heat and melting.

Clay Terms Raw clay- wet and unfired clay Leather-hard clay- clay beginning to dry and is firm but still damp and cool to the touch

Bisque-fired clay- clay that has been fired but not glazed Glaze- a thin layer of glass that is melted onto a pot for decorative purposes

Bone-dry clay- completely dry clay which is ready to fire Firing- heating clay to drive off all chemical water to make it permanent

Kiln- the box made of refractory materials (resistant to heat) that heats clay to extreme temperatures Slip- liquid clay that is used to attach wet clay pieces together

Potters Wheel- a machine used to “throw” or make pots Potters Wheel- a machine used to “throw” or make pots. Wedging- the action of kneading clay and compressing the air bubbles out of the mixture

Properties of Clay 1. Plasticity 2. Porosity 3. Ability to Vitrify

Clay must have Plasticity:. The ability to hold its form Clay must have Plasticity: *The ability to hold its form *Be pliable enough to be moved by the potters hands.

Porosity *To dry without cracking Clay must be porous enough to allow water to escape evenly from all parts of the ware.

Vitrification The process of becoming glasslike Vitrification The process of becoming glasslike. It is done in the kiln with extreme heat.

The End.