A Brief Introduction to Clay 3-D Design Ms. Burakowski

What is clay? Clay is a natural material which forms over millions of years and can be found in gardens, riverbeds, fields or even along roadsides. Clay forms mostly in areas containing large amounts of granite. Clay is composed of alumina, silica, and feldspar (granite) as well as other smaller amounts of minerals.

Two Main Types Primary clays: “china clay” (kaolin) and bentonite. These clays are found where they originally formed. They are used to make fine porcelain. Secondary clays: ball clays and red clays. These clays form in sedimentary layers, deposited over time usually by rivers or melting waters. These clays are used to make earthenware and stoneware objects.

History Clay has been manipulated by humans as long ago as 37,000-12,000 BC (Ice Age!) Clay was first fired by humans in what is now East Asia, and by 6,000-4,000 BC, firing clay had become widespread. Cultures on almost every continent now have long-standing ceramic traditions. Fired clay enabled humans to store grain and led to a more settled, agricultural existence. Glazes were first developed in 4,000 BC in Egypt/Mesopotamia. Glazes developed not only for decorative purposes, but they also made containers strong and waterproof.

Earthenware Matures at 1000-1180 ̊ C (1832-2156 ̊ F). Low fired! Rather porous, lighter feel Found around the world Can be grey, white, red, orange, buff, yellow and/or brown Red clay contains iron oxide, which gives it its color and keeps the firing temperature low. Often used to make flower pots, bricks, tiles, etc.

Stoneware Matures between 1200-1300 ̊ C (2192-2372 ̊ F). High fired! Hard, dense clay body which has a water absorption rate of 3% or less when fully fired Colors can be off-white, tan, grey and/or brown Often used for “art pottery”: jugs, mugs, plates, bowls, etc.

Porcelain Matures or vitrifies between 1240-1350 ̊ C (2264-2462 ̊ F) High Fired! Translucent, waterproof and “rings like a bell” when fully vitrified. Dense, smooth clay body that can be difficult to throw. Once a luxury item that drove global trade in the 17th century, it’s now readily available and used to make dishes, plates, mugs, bowls, figurines, etc.

Important vocabulary! Firing: “baking” the clay in a special clay oven called a kiln. There are bisque firings, which mature the clay body and glaze firings, which vitrify the glaze decorating the object. Kiln: The special clay oven which bakes the clay. Kilns can be gas, electric, coal or wood-fired. We use an electric kiln.

More Vocabulary! Leather-hard: The stage at which clay has dried enough to be picked up without warping the piece. However, it is still cool and slightly moist to the touch and can be carved, cut, or added to. Bone-dry: The stage at which the clay has completely air-dried and is ready to be bisque fired. It is VERY fragile at this point (like dried mud), “chalky” and not water-tight.

Um, sorry more vocabulary Wedging: working a lump of clay in such away to ensure that the lump is the same consistency all the way through. Wedging also works out any air-bubbles which may cause the clay to blow up in a kiln firing. Greenware: Completed pots that are not yet bone-dry. Bisqueware: Completed pots that have been through their first (bisque) firing. They are now hard and strong but not necessarily waterproof. Slip and score: a technique used to join two pieces of clay. It involves scratching up the two surfaces and adding liquid clay which acts like a glue.

Last slide, I promise Oxidized firing: the firing of a kiln with complete combustion so that kiln atmosphere produces enough oxygen to allow clay bodies and glazes to produce their oxidized colors. Our electric kiln only produces an oxidized firing. Pyrometric cones: cones made from compressed ceramic materials, which “melt” or slump at a predetermined temperature. Most of our firings are done between cones 06-04 (1855-1971 ̊ F).

Answer questions in complete sentences on a separate sheet of paper. What is clay? Clay is naturally found in the New England area. Why? (hint: think of New Hampshire) For how many years have human beings worked with clay? In what part of the world was the technology for firing clay first developed? Why was ceramic technology so important to the development of human civilization? Explain the main differences among stoneware, earthenware and porcelain. Explain the difference between the “leather-hard” and “bone-dry” stages. Why is it important to wedge your clay thoroughly before you begin working with it? What is the difference between bisqueware and greenware? How should one join two different pieces of clay together?