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 (22642462 ̊ 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 woodfired. 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.
1.
2.
What is clay?
Clay is naturally found in the New England area. Why? (hint: think of
New Hampshire)
3. For how many years have human beings worked with clay?
4. In what part of the world was the technology for firing clay first
developed?
5. Why was ceramic technology so important to the development of
human civilization?
6. Explain the main differences among stoneware, earthenware and
porcelain.
7. Explain the difference between the “leather-hard” and “bone-dry”
stages.
8. Why is it important to wedge your clay thoroughly before you begin
working with it?
9. What is the difference between bisqueware and greenware?
10. How should one join two different pieces of clay together?