Adventist Youth Honors Answer Book/Arts and Crafts/Pottery

1. Write or explain orally the different types and uses of pottery and the materials used in making it.
Pottery includes all tiles, dishes, and other articles that are made of baked clay. The finest type of pottery is called porcelain. All other pottery is called earthenware or stoneware. Man made earthenware long before he discovered how to make porcelain.

It is usually easy to tell the difference between earthenware and porcelain.

Earthenware is opaque. That is, no light will show through it. Thin porcelain is translucent; that is, light will show through it. The clay of which earthenware is made may be red, brown, yellow, gray, bluish, or white. The mixture of which porcelain is made is white all the way through.

CLAYS

Clays come from different geological sources and vary in the extent of the weathering of particles. In the course of erosion, they become mixed with each other, as well as with impurities. Because of these variables in their composi-tion, clays cannot be classified precisely. The clays are graded according to general type.

Kaolin

Kaoline is a very pure, white, primary clay. Because it has coarse particles, it is not very plastic and shrinks only slightly. It is very refractory -- that is, when fired, it matures at a very high temperature (3272° F.). Because of its low plasticity and high refractoriness, kaolin is rarely used alone. Other materials are mixed with it to enhance its workability and to lower its maturation temperature.

Ball Clays

These are fine-grained, highly plastic secondary clays. They are largely free of impurities, and they mature at a high temperature (2372° F.). Because of their great shrinkage, up to 20 percent when fired, they cannot be used alone.

Ball clays are often mixed with kaolin.

Fire Clays

These clays are very refractory, resistant to heat up to high temperatures (2732° F.). Some fire clays are quite plastic; others lack plasticity. Coarse-particled fire clay is sometimes added to stoneware clay to give it more "tooth," to roughen the texture of the clay and help it hold its shape when wet.

Stoneware

These are plastic clays that are fired to a fairly high temperature (2192° F.-2372° F.) Sometimes they are used just as they are found in the earth, but more often they are mixed with different clays and other additives.

Earthenware

These are the most common natural clays.

They contain significant

amounts of iron and other impurities, which act as fluxes. That is, they reduce the maturation temperature of the clay (1742° F.-2012° F.). Unlike stoneware and other higher firing clays, earthenware is somewhat soft and porous after it is fired. Earthenwares vary in their plasticity and color in accordance with the presence of different impurities.

Porcelain

Porcelain is made of kaolin, ball clay, feldspar, and flint (a form of silica).

It is the highest firing (2372° F.) workable clay, and it fires to a translucent white color. Its low plasticity makes it difficult to use.

The Persians used gorgeous and dazzling color effects in the glazed tiles that they used to decorate both the inside and outside walls of their buildings. Some of the finest and most prized blue and white Delftware owes its charm mainly to the decorations adapted from the designs on the Chinese blue and white plates, platters, bowls, and teapots. Italy is known for the glazed flora tiles of the Renaissance.

Stoneware is made in both America and Europe. It has a very hard gray body. It is salt-glazed and slightly decorated with underglaze blue. It occurs usually in the form of beer mugs, butter crocks, pickle jars, and the like.

2. What is the purpose of a glaze? Describe the specific dangers to be avoided.
Glazing puts a shiny coating on pottery. Sometimes a glaze is applied for practical reasons.

Glazing the inside of a bowl, jar, or pitcher will keep it from

absorbing any of the liquid it is meant to contain. Also, a coating of glaze will give a perfectly smooth, hard surface to a body of coarse or rough texture. Sometimes glaze is applied merely to decorate a piece or to make it appear more finished.

Glazes are of various sorts and have different properties. Lead glaze is made chiefly of a finely ground mixture of silicates or sand and oxide of lead. It is transparent. Tin glaze, or stanniferous glaze, is made of silicates and tin oxides finely ground together. It is opaque white. Salt glaze is made of salt and is transparent.

The lead and tin glazes are applied in a liquid state to a piece that has been air-dried or previously fired. Sometimes they are painted on with a brush. At other times the piece of pottery is dipped into the glazing mixture. The article is then allowed to dry before it is fired to fuse the glaze. As the glaze melts, it blends with the clay body to give a smooth, non-porous glassy surface. Salt glaze is applied by throwing salt into the top of the kiln.

Lead poisoning is a serious matter, and the possibility of contracting it while working with lead glazes should not be discounted. Glazes should never be sprayed.

3. Design and draw two pottery forms, one of which must be decorated.
Your first step will be on a piece of cardboard to make a full-size sketch of the pottery piece you want to make. If you are making something with a neck, be sure the neck is large enough to get your fingers inside. Once you are satisfied with the design, cut it out of the cardboard and then cut it in half. Use this to check your work to be sure in conforms to your design.

To start out, keep the designs simple - both the design of the project and the design of the decoration for the piece. Get some pottery books from the library to give you ideas for your design, but don't copy them. Be original.

f. Throw a simple vase on a potter's wheel
Given here are some general instructions in the use of clay no matter which project you may wish to accomplish.

Wedging

Every time clay is used, it should be wedged first. This is one of the oldest methods known for getting clay into good condition; and it is still one of the best.

Wedging board

Many potters use a wedging board (shown above). This is a heavy slab of plaster with an upright to hold a taut wire with a turnbuckle or some other device to keep the wire tight. A wedging board receives a lot of rough usage, so it should be constructed as solidly as possible. With use, the surface of the plaster will become scored and rough. For this reason, some potters fasten canvas over the plaster surface

To use the wedging board, take a lump of clay about the size of an orange; pass it beneath the wire. Then grasping it in both hands, lift it upward so that the wire cuts it in half. Throw one of the halves onto the plaster surface, and throw the other half on top of it so that one lump is formed. Pick this lump up, cut it in half again and throw the two halves onto the plaster once more, one on top of the other. Slam them hard! To get maximum mixing action, keep the layers going the same way.

A good device is to throw the halves together with the cut portions always pointing away from you. Cut and wedge about 20 times before using the clay. When the last cut has been made, the cut portion should be even in tone with no striations or air pockets.

Many potters prefer to condition their clay by kneading it almost the way a baker kneads his dough. A larger lump of clay - as much as ten pounds or more -- can be conditioned this way, and the method dispenses with the need for a wedging board. The kneading can be done on a heavy table with a bare wooden top or a top covered with canvas

Storing Clay

Moist clay can be stored in covered pails of galvanized iron or plastic; plastic is better.

Reclaiming Clay

Until it is fired, clay can be used over and over again. Dry clay should be broken into small pieces, tossed into a pail half filled with water, and allowed to soak a few hours. After the clay has settled into the bottom of the pail, the water may be poured off and the clay emptied into drying bats. A drying bat is a large plaster bowl into which liquid clay can be poured and allowed to dry until it is firm enough for wedging.

Tools

Don't buy too many tools for pottery. Many kitchen utensils make good potter's tools, such as paring knives, spoons, etc. Extra tools might include a potter's knife.

These are made of two kinds of steel: one is firm, the other is soft so that it can be bent into different hook shapes. You will also need some sponges, a wooden modeling tool or two (one with a wire loop end), a steel kidney-shaped scraper, and some type of turntable.

to be continued