The techniques

« The Jargon of Clay for Intelligent Beings »

Many books and articles have been written about clay art. Most of them assume that you are a ceramic artist or that you are a professor of fine arts with ceramic history as your major. We know better.

What we want to do in this article is bring you up to speed about clay and ceramics as quickly as possible. We want you to have an idea of what you are talking about when you discuss a ceramic piece with the artist who created it. We want you to have a better understanding of the ceramic jargon.

For example: Do you know what type of clay your favourite potter uses? Do you think that knowing the kind of clay is important?

What difference does it make to buy faience or porcelain? Is it important to know the firing temperature of clay when thinking of purchasing a mug or a bowl? What role does clay play in the fabrication of a piece of ceramic? Why are some clays red and other clays white? Do you understand what the clay artist is saying when he refers to raku or low fire clays? Does your favourite potter use lead in his glazes? Does your potter fire using an electric or gas kiln. Does it matter?

These are just a few questions that arise when we begin the process of looking for a piece of ceramic that we will use in our everyday lives. They are important questions and there are many more of them. Hopefully, we will be able to supply you with some of the answers to your questions.

What is clay?

This is not easy to define. We can say that it is the basic ingredient used by the potter when he creates your work of art. We can say that clay is the stuff that sticks to the boots of construction workers when they excavate the foundations of new buildings. Clay is the sticky stuff that children are so good at finding. Clay can be found everywhere on earth. In fact, clay materials make up to 90 % of the earth's surface and can be found in the mountain ranges, riverbeds, on the ocean floor, and in the desserts. Clay can even be found in our garden.

Clay is a natural substance. Clay, in its natural state, seldom allows the potter to create his work. His work may require him to use coloured clay, or clay that is very plastic. He may need clay that matures at a lower temperature or one that will allow him to fire to the high temperatures required for achieving porcelain. In order for a potter to use clay, he must combine a mixture of natural clays into what is called a clay body. Strangely enough, the clay body determines most of the technique used by the potter.

The chemistry of clay is a very large subject and we do not want to get bogged down in the finer points of this alchemy. What we need to know is simple. Is the object that we are about to buy made from the right clay, using the proper techniques to ensure a durable, long lasting clay object?

The Clay Body Every potter chooses a clay body that will work for his forming technique. For example, throwing clay must meet the demands of plasticity. It should hold its shape even when wet. Sculpture clays, however, demand a material that will dry quickly and safely without cracking. Casting clays require a mix of material that will flow easily in suspension and will not settle in the moulds. The potter may mix his clay from available materials in his region or he may purchase a commercially formulated body from a supplier. The number of clay formulas in existence is infinite. Nevertheless, for our discussion, we can break them down into four basic categories. They are porcelain, stoneware, earthenware and flame-ware. They are categorised mostly by the temperature to which they are fired, but also by the mix of materials required to make the body.

When you are planning to buy a piece of ceramic, ask yourself "What is the intended use of this pot"? If it is a vase and you intend to put flowers and water in it, be sure the potter guarantees that it will not weep or leak. If it is a pot that you intend to use to heat food in the microwave, again get a guarantee from the potter that it is microwave safe. Clay bodies that absorb liquid could burst in a microwave. If you plan on purchasing a sculpture that is to be put into the garden and left all year around, be sure the clay body and firing temperature ensure vitrification and minimal absorption of humidity. Otherwise the piece could shatter during the winter freeze. If you purchase a pot to use as a casserole, ask the potter if it is made from a clay body that will withstand heat shock.

Clay

One of the most abundant materials that we can find on this earth. It originates from the earth's crust. It is a dense, plastic, fine particle earth material. It is the result of years of erosion of igneous rock. The material used by the potter is a mixture of clay powders. The three most utilised clays used by potters are porcelain, stoneware and earthenware. Clay can be solid or in liquid form. It can be moulded, sculpted, thrown on the potter's wheel, assembled, pinched, carved, rolled, folded, coiled, smoothed, extruded, and poured. Although clay stiffens when dried, it must be fired to maturity in a kiln to render it non-porous, and strong.

Clay Body

A mixture of clay products. Clay dug directly from the ground seldom gives the characteristics necessary for a potter's requirement. Clay powders and various ceramic materials are mixed together to increase plasticity, give a desired colour, or determine the firing temperature. Clay is usually made by the potter or by commercial clay companies

Terra Cotta

Earthenware pottery- or sculpture.

Stoneware

Stoneware is fired from approximately 1 200 to 1 300 degrees Celsius. It is a hard non-porous clay that when fired to proper temperature, needs glazing only for hygienic or aesthetic reasons. Stoneware is one of the favourite clays of the studio potter.

Earthenware

This clay is fired from approximately 700 to 1 200 degrees Centigrade. To go above 1 200 degrees would deform or melt the clay as well as make a pot that would fracture easily. It is used by those who wish to save energy or those who do not have the resources to reach high temperatures. Earthenware clay is good for those who wish to work in brilliant colours.

Porcelain

Considered the most noble of the clay bodies. Its composition is pure white, translucent, and when fired to temperatures exceeding 1 300 degrees Celsius, it becomes a very strong, vitrified product.

Flame-ware

Pottery intended for use in the oven.. The clay is similar to earthenware or stoneware. The body is porous and non-vitreous, allowing it to expand and contract rapidly.

Paper-clay

Clay mixed with paper pulp. Paper-clay provides strength at the green-ware stage, and the finished product is much lighter in weight.

Slip

Slurry of clay, water and other ingredients. Coloured slips are used to decorate a clay surface. They can be applied by brushing, pouring or trailing.

Grog

A crushed, fired clay added to a clay body to increase its strength, reduce shrinkage, and prevent drying cracks. Large sculptural or architectural pieces usually require highly grogged clay. Raku ware also uses grog to increase the firing strength of the piece during the post reduction process.

Terry Lazaroff