pottery kiln

Burning the Earthware in the kiln

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The most important chemical operation to which all pottery wares are subjected, is that of burning or firing. This operation is carried on in kilns, that vary widely in character and construction. A variety, for which the different kinds of ware and the questions of handling and setting in the kilns, to best advantage, present many good reasons. But it cannot be denied, that in many instances, mechanical considerations which have determined the style of kiln, have been accepted without a clear understanding or due appreciation of the operation of burning in itself and its effects on the ware.
These are among the most important of the subject. The construction and size of the kiln, the character of its fire-places, and the means of creating and regulating the draught, must all be such, that for the purpose for which the kiln is built, it is possible :

1 . To obtain the necessary temperatures required in the proper intervals of time and to hold them at pleasure, as the work may demand.
2. To get as uniform a temperature throughout the kiln as possible by the ability to direct of advance the heat in its different parts, as the progress of the fire may require.
3. To be able to get the chemical quality of flame needed for any operation at will.
4. To get the maximum heat effect with a minimum of fuel.

The majority of even the best kilnmen waste considerable fuel by the admission of excessive amounts
of air to the kiln. How great this waste is, few potters perhaps realize.
From the standpoint of the chemist, who accepts the methods and apparatus of empirical work, but must modify or add to them, so as to eliminate the elements of chance, the first consideration in firing, bears on the question of production and regulation of the draught.
As the ultimately high temperatures produced in all pottery kilns causes a sufficiently rapid movement of the gases to bring an abundance of air into the firings for the combustion, many forms of kilns have no regular chimney. The smoke and products of combustion either escape from the imperfectly closed top, as in the old brick-clamp or from openings in the arched crown, as in the English pottery kiln.

Contact Chatzinikolakis pottery workshop in the traditional ceramic craft village of Trapsano, Crete, GR., to order your large terracotta artifacts.

WHY IS CLAY FIRED?
Clay becomes pottery at temperatures at about 1,000 degrees F (the beginning of glowing red heat - about 540 C). Traditionally, tribal earthenware is fired to about 1,400 degrees F (760 C). Heat removes the molecular water in the clay. The heat converts clay molecules to molecules that do not dissolve or slake in water. In modern societies pottery and brick is fired in kilns to temperatures ranging from 1,800 F to 2,400 F. Most of the common clays like clay shown here on the left found in our back yards start to deform and melt if they are fired higher than about 1,900 F. Modern toilets are fired from clay that has fewer contaminants. It is fired to 2,300 to 2,400 F., making it very strong and impervious.

FIRING WITHOUT A KILN
Kilns were invented to contain heat to reach higher temperature with less fuel. In tribal settings it is traditional to use an outdoor bonfire type of firing that is fueled with enough wood kindling under the pottery to exceed red glowing heat during the burn. The tempreatures of the pottery reach 1,000 F and hotter.

WHERE and how to do it SAFELY. Consider fire safety and local fire codes. Many cities and communities are very strict about open fires. In any case, do not do this where there is any chance that the fire will spread from your firing. Have an ample supply of water close at hand. Have a shovel and dirt that can quickly be used to put out an accidental fire. Do not leave it unattended. Teach careful and strict safety habits to children and students. Temperatures are much hotter than a cooking fire.

OUTDOOR FIRING WITHOUT A KILN Read more...