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It was this thought that encouraged me to study the beginnings of pottery, and that leads me to offer this book to those who would also start clay-working, with no other qualification than the wish to learn how to make pottery.

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The Clays and Tools

HOW TO MAKE POTTERY

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Clay is what might be called the drift of the rocks of ages past. Most stone consists mainly of silica and alumina. In some bygone age, the potash and other alkalies, under the action of heat, fused these materials into rock. Potash is affected by the atmosphere, so it gradually left the rock, which decomposed, and the many particles, the fine refuse, after various changes became clay. Perfectly pure clay, or hydrated silicate of alumina, is found where some granites and other felspar-bearing rocks have decomposed. In the course of years, the clays, especially those on the surface, gathered impurities. Black clay, for example, which is found at the top of the bed, contains a large per cent. of carbon, formed by decayed leaves and twigs—like coal or peat. Strange to say, this burns whiter than any other pottery clay. It contains more potash than the other clays, and fires at a lower heat. The different proportions in which certain minerals are found in clays determine their plastic or non-plastic, fusible or refractory character. Potters have not been able to agree as to the reason for the plasticity of clay. Some believe that the silica gives it plasticity; others that it is due to the water inherent in the clay (which is called the water of combination), and give as their reason for the belief the fact that burned clay loses its plasticity, never to get it again. Yet water alone does not make every clay plastic: other ingredients are sometimes necessary. The early potter used the clay just as it came from the ground, but when he began to bake it in the fire he found that tempering materials were necessary. Sand was often added to make it easier to handle, and coarse, sharp pieces of shell or rock helped to prevent the clay from cracking, by lessening the shrinkage.