Carolina Environmental Diversity Explorations
Clays of the Piedmont · By Dirk Frankenberg
From clay to pot
Figure 10. A clay pond used in contemporary pottery manufacture. (Photograph by the author. More about the photograph)
The remainder of this field trip is devoted to showing what humans must do to convert the clays recovered from the ground as shown in the first two photographs into the objects shown in Figures 3 through 9.
We need to begin by describing what happens to native clays to make them fully usable as material for pot making. All clays must be modified to some extent before than can be used to make large, non-porous objects like the pots made by European immigrants. Native Americans used somewhat modified clays to make early objects as large and well finished as the burial urns shown in Figure 5, probably using techniques unknown to us. Europeans, however, brought techniques for making clays better and materials for pot making with them when they immigrated. Modern Piedmont potters use traditional techniques as well as new techniques that developed as scientific knowledge of ceramics and their chemical properties increased.
All native clays must be dried, ground, and reconstituted with water before potters can work them. In addition, very few native clays are naturally well suited to the whole range of potential pot-making. In order to be suitable for working on a potter’s wheel (the most common method for shaping pottery by Piedmont potters), a clay must have the proper mix of plasticity and strength. Plasticity makes clay deformable and hence easier to shape into a pot; strength is needed to hold the developing pot together while it is being shaped. Rarely do these two properties occur in the optimum balance in native clays just as they come from the ground. In fact, this ideal combination is so rare that when an early Moore county potter heard of the quality of clay in Randolph County, he sold his farm and moved. In most cases, potters mix clays to achieve the properties that work well in their application.
One modern potter uses a mix of 25 percent native clay, 45 percent secondary kaolin clay, 10 percent Pee Dee River clay, 10 percent pyrophillite to reduce thermal expansion during firing, and 10 percent feldspar to create a chemical conversion during firing which both lowers the melting point of the mixture and makes the fired object glassier.
As you can see, clay mixtures are an example of the adage that “nothing is as simple as it appears to one who knows nothing about it”!
Figure 10 shows the beginning of the clay-to-pot transformation. This is the clay pond of a contemporary Piedmont pottery. This depression was made by years of clay removal. The resulting wetland is a fringe benefit of the pottery business.
