Dynamic Clay

The one constant when working with any raw material is ongoing change or alteration. The actual raw materials that compromise clay bodies are always shifting in mechanical water content, chemical water content, organic content, pH level, particle size, mineral content, and tramp mate­rial. Several factors can alter a clay body. Some of these factors take place subtly over years, but others are more: dramatic, occurring immediately after the first bag of clay is opened. Changing clay can affect a finished product’s color and glaze fit. For example:, higher iron content in a clay can result in a darker fired color. Or a shift in a clay’s silica con­tent, which changes the rate at which a day body shrinks or expands, can adversely influence glaze fit. Sometimes a change will occur in a single: bag of day, causing clay or glaze defects. Occasionally, a clay alters over a period of months or years, causing a slow transformation in a clay body color or texture. While mines and ceramics sup­pliers strive for consistency and for the most part they succeed – a few small changes in clays can add up to a big change for the entire clay body formula. Unfortunately, clay variations are mostly reflected in the finished ware. If you choose to mix your own clay body formula, as opposed to ordering clay from a supplier, you will have more immediate control over the weighing and mixing process. But direct control does not always translate into improved quality. Even when mixing one’s own clay, a defective clay component in the formula is often discov­ered only when the finished ware is removed from the kiln. There are many reasons for a clay body to fluctuate, some of which involve a predetermined adjustment by potters who mix their own clay or the ceramics supplier who mixes and sells moist clay. A clay body can also fluctuate, due to inaccurately weighing the dry materials or incorrect mixing procedures. Knowledge and expertise in mixing clay can prevent these problems. You will decide whether it is appropriate and efficient to mix clay yourself or to purchase.