Clay Times Back Issues Vol. 2 Issue 4 • May/June 1996 - Page 11

To Mix or Not To Mix: Weighing the Benefits of Wet vs. Dry Clay BY JEFF ZAMEK Obtaining a moist clay body suited to your individual requirements is a critical aspect of production. After all, you can’t make very good pots if the clay fails to perform well during the formation of the pot, or doesn’t yield the necessary qualities to enhance the finished piece. But which is the best solution to your clay supply situation: to mix it yourself, or buy it pre-packaged? Clay Bodies First, you need to select a clay body formula which meets your forming and firing needs. Combinations of clays, feldspars, talc, grog, and other materials can constitute a clay body. Exactly what proportions and which combinations of raw materials are necessary for each project are determined in part by the desired firing temperature range, forming method, rates of shrinkage and absorption, fired color, and intended function of the ceramic object for which the clay body is designed. Successful results depend on the suitability, accuracy and consistency of the clay body formula, whether it’s mixed in the potter’s studio or purchased in premixed form. Stock Clay Body Formulas and Custom Formulas Knowledge of available stock clay bodies and custom clay body formulas can prevent many potential problems later. When purchasing pre-mixed clay or developing your own custom clay body formulas, try to work with formulas which perform well under various forming and firing conditions. A desirable clay body formula can function well even when mixed slightly differently from the original formula. Ideally, variation of a few percentage points of each raw material in the formula should not cause a significant difference in the forming characteristics or fired qualities of the clay body. A good clay body formula will also tolerate slight variations in kiln atmosphere and firing temperatures (a two or three pyrometric cone range is realistic) and still produce acceptable results. The best situation is to find such a clay body, and to move toward an aesthetic objective in your own work that allows for slight variations in size, texture, and color. Some potters make the initial mistake of trying to produce an item to exact specifications, only to learn that their raw materials and forming methods cannot meet their unrealistic ideals. Whether mixing your own clay or buying clay from a ceramic supplier, it is always a good idea to mark the pots in some small way to distinguish each new batch of clay. The mark can be used as a code to identify each batch of mixed clay as it goes through the production process. If a problem does develop with the clay, the entire production from the suspect batch can be taken aside for further testing. Mixing Your Own Clay If your clay body depends on a very specific finished characteristic or color, or if the forming qualities of the moist clay require a close tolerance in adhering to the exact clay body formula, consider mixing your own clay. A clean-firing porcelain clay body requiring clean mixing conditions often unavailable at commercial clay suppliers would be a good example of a clay body which you might prefer to mix yourself. Mixing your own clay requires knowledge of raw materials and the ability to formulate a clay body. Raw materials can change in chemical composition, particle size, and levels of contamination. Whoever develops the clay body formula should know what irregularities will affect the moist clay, and how to adjust the clay mix as required necessary. Doing your own mixing under specific, controlled conditions can offer many benefits, yet the clay worker should carefully consider whether the advantages are worth the labor, effort, and expense. Two major benefits are greater speed and flexibility in adjusting the clay body formula and its moisture content. Also, quality control is ensured at the earliest stages of production. Yet the process of mixing one’s own clay is a full-scale production in itself, requiring specialized equipment, location in a speciallyventilated area or shed outdoors, the wearing of a respirator with filter approved for use with silica dust, and a great deal of time. It is by no means for the amateur or flyby-night clay hobbyist. Yet if you’re a seasoned professional who’s serious about maintaining full control over your clay supply, the decision continued on page 14 11 ▼