How do ball clays affect the color of lower-grade whiteware?

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traditional ceramics Stages in the slip casting of a thin-walled whiteware container. Clay powder is mixed in water together with a dispersing agent, which keeps the clay particles suspended evenly throughout the clay-water slurry, or slip. The slip is poured into a plaster mold, where water is drawn out by capillary action and a cast is formed by the deposition of clay particles on the inner surfaces of the mold. The remaining slip is drained, and the cast is allowed to dry partially before the drain hole is plugged and the mold separated. The unfinished ware is given a final drying in an oven before it is fired into a finished product.

In the production of lower-grade whiteware, ball clays are used as the primary plastic component. Unlike kaolin, which is a pure, white-burning clay, ball clays contain a mixture of ordered and disordered kaolinite along with various other clay minerals and impurities.

These impurities, particularly iron oxides, are responsible for altering the appearance of the finished product. During the firing process, these substances cause the ceramic to take on an off-white, gray, or tan color rather than the pure white associated with higher-grade, kaolin-based wares.1