gradually absorbed into the plaster to form a firm layer of clay at the mold surface. The composition of the slip is typically 25% to 40% water, the remainder being clay often mixed with other ingredients. It must be sufficiently fluid to flow into the crevices of the mold cavity, yet lower water content is desirable for faster production rates. Slip casting has two principal variations: drain casting and solid casting. In drain casting, which is the traditional process, the mold is inverted to drain excess slip after the semi-solid layer has been formed, thus leaving a hollow part in the mold; the mold is then opened and the part removed. The sequence, which is very similar to slush casting of metals, is illustrated in Figure 17.5. It is used to make tea pots, vases, art objects, and other hollow-ware products. In solid casting, used to produce solid products, adequate time is allowed for the entire body to become firm. The mold must be periodically resupplied with additional slip to account for shrinkage because of absorbed water.