The process of pouring ceramic molds is called casting or slip casting. Before you begin, it is a good idea that you know how the mold works. Ceramic molds are made of plaster as opposed to other molds being rubber, sponge, metal or plastic. The reason is that plaster absorbs water.
Slip is liquid clay, it has a lot of water in it (see “What is Ceramic or Clay Slip”) and in order for it to hold a shape, the water needs to be removed. Enter the plaster mold.
There are many kinds of plaster molds, ranging from one piece to two piece to multiple pieces that fit together and form a cavity to hold the slip. Most common, and addressed in this article, is the two piece mold. These molds are designed to fit together tightly to form a cavity with a single opening that is used to receive and expel the liquid clay. See “What is a Ceramic Mold”.
When you fill your mold with liquid clay, the plaster begins to absorb the water and the clay platelets begin to stick to the sides of the mold. This creates the shell that will ultimately form your finished item. The longer you leave the slip in the mold, the more water that will be drawn out and the thicker the shell will be. When the shell is as thick as you want it, you then drain off the excess slip and you are left with a hollow item.
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Tags: cast, ceramic, Ceramics, greenware, mold, mold casting, molds, slip, slip casting