There are two basic reasons why you might want to make your own pottery clay and slip. First, in rural areas, it may be a long drive to the city to get it. Second, in large production runs, pottery clay can become expensive. The answer is in the pet supply stores and the pet department of every supermarket: 100 percent clay kitty litter.
Considerations
All-clay kitty litter is made of bentonite, which is used in Indonesia to make household pottery and art pieces (Reference 1). It can absorb up to 10 times its weight in water. A 1-to-4 ratio will give you a malleable sculpting clay. Kitty litter makes lower quality clay and slip than porcelain or other white clays, so make your items a little thicker than usual. Impurities will cause any thin sections of your creations to fail (Reference 2). Start with thick sculptures and castings until you get used to working with this type of clay.
Making Slip
Slip is liquefied clay used to make molded pottery. Allow the kitty litter to soak in water overnight until all the granules are softened. The next morning, stir the container and add water a cup at a time until the clay reaches a smooth, pourable consistency. There should not be any lumps or granules.
Using Kitty Litter Slip
Pour your 100 percent clay kitty litter slip into molds just like regular slip.Turn your molds to ensure an even distribution, and allow to set for a few minutes. Pour a second layer of slip into the mold and turn again. This ensures that your walls will be thick enough to overcome any impurities in your do-it-yourself pottery clay.
Make Sculpting Clay
Pour enough clay kitty litter to complete your project into the bottom of your bucket. If your project would usually require 20 pounds of clay, use a five-pound bag of clay kitty litter. Add water until it is even with the top of the kitty litter. Let the water and clay rest overnight to allow the water to be absorbed into the clay.
Using Bentonite Sculpting Clay
Knead your clay to work any remaining water into it. Adjust the stiffness as desired by adding more water or kitty litter. If you add more kitty litter, rest the clay overnight a second time with a tight-fitting lid on the container. Use as you would normal sculpting clay, but make everything with slightly thicker walls. This clay will have a coarse surface when dry and fired, because it is lower-quality clay. Consider this in your design, glazing or painting plans.
