Cold porcelain is a very versitile air-dry clay that you can make at home with simple ingredients. It cures/dries to a hard, durable 'porcelain-like' finish. In this video, Sangeeta Shah shows you how to make her basic cold porcelain recipe, which she cooks in microwave for just a few minutes. I've followed this recipe myself and I can testify that it is very easy to make cold porcelain this way!
More about cold porcelain at Cold Porcelain Tutorials