Some do not consider porcelain to be a true clay because it never occurs as a natural mixture—it is always man-made.
Primary clay is composed of kaolin, a name derived from a Chinese word meaning “high ridge.” It was first discovered and used by the Chinese as early as 200 B.C. Kaolin is too heat resistant (refractory) to be used on its own, but it does form an important part of both clay bodies and glazes. Kaolin is the primary ingredient in porcelain, with silica added for strength, along with calcium, in the correct proportion, to flux the kaolin and silica together. Some do not consider porcelain to be a true clay because it never occurs as a natural mixture—it is always man-made.