A variety of German companies produced doll heads for sale in the United States. Most of these companies were located in the province of Thuringia, a region rich in the kaolin needed for the porcelain clay and rich in the wood used to fire up the kilns. Doll makers found porcelain a suitable material for the heads because it could be easily forced into molds with intricate details. The earliest doll heads were made with a press-mold method in which sheets of malleable clay were forced into a mold of two parts. When the clay body hardened, the two parts of the head were joined together. In the slip-casting method, begun by about 1860 and widely used by 1890, a liquid clay mixture was poured into a mold and left to harden. Americans imported doll head dolls from about 1840 until the 1930s.