Pottery is the process and the products of forming vessels and other objects with clay and other ceramic materials, which are fired at high temperatures to give them a hard, durable form. Major types include earthenware, stoneware and porcelain. The place where such wares are made by a potter is also called a pottery (plural "potteries"). The definition of pottery, used by the ASTM International, is "all fired ceramic wares that contain clay when formed, except technical, structural, and refractory products." In archaeology, especially of ancient and prehistoric periods, "pottery" often means vessels only, and figures of the same material are called "terracottas." Clay as a part of the materials used is required by some definitions of pottery, but this is dubious.