Pottery is the process of forming vessels and other objects with clay and other ceramic materials, which are fired 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 American Society for Testing and Materials (ASTM) is "all fired ceramic wares that contain clay when formed, except technical, structural, and refractory products." A different definition, used within the field of ceramics, is "everything which is not porcelain". In archaeology, especially of ancient and prehistoric periods, "pottery" often means vessels only, and figures etc of the same material are called "terracottas". Clay as a part of the materials used is sometimes said to be essential, but this is dubious.
Pottery is one of the oldest human inventions, originating before the Neolithic period, with ceramic objects like the Gravettian culture Venus of Dolní Věstonice figurine discovered in the Czech Republic dating back to 29,000–25,000 BC, and pottery vessels that were discovered in Jiangxi, China, which date back to 18,000 BC. Early Neolithic pottery artefacts have been found in places such as Jōmon Japan (10,500 BC), the Russian Far East (14,000 BC), Sub-Saharan Africa and South America.
Pottery is made by forming a ceramic (often clay) body into objects of a required shape and heating them to high temperatures in a kiln which removes all the water from the clay, which induces reactions that lead to permanent changes including increasing their strength and hardening and setting their shape. A clay body can be decorated before or after firing; however, prior to some shaping processes, clay must be prepared. Kneading helps to ensure an even moisture content throughout the body. Air trapped within the clay body needs to be removed. This is called de-airing and can be accomplished either by a machine called a vacuum pug or manually by wedging. Wedging can also help produce an even moisture content. Once a clay body has been kneaded and de-aired or wedged, it is shaped by a variety of techniques. After it has been shaped, it is dried and then fired.
Clay ware takes on varying physical characteristics during the making of pottery.
Greenware refers to unfired objects. At sufficient moisture content, bodies at this stage are in their most plastic form (they are soft and malleable, and hence can be easily deformed by handling).
Leather-hard refers to a clay body that has been dried partially. At this stage the clay object has approximately 15% moisture content. Clay bodies at this stage are very firm and only slightly pliable. Trimming and handle attachment often occurs at the leather-hard state.
Bone-dry refers to clay bodies when they reach a moisture content at or near 0%. At that moisture level, the item is ready to be bisque fired.
Biscuit (or bisque) refers to the clay after the object is shaped to the desired form and fired in the kiln for the first time, known as "bisque fired" or "biscuit fired". This firing changes the clay body in several ways. Mineral components of the clay body will undergo chemical changes that will change the colour of the clay.
Glaze fired is the final stage of some pottery making. A glaze may be applied to the bisque form and the object can be decorated in several ways. After this the object is "glazed fired", which causes the glaze material to melt, then adhere to the object. The glaze firing will also harden the body still more as chemical processes can continue to occur in the body.