Clay Products

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 pottery (plural "potteries"). The definition of pottery, used by 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. 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 and pre-Neolithic pottery artifacts have been found, in Jōmon Japan (10,500 BC), the Russian Far East (14,000 BC), Sub-Saharan Africa (9,400 BC), South America (9,000s–7,000s BC), and the Middle East (7,000s–6,000s BC). Pottery is made by forming a ceramic (often clay) body into objects of the desired shape and heating them to high temperatures (600–1600 °C) in a bonfire, pit, or kiln and induces reactions that lead to permanent changes including increasing the strength and rigidity of the object. Much pottery is purely utilitarian, but much can also be regarded as ceramic art. A clay body can be decorated before or after firing. Clay-based pottery can be divided into three main groups: earthenware, stoneware, and porcelain. These require increasingly more specific clay material, and increasingly higher firing temperatures. All three are made in glazed and unglazed varieties, for different purposes. All may also be decorated by various techniques. In many examples, the group a piece belongs to is immediately visually apparent, but this is not always the case. The frit ware of the Islamic world does not use clay, so technically falls outside these groups. Historic pottery of all these types is often grouped as either "fine" wares, relatively expensive and well-made, and following the aesthetic taste of the culture concerned, or alternatively "coarse", "popular", "folk" or "village" wares, mostly undecorated, or simply so, and often less well-made. Clay is a term for any type of naturally occurring soil-like material that is rich in aluminium phyllosilicates. The balance of such phyllosilicates alongside other compounds, combined with the conditions of formation and crystal structure determines the physical type of clay, which is grouped into kaolin-type (including kaolin itself), smectite-type (including montmorillonite), and ilite-type (of which ilite is the only major example). Perhaps more useful is grouping clays by their use type - which is indirectly related to their chemical and physical compositions. Most of the clay types discussed here are of the kaolin type.