An earthy material that is malleable or easily shaped when moist but hard when fired, it is composed primarily of fine particles of hydrous aluminum silicates and other minerals. Clay is used for brick, tile, pottery, ceramics and the initial shaping of much sculpture that is ultimately cast in bronze. Source: "Merriam-Webster Online Dictionary"<br><br>1. A native earth consisting mainly of decomposed feldspathic rock (feldspathic: grouping of crystalline minerals that consist of aluminum silicates with either potassium, sodium, calcium or barium) containing kaolin and other hydrous aluminous minerals. Becomes hard when baked or fired. See Terra cotta. Used wet by the sculptor to build or model the form, often over an armature of wood or metal: it is then called wet clay - as compared with what is often called modelling clay 2. Sold under various names such as Plasticine and Plastilina, originally made in Italy with tallow, sulphur and high-quality clay. Also made less expensively with clay, an inert filler and various petroleum oils and greases heated and thoroughly mixed - can be variously coloured, i.e. made with graphite oil it is blackish and yellow/green if made with normal car oil.<br><br>Mud; moist, sticky dirt. In ceramics, clay is the basic material, usually referring to any of a certain variety of mixtures of such ingredients ? fine-grained, firm earthy material that is plastic when wet, brittle when dry, and very hard when heated. There is a temperature with ceramic clays at which their particles fuse (vitrification), and this is most commonly controlled by heating (firing) them in a kiln. The most common types of ceramic clays are earthenware (terra cotta when fired, terra cruda when not), stonewares, and porcelain. Also, a hardening or nonhardening material having a consistency similar to clay, often called modeling clay or Plasticine, and others including polymer clay. Works in clay are more acceptable when unfired if they are expected to be impermanent, or if they were produced by very young children for whom permanency is likely to be unimportant, or if firing the clay is too likely to cause it to break up.Examples of works in unfired clay: Mesopotamia (possibly Nippur. Ur III, c. 2044 BCE), Tablet in an Envelope, clay, Michael C. Carlos Museum, Emery U, Atlanta, GA. A writer who wished to prevent tampering with a letter or another important text sometimes wrapped it, as this one was, in a clay envelope on which the writer re-recorded the text and applied a seal. Any effort to tamper with such a message would then be discovered.