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. (

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