History
Terracotta is a clay-based unglazed or glazed ceramic,where the fired body is porous.The term is also used to refer to the natural, brownish orange color, of most terracotta, which varies considerably. Glazed architectural terracotta and its unglazed version were used in Asia for some centuries before becoming popular in the West in the 19th century.
Terracotta/earthenware was the only type of ceramic produced by Western and pre-Columbian people until the 14th century, when European higher fired stoneware began production. Terracotta has been used throughout history for sculpture and pottery as well as for bricks and roof shingles. In ancient times, the first clay sculptures were dried (baked) in the sun after being formed. They were later placed in the ashes of open hearths to harden, and finally kilns were used, similar to those used for pottery today. However, only after firing to high temperature would it be classed as a ceramic material.
Production and properties
An appropriate refined clay is formed to the desired shape. After drying it is placed in a kiln or atop combustible material in a pit, and then fired. The typical firing temperature is around 1,000 °C (1,830 °F), though it may be as low as 600 °C (1,112 °F). The iron content, reacting with oxygen during firing, gives the fired body a reddish color, though the overall color varies widely across shades of yellow, orange, buff, red, "terracotta", pink, grey or brown.In some contexts, such as Roman figurines, white-colored terracotta is known as pipeclay, as such clays were later preferred for tobacco pipes, normally made of clay until the 19th century.
Fired terracotta is not watertight, but surface-burnishing the body before firing can decrease its porousness and a layer of glaze can make it watertight. Terracotta, if uncracked, will ring if lightly struck. Some types of terracotta are created using recycled terracotta ("grog").
Painted ("polychrome") terracotta is typically first covered with a thin coat of gesso, then painted. It has been very widely used but the paint is only suitable for indoor positions and is much less durable than fired colors in or under a ceramic glaze. Terracotta sculpture was very rarely left in its "raw" fired state in the West until the 18th century.
