Glazed architectural terra-cotta

Glazed architectural terra-cotta is a ceramic masonry building material used as a decorative skin. It has been popular in the United States from the late 19th century until the 1930s, and still one of the most common building materials found in U.S. urban environments. It is the glazed version of architectural terra-cotta; the material in both its glazed and unglazed versions is sturdy and relatively inexpensive, and can be molded into richly ornamented detail. Glazed terra-cotta played a significant role in architectural styles such as the Chicago School and Beaux-Arts architecture.

The material, also known in Great Britain as faience and sometimes referred to as "architectural ceramics", was closely associated with the work of Cass Gilbert, Louis Sullivan, and Daniel H. Burnham, among other architects. Buildings incorporating glazed terra-cotta include the Woolworth Building in New York City and the Wrigley Building in Chicago.

Glazed architectural terra-cotta offered a modular, varied and relatively inexpensive approach to wall and floor construction. It was particularly adaptable to vigorous and rich ornamental detailing. It was created by Luca della Robbia (1400-1482), and was used in most of his works.

Terra-cotta is an enriched molded clay brick or block. It was usually hollow cast in blocks which were open in the back, with internal stiffeners called webbing. Webbing substantially strengthened the hollow blocks with minimal weight increase. The blocks were finished with a glaze, with a clay wash or an aqueous solution of metal salts, before firing. Late 19th century advertising for the material promoted the durable, impervious and adaptable nature of glazed architectural terra-cotta. It could accommodate subtle nuances of modeling, texture and color. Compared to stone, it was easier to handle, quickly set and lower cost. The cost of producing the blocks, when compared to carving stone, was a considerable saving, especially when casts were used in a modular fashion—that is, used repeatedly. It never needed paint, and periodic washings restored its appearance.

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