Are yams and sweet potatoes the same?
(Italian: "scratched"), in the visual arts, a technique used in painting, pottery, and glass, which consists of putting down a preliminary surface, covering it with another, and then scratching the superficial layer in such a way that the pattern or shape that emerges is of the lower colour. During the Middle Ages, especially in panel painting and in the illumination of manuscripts, the ground was often of gold leaf. In wall painting, or mural painting, two layers of different-coloured plaster are usually employed. In stained glass, the scratching is done through a top layer of coloured glass, revealing clear glass beneath; in pottery the pattern is incised through a white or coloured slip (mixture of clay and water washed over the vessel before firing), revealing the body colour beneath. Sgraffito ware was produced by Islamic potters and became common throughout the Middle East. The 18th-century scratch blue class of English white stoneware is decorated with sgraffito patterns touched with blue. Sgraffito ware was produced as early as 1735 by German settlers in colonial America