White coating used as a ground for painting and in the preparation of wood for gilding. It comprises glue-size, mixed with either calcium sulphate (a form of gypsum), which produces the soft gesso that was used in Italy in the Renaissance, or calcium carbonate (chalk), which produces a hard gesso that was used in northern Europe. It is inflexible and absorbent and, once dry, may be worked to produce a smooth surface. Variations on the basic recipe occur, notably the inclusion of white pigment to increase its brilliance. Gesso grosso is a traditional form made from burnt gypsum and hide glue. The glue slows down the setting action of the plaster and makes it considerably harder when dry. Similar compositions are used in decorative plasterwork. Gesso grosso is comparatively coarse and was used as a base coat on wooden panels being prepared for tempera painting. It would be covered with several coats of gesso sottile, another traditional form made by steeping burnt gypsum in an excess of water and stirring it to prevent setting. Gesso sottile is fine, soft, and smooth; it was originally bound with parchment glue for use. Cennino Cennini, writing in the 14th century, describes the use of these materials, as does Pacheco, who, writing in the 17th century, refers to them as yeso grueso and yeso mate.