Wikipedia
Pastiglia , an Italian term meaning "pastework", is low relief decoration, normally modelled in gesso or white lead, applied to build up a surface that may then be gilded or painted, or left plain. The technique was used in a variety of ways in Italy during the Renaissance. The term is mostly found in English applied to gilded work on picture frames or small pieces of furniture such as wooden caskets and cassoni, and also on areas of panel paintings, but there is some divergence as to the meaning of the term between these specialisms.
On frames and furniture the technique is in origin a cheaper imitation of woodcarving, metalwork or ivory carving techniques. Within paintings, the technique gives areas with a three-dimensional effect, usually those representing inanimate objects, such as foliage decoration on architectural surrounds, halos and details of dress, rather than parts of figures. In white lead pastiglia on caskets, the subject matter is usually classical, with a special emphasis on stories from Ancient Roman history.