The material applied to a support in order to prepare it for painting. The term can be synonymous with the word priming. Different types of grounds can be loosely associated with different periods and schools of painting. Grounds were often colored with pigments and filler materials. In Northern European Renaissance painting, for example, grounds were traditionally made from mixtures of chalk (calcium carbonate) and rabbit-skin glue; in Italy during the same period, gypsum (calcium sulfate) was used. Venetian painters of the Renaissance favored red grounds; this practice eventually led to the wide use of a variety of ground colors, including dark earth tones, blacks, and even rich grays. Grounds of lead white and oil were popular during the late eighteenth and nineteenth centuries.

Many artists have used double grounds, choosing to use different colors in distinct layers that, in combination, produce a special effect.

Source: Looking at Paintings: A Guide to Technical Terms / eds. Tiarna Doherty and Anne T Woollett. (Los Angeles: J. Paul Getty Museum, 2009), p. 40.