In visual arts, the ground (sometimes called a primer) is a prepared surface that covers the support of the picture (e.g., a canvas or a panel) and underlies the actual painting (the colors are overlaid onto the ground). Occasionally the term is also used in a broad sense to designate any surface used for painting, for example, paper for watercolor or plaster for fresco.[1]
The main purposes of the ground are to block chemical interactions between the paint and the support and to provide desired texture for painting or drawing.[1]
The ground is also used to highlight the colors,[1] and its color and tone affect the appearance of paint levels above, therefore the painters might have individual preferences for the color of the ground: 19th century artists, especially the impressionists, preferred the white ground (first used by J. M. W. Turner[2]), while Rembrandt preferred brownish tones and Poussin the red ones.[3] The oil painting becomes more transparent with age, so to avoid a gradual brightening of the picture, a pale beige color of ground is considered neutral.[4] White ground provides the greatest freedom of choice for colors, while colored grounds reduce the color range and force the use of more opaque paint application.[1]
For paintings on panels, gesso is typically used as a ground; on canvas the ground can be yet another (inert) paint layer.[5][3] Two layers are occasionally applied, forming a double ground.[3] On canvas, the ground is typically applied after sizing (typically rabbit-skin glue). Although it is possible to paint on the sized canvas directly, without any ground at all,[6] size is not a replacement for ground, as it is not intended to form a level surface for painting, its purpose is to simply fill pores and isolate the canvas from the overlaying paint.[7]
Oxford Companion to Art lists the following requirements for the good ground:[1]