Term: Gesso

Gesso is a white paint mixture used as a preparation for any number of supports (as both sizing and primer). Its absorbency allows it to work with all painting media, including water-based media, different types of tempera, and oil paint. Historically gesso consisted of a binder mixed with chalk, gypsum, pigment, or any combination of these. It was applied only to rigid surfaces because it dried brittle. Modern gesso is a combination of calcium carbonate mixed with an acrylic polymer medium (or latex) and is flexible enough to be applied to canvas and other non-rigid supports. The color of gesso is usually white but it can be tinted, either commercially or by the artist.

Although it is generally believed to be acceptable, some question whether modern gesso should be used under oil paint. Certain materials that are used in oil painting, such as mineral spirits, can leach through the gesso and damage the surface.