What do artists put on canvas before painting?

What artists put on canvas before painting depends on medium and desired effect, but most commonly they apply a primer called gesso to prepare the surface. Gesso, typically white acrylic gesso, is a mixture of binder, chalk, and pigment that seals the canvas fibers, prevents paint from soaking directly into fabric which would cause deterioration especially with oil paints, and creates a slightly textured, absorbent surface that helps paint adhere and colors appear vibrant. For acrylic painting, one to three coats of acrylic gesso, lightly sanded between coats, is standard, though many pre-stretched canvases come pre-primed with gesso. For oil painting, artists may use acrylic gesso or traditional oil-based primer like lead or titanium oil ground after sizing the canvas with rabbit skin glue or acrylic medium to prevent oil rot. Some artists also apply a toned ground, such as a thin wash of burnt sienna or gray acrylic, called imprimatura, to set overall mood and make color judgment easier. Others add texture paste or modeling paste for texture. So most artists put gesso primer before painting, sometimes followed by toned wash, to seal, protect, and create ideal painting surface.