Underpainting is a preparatory monochromatic or limited-palette layer of paint that establishes composition and tonal values before colour is applied.
Underpainting is the practice, central to traditional oil-painting technique, of establishing the composition, tonal structure, and basic forms of a painting in a preliminary layer before any local colour is applied. The underpainting is typically monochromatic — a brown 'imprimatura' (a thin tinted layer over the white ground) was favoured by Caravaggio and his followers; a grey 'grisaille' was a common alternative; the Venetians used warm reddish-brown underpaintings; the Flemish often built their pictures on a green-grey 'verdaccio'. Once the underpainting was dry, the artist worked up the surface in successive layers of opaque scumbles and transparent glazes, building colour and detail over the established tonal structure. Modern conservators using infrared reflectography can often see the underpainting through the finished work, revealing changes the artist made during execution. With the rise of alla prima painting in the 19th century, formal underpainting fell out of fashion among avant-garde painters but has remained essential to academic, classical-revival, and hyperrealist traditions to the present day.