The painting surface consists of a support, either a wood or composition panel, or more frequently, linen, cotton, or jute canvas stretched on a frame or glued to a board. The support is covered with a ground, a thin coating of gesso or other gypsum and glue, or size. The ground makes the support less absorbant and provides an even painting surface that is neither too rough nor too smooth. The ground may be white but is often given a toning coat of gray, tan, or pink.

Traditionally, oil painting proceeds in stages. First the design may be sketched on the ground in pencil, charcoal, or paint diluted with turpentine. Then broad areas of color are filled in with thin paint. They are successively refined and corrected in thicker paint to which oil and varnish are added.

The paint is usually applied with brushes made from stiff hog bristle, although softer brushes of badger or sable hair may be used. Paint may also be applied with a flexible, wide-bladed painting or palette knife, or the fingers. The process may require only a few sessions or extend over months or even years.

Once the painting has dried, at least a year after completion it is varnished to protect it from dirt and to enrich the color. Because all varnishes eventually darken, the varnish used should be removable and eventually replaced.

3. HISTORY  

Oil painting was traditionally thought to have been invented by the Flemish painter Jan van Eyck in the early 15th century, but it is now known to have existed earlier. Van Eyck explored the medium within the linear conventions of tempera, making a detailed drawing on a gesso-covered panel and then building up layers of transparent oil glazes.

The technique was popularized in Italy by the Sicilian painter Antonello da Messina and was fully exploited by Renaissance painters. The Venetians took the further step of painting on canvas, which provided a much larger surface and could be rolled up for shipping.

They developed a freer style based on a rough monochrome underpainting in tempera with added oil glazes. Dutch painters such as Rembrandt and Frans Hals and the Spanish painter Diego Velázquez experimented with impasto. Academic painters of the 18th and 19th centuries did under-painting in black and gray oil, then repainted in color. The range of colors was limited, however, and many have faded. All work was done in the studio.

In the 19th century, developments in chemistry produced new and brilliant pigments. The invention of collapsible tin tubes, replacing the old bladders, meant that artists could work outdoors directly from nature. Chemical additives to keep paint fresh made possible greater use of impasto. Underpainting virtually disappeared. French impressionists applied masses of small dots of bright color directly to the canvas.

With the development of nonobjective painting in the 20th century, painters experimented with new techniques. They built up texture with sand, ashes, or plaster, stained canvases, and worked with commercial house paints and spray paints.

They combined paint with photography and printed materials in collage. The versatility of oil paint has made it one of the most expressive media of the 20th-century artist; nevertheless, since the 1960s many artists have found acrylic paints better suited to their needs