Oil painting is the process of painting with pigments with a medium of drying oil as the binder. Commonly used drying oils include linseed oil, poppy seed oil, walnut oil, the choice of oil imparts a range of properties to the oil paint, such as the amount of yellowing or drying time. Certain differences, depending on the oil, are visible in the sheen of the paints. An artist might use different oils in the same painting depending on specific pigments and effects desired. The paints themselves also develop a particular consistency depending on the medium, the oil may be boiled with a resin, such as pine resin or frankincense, to create a varnish prized for its body and gloss. Its practice may have migrated westward during the Middle Ages, Oil paint eventually became the principal medium used for creating artworks as its advantages became widely known. In recent years, water miscible oil paint has come to prominence and, to some extent, water-soluble paints contain an emulsifier that allows them to be thinned with water rather than paint thinner, and allows very fast drying times when compared with traditional oils. Traditional oil painting techniques often begin with the artist sketching the subject onto the canvas with charcoal or thinned paint, Oil paint is usually mixed with linseed oil, artist grade mineral spirits, or other solvents to make the paint thinner, faster or slower-drying. A basic rule of oil paint application is fat over lean and this means that each additional layer of paint should contain more oil than the layer below to allow proper drying. If each additional layer contains less oil, the painting will crack. This rule does not ensure permanence, it is the quality and type of oil leads to a strong. There are many media that can be used with the oil, including cold wax, resins. These aspects of the paint are closely related to the capacity of oil paint. Traditionally, paint was transferred to the surface using paintbrushes. Oil paint remains wet longer than other types of artists materials, enabling the artist to change the color. At times, the painter might even remove a layer of paint. This can be done with a rag and some turpentine for a time while the paint is wet, Oil paint dries by oxidation, not evaporation, and is usually dry to the touch within a span of two weeks. It is generally dry enough to be varnished in six months to a year, art conservators do not consider an oil painting completely dry until it is 60 to 80 years old
Image: Mona Lisa, by Leonardo da Vinci, from C2RMF retouched
Self-portrait of Rembrandt, 1630. An example of oil painting on copper.