Oil painting is the process of painting with pigments that are bound with a medium of drying oil — especially in early modern Europe, linseed oil. Often an oil such as linseed was boiled with a resin such as pine resin or even frankincense; these were called 'varnishes' and were prized for their body and gloss. Other oils occasionally used include poppy seed oil, walnut oil, and safflower oil. These oils confer various properties to the oil paint, such as less yellowing or different drying times. Certain differences are also visible in the sheen of the paints depending on the oil. Painters often use different oils in the same painting depending on specific pigments and effects desired. The paints themselves also develop a particular feel depending on the medium.
Oil paint was first used, as current knowledge shows, in western Afghanistan sometime between the 5th and 9th Centuries. From there its practice likely migrated westward until, when in the Middle Ages, (Theophilus mentions oil media in the 12th Century) it came into use, although not widespread, in Europe. It later became the principal medium used for creating artworks; the transition beginning during the 15th century with Early Netherlandish painting in northern Europe. By the height of the Renaissance oil painting techniques had almost completely replaced tempera paints in the majority of Europe. (Reference: http://en.wikipedia.org/wiki/Oil_painting)
Public Art & Design For This Medium