Oil paints are made by mixing pigments that contain color with oil. Different colors consist, or today buy pre-mixed, before the painting begins, but further shades of color are usually obtained by mixing small quantities together as the painting process is ongoing, traditionally on an artist's palette, thin wooden boards held in hand. Pigments may be a number of natural or synthetic ingredients with colors, such as sulfur for yellow or cobalt for blue. Traditional pigments are based on minerals or plants, and many have proven stable over a very long period, so many old paintings look very different from their original appearance. Modern pigments are often used synthetic chemicals. Pigments are mixed with oil, usually flaxseed oil but other oils can be used too. Different dry oils have different effects.
