What is oil on canvas?

A type of paint that dries slowly and consists of pigment particles suspended in oil for drying, mostly linseed oil. By adding a solvent like turpentine, the paint's viscosity may be modified and vanish can also be added to increase glossiness of the paint film that's dried. Use of oil began long time ago in Europe from as early as the 12th century where it was commonly used for decoration. It was however, not adopted to be used as a medium up until the 15th century.