Oil paints may require the use of thinners such as white spirit or turpentine , various types of vegetable oils (sometimes unrefined thinners have a pungent odor. There are no water-miscible oil paints. There is a type of tempera - "wax-oil", which can be mixed with oil paints and behaves like oil, or with gouache and water-soluble tempera - then it behaves like tempera.Oil paint layers may turn yellow over time if low-quality varnishes were used during application.Some natural pigments also lose their color intensity over time, their shades go yellow or turn gray.