. The most commonly used ones are Resins and wax. Both add to the effect of the oil pants and at the same time affect the sheen and texture of the oil paints. The use of other mediums can even adversely affect the design of the painting. But this is true for any art form that attempt to mix two different mediums. The oil paintings have to be coated with a layer of varnish before it is considered finished. The varnish helps to protect the painting.