The Oil Painting Medium. Improves flow, increases gloss. Add directly to color or thin with "Grumtine," which I've never used. Mixed with turp is the best medium for oil once you've got a nice, dry i.e. turpentine only, background. When used excessively it creates that 'waxy' look that seems so familiar on canvas. Used even more excessively, it will run according to gravity versus how thick you paint.