Colorless Painting Medium - Lefranc & Bourgeois - The essential medium for oil painting. A fairly recent innovation, compared with oil painting, this medium includes synthetic resins that give it a greater lightfastness than natural resins, while being very easy to use. This colorless painting medium is formulated with ketone resin, heated oil and rectified turpentine. Perfect for glazes, it provides rapid setting (one hour), smoothes out brushstrokes, heightens gloss, and increases the transparency and brightness of colors.