High quality linseed oil modified by the removal of the parts of the oil (fractions) that reject water.  The result is an oil that improve flow, increases gloss, and yet does not significantly alter drying time.  It does not inhibit MAX oils from mixing freely with water and actually enhances the water mixibility of colors.  Although compatible with conventional oil paints and mediums, it will not make them water mixible.  In a 2.5oz. bottle.