Fat oil is formed when pure spirits of gum terpentine is allowed to evaporate. It is commonly used to mix with powdered paints because it stays open for a long time. Many artists blend fat oil with other natural oils to create a specific amount of drying time in their painting mediums. Add fat oil to your medium if you want to increase the time before the medium dries. Made in Germany, it is supplied in 1 ounce bottles. California residents see Prop 65 Warnings