Cold pressed linseed oil. Linseed oil is the most widely used fatty oil for diluting oil paints. It dries faster than safflower oil and forms a harder film. The negative effect of linseed oil is yellowing on older paintings, so if you want to limit yellowing, we recommend using it on darker paints and using polymerized linseed oil or thinner on lighter paints. The oil can also be thinned with turpentine or mineral spirits.