Our walnut oil is is cold-pressed from freshly dried walnuts (Juglans regia) grown in California, and then lightly refined. It is a clear, pale yellow oil that is odorless. As a thin oil, it is used to make oil paint more fluid. As it yellows less than linseed oil (but more than safflower oil) it is good for making pale oil colors. Walnut oil dries more slowly than linseed oil, drying in four or five days. It is said to have a less tendency to crack than linseed oil, but this has not be verified by research.
As early as the fifth century walnut oil was recommended by Aetius for varnishing wax pictures and gilt surfaces. It is recommended for all light pigments in the treatises on painting by Leonardo da Vinci, Vasari, Borghini, Lornazzo, Armenini, Bisagno, Volpato, and others.