A natural, colourless drying oil pressed from the nuts of a walnut tree, Juglans regia. Walnuts contain approximately 65% oil. The cold-pressed oil is pale yellow while the hot-pressed oil has a green tinge. Walnut oil dries slower, yellows less and cracks less than linseed oil; it dries faster than poppy seed oil. It was popular as a paint medium in Italy, the Netherlands and Germany. Walnut oil will turn rancid and develop a strong odour on storage. The application of oil, including nut oil, to the surface of stucco marble has always been quite common in order to increase the gloss of an already well polished surface. Synonyms: nut oil. Wittenburg (1999); Museum of Fine Arts, Boston (2000). [J. Cassar, R. de Angelis]