For information on the processing of fixed vegetable oils, see . Exposure to air causes fixed oils to thicken. Drying oils absorb oxygen from the air to form a tough film. They are widely used to make paints and varnishes. Important drying oils include linseed, perilla, tung or chinawood, soybean, oiticica, hemp, walnut, poppy seed, and sunflower.
Linseed oil comes from flax seeds.
It is one of the most important drying oils. It is used in making paints and varnishes. Tung oil is a valuable oil used in waterproof varnishes and quick-drying enamels. Semidrying oils absorb oxygen from the air to become very thick, but not hard. Cottonseed, corn, and sesame oils are of the semidrying type.