drying oil, any of several natural oils which, when exposed to the air, oxidize to form a tough, elastic film. The common drying oils are cottonseed oil (see cotton), corn oil, soybean oil, tung oil, and linseed oil; the first three oils mentioned are more properly called semidrying oils. Linseed oil is the most widely used. Drying oils are used mainly in paints, varnishes, lacquers, and printer's ink. Use is recorded as early as A.D. 200 of boiled linseed oil, which dries faster than raw oil. Tung oil is imported from China, and linseed oil mainly from Argentina. Drying oils have also been prepared from various nondrying fish oils (e.g., sardine and herring oils) and from whale oil.