Tung oil or China wood oil is a drying oil obtained by pressing the seed from the nut of the tung tree (Vernicia fordii). As a drying oil, tung oil hardens (dries) upon exposure to air. The resulting coating is transparent and plastic-like, a property exploited in most of its applications, which include wood finishing and the composition of oil paints and printing inks. Related drying oils include linseed, safflower, poppy, and soybean.The oil and its use are believed to have originated in ancient China and appear in the writings of Confucius from about 400 B.C. Raw Tung oil tends to dry to a fine wrinkled finish; the US name for this is gas checking: this property is used to make crystal finishes. To stop this, the oil is heated to gas-proof it, and most oils used for coating are gas-proofed. This property was used to make wrinkle finishes, usually by adding excess cobalt drier.