From Yangtze: Nature, History, and the River, by Lyman P. Van Slyke (Stanford Alumni Assn., 1988), pp. 106-107, 109:
If tea and silk are full of history and romance, familiar to all and identified with China, tung oil is a blue-collar product few have ever heard of. But tung oil resembles these more aristocratic products because its properties, like theirs, are unmatched by any other natural substance and because it was produced almost nowhere else. Although used in China for millennia, it did not attract international attention until the late nineteenth and early twentieth centuries. The tung oil trade grew spectacularly in both volume and unit price between 1918 and 1937, with about 70 percent of the product shipped to the United States. In 1937, the first year of the Sino-Japanese War, over 20,000,000 gallons were exported (at about $1.40 per gallon), making it China’s most valuable single trade product. In just a few years, tung oil had soared past tea, cotton yarn, metals, eggs and egg products, skins and furs, and raw silk. War devastated this trade and U.S. chemical industries, impelled to invent alternatives for many products now unavailable, developed petroleum-based substitutes to take the place of tung oil in most uses. In this, too, tung oil resembles silk, which also fell victim to the chemical industry’s rayon and nylon.
Tung oil is classified as a “drying oil,” by which is meant that when exposed to air it oxidizes readily, forming a tough, hard, waterproof film. Tung oil can be applied alone as a waterproofing varnish, and this is one of its main uses in China. The Chinese also use tung oil for preparing caulking materials (chunam), dressing leather, waterproofing paper, making soap, treating skin afflictions, and producing lampblack for solid inksticks.
But perhaps its most important function is (or was) in the manufacture of paint…. For this purpose, tung oil is superior to linseed oil, traditionally the most widely used drying oil in Europe and the United States; tung oil dies faster and produces a harder, more durable film.
Tung oil (sometimes also called wood oil) is obtained from the nut of the tung tree (Aleurites cordata) [now Vernicia cordata], which is native to China. Almost all commercially grown tung trees are found in the central provinces, north and south of the Long River, particularly in Szechwan and Hunan. As the demand grew, more and more trees were planted, particularly on hilly, otherwise unproductive land along the navigable tributaries of the Long River, in order to reduce the cost of overland transport—usually by shoulder pole—which could quickly erode the profits to be made.
Had the war and war-induced substitutes not intervened, tung oil would almost certainly have had a bright future. Indeed, so valuable was the product that in the 1930s efforts were made to experiment with tung plantations along the Gulf Coast of Florida, Mississippi, and Louisiana, but DuPont’s chemists made them unnecessary just as they were beginning to produce a little oil.