- Two species, Aleurites fordii and Aleurites Montana, are the common tung trees. Historically, China has used tung oil both as a finish and to preserve wooden ships. Because tung oil is nontoxic, you can use it as a sealer for wooden cutting boards and other food surfaces, such as bowls. "Wooden Details" cautions, however, that you should only use pure tung oil for food applications. Other finishes, such as "tung oil rub," may contain varnish or paint thinner as the ingredients. Furthermore, it takes a long time for tung oil to cure fully, or until the smell goes away.
- Many producers of finishes add varnish, paint thinner, or fast-curing compounds to tung oil. According to contributing editor/finish expert Bob Flexner of "Popular Woodworking Magazine," these finishes are a mixture of varnish and thinner. Other finishes contain various amounts of tung oil mixed with other chemicals, such as polyurethane or soya oil. Some finishes do not contain any tung oil but carry the name only.
- Pure tung oil has its pluses and minuses. One plus is the nontoxic factor: Since you'll generally wash wooden cutting boards and bowls after every use, the tung oil will preserve the wood. On the minus side, it does not have a long shelf life. If you see a plastic-like film on the surface, you cannot use the oil, since it will not cure properly. Another minus is the slow curing time. The other finishescame about to overcome the downfalls yet still give woodworkers the appearance of a tung oil finish.
- A tung oil finish will produce a glossy, wet-looking surface. Usually, four or five coats will produce a sufficiently thick finish. After each coat has dried fully, buff the surface with 0000-grade steel wool before applying the next coat. Tung oil accentuates the wood grain, making it highly visible. However, it also accentuates any little scratch or surface imperfection.
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