Some law of woodworking undoubtedly dictates that the difficulty of a project and the amount of labor involved are directly proportional to the chances of messing up at the finishing stage. In retrospect, even the most complicated construction looks easy when you're faced with a bewildering selection of primers, stains, fillers, and finishes. How do you determine, with reasonable success, the properties of various types of finishing materials and their compatibility with the other products you plan to use? Read a lot. Leave the wood unfinished. Or use tung oil.

Tung oil is dead easy to use, builds well, dries quickly, and produces a durable, clear finish with contrast and depth. The oil is extracted from the nut of the tung tree, native to China but also grown in South America. In a pure form, the oil is an amber color, and has the approximate consistency of glycerine. Polymerized oil usually has thinners in it, normally of a purplish cast, which maintain the wood's natural color.

Pure or Polymerized
Unless you are finishing a food-contact item like a salad bowl or spoon, your choice should be polymerized tung. Not only does it dry much faster, but you can use it to create finishes that range from nearly matte to high luster.

Tung oil cures by polymerization (molecules combining to form long chains) and oxidation (combining with oxygen from the air). Polymerized tung oil has been heated to complete the polymerization half of the process. Polymerized tung cures by oil oxidation and evaporation of thinners after application, so the curing (drying) process is faster than that of pure tung.

Pure tung will give you a matte finish because it expands as it polymerizes, creating a fine-textured surface, which, under a microscope, looks somewhat like the surface of the brain. With polymerized tung oil, you get a smooth finish because the expansion has taken place before application.

How to Apply Tung Oil
Both forms of tung oil are easy to apply. They are wipe-on, wipe-off finishes. Both penetrate well, sealing the pores of the wood. And both pure and polymerized tung oil build quite quickly. A sealer coat, plus one or two top coats, is usually all you need for a smooth and durable finish.

Pure Tung
For non-food contact use, always thin with 50% mineral spirits for the first coat. Subsequent coats can be full strength, but must be wiped down after 15 minutes. Always allow ample drying time (48 hours+).

Tung Oil Sealer
Sealer is 20% poly tung and 80% driers. It penetrates well and dries quickly.

High Luster Polymerized Tung Oil
Wipe on, then wipe off after five minutes. Gives a hard, tough finish with a hand-rubbed appearance.

Medium and Low Luster Finishes
For a medium luster finish, add one part Sealer to two parts High Luster. For a low luster finish, add two parts Sealer to one part High Luster.

Some Suggestions for Storing Tung Oil
Although tung oil will keep indefinitely in an airtight container, it will skin over and congeal if stored in a partially filled container. If you find your oil has thickened, you can restore it to its original viscosity by adding mineral spirits.

Once you have opened a new container of tung oil, and used part of the contents, transfer the remaining oil to a variable volume container, or transfer it to several small containers. Baby food jars work well, but they should be checked for a good seal.

– L.L.
03/94


 
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