Does Tung Oil Finish Darken Wood?

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We’ve moved away from wood stains, both water-based and oil-based stains, for our woodworking projects and graduated to drying oils.  We love the look and the feel, and we enjoy the cloth rub to apply it to the wood. There’s nothing wrong with wood stains, and there are projects where we still might turn to one, but wood stains, in our mind, do not compare with a wood oil finish.

Key Points:

  • Tung oil comes from the tung tree, which is native to southern China and Southeast Asian countries.
  • It penetrates wood and dries/cures to a hard and durable surface that is waterproof and resistant to mold and mildew.
  • It does not turn yellow or darken wood over time like linseed oil will.

When we want a little more color or a particular color, we might turn to a Rubio Monocoat.  In fact, at the moment, we are just finishing up a new bed frame project for daughter #1, and Rubio Monocoat was our choice.  We’ve written extensively about Rubio Monocoat because we like it, and you can find past articles about it on drying time, food safety, and waterproofing.

But today, we want to talk about tung oil as a wood finish.  There are many wood oils to choose from, including linseed oil, boiled linseed oil, walnut oil, and others.  Each of those alternatives, like tung oil, is a natural drying oil, and each has its own qualities to consider.  Tung oil, though, stands out to us for a few reasons.  

What Is Tung Oil?

It’s a natural product that comes from the seed of tung trees, which are native to southern China and southeastern Asia.  The seeds come from the fruit of the tung tree, qualifying as a “drupe,” a category that includes cherries, peaches, and plums in that the fleshy fruit surrounds the “pit” in which the seed is found.  

It’s been used as a wood preservative for thousands of years, including in sealing boats.  It has the advantage over linseed oil, another natural product that also comes from a seed (of the flax plant), in that tung oil will not turn a soft yellow as linseed oil does.  This makes it a good choice when using light-colored wood like maple.

Tung oil was used as a waterproofing measure on ships during the Song Dynasty (960 – 1279 CE), and written records of tung oil use date back to Confucius about 2,500 years ago.  In addition to using it to waterproof ships, it was also used to make oil-paper umbrellas, which remain common to this day in China and Japan. It protects the paper from getting wet and thus makes a fine protective umbrella on rainy days.

It hardens when it has been exposed to air, a process referred to as polymerization. In that process, small molecules called monomers (mono = single) are combined chemically and become polymers (poly = many). You may already know that polymers are used to make plastic products, and the process of polymerization in this regard is similar.  This will form a protective film on the wood, a protective film that will offer waterproofing effects.

The coating created by tung oil, when used as a wood finish, is transparent and has a deep, damp look, that “wet” look that has become popular, for instance, with lip gloss products. When used as a finish on wood, and after numerous coats, it can even acquire an almost plastic appearance.

It enhances the features of the wood grain and creates a warm and glossy finish to the wood.  As we said, it also provides a waterproof finish, something that neither a stain, a water-based or an oil-based stain, can do. 

After applying several coats, and we’ll address this in a moment, tung oil will provide not only strong water resistance but, with both a thinned and a thicker application, will create that hard surface that will be waterproof. It offers a beautiful finish to your woodworking project, and as you will see when you read on, it is also a safe finish.

Like linseed oil, it is eco-friendly, non-toxic, and food safe.  The FDA has stated it as food safety, and the FDA regulations about the use of oil finishes as of January 2023 say as much.  As such, food-grade tung oil is a good choice for kitchen use on butcher blocks, countertops, cutting boards, salad, dessert, cereal bowls, salad utensils, and many others.  It is also a favorite of the craftsmen who make musical instruments. 

It requires more coats than other oils, as it penetrates into the wood fibers and is absorbed into the wood.  When it dries, it forms a hard and durable surface on the wood that is waterproof and resistant to mold and mildew. 

It should always be used in its 100% purity rather than some other form of tung oil compound where other oils are added.  However, it can be thinned with a citrus solvent like Orange Oil Natural Citrus Solvent, which will evaporate as it dries, leaving a pure tung oil coating.  Mineral spirits can also be used to thin it.

Mineral spirits don’t have the pleasant and mild citrus-y, smell, but they will still thin the tung oil.  the thinning ratio for each is 1:1 if you want to reduce its viscosity for easier application.  D-Limonene is another thinning agent that works well to thin out tung oil.

Applying Tung Oil To Wood

Don’t skimp on your first coat.  Remember, the wood will absorb tung oil, and you want it to penetrate the wood deeply.  It can be applied by brush (bristle or foam), but we prefer to use a clean cloth for the pleasure of a hand-rubbed finish. Rub in the direction of the wood grain, too.

Allow that first coat to sit for at least 24 hours, and then apply a second coat.  After waiting for the wood to absorb more of the oil and dry to the touch, use 0000-grade steel wool to gently rub the wood surface before adding a 3rd coat.  We recommend a minimum of 4 coats of the oil on your project, although, on more porous woods, an additional coat or 2 might be warranted.

Waiting an hour between coats is recommended, as we say.  Give each coat at least 24 hours before you consider adding the next.

At every point, be sure to wipe off excess oil that has not been absorbed.  

After you have finished the number of coats you have decided to apply, allow the project to sit untouched. The oil will take 2 – 3 days to begin to harden and will thereafter begin to cure in about 10 days.  After that, you should expect between 2 – 4 weeks to fully cure.  Once the tung oil finish has cured, you will have a durable finish that is not only water-resistant but also waterproof. It will cure faster in a warmer room, too.  

This protective finish will last a long time for you, and the durable finish will need only an occasional touch-up every year or so, depending on appearance.  This will depend on how the workpiece is used; if it’s walked on or used frequently where wear and tear may take a toll, it might need touch up more frequently. Even then, though, a thinned oil rubbed on and allowed to dry will be enough to restore its original appearance.

A tung oil finish will have a glossy appearance that will harden to an almost plastic-like look, but in a good way.  Food contact will be safe, and the protective film will not allow any food bits to embed that could lead to bacterial growth.

No other sealant is necessary when using tung oil, as it will dry and cure to a resistant finish that will protect the wood.  No topcoat like polyurethane or shellac is needed.

Tung Oil and Linseed Oil Comparisons

We’ve mentioned linseed oil as another wood finish, and yes, it does dry faster than a tung oil finish.  Faster, though, is not necessarily better.  There are some other differences worth noting, though.

  • Tung oil creates a harder finish that is more durable than linseed oil
  • Tung oil is more water-resistant than linseed oil
  • Raw linseed oil will take much longer to fully cure than tung oil
  • Tung oil costs more than linseed oil
  • Linseed oil will dry and cure to a yellow hue over time.  It will also tend to darken the wood if it is not in direct sunlight.  
  • Tung oil, though, does not develop that yellow hue and will not darken the wood.  

We were recently asked by one of our readers about these oils for use on teak.  His boat has a teak deck, and we wanted to know which, if either, would darken his teak.  We recommended tung oil to him as it will not, whereas linseed will over time.

Downside To Tung Oil

We like tung oil and are hard-pressed to provide a list of its downsides.  But, to be fair, we will mention that yes, it does take some work:  more coats should be applied than linseed oil; it may require more maintenance coats every year, if not every 6 months depending on use, wear & tear; there is an odor to tung oil, although it is a natural, nutty aroma; and, it costs more than linseed oil.

All in all, though, these are minor concerns, at best, and should not dissuade you from using them.  It doesn’t hold us back at all.

Some Video Thoughts About Tung Oil

This video makes some important distinctions between pure tung oil and tung oil products.  We’ve mentioned in several places that distinction and have discussed using pure tung oil.  In this video, the woodworker distinguishes between pure oil and oil products, some of which may not include any tung oil, notwithstanding the fact the label may call it tung oil.  

A tung oil finish is beautiful.  Master craftsmen and musical instrument makers choose it for that reason.  That’s why we choose it, too, and that’s why we think you should, as well.  

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