We were discussing finishes the other day with a friend, a fellow woodworking hobbyist, and in particular, our current preferences. We talked about stains and topcoats and such, finish products we’ve both used in the past, and we found we’d both moved from them for our projects.
He is working on a new exotic wood for an addition to a small altar in his home (he’s a monk), and I’m working on a new bed frame for my daughter. As an aside, when it’s done, pictures will be shared, as well as the story of its construction. He is intending to use tung oil on his piece, and I’m going to be using Rubio Monocoat, a product we’ve presented here often.
Neither of these two products will come in contact with food, but since we have already written about Rubio Monocoat and food safety, we turn now to tung oil and whether it is rated as being food safe.
The Tung Tree, Its Seeds, and The Oil From Them
The tung tree grows in southern China and has been specifically grown for tung oil which is derived by pressing the seeds that come from the nut of the tung tree. Its botanical name is Vernicia Fordii, for those of you who like Latin.
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. The name “tung” is a somewhat Anglicized version of the Chinese word tong, a word that, in a different context, also means “boy.”
In addition to using it to waterproof ships, tung oil 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.
Tung oil 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.
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.
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.
Some of the more well-known and often-used oils include linseed oil, safflower oil, walnut oil, and soybean oil. You have probably used linseed oil, or boiled linseed oil, in your woodworking projects, too, as both a protector or preservative, at the least on your front door step, a very common use.
We’ve written about linseed oil in the past and know that it, too, is organic and comes from the flax seed. In its rawest form, without any additives, it is a safe and non-toxic oil that you can even purchase in capsule form as a dietary supplement for its omega-3 fatty acids. It, too, is food safe in its rawest form as a finish for wood.
Using Tung Oil As A Wood Finish
Tung oil is a popular wood finish product today. It is favored not only because it is a natural substance but also because it dries and cures to a hard finish that is easy to repair. It is a common finish on wooden boat decks and even on new floors.
When finishing fine-grain wood, it is often thinned to reduce its viscosity and allow it to penetrate deeply into the wood fibers. Citrus-based thinners have also become somewhat popular for this purpose, one of which is D-Limonene, a natural product that is produced by distilling citrus peels (lemons, oranges, etc).
It is a somewhat volatile product, and you should become aware of the precautions on container labels and follow them carefully. For instance, it should be kept safe from children who might be attracted to its citrus smell and think it is safe to drink. It evaporates fairly quickly as the thinned tung oil dries and leaves no toxic or unsafe trace behind.
When working with softer woods that will be more porous, less thinning may be required for the oil to penetrate deeply into the wood fibers. If you have any questions about hardwoods and softwoods and their porous natures, we’ve written many articles on them, and a quick search of this site (see that little magnifying glass icon in the upper right?) on a wood to determine whether it is a hardwood or softwood, will turn up many results.
How To Apply Tung Oil
The how of applying tung oil to your project will depend a little bit on the type of wood you are using. We’ve already mentioned fine-grained woods, but sometimes we’re working with more porous woods, and each will absorb a chosen finish in different ways.
You will want to dull the wood’s surface to a matte appearance using a scouring pad to scratch the surface. This will prepare it to absorb the oil deeply. Use a paper towel or clean cloth to apply a good coat of the oil and allow it to sit for 10 minutes or so to allow the wood to take it in, and then wipe off any excess. Let the application set for at least a half day, or overnight, before considering a second coat.
When it comes to coats of tung oil, two coats of thinned oil will be better than one thick coat. More oil will be absorbed, and thus more protection for the wood.
Tung Oil and Food Safety
We’ve already established that tung oil is a natural product derived from seeds in the nut of the tung tree. In its pure form, with no additives or thinners, it is non-toxic and safe. As such, you might have guessed it is food safe.
But, to establish that with some more authority than this article, we consulted the FDA as a part of our research. When searching for government agency policy, you go to the Code of Federal Regulations (CFR), where all agencies publish their regulations.
The FDA regulations and policies can be found in the Code of Federal Regulations Title 21, where in section 175, resinous and polymeric coatings are discussed. That sounds pretty boring, we know, but it is authoritative.
In the section on “drying oils,” including fatty acids (remember that from earlier?), a long list of oils appear, including:
- Chinawood (tung)
- linseed (remember that one, too?)
- and many others.
These drying oils are deemed to be, in their pure form, food safe, meaning food may come in contact with them without issue for eating.
These regulations are current as of January 17, 2023.
Using Tung Oil in a Food-Safe Way
When working with tung oil, you want as deep a penetration into the wood as possible. This will take several applications, and we tend to lean toward three as a good finish. Make sure you have a pure tung oil product and not one containing any additives or thinners.
Your wood should be very finely sanded smooth, to at least a 400-grit level, if not a 600-grit smoothness.
For a hard wood with a fine grain, the oil should be thinned to a 50/50 mixture of oil to thinner. Again, we recommend a citrus-based thinner, the distillation of citrus peel, as long as you follow the safety precautions on the container label. For a softer, more porous wood, a 70/30 mixture, oil to thinner, may work better for you. This is where experimentation comes in on a scrap of wood to make sure it will be what you want for your finish.
Applying a thin coat of the thinned oil, let it stand for 10 – 15 minutes to be absorbed. Resist the temptation to load up on the first coat or to touch it too soon. After that time has passed, wipe off the excess, and let it alone for 24 hours. Yes, 24 hours.
After you’ve waited patiently for a day, thin out the tung oil to an 80/20; mix oil to thinner and apply it, and rub it in with wet and dry sandpaper, and after another 150 minutes, wipe the excess away.
If you are working with a softwood, you might want to add a second coat of the first thinned oil, and then after drying, move to the 80/20 mixture application.
With respect to the sandpaper you use in rubbing in the second (or third) coat, use one higher grit than you used in the pre-oil sanding. If you used 400-grit paper, go to a 600-grit; if you used a 600-grit, go to 800-grit paper.
The wet and dry sandpaper rubbing will create a desirable wood grain filler that will take in the final oil application and lead to a smooth and even color of the wood, and the appearance will be of a natural oil finish on your project.
Don’t touch it for at least 24 hours once again, and then only to move it if necessary. Your project should be ready to use 24-48 hours later.
What Projects To Use Tung Oil With For Food Safety
Now let’s turn to the types of woodworking projects for which tung oil is a good choice. We want it to be safe for contact with food, but it’s important to know which kitchen or table items will be safe.
On the list would be such turned items as salad bowls of all sizes, cereal bowls, and even soup bowls. Salad-tossing utensils would also be on that list, as well as large wooden spoons for mixing.
As for wooden countertops, though, there is a caveat. It’s the same caveat that applies to wooden cutting boards. Knives can penetrate the surface of the oil coating after repeated use, and this would expose the wood beneath the cut to food items and juices to penetrate, where they could contaminate the countertop or board for future use.
If you will be sure that a cutting board (plastic or non-wood, at least) will be used always in the kitchen, tung oil can be a safe finish for your countertop. But, for cutting boards, you do run the risk of breaking the surface and allowing food bits and juices to seep in and cause some contamination (bacteria).
While this has little to do with food safety but rather with health considerations, it is nonetheless an important point. The waterproof finish afforded by using tung oil is good only until you break the surface with your knife. So, be careful and be smart.
Video Discussion on Food-Safe Wood Finishes
We found a video that confirms what we have reported to you, so if you don’t want to take our word for it, or the word of the US FDA, here’s a fellow woodworker discussing food-safe finishes.
Pure tung oil is food safe. Follow our suggestions for its application, and then sit back without worrying about it being food safe. Drying time, curing time, the wood you use, the environment in which your project will sit will all affect when you can safely use your bowl or spoon, or countertop.
But, other than that, it’s a safe finish, and you and your family will be fine.