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Saturday, April 20, 2013

Finishing with Tung Oil

Learn how to finish a  woodcarving  with Tung Oil...


If you want to achieve natural finish for one of your carving projects, consider using pure Tung oil.  This traditional finish penetrates deeply into the wood and over time its surface cures hard, providing limited scratch resistance and water resistance. As the finish ages, it will yellow slightly, producing a warmer appearance.
Tung oil penetrates deeply into the wood. As the finish ages, it will yellow slightly, producing a warmer appearance. 
While finishing with oil can produce an aesthetically appealing appearance, there is a downside. Pure Tung oil is not used frequently because its application is very time consuming.  To achieve a pleasing satin finish that resists water, you need to apply at least six or seven coats. What’s more, the surface does not harden for a month after the final application of oil.


To achieve a pleasing satin finish, apply at least six or seven coats of tung oil.


What is Tung Oil? 


 Tung oil was first “Made in China” more than 1500 years ago. The oil itself is pressed from the nuts of the Tung tree, native to the southern part of that country. (CAUTION: If you are allergic to nuts, you could potentially suffer a reaction to this finish.) While the Chinese have used Tung oil for finishing for centuries, it was not introduced to the United States until the early 1900s.

Real Milk Paint Pure Tung Oil




● 100% Pure Tung Oil without any additives and no thinners.
● Penetrates deeply into the wood fibers providing water resistance.
● Enhances the natural beauty of wood.
● Excellent finish for woodcarvings, wood bowls and wood flooring.  
● Produces an elastic oil finish, which expands and contracts with changes in the substrate. 




Can You Substitute Linseed Oil for Tung Oil? 


 You may have heard that linseed oil is a good alternative to Tung oil and that, other than the higher cost of Tung oil, the only difference is that linseed oil has a darker yellowish hue, while Tung oil is relatively clear. While both of these drying oils are similar, the big difference is durability. Both oils apply easily with either a foam brush or by wiping with a rag.  However, when linseed oil has cured, the finish is softer and offers very little protection other than some moisture resistance.

Truth be known, proper application of 100% Tung oil does involve considerably more time and effort than linseed oil. Finishing a carving with Tung oil requires several applications – typically six to seven coatings to achieve a professional-looking finish.  What’s more, you must buff the surface with 0000 steel wool, after every application, except the last one.


After applying the Tung Oil, buff the surface, which produces a beautiful finish.


All this work, though, is worth it in the end. If you follow the instructions in this article, you can expect to achieve a beautiful, clear, natural finish. More importantly, when the finish cures thoroughly in about 30 days, the oil coating will harden providing greater durability than linseed oil.   

In addition to providing water resistance, Tung oil resists some solvents such as alcohol and acetone. Even though the ancient Chinese used Tung oil to waterproof their boats, it is not recommended to outdoor projects. The primary advantage of Tung oil is not durability, rather it is its aesthetic appeal. Finishing with Tung oil will accentuate the grain of the wood and will impart a warm, yellowish hue to your carving or furniture. 

Caveat Emptor: Tung Oil Finish is not 100% Tung Oil. 


 When you shop for tung oil, be aware of some deceptive labeling.  Products labeled as “Tung Oil Finish” are not 100% Tung oil. Some of these products are mixtures of oil and varnish consisting of very little or no Tung oil.  If the packaging does not read “100% Tung Oil” or “Pure Tung Oil”, is probably isn’t the real thing.  Another way to find out what is in a product is to read the MSDS bulletin.


 If the packaging does not read “100% Tung Oil” or “Pure Tung Oil”, it probably isn’t the real thing.

Some pure Tung oil is as thick as molasses. Many other brands of Tung oil are mixed with a solvent such as mineral spirits to lower its viscosity and make it easier to apply.

Out of the bottle, the thick Tung oil will not sufficiently penetrate the surface of the wood.  The first coatings of the oil must be thinned so that it can soak into the wood. Common solvents used include turpentine, mineral spirits, naphtha and d-limonene (which is a less toxic, citrus-based product). Use the citrus solvent for any item that will come in contact with food.
Thinning the Tung Oil with turpentine allow the mixture to penetrate the wood. 
Whichever solvent you use, mix it with Tung oil at a ratio of 2 to 3 parts of solvent to 1 part oil for the initial coats.  The diluted oil will penetrate the wood and serve as a foundation for the thicker final coatings.

The real tung oil is available in two varieties: pure and polymerized. They are not the same thing.  The polymerized variety has been cooked.  Cooking starts the curing process in which the molecules begin to polymerize. After the partially polymerized oil is applied, the curing process continues until the oil completely polymerizes and hardens. These polymerized oils dry much faster than 100% pure tung oil. Polymerized oils will also dry to a glossier finish.

Preparation Prior to Applying Tung Oil. 


 While tung oil will accentuate the texture and grain of the wood, it will also make imperfections in your carving more noticeable. For this reason, you should take care to prepare the surface prior to the application of the oil.  After finishing you project, lightly sand the wood with 220-grit or 320-grit sandpaper.


Pure tung oil only darkens the wood slightly.


Staining. 


 Treating a carving with pure tung oil only darkens the wood slightly. If you are looking for a darker color, you can use a wiping stain  or dye to color your carving prior to oiling the surface. (See my article: Differences Between Stains and Dyes.)

Application of Tung Oil. 


 You can certainly use a brush Tung oil onto the surface of the wood.  The more accepted method among woodworking aficionados is to apply the oil with a lint-free cotton rags. The commonly-held opinion is that the heat generated in the rubbing process facilitates the absorption of the oil into the pores of the wood.  Some also believe that the heat produced in rubbing accelerates the polymerization process.

  • Fold a lint-free cotton rag into a pad. Application tip: One way to prevent lint from getting into your finish, is to cover a folded rag with a nylon stocking.

  • If you are using 100% Pure Tung Oil rather than polyermized oil, then you will need to thin the mixture with 75% solvent and 25% oil. The viscosity of the oil required will vary depending on what type of wood that you are finishing.  If you are finishing a hard wood, such as oak, you will need to thin the oil more so that it will penetrate deeply into the surface.
  • Apply the oil using either a rag, rubbing it onto the surface of the wood, rubbing in the direction of the grain. The heat generated in the rubbing process also aids in accelerating the curing of the oil.  Continue to apply the oil/solvent mixture until the wood is thoroughly saturated with oil. Reapply the oil to any areas of the wood that have a matte finish. Note: you can also apply Tung oil with a brush.



  • After waiting 30 to 40 minutes, wipe off any excess oil with a clean cotton rag.

  • Allow the tung oil to dry for 24 to 48 hours.

  • Buff the surface with 0000 steel wool.

  • Repeat the process applying six to seven coats of oil, depending on personal preference. How many coats that are needed will depend in part on how the wood soaks up the oil. It also depends on the look that you are trying to achieve. If you are looking for a glossier finish, keep applying the oil until you attain the desired results.

  • On the final coating, apply undiluted tung oil. Do not buff the last coat with steel wool.

Pure Tung oil requires time to polymerize and fully cure to a hard, satin finish. As the tung oil absorbs oxygen, the coating continues to thicken and harden.  The absorption of oxygen initiates a polymerization process. The reaction with oxygen takes a very long time – typically about 30 days.  Elevated temperatures, exposure to sunlight and chemical additives can accelerate the curing time.  After the oil is applied, it reacts with oxygen, which initiates polymerization. Polymerization is the process whereby smaller monomeric molecules bond together forming much larger molecules called polymers. Over time these larger polymer chains join together in a process called crosslinking. As the crosslinking occurs the oil coating thickens and becomes more inflexible until it forms a hard surface. Fully cured, permanently bonds to the wood and is insoluble to water or organic solvents, such as acetone or IPA.
As tung oil absorbs oxygen, it initiates polymerization.
After the final coat has dried, some woodworkers will apply beeswax or paste wax to the surface.  Others prefer not to wax the wood. Instead, they prefer to periodically rejuvenate the finish a couple of times a year with additional coats of tung oil. 

To revitalized and maintain the finish, you should periodically apply a coating of tung oil two to three times a year. Note: if you have applied beeswax or paste wax on top of the tung oil, you must remove it with mineral spirits, before applying additional coatings of oil.

You can also apply tung oil to woodcarvings which have been dyed. After the final coat of tung oil has cure for 30 days, you can apply varnish or shellac over it.


Safety tip:  Boiled linseed oil and polymerized tung oil are prone to exothermic reaction, which can produce spontaneous combustion. To prevent fire dispose of the oily rags in a fire-proof metal container or dump the rags in a five-gallon bucket of water. 





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About Jim Hingst: After fourteen years as Business Development Manager at RTape, Jim Hingst retired. He was involved in many facets of the company’s business, including marketing, sales, product development and technical service.

Hingst began his career 42 years ago in the graphic arts field creating and producing advertising and promotional materials for a large test equipment manufacturer.  Working for offset printers, large format screen printers, vinyl film manufacturers, and application tape companies, his experience included estimating, production planning, purchasing and production art, as well as sales and marketing. In his capacity as a salesman, Hingst was recognized with numerous sales achievement awards.

Drawing on his experience in production and as graphics installation subcontractor, Hingst provided the industry with practical advice, publishing more than 150 articles for  publications, such as  Signs Canada, SignCraft,  Signs of the Times, Screen Printing, Sign and Digital Graphics and  Sign Builder Illustrated. He also posted more than 325 stories on his blog (hingstssignpost.blogspot.com). In 2007 Hingst’s book, Vinyl Sign Techniques, was published.

Slides of Jim's Artwork

© 2015 Jim Hingst

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