Cynthia White

Page 1 of 10 Working Title: Tung Oil: Debunking the Myths Byline: Cynthia White Word Count: 2485 TUNG OIL: Debunking the Myths If you’re a woodworker, then I bet you have a strong opinion about Tung Oil. As a rookie, I became preoccupied (okay, obsessed) with Tung Oil because I heard so many different opinions about it from veteran woodworkers. Some loved it and some hated it. So I started researching and found that the information available about Tung Oil was often incorrect, conflicting, and/or misleading. Let’s examine and debunk some of the myths. Myth #1 Tung Oil was invented by Homer Formsby in 1965 (Formsby’s Tung Oil Finish). Nope. Tung Oil has been around for thousands of years. There’s no doubt that Homer Formsby put Tung Oil on the map in North America in the late 1960’s when he started marketing his special finish—which is still available--but according to Bob Flexner in his book, “Flexner on Finishing”, Formsby’s concoction was really a wiping varnish made with (maybe) a little Tung Oil, a resin, and a thinner. When you buy Tung Oil, you have to carefully read the ingredients on the package to have an idea what you’re dealing with. I got my hands on several products labeled Tung Oil that actually contained solvents, and/or metal compounds that speed up polymerization (or drying), and/or other mystery ingredients. Sometimes there was a little Tung Oil in there too. It’s also possible to buy partially polymerized Tung Oil, which hardens faster. I’m not criticizing any of those products, but for the purposes of this article I’m referring to pure Tung Oil with no additives. By the way, Lee Valley was kind enough to send me several samples of the real thing for testing in this article. Page 2 of 10 The earliest reference I can find to the use of Tung Oil is in the writings of Confucius around 500 B.C. The Chinese have used Tung Oil also known as China Wood Oil for at least 2500 years for wood finishing, wood waterproofing, caulking, inks and paints. I also found some references to using Tung Oil for medicinal purposes in ancient history. I don’t suggest you ingest it or take a bath in it, but apparently some primitive cultures did use it that way. In the 13th century Marco Polo wrote about the Chinese using Tung Oil to build and waterproof their traditional boats called “junks”. In 1905 a USDA scientist brought Tung tree seeds to the US to try to cultivate them in Florida. The crop grew well, but bad weather and a succession of hurricanes spelled the end of most of the US production by 1969. Blake Hanson, President of Industrial Oil Products, the only global supplier of Tung Oil from all sources, told me that there was some US production again from 1998 to 2005 (from his company) until Hurricane Katrina reared her ugly head. Today world Tung Oil production comes mostly from China (83%), then from Paraguay (about 14%), Argentina (2.75%), and Brazil (a tiny bit) and it is used in wood finishing, paints, inks, fuels, and other things. According to Professor B. Sivasankar, who wrote a recent textbook on Engineering Chemistry, these drying oils form stable films that protect surfaces from corrosion and weather. This is why Tung Oil and Linseed Oil, for example, are essential components in paints. “Without these drying oils, paints cannot function as protective coatings.” Myth #2: Tung Oil dries in the air by evaporation. Nope. Tung Oil definitely gets hard, but it doesn’t happen by evaporation. Chemists classify oils as “non-drying”, “semi-drying”, and “drying”. The word “drying” is misleading because the oils don’t really “dry” or evaporate, they “harden” or cure. The most commonly known drying oils in woodworking are Tung and Linseed Oil. They polymerize or solidify by a chemical process that requires oxygen (from the air) to create Page 3 of 10 cross-linked compounds that make the oil get hard little by little, until it is completely hard all the way through--cured. Myth #3: BLO is just like Tung Oil, but better and cheaper. Sorry, but that’s wrong too. Comparing BLO (Boiled Linseed Oil) to (pure) Tung Oil is like comparing apples to oranges. So let’s look at both: BLO Pure Tung Oil Has added metal compounds Pure Dries faster (because of added compounds) Dries more slowly Will yellow with age Doesn’t yellow Can go rancid Nope Can mildew Nope Nope Has waterproofing qualities Nope Retains some flexibility when hardened Cheaper More expensive Linseed Oil, which comes from flax seeds, has a long history. Flax (cloth) fibers have been found from 30,000 years ago, and we know Linseed Oil was used in oil paints in Europe in the 14th century. Woodworkers have used Linseed Oil in wood finishes for a long time because it was readily available, flax being grown easily all over the world. Pure Linseed Oil dries more slowly than pure Tung Oil, but no one knows that because everyone buys Boiled Linseed Oil, which dries fast because of all the added chemicals! BLO is definitely cheaper, and it is good; but it’s not better. Myth #4: Don’t use Tung Oil on food surfaces (like counters and cutting boards) because it’s risky for people with nut allergies. Page 4 of 10 Wrong. I heard this information stated adamantly and authoritatively several times in different internet woodworking discussion forums, and I was determined to find out if there is any basis for it. It’s just plain not true. First, depending on whose statistics you believe, approximately 7% of the population in Canada has some kind of food allergy. Only about 1% has an allergy to tree nuts. Furthermore, according to Dr. Gerry Allen, Associate Professor of Biology at University of Victoria, Tung nuts from the Tung tree (species Aleurites fordii) are not true tree nuts at all. They are the seeds of the fruit (drupe) like the seed inside a peach pit. So are allergies to tree seeds as prevalent as allergies to tree nuts? Again, it depends on who you ask, but probably not. The Journal of Allergy and Clinical Immunology says the incidence of allergy to seeds is 0.1% in Canada. We also know that allergies to seeds are more common in cultures where the population comes in regular contact with them. Aside from woodworkers, I’d say the general population in North America rarely comes in contact with Tung “nuts”, seeds, or oil. So now our risk of allergy to Tung Oil is down to 0.1% of the population. We know from a study published in the British Medical Journal in 1997 that in a test group with known allergies to tree nuts, none of the test group (ZERO persons) had a reaction to nut oil that had been refined. In that same study, when individuals with known nut allergies were exposed to unrefined cold-pressed nut oils, 10% of the individuals showed some reaction or 90% did not show any reaction. So if Tung Oil comes from a seed, and if it is unrefined, the probability of an allergic reaction upon exposure is now reduced to 1/10 of 0.1% of the population. Is Tung Oil refined? Sometimes. Blake Hanson told me that often it’s sold as pure unrefined oil but sometimes a solvent extraction (or refining process) is used. So the probability of being allergic to it is now somewhere between 0 and .01% of the general population. And I’m talking about the liquid oil, not the cured hard oil, which has likely significantly less risk. So avoiding Tung Oil because you’re worried someone somewhere someday might be allergic to it--well it’s just not a valid argument. Direct your worries to Walnut Oil, Page 5 of 10 which is not refined, is from a true tree nut, is arguably not a real “drying oil” (won’t cure), and can get rancid. Is it possible to be allergic to Tung Oil? Sure, anything is possible, and people with known nut or seed allergies should obviously proceed with caution. However, it’s also possible someone can be allergic to a type of wood, petroleum products (like mineral oil, forever the go-to “safe” oil for woodworkers), turpentine, metal “driers”, linseed oil! or unlimited other things. It’s been documented that some people feel unwell if they breathe in the fumes of Tung Oil for too long. Well it’s also documented that people die from breathing in the fumes of methanol. Has anyone read the MSDS for a can of lacquer lately? Ever breathe in the air in New York or Los Angeles? I suspect it’s not too healthy to breathe in any of the products we use; so let’s not make Tung Oil the bad guy. Myth #5: Tung Oil never dries and you can’t get a good result from it. Yes it does, and yes you can. There are several reasons why some woodworkers have difficulty using Tung Oil and get mixed results. I hope a few hints below will greatly increase your success rate. Almost all of the experts agree that using a cloth moistened with warm water is the easiest way to raise the grain on your project before oiling. So, raise the grain, sand, and then begin. Bob Flexner says that applying oil is simple, “wipe, wait, sand, repeat.” Apply the oil liberally with a soft cloth or brush and then wipe it off like you mean it. Check after an hour or two, and if extra oil has beaded on the surface, wipe it away again. Don’t forget that rags used to apply drying oils are highly combustible. When you’re finished with your rag, hang it outside to dry. Some even recommend dousing the rags with water first. Be careful disposing of them. When using pure Tung Oil, you need several coats. And it’s very important that you thin each coat with the first coat being the thinnest (I recommend 70% solvent). Each Page 6 of 10 successive coat should be thicker (less thinned), and the last coat must be the thickest. Your thinner needs to be an organic solvent—one that is carbon based like turpentine, mineral spirits or the newfangled “citrus solvent”. The reason why it has to be applied like this is because of the old “Fat Over Lean” Principle in fine art. In the Middle Ages, European oil painters, who used Linseed oil in their paints, learned that they got better results by using thinner paints layered with successively thicker paints. Unless the painters layered paint in this fashion, they found that their paintings had top layers that crackled, wrinkled, and moved. This is because the thinner layers harden faster than the thicker ones, and you want your Tung Oil to harden from the bottom up or inside out. The thinner the oil, the faster it dries, the more quickly the solvent evaporates, and the better the oil penetrates the wood. This application method is the only way to insure that your finish hardens in a stable fashion. Every layer except the last must be sanded. Drying oils do not function like lacquers where with each successive layer the solvent actually starts to dissolve the previous coat, so each new coat blends with and bonds with the previous coat. With a drying oil like Tung Oil, you have to sand because that’s how each layer bonds with the previous one— mechanically. Sanding creates the “tooth” that grips the distinct next layer. Sven Hanson said in a Taunton Finishing book that you shouldn’t be afraid to sand between coats because a light sanding with 320-grit sandpaper will “shear off the wild hairs, cut open the bubbles and knock down the few beads” aside from creating the tooth. When sanding between coats you have to go lightly or you will suddenly sand through one or more previous coats and you will have dreaded witness lines. And if you ever want to completely remove a pure Tung Oil finish, be prepared to sand all the way through it because once cured, the oil actually becomes one with the top layer of wood. Getting good results requires using the right techniques and not being in a hurry. I would allow at least a week between coats although I have heard of people doing it faster with good results. There are tons of other finishes better suited to a tight schedule. Varnishes, Page 7 of 10 lacquers, and even BLO. In fact, Waterlox makes an “Original Finish” that is a wiping varnish made with real Tung Oil. However, if you want to use oil, and you have some time to devote to the finish, pure Tung Oil is in a class by itself. There is no other drying oil that has the same resistance to water, mold, bacteria, yellowing, darkening, but offers strength and flexibility. Well, all that is wonderful, but is Tung Oil safe? I asked Marc Spaguolo (of internet Wood Whisperer fame and a woodworker with a background in molecular biology) what his opinion was of Tung Oil. He said, “It is my belief (interpretation), that yes it is safe once cured. In general, most of the "bad stuff" in mineral spirits and other petroleum distillates goes away upon evaporation. Any remaining residue can be washed away with soap and water.” He also added, “The biggest difference [between BLO and Tung Oil] is probably cost. BLO is going to be significantly cheaper. But if one is really concerned about chemicals and food safeness, they would probably be happier with tung oil, since BLO has chemical driers added to it.” So let’s recap: Tung Oil is more expensive than BLO, and it takes longer to dry. The chances of allergy to Tung Oil are remote, and Tung Oil has several other advantages over Linseed Oil. Professor Norm Kenkel, a biologist at the University of Manitoba reminded me of another reason to use it: “Tung oil is an environmentally safe and sustainable wood finishing product.” There are reasons why Tung Oil has been used as a wood finish for thousands of years. It’s great stuff. For a traditional pure oil-rubbed finish, it’s the only game in town. Page 8 of 10 I suggest a box or inset (or whatever you call it in magazine talk) with this: Dave Hawksford, a professional refinisher of museum-grade pieces (http://colonialrestorationstudio.com/) uses this recipe for Tung Oil: ➢ I thin the first 3-4 coats 50/50 with turpentine, and the next 2 coats are 70/30 % (tung:turpentine) then the final two coats are full strength, ➢ I let the project dry 24 hours between coats, and then sand with 320 grit. ➢ After the final coat I use the white very fine Scotch Brite pad and a mixture of Comet and turpentine to make a paste. I then apply the Scotch Brite pad to a random orbital sander and use the paste to buff out the finish. ➢ The final step is to use Liberon 0000 steel wool and a good wax. Wax out the piece to finish. “ It takes a bit of work but any piece of furniture worth have a oil finish on is worth the work. “ Page 9 of 10 SOURCES: Books: Flexner, Bob. Flexner on Finishing. Cincinnati, OH: FW Media, Inc., 2010 Finishes and Finishing Techniques. Newtown, CT: The Taunton Press, 2000. Documents: FDA document saying Tung Oil is safe: http://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfcfr/CFRSearch.cfm?FR=175.300 Interviews: Dr. Geraldine Allen, Email interviews. 29 April and 2 May, 2011 Associate Professor of Biology, University of Victoria, Victoria, BC, Canada. Dr. Greg Beaulieu. Email interview. 29 April 2011. Senior Instructor, Department of Biology, University of Victoria, Victoria, BC, Canada. Dr. Bruce Ford. Email interview. 2 May 2011. Professor and Curator, University of Manitoba Herbarium. Winnepeg, MB, Canada. Dr. Norm Kenkel. Email interview. 2 May and 3 May 2011. Department of Biological Sciences, University of Manitoba, Winnepeg, MB, Canada. Dr. B. Sivasankar. Email interviews. 28 April and 8 August, 2011. Page 10 of 10 Retired Professor of Chemistry at Anna University Chennai 25 and currently Visiting Professor at same Dept. of Chemistry. Chennai, India. (He wrote an Engineering Chemistry textbook published in 2008, which is why I contacted him). Dr. Julie Wu. Email interviews. 29 April and 5 May, 2011. Technical Writer-Editor, Office of Communications and Government Relations National Institute of Allergy and Infectious Diseases, NIH, DHHS, Bethesda, Maryland, USA Altilia, Jim. Email interview. 2 May 2011. Manager, Sales & Business Development University of Guelph Agriculture & Food Laboratory, Guelph, ON, Canada Bantock, Laura. Email interviews. 28, 29 April and 3 May 2011. Director, Western Region, Anaphylaxis Canada. Kamloops, BC, Canada Hanson, Blake. Email interviews. 29 April and 9 August 2011. President, Industrial Oil Products, Woodbury, NY, USA. Spagnuolo, Marc. Email interview. 2 May 2011. Schaffner, Kellie Hawkins. Email interviews. 22 and 28 April and 10 August 2011. Vice President, Waterlox Coatings Corporation. Cleveland, OH, USA. Wilson, Wally. Email interviews. 28 and 29 April 2011. Marketing Relations, Lee Valley Tools, Ltd. Ottawa, ON, Canada.