[brad]

I was reading my buddy's blog (Sarge), and some of your comments, as a result Sarge and I started talking about his favorite finish "Tung Oil" which brought up the questions…what is tung oil,(all products called tung oil aren't really tung oil? That lead to how do you use it? when do you use it? why use it/why not? We thought this would ne a good place to see what everyones experience has been and comments about anything "tung oil " related

 

[SPalm]

I love it, but it does need to be 'rubbed' in to really work.

It is from the nut of the Tung tree. The story I have heard is that the British were blow away by the Chinese Junks and their water tightness and beauty. At that time the Tung tree was only in China and the British used pine tar to waterproof their boats (yuck). Anyway, Tung oil is unique in that it is one of the few oils that polymerizes or actually hardens. It becomes water proof. The concept of Tung Oil Finishes (Watco, etc.) are blends of Tung and other oils to produce an easier to apply oil with less cost.

Then again, I could be wrong.
Steve

 

[SteveRussell]

Hello Brad,

Here is a bit of detailed information to help you understand Tung Oil. Tung oil is obtained from the seed kernels of the Tung tree, Aleuritis fordii (Chinese tung oil) or Aleuritis cordata, syn. vernica and verrucosa (Japanese tung oil). The principal source of raw tung oil is China and South America. The nuts of Aleuritis montana, Aleuritis trisperma (kekunaoil) and A. moluccana or A. triloba (lumbang oil) also produce oils with properties that are similar to Chinese tung oil.

In 1298, Marco Polo reported that tung oil together with lime had been used for impregnating and sealing wooden ships. As early as 1894, tung oil was being imported into Europe and the United States as a substitute for linseed oil. Tung oil is produced by mechanical pressing, or by solvent extraction. The resulting oil is then filtered to remove any impurities.

Drying oils, including linseed and tung, can be defined as liquid vegetable oils that, when applied in thin layers to a non-absorbent substrate, will dry in the air to form a solid film. This drying is a result of polymerization by the action of atmospheric oxygen, i.e. autoxidation.

The resultant films are typically hard, non-melting and are usually insoluble in organic solvents. (This varies with the particular drying oil) Semi-drying oils, like soybean oil and some nut oils, form tacky, somewhat sticky films when dried. Non-drying oils like mineral oil undergo no marked increase in viscosity upon exposure to air.

Drying oils are typically subdivided into three main groups for classification purposes, non-conjugated, conjugated and other oils. Non-conjugated oils, such as linseed, soybean, sunflower and safflower oil, are fatty oils that contain polyunsaturated fatty acids, whose double bonds are separated by at least two single bonds (i.e. isolated double bonds make up the non-conjugated oils).

Conjugated oils on the other hand, such as tung, oiticica, dehydrated castor oil and isomerised non-conjugated oils are polyunsaturated fatty acids whose double bonds are partly or fully conjugated (i.e. alternate single and double bonds in the carbon chain are the fatty acids). Other oils include those with multifunctional fatty acids, which acquire their drying characteristics by chemical conversion, such as raw castor oil and tall oil. A simple way to classify fatty oils is by their iodine value. Drying oils have iodine values above 170, whereas semi-drying oils range between 110 and 170.

Conjugated oils like tung oil are considerably more reactive than non-conjugated oils. Conjugated double bonds favor polymerization and oxidation and dry more rapidly than non-conjugated oils, offering excellent surface-dry, through-dry and hardness. The resultant film offers a high resistance to yellowing and increased resistance to water and alkalis.

The principal drying component in tung oil is eleostearic acid, a conjugated octadecatrienoic acid. The oleic acid contained in the fatty oils and unsaturated fatty acids plays a small part in the drying process as well. The saturated fatty acids present, however, act only as plasticizers.

The drying of films typically progresses in three overlapping steps:

Induction - Through a process known as autocatalysis, the oxygen uptake, which is slow at first, steadily increases. Factors such as temperature, light and heavy metals/inhibitors in the oil affect the overall uptake rate.

Initiation - As the film continues to take up oxygen, its mass increases. The double bonds in the film begin to rearrange and polar groups such as hydroxyl and hydroperoxy develop in the film. This leads to the association of molecules, through forces such as hydrogen bonding.

Cross-Linking - As the number of double bonds in the film begins to diminish, larger molecules form, and volatile and non-volatile carbonyl compounds are generated. The exact chemical reactions, as well as the structure of the film-forming polymers, are not completely understood. The initial autoxidation step in non-conjugated oils is dehydrogenation of the unsaturated fatty acid by molecular oxygen, which forms a radical. This starts a catalytic radical chain reaction that increases incrementally with time, leading to the formation of a hydroperoxide.

At low levels, the hydroperoxides produced during autoxidation decompose to form free alkoxy and hydroxyl radicals. Higher levels of hydroperoxides form free radicals through biomolecular disproportionation. The resultant free radicals react in various ways to accelerate the autoxidation process.

The drying of tung oil varies considerably from linseed oil. Tung oil typically absorbs approximately 12% oxygen (linseed oil absorbs approx. 16%) and quickly forms a skin on the surface. Since less oxygen is absorbed, the viscosity of the oil increases at a faster rate. Unlike the hydroperoxide formation during autoxidation in linseed oil, tung oil forms cyclic peroxides. The methyl eleostearate that is formed has a higher molecular mass than linoleic acid esters.

The direct attack on the double bonds by oxygen forms cyclic peroxides. The resultant reaction of the peroxides with allylic methylene groups, leads to the formation of radicals. This creates a radical chain reaction that forms polymers. The molecular mass created during tung oil polymerization is less than that achieved through linseed oil polymerization. To speed up the film formation and curing process, manufacturers add "driers" to the oils.

Both non-conjugated and conjugated drying oils like linseed and tung can be polymerized by heating under an inert atmosphere. These polymerized oils are then referred to as "Bodied Oils." To achieve the higher viscosities of bodied oils, non-conjugated oils are heated up to 320° Centigrade and conjugated oils are heated up to 240° Centigrade.

This increase in viscosity, or "body," is caused from thermal decomposition of naturally occurring hydroperoxides. This decomposition yields free radicals that contribute to a limited amount of cross-linking.

The heating of tung oil must be carefully monitored, or the polymerization will lead to gelation of the oil. The viscosity can also be increased by passing air through the oil (known as Blown Oils) at high temperatures up to 150° Centigrade. Reactions similar to those observed in cross-linking cause oligomerization of the oil.

Polymerized tung and linseed oils dry faster, harder and are more durable than raw oils. In addition, polymerized oils produce a smooth glossy finish, whereas raw oils produce a matte sheen. This matte sheen is a result of the natural expansion that takes place during polymerization. This expansion creates a very finely textured surface that appears to the naked eye as a matte finish.

Some highly specialized polymerized tung oils are processed at extremely high pressures and temperatures. These are called Thermalized Tung oils and are used in the manufacture of nitro-cellulose lacquers. This process improves the drying, hardness and luster of the oil.

I hope this helps you to understand Tung oil a wee bit. Take care and all the best to you and yours!

Steve Russell
EWW, WVP, EWWFS
The Woodlands, Texas

 

[Karson]

We just asked for the time, not how to build a watch. LOL

Thanks for the explanation.

Is this a cut and paste or did it all come from your flying fingers.

 

[Dadoo]

Zzzzzzz-zzzzzzzz* Wha?

Just kiddin! LOL!

 

[SPalm]

Cool, we got ourselves an expert.

Steve, do you have any recomendations for a cutting board finish?

Take care,
The other Steve

 

[Hutch]

OK, but are some finishes that are labeled Tung Oil really an oil/varnish blend, not just a combo of different oils?

 

[CharlesNeil]

cutting board finish,yep, the total concept of "food safe " is a hype pure and simple, in years past the metal driers in finishes contained lead, definately unsafe, today the driers do NOT contain lead, fact is there is no known clear finish that is harmful ,once it has cured and driers cure it,with exception to shellac ,none of them will ever return to a liquid state, thus not be a digestable concern, shellac is actually used for "time released medicine's", as it dissolves slowly and actually dissolves in the intestines thus the time release.General finish has a Salad bowl finish that actually works, it is actually blo with some good resins and driers to actually protect and seal wood,the typical "food safe " stuff is mineral oil, which does nothing to protect the wood ,but remains wet so it makes it look good, its just that it doesnt go rancid,so its safe ,it is sold at the drug store as a laxitive, in a class one time i took a big swig to demonstrate my point, wouldnt suggest that, it works for its intended purpose but for wood it isnt a good choice, i was absent from class numerous times for the balance of the day!

 

[SteveRussell]

Hello Karson,

Please accept my apologies for the long post. Chemistry is a hobby of mine, so I tend to get excited about it, although it's a sure cure for insomnia for most folks. The post is excerpted from an article I wrote for the British "Woodturning" Magazine a few years ago. Since I'm a lousy typist (my wife says I type with my elbows… She types over 140 WPM :-o), I try not to reinvent the wheel if possible.

I wrote articles for Woodturning magazine for a few years. They were the ONLY magazine that would let me publish in-depth technical articles. Most magazines want you to write for an 8th grade education level, I think woodturners and woodworkers are smarter than that… So I rarely write articles for magazines anymore. Since I have a website now, I tend to publish my articles online now.

Dadoo… Apologies for putting you to sleep.

Steve - I like your name! Usually, Mineral oil is recommended for cutting boards. MO will not cure as it is a non-drying oil and will continually leach out with every washing, requiring periodic reapplication. It will also leave a mess on your countertops if you apply too much… Ick! The problem with cutting boards is that you cut on them, so any type of film finish is pretty much out of the question.

If you cut raw meat on your cutting board, it's a good idea to perform a salt rub every so often to insure a sanitary surface. Wet the board slightly and pour salt all over it. Let it sit for an hour or so and wash it off. Many folks have switched to plastic boards for meat, but some purists prefer still prefer wood. I have Walnut oil on my cutting boards, which I reapply periodically. I just don't care for Mineral oil…

Hutch - It depends on the specific finish. Some finishes labeled as "Tung Oil Finish" do not contain a single drop of Tung oil. Some have a small amount of TO, blended with other oils. Some are "Pure" 100% Tung oil. You have to be careful though because manufacturers and re-labelers seem to be able to call their finish almost anything these days, without repercussion. It's false advertising, but unfortunately a common practice with some finishing companies.

You can request an MSDS sheet and see if Tung oil is in a particular finish, but even that is not a 100% guarantee it seems. If you've got a gawalop of cash, you can order a GCMS test, with supplemental flash point testing. This is pretty expensive though… You would know for sure though… Take care and all the best to you and yours! I'll retreat to my laboratory now and refrain from posting long responses…

Steve Russell
EWW, WVP, EWWFS
The Woodlands, Texas

 

[SST]

Now if only I could find a Groove tree, extract some groove oil, and mix it with the aforementioned oil, I'd have the perfect finish for my floors…Tung & Groove oil.
Oow…I really hate it when I do that…but it was just a little slip of the tung or maybe…a tung-in-cheek remark… -SST
Wait, I've got another…it's…it's…nuts, it's right on the tip of my tung…
Ok, I'm really done, now…I'm all tung-tied.

 

[SPalm]

TO sst, your humor is BLO me.

So good, I have been using walnut oil on my cutting board counter and it is OK. (you can buy it at the supermarket)

Charles, thanks for the visual.
I will try out that Salad Bowl Finish.

Steve

 

[SteveRussell]

Hello Charles,

I use General Salad Bowl Finish all the time… It contains the following:

C.A.S.#

8052-41-3 Mineral spirits 20-40%
64742-47-8 Mineral spirits 10-20%
64742-48-9 Mineral spirits 5-10%
111-84-2 Nonane 5-10%
Proprietary Oil modified urethane resin 10-35%
Proprietary Resin 0-25%
95-63-6 1,2,4-Trimethylbenzene 0-1%

You're right that modern driers do not contain lead anymore… (Driers are oil soluble metal salts of organic acids. When these driers are dissolved in aliphatic or aromatic hydrocarbons, they are known as siccatives. When driers are added to drying oils, they are known as Boiled Oils).

Traditionally, driers contained combinations of oil-soluble metal salts like Cobalt and/or Manganese with Zirconium, Lead or Calcium salts of 2-ethylhexanoic acid or naphtenic acids. Cobalt and Manganese salts act as surface driers and aid in the drying of the film on the surface, where oxygen concentrations are the highest.

Lead and Zirconium salts catalyze throughout the film and are known as through driers. To avoid the use of Lead, which is highly toxic, modern siccatives employ blends of Cobalt and Zirconium. This combination reduces surface drying speed, promoting even drying throughout the substrate. Calcium salts are sometimes used as well, mainly to reduce the amounts of other driers that may be needed. Various other compounds may also be present in some siccatives including Beryllium, Cadmium and Nickel. Take care and all the best to you and yours!

Steve Russell
EWW, WVP, EWWFS
The Woodlands, Texas

 

[Betsy]

dag gum it, I've always thought that mineral oil was the end all on the topic of cutting boards. So now, let me recap.

Mineral oil = ok - but leeches and needs reapplied. Will go rancid and if swallowed in great gallops in class - makes you go and go and go and go.

Walnut oil = ok - tastes better than mineral oil. Probably not a good idea to drink straight from the bottle, but probably could.

Someone needs to rap SST on the knuckles (I digress).

Pretty much any finish is ok for a cutting board except shellac because it can be reliquified (is that a word?).

General Salad Bowl Finish is a favorite and probably a no brainer to put this baby to bed.

Steve - I've never understood chemistry. Buuuuuuuuuuuuuuuuuuutttttttttttt - oh geez sorry - I got a little sleepy there. Whew - ok. so back to chemistry. Really a good article. My brother is sicentist of the USDA and honestly, I can't get by the titles of his papers. He once used the words "potatos" and "bug" together. I felt like I finally understood him. First time in years.

Now back to this finish thing-- with the fact that all these finishes - dry - except that shellac-- does this also mean that walnut oil would probably not cause a problem with those who suffer nut allergies?

Ok - enough questions. Need some answers before SST comes up with anymore tung and cheeck groaners.

 

[SST]

Sorry, Betsy…I'm oil finished. -SST

 

[SteveRussell]

Hello Betsy,

Mineral oil will not go rancid over time… It will not dry (or cure) either. Mineral oil is a non-drying oil and as such, it will continue to leech out of the wood when it's washed. If you apply too much, it weeps it's way through the board/bowl etc, leaving a nice greasy ring on your counter, or on your Mums Irish lace tablecloth (don't ask). It is considered food safe and a version of it is sold in drug stores for intestinal disorders.

Walnut oil does indeed taste better than Mineral oil… I cook with Walnut oil (from the grocery store) all the time. In fact, it's about the only oil I use in baked goods anymore. I prefer Walnut oil for Treenware (utility wooden objects like bowls, platters, cutting boards etc) because it's made from edible nuts. Mineral oil is made from petroleum. If I have to eat one, I choose Walnut oil! ;-)

In my studio, I have numerous clients who are concerned about finishes that may have contained toxic ingredients (as they define them). Still more that have asthma and other respiratory ailments that make them sensitive to fumes, or are extra concerned about anything they have in their homes.

To address these concerns, I offer a line of what I call "sensitive" finishes, for those clients who prefer a more natural finish on their woodenware. These include pure Beeswax, Walnut oil and Shellac thinned with a drinkable (from the local liquor store) alcohol, along with a few other exotic food based oils.

Whenever this subject comes up in woodturning circles there are always responses like: "All finishes when cured are food safe"... and similar comments. While that may or may not be true, it is irrelevant in the grand scheme of things. Why, because the client's opinion is the ONLY one that matters… Period. It's their money and their life, so they get to make the decision. I can talk till I'm blue in the face about cured finishes and their safety, but that carries no more weight than a grain of sand on an endless beach. If I do not satisfy the clients needs/wants, they look elsewhere. It's just that simple.

Having said that, I use and believe in lots of petroleum based finishes, as well as others that are toxic until fully cured. For those who prefer something else, I offer those as well, so everybody's happy.

You could in fact use Shellac on a cutting board if you wanted to, but I would not choose it personally. Cured shellac can be liquified with alcohol, so unless you're mixing drinks on your cutting board and you spill some of your drinks on the board, you're probably going to be ok. Shellac is more of a film finish and as such, would not be the best choice (IMHO) for something like a cutting board that you use a knife on. Shellac does in fact dry, it can however become liquid again if exposed to alcohol, whereas most cured finishes are resistant to liquefaction once fully cured, lacquer being an exception… Shellac was used on furniture for many years and is still the preferred finish on some high end pieces. I like General Salad bowl finish and use it on some of my production bowls. It has a nice luster, that's not too glossy and it's resistant to staining. Very nice indeed!

As for the safety of Walnut oil with those who suffer nut allergies… Good question, my answer: Maybe.

I always ask my clients up front what finish they prefer and let them choose. The problem with saying it's safe for those with nut allergies is that some of these folks have very severe allergic reactions when nuts are even in the same room with them… I saw a documentary on TV that showed a small boy who could not even smell a peanut without going into shock. His mother said they could not have a single peanut in the whole house and his friends could never eat peanuts before visiting. Just smelling them on their hands was enough to send him to the hospital.

So, who knows. I let the client decide and offer them the choice, or if I'm selling spec bowls, I tell them what finish was used. If I had a client with a nut allergy, I would not advise them to use a nut based finish. Why take the risk (no matter how small) that some small child somewhere might be sensitive to any trace amounts of compounds in the oil? Better safe than sorry. They could always use beeswax, mineral oil, or nothing at all. Some of my clients want no finish whatsoever on their Treenware. Many years ago, this was standard practice, so that's another option for the nut allergy folks as well. YMMV. Take care and all the best to you and yours!

Steve Russell
EWW, WVP, EWWFS
THE Woodlands, Texas

 

[MsDebbieP]

more great info. Thanks Steve!
I've never noticed "walnut oil" in the grocery store. I guess I'll have to drive to "the big city" to see what I can find.

(re: peanut allergy .. just another story. In a day care in our area a grandfather, who had eaten peanut butter for breakfast) kissed his granddaughter goodbye in the morning. Somehow the kiss residue got transferred to another child in the daycare who was allergic to peanut butter and he ended up in the hospital that morning.)

 

[DanLyke]

Steve, great info. Gonna have to go back and re-read the chemistry heavy post a few more times!

I too use walnut oil for my food safe finishes. I can get it at my grocery store (Ms Debbie, you might want to check your local health food store, I live in an area where the lines between grocery store and health food store are pretty blurred and I'd imagine that more rural areas don't have the amazing stock I'm blessed with), it doesn't bother my sweety who gets mouth sores from eating walnuts (not a true allergy, but a susceptibility), and it dries hard and is easily replenishable.

 

[SPalm]

For what it is worth, I just bopped over to John Boos Cutting Boards for a look (www.johnboos.com). These are probably the most famous Yuppie boards around for use in the kitchen for actual cutting and chopping. So… this brings us full circle back to Tung oil mixtures.

Boos Mystery Oil

John Boos Mystery Oil Is Recommended For Care Of Tops And Blocks That Are Used As A Working, Cutting Surface. This Fine Oil Is A Mixture Of Mineral Oil, Linseed Oil And Tung Oil And Will Give Your John Boos Product The Same Quality Finish As The Factory.

We Recommend Oiling Your Tops Or Blocks Every 4-6 Weeks. This Food-Safe Oil Finish Keeps Your Blocks Looking New.

Steve

 

[Russel]

Now that I've read all this, where do I go to apply for my chemistry degree?

 

[Karson]

When I made my butcher block. Notice I said butcher block, not cutting board. The top was 6" thick and the apron around was 12" thick..

I used paraffin on the surface. I melted it with my wife's iron and ironed it into the wood. It went deep, but it did require replenishing, but it kept the meat juices from soaking into the wood.