Drying Oils (Linseed, Tung, Walnut)

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egnald

egnald

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There have been a few posts recently about various drying oils like Boiled Linseed Oil and Walnut Oil, so I thought I would put out a little general information related to them.

Drying oils harden by crosslinking (polymerizing) in oxygen and not through the evaporation of solvents. This makes them significantly more food friendly as 1) they do not rely on a chemical solvent, and 2) oxygen does not cause them to go rancid - it causes them to polymerize instead. This reaction with oxygen releases heat which is why rags and paper saturated with them are susceptible to spontaneous combustion. Common drying oils include linseed oil, tung oil, walnut oil, and poppy seed oil.

Note: Danish oil is a formulation that uses tung oil and/or polymerized linseed oil and is therefore not a single material specific drying oil.

Boiled Linseed Oil is also a processed formulation that dries faster than raw Linseed oil because it is already polymerized (or partially polymerized) and usually contains some form of metal salts to further speed up it's reaction with oxygen. Boiled Linseed Oil dries completely in 2 or 3 days compared to 2 or 3 weeks for raw Linseed Oil.

Of course, the following is relative information and is dependant on a lot of factors, like thickness, humidity, temperature, etc. But for comparison, listed fastest to slowest for drying and curing:

Boiled Linseed Oil
Tung Oil
Walnut Oil
Raw Linseed Oil
Poppyseed Oil (Primarily used in artist's oil paints - usually whites)

Dave
 
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To add to Dave's excellent summary:

First - relative to color: BLO and Linseed oil are the most amber (but see the comments below regarding safflower oil), followed by Tung Oil and then Walnut Oil.

Second - manufacturers can be a bit fast and loose in applying names to products that incorrectly infer what they are made from. So we have to be a bit careful (ie, sceptical) about specific products.

There are a number of products on the market that are labeled 'Tung Oil' that more correctly should be described as a form of Danish Oil. Examples include MinWax Tung Oil, Formby's Tung Oil, Mohawk Tung Oil, and a few others. They are perfectly good finishes, but they typically contain metallic dryers and possibly solvents. Actually, some of these products may not contain Tung Oil, but instead may use less expensive drying oils such as BLO.

Pure Tung Oil is rarely stocked by the major chain stores - Ace, Home Depot, Lowes, etc - but it is available if you look hard enough. If all else fails, there is Amazon. The major brands include Hopes, The Real Milkpaint Company, Sutherland Welles and a few others. The key is to look for the word Pure in the name. Also, Tung oil smells better than BLO (at least to my nose - YMMV).

There is a product labeled Teak Oil. No, its not derived from teak. Instead, its a form of Danish oil that is designed to produce the color most often associated with Scandinavian teak furniture. Again, its a perfectly good finish - just not what the name on the label implies.

Finally, manufacturers in this space will sometimes substitute a less expensive material in place of a more expensive drying oil. The most common example involves safflower oil which comes in two varieties - one that is monosaturated and used as a cooking oil in situations were olive oil is deemed to be either too expensive (or too high in fat), and one that is polyunsaturated and that is sometimes substituted for linseed oil in making Danish oils and varnish. Safflower oil has a stronger amber color than linseed oil, so some of the complaints people have about BLO being too amber may be because safflower oil has been used to reduce the material cost.
 
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Be very careful and do your own due diligence when "Food Safe" is one aspect of choosing a finishing oil. BLO that has not cured, because it most likely has metals to help cure is not food safe until it is cured, completely.
Also. Boiled Linseed Oil is not the same as Linseed oil. And, please do not try to make your own Boiled Linseed Oil by boiling Linseed Oil.
If you have any concerns or questions whether or not a finishing oil you are going to use is food safe or not, using a search engine like Google or Bing etc is/are your friends.
It is general knowledge that almost all finishes are food safe once they have completely cured. The key here is "completely"
 
So I was looking on Amazon and curiosity got me ... Is there any difference between the 8oz bottle of walnut oil labeled as a finish, and the 96oz jug of "pure organic, cold pressed, virgin" walnut oil for cooking? Other than the fact the 8oz bottle of finish costs almost as much as the 96oz jug.
 
goldendj said:
So I was looking on Amazon and curiosity got me ... Is there any difference between the 8oz bottle of walnut oil labeled as a finish, and the 96oz jug of "pure organic, cold pressed, virgin" walnut oil for cooking? Other than the fact the 8oz bottle of finish costs almost as much as the 96oz jug.
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Mahoney's Walnut Oil . The oil has been heat-treated to make the oil dry faster and to remove any possible allergens. (from his website).

Mahoney's Finishes
 
Adding a bit on Dave`s and Louie`s tung oil comments . Lee Valley is one supplier of Pure tung oil . They also sell polymerized tung oil and a polymerized tung oil sealer . The polymerized tung oil is heated to a greater degree than the pure tung oil , to induce more polymerization and hasten drying . That raises the viscosity , so mineral oil is added to make it easier to apply . They also sell a polymerized tung oil sealer , a bit thinner with more additives , faster drying , but to a matte finish . The polymerized products are U S made .

For a full description of all three products , read the Care & Use files on them . I think it is a good idea to take their suggestion to add water to the container after use , thereby minimizing the oil`s oxygen exposure . I use the sealer on most larger diameter turnings , and sometimes the polymerized oil on top of that when I want high gloss .
 
1080Wayne said:
. The polymerized tung oil is heated to a greater degree than the pure tung oil , to induce more polymerization and hasten drying . That raises the viscosity , so mineral oil is added to make it easier to apply .
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I'm scratching my head trying to figure this out. Adding a non drying oil to a polymerized drying oil sounds like it defeats the purpose.
🤔
 
Mortalis said:
I'm scratching my head trying to figure this out. Adding a non drying oil to a polymerized drying oil sounds like it defeats the purpose.
🤔
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Certainly sounds counter-intuitive . Went back and re-read the Care and Use files . The pure is heat treated to prevent premature gelling . Then it says that drying can be accelerated by cutting with mineral spirits by 50 % . The finish will be matte unless buffed or waxed . On the polymerized product , the file says it is harder to use because the high oil concentration causes it to set faster than lower lusters, and that it has no additives other than thinners and driers needed to speed the drying process .
I should have said `can be added` , not `is added` . Too many 35 C days have gelled my brain !
 
Mortalis said:
Be very careful and do your own due diligence when "Food Safe" is one aspect of choosing a finishing oil. BLO that has not cured, because it most likely has metals to help cure is not food safe until it is cured, completely.
Also. Boiled Linseed Oil is not the same as Linseed oil. And, please do not try to make your own Boiled Linseed Oil by boiling Linseed Oil.
If you have any concerns or questions whether or not a finishing oil you are going to use is food safe or not, using a search engine like Google or Bing etc is/are your friends.
It is general knowledge that almost all finishes are food safe once they have completely cured. The key here is "completely"
Click to expand...
Because of US Law. All wood finishes are food-safe once they are completely cured. Just not all are practical for food use.
 
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