Boiled Linseed Oil Quality?

Woodmolds

Woodmolds

Well-known member
I just finished a workbench top(Qtr. SYP) where I thinned the BLO with paint thinner and heated the mixture( double boiler on hot plate) it seemed to penetrate real well with one coat. I kept wetting it til it stopped soaking in, then let it set for awhile and wiped any excess off. I was well pleased with the result, of course one coat was all that was needed for a workbench.

Is there a difference in the quality of BLO offered by the "Big Box" versus other sources. Are some brands better than others? Does anyone heat it prior to application? Any type thinner used, for better penetration or drying? Xylene, Toluene, Naphtha? Anyone tried the mentioned thinners or others with success - failure?

Tony Joyce

 
Tony - From a chemistry perspective, BLO is pretty much the same.  It used to be made with "white lead" - lead oxide, but lead-free paint regualtions passed in the 1970's forced the manufacturers to switch over to primarily cobalt salts.  To my knowledge, there are very few boiled linseed oil manufacturers - their products are put in many different brands, so it's likely to be pretty uniform.

Regarding solvents, I would not recommend anything other than mineral spirits, either the "paint thinner" grade or the "low-odor" grade.  The reason is that these thinners are primarily long-chain saturated alkyl molecules, with very little aromatic ring content (like xylene and toluene), and they are thus safer to breathe the fumes from the evaporating solvent.  Both xylene and toluene are hazardous to your health, in that they're carcinogens.  They're not nearly as bad as their close relative, benzene, but the long-term effects of breathing them are not good.  Toluene, by the way, is likely to be hard to get anyway, as it's a precursor to TNT.

If you want to produce your own BLO, you can get raw linseed oil, heat it (outside, please!) to about 350 degrees F, and stir in Japan Driers.  Allow the mixture to cool, and pour off the clear liquid.  I can't be definitive about the amount of Japan driers to use, as brands vary in their metallic salts content.  You may have to experiment with it to get the right balance of wood penetration/curing time.

By the way, this is a dangerous procedure if you don't take precautions.  Linseed oil is highly flammable if spilled on an open flame, and hot oil is an incredible burn agent - it sticks to skin and transfers heat very well.  I would suggest similar safety measures to frying a turkey - that is, not to be done anywhere near an enclosed structure, a correct fire extinguisher close by, and heat-resistant welding gloves and a face shield.
 
While I'm sure others will appreciate the technical information, I was not looking for a dissertation on finishing with BLO. I was simply asking for peoples experience on what works for them and if they found any differences in products.

Tony
 
Hi tony,
I in your case,would have added 10% of white spirit to the BO,this would help it penetrate deeper into the timber,then say next day finnish just as you started.

hope this helps you
              rococojo
 
I attended a finishing seminar by Bob Flexner years ago.  He said (if my memory is correct) that BLO can take months to cure.  Can any of you chemist confirm this?  Bob said a simple test is to place a small pool of BLO on a glass plate.  After a few days (or weeks) use your fingernail to give it the hardened test.  If your fingernail pentrates the finish then it is not cured yet.  Has anyone tried this?  Also, I believe BLO will darked mahogany with time.

Dennis Bork
Antiquity Period Designs, Ltd.
 
Hi Dennis, your correct in your assumtion, BLO dries very slowly, and on mahogany it darkens to a Rich Chocolate brown, in: Thomas Chippendales day, all furniture was treated this way? Then left to dry for up to 3 months, then bee's wax applied, this 250-year-old finish is what antique dealer, bust a gut for today, Patina is its name. We imitate this today with French polish and a knock back, with wax and fine wire wool, always with the grain, then when dry a good buffing.

      Sharing the tricks of the trade.
                          Rococojo
 
Sorry, Tony - I should've been a bit more explicit in my answer.  When I said that BLO was pretty much the same with different labels, I should've mentioned that was my direct experience.  I've tried many brands, including Kleen Strip, Sherwin Williams, Qualex, Behr, and quite a few others.  I really couldn't distinguish between them, and so I did a bit of digging and found out that they were almost all produced by 1 or 2 suppliers, and just put in different labeled cans.  Make sense why they'd be pretty much the same.

The Japan drier comment was based on my own preparation of BLO from raw linseed oil and the driers in an effort to vary the applicability (how thick the material is, and how easy it is to apply) and the drying time.  As you'd expect, the more Japan Drier you put in the oil, the faster it cures, to a point.  I found that I could not get it to cure any faster than about 3 days no matter how much drier I put in the oil, nor how long I heated it.

As Joe stated, adding a thinner to BLO seems to help quite a bit with penetration of the wood fibers.  I believe that Christian Becksvoort heats his BLO to a couple of hundred degrees and applies it hot to his furniture as another method to aid in penetration.  To my knowledge, he's used this method for 20-30 years, and has produced hundreds of cherry Shaker pieces, so I'm assuming he's found this method to be good one, but I've not personally tried it.

Dennis - In regards to the chemistry of the "curing" of BLO, what's happening is the polymerization of the short-chain oils into long-chain and cross-linked polymers in the presence of oxygen in the air.  How fast that happens sensitively depends on the temperature, air circulation around the piece, and the amount of driers added to the oil (those metallic salts catalyze the oxidation of the oil into the cured film).  But in regard to Bob's comment, BLO never really stops curing - most of the reaction occurs in the first few days, but continues indefinitely.  Some of the darkening of wooden objects treated with linseed oil over a period of years is part of this reaction.
 
David,
The fact that there are only a couple companies that produce BLO should indeed indicate there would be little difference in them. Based on the information I'm finding most BLO produced today is not "boiled", but as you say has chemical driers added instead to induce drying, which I guess does the same thing. I don't need to understand the nut & bolts of how these things work, but simply what works. I guess I'm at the point where I don't feel I should spend time studying up on all these technical things, when I could be working in the shop doing what I enjoy most. Your last answer was most helpful and more on the level I can absorb quickly. Thanks!

I remembered where I got the idea of heating BLO to reduce viscosity was from a DVD(Hand-Applied Finishes) by Jeff Jewitt. Although he does not mention using a thinner, that was my own idea. At any rate the end result was quite satisfactory for a work bench. I'm not sure I would use the same method on furniture, probably just the heating.

As to the darkening of oil finishes, this would seem to be true, My father used only BLO on some pieces of furniture he made for himself about 40-45 yrs ago. All are darker than pieces he used lacquer finishes on and now all of them look dry and lifeless. They are in much need of renewing with oil or top coating.

Tony
 
Hi Tony,
You can follow your fathers work, and recoat with just BO, but if I was restoring your piece(s), I would follow (after the BO was fully dry) with a wax finish, possibly 3 coats.  Would suffice. When dry buff to an antique finish.
Making a far better looking, more manageable, (by closing any open grain/pores in the wood) finish.

        Joseph Hemingway
        40 years in business, 1968- 2008. 
 
 
Tony - FYI, museums used to coat their treasured antiques with BLO every few years in the belief that they were "nourishing" the wood and preventing them from drying out.  Those museums now very much regret those decisions, as their furniture treated in this way is very close to black.  This coloration may be irreversible - several hundreds of thousands of dollars has been spent in researching ways to restore the furniture's original appearance, though I haven't kept up with the Wooden Artifacts Group's efforts in this regard and don't know if a solution has been found.

Antique collectors/msueum curators now recommend doing nothing to wooden surfaces other than dusting and keeping them out of sunlight and in a relatively stable humidity atmosphere.  At most, "renewing" a surface that looks dried-out is done with a coating of beeswax or micro-crystalline wax in a mineral spirits carrier.
 
Tony,
Follow them masters, is my advice, in the 1750's,BLO was the finish, to stop the sticky /tacky surface, after warming in the sun, a wax finish was developed and applied, never touched by BLO again.
Just waxing for 250 years, In your case, you are proposing to recoat just once with the BLO, If the colour of the timber is OK before you recoat, its not going to go black on anyone, it might darken a little, but in my book that’s adding to finish.

                                    Joseph Hemingway (rococojo)
                                        40 years in business, 1968-2008
 
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