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Linseed oil and wood
Aug. 7th, 2003 02:34 pmBeing the curious type, I wondered why all the texts I found invariably recommended using linseed oil (rather than other oils) for finishing wood. So I dug around some more, and found an answer (on a page for maintaining bamboo flutes, of all places). Linseed oil, it turns out, is a hardening oil. What that means is that it has a sufficient amount of the right sort of kinks in its molecular structure to undergo a polymerization reaction when exposed to air, turning into a substance by the name of linolyn. Which, if you're not familiar with the term "polymer", basically means that it turns into a kind of primitive plastic. The polymerization takes a relatively long time (24-48 hours for linseed oil that's been heat-treated, 45-60 days for untreated oil), so when you spread it over a wooden surface it has plenty of time to sink into the fibrous structure of the wood. The aim is then to put enough oil on the surface that it'll fill up all the microscopic air pockets in the wood, so that when the oil polymerizes you get a surface consisting of cellulose and linolyn reinforcing each other. One will almost always mix the oil with turpentine, to lower its viscosity and thus make it easier for it to penetrate into the wood.
While linseed oil is the naturally occuring oil with the strongest polymerization reaction, tung oil and walnut oil will also polymerize fully (that is, they are also hardening oils). Most oils fall into the semi-hardening category. A few count as non-hardening (that is, they won't polymerize at all), with olive oil at the very bottom. So if you treat your wood with olive oil, it'll look pretty but it will never ever stop feeling oily.
Also, this explains why cloths drenched in a linseed/turpentine mix (like ones that's been used to spread the mix over a wooden surface) are a serious fire hazard. Turpentine has a very low flame point, and the linseed polymerization reaction is exotermic. Given a large enough surface area (like cloth has), the reaction can produce enough heat to ignite the turpentine. Which is probably not good for your working environment.
While linseed oil is the naturally occuring oil with the strongest polymerization reaction, tung oil and walnut oil will also polymerize fully (that is, they are also hardening oils). Most oils fall into the semi-hardening category. A few count as non-hardening (that is, they won't polymerize at all), with olive oil at the very bottom. So if you treat your wood with olive oil, it'll look pretty but it will never ever stop feeling oily.
Also, this explains why cloths drenched in a linseed/turpentine mix (like ones that's been used to spread the mix over a wooden surface) are a serious fire hazard. Turpentine has a very low flame point, and the linseed polymerization reaction is exotermic. Given a large enough surface area (like cloth has), the reaction can produce enough heat to ignite the turpentine. Which is probably not good for your working environment.
