"cooking" raw linseed oil

[paul cottingham]

I use tried and true almost exclusively, as I have a daughter who is very sensitive to chemicals. I often put it under shellac.
the key is to put it on really really thin. Rub it in with a cloth after it has sat for a bit. Works great.
it helps to warm it first, especially the finish that has beeswax in it.

[Jacob Reverb]

Edible linseed oil is not polymerized,and I don't know if it would effectively dry or not. I started using edible linseed oil(flax oil) in my varnish since it is a LOT clearer than the hardware grade oil. BUT, it needs to be polymerized. This is dangerous if you aren't experienced. You MUST work out doors. Use a DEEP container. Oil can get too hot and suddenly foam over the top in an instant,turning into a LARGE ball of fire before you can get the pan off the hot plate.

I AM NOT RECOMMENDING THIS AS IT IS DANGEROUS,TOO,but,I used to saw the top off of an EMPTY,EMPTY propane bottle to get a real tall container. You can blow up the container if any gas is left in it,so I cannot recommend it.

I'd carefully SIMMER the oil and not let it get past simmering for about 20 minutes. It would turn a rich,golden color(from the pale color it was before). Then,the oil was polymerized,and would then be a drying oil. Do not eat it after it is polymerized!!!!

After the oil was golden,I'd add the resins,and carefully simmer it till a drop gotten on the end of a longish stick,would make gossamer cobwebs when touched and pulled away from a bottle. That means the varnish is done. I'm not getting too technical here.

That's great information, George. Thank you!

[Zach Dillinger]

The food grade stuff will dry. You just can't flood the surface of the wood and you have to rub it into the wood. I do this often.

[David Keller NC]

I would like to buy boiled linseed oil WITHOUT the petrochemical dryers. Just raw oil that is "boiled".

What can you tell me about stand oil? Does it noticeably decrease dry time? I have seen BLO thicken from sitting in an open container for an extended period of time, its that similar?

Generally speaking, "boiled linseed oil" doesn't have petrochemicals in it (despite what the Wiki article says). The old-school method that period sources refer to (all the way back to the 16th century) had lead oxide added as a metallic drier. Modern "Boiled" linseed oil uses non-hazardous metallic salts as driers - typically zinc oxide or zinc carbonate. These can be purchased as "Japan Drier" if one wants to make their own.

The principal difference between linseed oil polymerized by exposure to oxygen, heating and exposure to oxygen, or exposure to UV (sunlight) is that the polymers that form in the liquid are of a different chemical structure than metal-catalyzed polymers in commercial linseed oil. These polymers form a finish that typically takes much more time to dry than metal-catalyzed BLO, and the resulting finish is typically much softer.

And - George is dead-on about the dangers of making your own "short-oil varnish" - made by heating linseed oil or heating linseed oil and dissolving tree resins in the hot oil. Because the polymerization of linseed oil in the presence of oxygen is highly exothermic (produces heat), the reaction can quickly get away from you, leading to 3rd degree burns, a house fire, or both.