Originally Posted by Richard Saylor
I have some flaxseed oil in capsules for oral consumption. I have tried to use it as a wood finish, and it dries so slowly that I don't think it would be suitable as a painting medium.
I would assume that oil capsules have a lot of anti-oxidants added, so that the oil does not covert to an indigestible polymer over a period of time. A quick search found this page
, which I assume is representative of the technology.
Bottled salad oil probably has anti-oxidants added, but if the oil congealed in the bottle, you'd throw it out. You wouldn't notice, if the oil is inside a capsule.
On the other hand, drying oils do not dry quickly without a catalyst. The most commonly-used catalysts involve divalent metal compounds (such as the famous cobalt driers). That kind of stuff is not good for your health, and certainly shouldn't be found in products intended for the natural foods and dietary supplement markets.
Now, if you merely desire to use food-grade flaxseed oil as a cleaner for oil painting brushes, I think that should be OK. I do that with safflower oil. It works well, and I presume that any trace contaminant left in the brushes won't have much effect on later paint. Since the food-grade oil is not intended for fast curing, I am not concerned about leaving the brushes for a short while before I finish with soap and warm water.