MITRA Forum Question Details

​I think that was the right answer. Boiled Linseed Oil is heated to high temperatures and processed with jets of air, while it receives heavy doses of catalytic siccatives (driers) that would not be used in artistic painting, at least not in such high concentration. Formulated mainly as a wood finish, Boiled Linseed Oil is not intended for application as a thick, continuous film like painting oils. Top driers (siccatives that induce oxidation on the surface) cause boiled oil to skin over and wrinkle, becoming solid on top but remaining wet beneath. The dark color change of Boiled Linseed Oil is considered advantageous in its role as a wood finish, but it's a big drawback in artistic painting. 

Raw linseed oil from the hardware store might be a better choice, but this expeller-pressed oil (pressed with steam for higher yield) is not alkali refined ("washed") to remove undesirable components which affect drying, film formation and overall durability. So , still to be avoided for the studio.

Food grade flax oils are technically "cold pressed linseed oil" but edible oils are usually from a different flax variety than painting oils, have a different fatty acid makeup, and contain a "foot" of mucilage which might be good for people, but bad for paint. They also cost a lot more than alkali-refined linseed oil or stand oil (heat-polymerized, thickened linseed oil suitable for painting). 

I just logged on to comment after seeing the notification on my phone only to see that Matthew stole my thunder. As always, thanks Matthew for your thoughtful, educated responses. To just add a tiny bit, hardware store linseed oils, even if they do not contain driers, and even if not heat processed, do tend to yellow strongly due to their unrefined nature.

​​That is certainly a possibilty with health store flax oil (linseed oil) but it would be very unlikely in hardware store linseed oil.