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Originally Posted by Sharon Knettell
. . . have independent scientific studies been done to decide the superiority of any of the oils in relation to each other ? . . . a lot of the information is anecdotal and not-scientific. . . . Michael Harding . . . said cold-pressed is somewhat of a misnomer. All painting linseed oil has to go through a stabilization process using heat, just not the use of alkali . . .
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Far as I have been able to find, systematic studies analyzing linseed oils were geared mostly to the paint and coatings industry (and are now very passe). They provided a basis of information for standards applied to the production of linseed oils for meeting criteria for producing paints and varnishes used on ships, barns, houses and machinery, but don't address fine art painting as such. What we are likely to learn from other painters of the recent past and currently, reflects their well-intentioned efforts to apply some semblance of scientific methods to personal experiments.
What you learned from Michael Harding agrees with what little I have been able to learn about cold-pressed oil. The colorman's objection to alkali refined linseed oil has much to do with an ideal ph. Wetting pigment stuffs efficiently requires an oil with a certain acid number. With embarrassed apologies for my own quasi-scientific anecdotes,
I' ve been unable to see marked differences in clarity, film strength or flexibility between cold-pressed and alkali refined oils. However, the test samples are pretty darned young in view of 500 years of oil painting!