Mr. Elliott!
Thank you for contributing your uniquely valuable expertise to our thread!
I know what you mean about Ralph Mayer (whom I obviously respect) -- he's perhaps the most quoted authority on painting in recent years; but we really do need another, more updated authoritative work -- I'm sure I speak for all of us in saying that we eagerly await your forthcoming book (Having written some handbooks and software, on other subjects, and having proofread and edited books and articles for other authors, I also know what you mean about an author's "prejudices"; but that's part of what adds to the "personality" of a work, for better or worse).
Since you are also a world-class expert (serving with the ASTM, no less), let me put one of my questions to you -- it is along the lines of your advice, and it also quotes from Mr. Mayer's book. Perhaps there is some common ground; there appears to be some historical precedent...
To my hypersensitive nose (which I seem to have inherited from both parents), even the alkyd mediums are somewhat irritating; and because turpentine is out of the question, I am trying to eliminate all resins from my painting, even though they seem to be standard ingredients in painting mediums since the 18th Century (and my methods of rendering the lifelike translucency of fleshtones requires mediums, in order to apply thin "velaturas" of translucent, not completely transparent, paint).
In an apparently new piece of literature from Gamblin, "Oil Painting Mediums", I read the following: "According to the scientists of the Rembrandt Research Project at the Rijksmuseum, Rembrandt did not use mediums that contain resin varnish. He used the oldest painting medium: a simple mixture of linseed oil and solvent."
Which I believe is like what you are recommending, Mr. Elliott (I believe the addition of solvent is to prevent wrinkling, a common problem with the addition of oil).
I have also just read an article by you, Mr. Elliott, in the website for the ASOPA...
http://www.asopa.com/publications/19.../rembrandt.htm
...in which you describe Rembrandt's medium: "The consistency of the paint was modified by the addition of a medium containing a long oil (sun-thickened linseed or walnut oil or boiled oil) and sometimes a resin, to give it a long brushing quality. Paint exposed to the air for several hours begins to take on this same characteristic, as the oil begins to polymerize."
Similarly, the Gamblin literature says: "In the style of Van Eyck, painters use high viscosity mediums (50% OIL to 50% SOLVENT) to create thin, illusionary surfaces with no brush marks. Linseed Stand Oil, the polymerized oil of the 19th century [I believe sun-thickened linseed oil served a similar purpose previously], mixed with solvent makes a similar high viscosity painting medium that is also slow drying." And previously the literature stated: "Slow drying painting mediums are useful for painters blending colors, such as portrait painters who need more time to blend flesh tones..."
Personally, I find that last point can go either way, given the number of "veils of color" that I must apply.
But still wanting an ingredient like a resin to enhance the "feel" of the medium (as the Gamblin and other literature puts it) and to "toughen" the resultant paint films (although the Gamblin literature also mentions the cracking dangers from natural resins, as you have alluded to), I remembered reading in The Artist's Handbook:
"The mixture of linseed oils of various degrees of refinement is a procedure of considerable antiquity...A small amount of a linseed oil of ordinary consistency added to stand oil will impart a certain hardness, body, or solidity approaching that produced by a resin; some of the old effects which may be approximated by the use of Venice turpentine and oxidized oil may also be duplicated by the above mixture, particularly as regards manipulations and brush stroking."
So I am inclined to create a medium that incorporates the features of those mentioned above: Solvent (Odorless Mineral Spirits in this day and age), Stand Oil, and Linseed Oil (and because alkali-refined linseed oil has a reputation for oxidizing to greater hardness than cold-pressed, which I've found to yellow too much -- despite Mr. Mayer's favoring it -- I am now strongly leaning towards including alkali-refined linseed oil in this medium, hoping that the stand oil content will control any "suede effect", and also using paints with pigments ground in alkali-refined oil). Such a medium would have an odor very similar to the paint itself, which I actually find rather pleasant.
I have read further in other literature but have found no other references to the mixing of linseed oils of various states of polymerization (and could chemical analysis of the final, oxidized films of historical works even tell us what states of polymerization the original oils were in when applied? As Mr. Mayer continues in his book, he seems to indicate otherwise.).
If you could give us any guidance on this point, Mr. Elliott, (as to the historical precedent or proportions of linseed oils of various degrees of "refinement" or polymerization in successful mediums) I would be very appreciative. I know of no one who knows more on such subjects than you (or, equally respectfully, the other authority I am consulting).
Thanks again for all your helpful information!