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Originally Posted by Michele Rushworth
Virgil, what's the downside of using alkyds as a varnish? If they're non-yellowing they would never need to be removed, right? Gamblin recommends using that 50/50 Galkyd Lite/OMS mixture as a retouch varnish. What if, after doing that, the painting then had sufficient overall gloss that it didn't need a final varnish?
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Michele,
The potential downside is that if the alkyd resin
does ever develop a defect of any kind that interferes with the viewing of the painting itself, it will have to be removed, and alkyds require very strong solvents to remove. Thus there would be increased risk to the paint layer. Yellowing is not the only concern, but we cannot say with certainty that it won't yellow over the long term, or crack, or cross-link and become less transparent. It's also a fast-drying substance, and carries the possibility of interfering with the thorough drying of the paint underneath. Of at least equal importance to "fat over lean" is
slower-drying over faster-drying. Doing it the other way around can lead to various problems.
I'm sure Gamblin's advice regarding the use of their alkyd medium as a retouch varnish was intended to mean as a couch to paint into while the painting is in progress, as in oiling out over a dried layer in order to re-saturate it to facilitate precise color-matching and to lubricate the surface so new paint will blend into the image more seamlessly. I would still question the advisability of using alkyds for that purpose on any painting whose paint layers have not cured sufficiently. Linseed or walnut oil would be safer choices, in my opinion, with the proviso that as much should be wiped or blotted off as will come off with a dry rag or paper towel immediately after it's brushed on. Very little is needed to accomplish its purpose. Whereas you might get by with using alkyd medium for that purpose, why take the chance? You went to a great deal of trouble to paint the picture, and your collector is probably paying a good price for it. Why risk screwing it up?
Virgil