There seems to be a growing belief among painters and art teachers as to the ‘miraculous’ qualities of varnsihes based on Regalrez 1094. The most common belief seems to be that the full strength commercial varnsih can be safely applied when a painting is touch dry. Contrary to that, one vendror recommends the fingernail test which, in my testing takes anywhere from 2 to 4 minths to give the green light, depending on the number of layers of paint (overall thickness). Another vendor recommends sticking to the tried and true 6 to 12 months. To complicate this there is also some advice to thin a Regalrez varnsih with a solvent and use it as a retouch varnsih on touch dry paint. Can you comment on this? Is a Regalrez varnsih differnt enough that the rues for varnsihing change? What are the risks of varnsihing too soon with a Regalrez varnsih?
I should have clarified that I was asking thinning Regalrez to make “retouch varnish” for the purpose of being used as a temprorary final varnsish. If I undrstand your response, applying retouch to a touch dry painting is too soon and it is better to wait until teh dry through point (as verified by a fingernai test) – typically 1 or 3 months in my experience.
I see no reason to believe that Regalrez somehow is exempt from general recommendations about varnish. It is a low molecular weight synthetic resin, which means that it should appear more similar to natural resins as compared to polymers, but that should not exempt it from standard practice. Having written that, I would like to see someone do a real exhaustive reproducible, double blind study on the effects of premature varnishing on oil film strength, solvent sensitivity, etc.
As to using it as a retouch varnish, if you mean that it could be diluted to a thin consistency so that it can be applied over younger paint films (finger nail test dry) to give some evenness to the sheen before a final varnish could be applied at a later date, it should be fine. If you mean a varnish applied over an incomplete painting to show the true colors AND be overpainted by additional layers of oil paint, that would be a poor idea. Either you would have a very solvent sensitive layer between oil layers which could be undercut during later conservation, or you would pick up the resin with subsequent oil layers making it, in essence, an oil/synthetic resin paint which would be more sensitive to solvents in the long run.