The Unvarnished Truth about Synthetics by EnPassant

I’m still sleuthing my undercover story (couldn’t resist the pun) about varnishing and came across a technical article from the American Institute for Conservation on the removal of synthetic varnishes from paintings.
It has some interesting points to make about the changing solubility of synthetic varnishes over time. It’s pretty dry to wade through (the article that is – not the varnish of course) but I quote the conclusion below for anyone who hasn’t already tuned out:-

For those of you with a cast iron constitution or with time on your hands the whole article can be found here.

IT HAS been shown previously on the basis of accelerated aging studies that certain methacrylate polymers will tend to cross-link and lose their ability to be removed efficiently. In order to monitor this effect, a program of varnish removability testing was initiated. A combination of infrared spectroscopy, visual examination, and fluorescence in ultraviolet light was used to monitor removability of poly(isoamyl methacrylate) and poly(n-butyl methacrylate) varnish coatings. The results of these tests show that some cross-linking of these varnishes has occurred under natural aging conditions with ultraviolet-free light, but that although the varnishes were applied between 10 and 40 years ago, they are still removable. Usually the application of solvents such as cyclohexane-toluene mixtures causes the varnish to gel but does not remove the varnish completely. Solvents of higher polarity (toluene or toluene-acetone mixtures) were necessary for complete, effective varnish removal. The word effective needs to be stressed here. Although a varnish may be eventually removed in a milder solvent, a slightly stronger solvent may be preferred to avoid the need for excessively vigorous rubbing with the swab. It must also be noted that this qualitative removability test does not indicate the amount of cross-linked material or the expected lifetime of the coating.

I bet you’re glad you didn’t go to the full article !!!!!!!
PS I meant to say also that, in tests, where changes had occurred in the varnish, the conservationists had to resort to using toluene to remove it. Toluene is not a nice substance!