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I decided to play without the chinrest today (as an experiment, and I'd like to continue for a while without the chinrest).
After I unscrewed the clamps, I discovered that the cork part was glued to the violin. A little tug got the chinrest off, but the cork is stuck to both the front and back of the violin.
My options are: 1) just leave it as is, 2) try to pry it away with my fingernail, and hope the varnish or wood doesn't get damaged, 3) use some type of liquid violin polish or cleaner that won't damage the varnish, or 4) anything else?
I imagine this might be a somewhat common problem, since varnish can stay tacky even after a long period, and the chinrest might have been installed when the varnish was still a little wet. This is a Strobel Eastman violin from 2006, that I bought used.
I would leave it alone. You will probably put the cr back on after a couple of months. I did. It's fun to play without the cr and shoulder rest, liberating. But then after a while the negatives start showing up. Nothing big so you may like it forever that way.
I think that it sometimes is a combination of soft varnish and adhesives in the cork that cause the situation, some "airing out" may help them just fall off. I do not know what WD40 would do to your varnish, but I have used it on mine without harm.