As a fiddler, John in Kansas nailed it.
I've done it myself, and without his caution about not getting the alcohol on the fiddle, managed to remove a lot of rosin from that... and a few layers of varnish. Might not be a bad idea to put something on the surface of the fiddle before you start.

I also cleaned my bow off after somebody spilled dinner-related materials, including oil, on it. You can use a whole cake of rosin, but if there's oil on your bow hair, it ain't gonna work!