I recently varnished an hardwood frame for a mirror with a water based urethane varnish. My painter's tape did protect most of the mirror's edges, but it failed for one or two spots. The varnish found it's way under the tape. I want to get rid of the spots without scratching my mirror. I tried to use soap and water as suggested on my varnish's label, but that's clearly for when the varnish is not dry. So, I'm wondering what's a good way to remove dry varnish from a mirror. Obviously, my top priority is not to scratch the mirror itself.