I have a large wall mirror in our bathroom, secured with the usual
clips. In places the bottom has desilvering or blackening about 1.5
inches up from the edge.

I intend to cover the edges with wood framing to hide the bad spots,
but it would be good to find a way of "stopping the rot." Does anyone
have experience with a product I can safely use to seal the bad parts
of the silvering before I cover them?

Thanks, Alexander.
(My mail is at shaw.ca and you can call me fony.)
Alexander