The basement bathroom mirror was damaged at the bottom edges. I read that moisture gets behind the coating on the back of the mirror and eats away the mirroring on the glass. The solution was to coat the back of the mirror with polyurethane to protect it from further damage and then hide the damaged edge.
The mirror was cleaned throughly with glass spray and dried. Then the back of the mirror was sprayed with two coats of polyurethane. The mirror front was protected with cardboard and a margin at the edge was taped for spray painting with metallic chrome.
Blue painters tape was used to define the edge to be painted. After the paint dried the tape was peeled off carefully.
Unfortunately the tape did not reveal a perfect edge all around the mirror even with scoring the edge of tape with a razor knife but it was judged “Good Enough!”
The mirror was re-hung over the new sink and counter in the bathroom. The jagged edges are not that noticeable. Much better than the damaged edge anyway. The painted edge is delicate and could be scratched easily. But it is possible to keep the mirror clean with glass cleaner and a soft cloth.