DIY & Home Improvement

Depending on the age of the mirror, and the method of silvering, it may be soluble in various concentrations of ammonia.

Yes, I would imagine that the backing colors will have an effect. In the case of metal leaf work, various bole colors are used to impart warmth, etc. And, depending upon the point at which it is done, sizing can also "drown" the leaf, reducing it's vibrance. I don't know if any of this works on whatever method was used to silver your mirror.

I think layering is the key in the approach you are taking.

Good luck, and post a photo of the results.