Can you restore a old mirror?
What part needs restoring? Is it the mirror itself? The frame?
You can take to a glass and mirror shop to have re silvered, but don't faint when you hear the price.
On the show, Home Town, the host and her friend refinished a mirror and then antiqued it. I believe they used Rustoleum spray paint. The antiquing was done with vinegar. Skip the vinegar and you should have a new mirror.
If its an antique, it will lose its value if your redo the silvering. People value the aged mirror look.