Antique mirrors often reflect their age to the world by not reflecting an image. This occurs because the silver backing breaks down with age and begins to look blotchy. Although stripping the backing and applying a new backing will lower the value of an antique mirror, it is the only way to improve the mirror's performance. Antiques restorers and glass shops are both good places to get a new backing for a mirror. But you can also restore the mirror yourself.
Remove the glass portion of the mirror from its frame and lay it with the silver side facing up.
Scrape the backing away from the mirror using a paint scraper. Rub paint remover over the glass to remove stubborn paint.
Soak a paper towel in acetone and rub the glass to remove any residue left by the backing.
Clean the mirror glass with glass cleaner to remove any residues left by paint remover and acetone.
Open a resilvering kit and familiarize yourself with any instructions and warnings. You can purchase a resilvering kit through retailers of stained glassmaking supplies.
Mix the silver nitrate with the chemicals included in the kit. Place the chemicals in a resilvering sprayer and spray an even coating of the chemicals over the back of the mirror. The chemicals allow the silver nitrate to stick to the back of the glass. The coating will appear clear until it dries. At that point it will turn silver.
Apply the copper paint from the kit to the back of the mirror once the silver nitrate dries. The paint will be labeled with proper application methods. Methods vary depending on the manufacturer.
Apply backing paint to the back of the mirror once the copper paint dries.
Return the glass mirror to its frame once the backing paint dries.