Repairing a reflective coating on a mirror is nearly impossible. The only way to restore shine and reflection to a mirror is to remove the old coating and replace it with an entirely new reflective coating. This process is effective in most cases, but it does not always work for scuffed or green mirrors. Unless the mirror is very expensive and an antique, recoating is usually not worth the expense and effort.
Put on a respirator mask, eye protection and rubber gloves when working with harsh chemicals. Almost all chemicals necessary to fix a reflective mirror coating are dangerous, so follow proper safety measures. Work in a well-ventilated area or outdoors.
Remove the mirror from the frame and remove any backing, such as paper, from the surface of the mirror.
Remove the old mirror coating with a chemical paint stripper. You must remove the entire mirror coating and add a fresh coat to fix and repair the mirror coating. Allow the stripper to sit on the surface of the mirror for 10 minutes. Scrape the old coating away with a plastic scraper. Repeat the process if necessary to remove the entire mirror coating.
Spray the surface of the mirror with nitric acid. You can also pour some nitric acid onto a soft cloth and rub the back surface of the mirror. Remove all of the silver coating with nitric acid.
Wipe the surface of the glass with deionised water and a soft cloth to remove all traces of nitric acid.
Place the silver nitrate paint into the paint sprayer. Spray the surface of the mirror with the silver nitrate. Allow the coating to dry for one hour. Then spray a second coat onto the mirror.
Replace the silver nitrate with copper backing paint. Spray the back of the mirror with the backing paint. Allow the paint to dry for two hours.
Apply one final coat of paint to the back of the mirror with the grey backing paint. Allow each coat to dry for one hour. Apply two coats. Allow the mirror to sit for 24 hours before handling it.