Over time, the silver on a mirror will wear away or turn green or brown. This problem occurs the most frequently with bathroom mirrors because moisture can easily tarnish quicksilver. To repair the silver on a mirror, you must remove all the old coating from the mirror and replace the entire silvering with a homemade quicksilver recipe. This complicated procedure can become dangerous; always wear work gloves, safety glasses and a respirator mask.
Remove the old silver and backing paint from the mirror. Pour paint remover over the back of the mirror, and allow it to stand for about 10 minutes. Scrape the paint and silver away with a plastic scraper, and discard it. Pour nitric acid over the back of the mirror, and allow to sit for five minutes. Repeat the scraping process.
Wash the glass with distilled water and glass cleaner. Dry the glass with a lint-free cloth.
Mix 118ml. of water with 40 grains of silver nitrate until the nitrate dissolves. Add 30 drops of ammonia to the solution. Add 32 grains of silver nitrate, and stir with a glass stick until it dissolves. Pour the mixture into 1 pint of distilled water. Set the mixture aside.
Mix 24 grains of Rochelle salts into 1 pint of warm distilled water in a non-metal pan on the stove. Heat the mixture until boiling. Add 25 grains of silver nitrate, and boil for five minutes. Allow the mixture to sit for one hour.
Place the glass on top of four blocks of wood near each corner of glass. Heat the glass with a hair dryer or heat gun until it reaches about 100 degrees.
Pour the two mixtures together and stir quickly with a glass stirring rod. Pour the mixture into the centre of the glass. Let the silver flow for a few seconds, then pour the mixture in a circular motion around the edges of the glass. Allow the silver to sit for 30 minutes.
Tip one corner of the mirror up to allow excess silver to drain off the mirror. Rinse the glass with distilled water, and stand the glass on edge to dry.
Create a mixture of equal parts white Demer varnish and asphaltum varnish. Apply the varnish to the back of the mirror with the camel hair paintbrush. Allow the paint to dry for several hours before framing the mirror.