For a mirror to be properly resilvered, the original backing needs to be removed and a whole new silver lining applied. This process is worth the effort and expense if the mirror is very old or an antique, bevelled, has great sentimental value and the glass is in good condition. The timely process involves working with strong caustic chemicals, so it is recommended that this procedure be done by a professional, not by do-it-yourselfers.
Adequate ventilation is essential when resilvering a mirror. Concentrated solvents used to remove the old mirror backing contain chemicals that can be harmful when inhaled. Because this is a lengthy process, you will also need to have a work area that can be kept undisturbed for a period of time, from several days to a week.
First, the backing must be stripped from the mirror. Use a razor scraper to carefully scrape away the silver backing. You can also use a commercial paint stripper for this step applying a liberal amount of solvent on the surface. You then need to remove the silver with nitric acid. Once the paint and silver have been removed, clean the glass thoroughly to remove any dirt or debris. Material caught between silver and glass will show up as blemishes, so it is important that the surface is completely clean. Do not use any cleaning products that may leave a residue or film as this may cause the silver to improperly bond to the glass.
For the resilvering itself, special chemicals, including silver nitrate, are mixed with deionised water and applied evenly to the glass with a spray gun. A chemical reaction occurs causing the silver to adhere to the glass. The mirror is then completely dried, optimal time is 24 to 48 hours, and coated with a special copper paint. A coat of copper paint is applied which seals in the silver; this metallic layer is then covered with one or more coats of a grey-coloured paint. These final coatings will help prevent scratches and damage to the reflective material. Each coat needs to be thoroughly dried before applying the next.
If a mirror is a simple rectangle without bevelling or intricate edge work, it is usually cheaper and easier to replace the mirror rather resilvering it. Putting a new silver coating on is quite tedious, difficult, time-consuming and hazardous. Silver contains mercury and other dangerous components so caution is needed when disposing of the removed silver backing. Scratches, cracks and nicks on the surface of the mirror will be apparent and more accentuated after the mirror is resilvered.