Typically, if your mirror has developed a bare spot somewhere, it is also an antique. This often means that the mirror is not simply replaceable; in many cases, the mirror carries immense personal or monetary value. This can be a tricky job, but the main concern is safety during the project. The steps themselves are not so difficult, but the materials can be harmful to the lungs and skin if caution is not exercised.
Gently remove the mirror from the furniture or frame that it is set in. Lay a soft cloth out on a flat, sturdy work surface and place the mirror glass side down.
Use the safety scraper to softly scrape away the deteriorating silvering material on the back of the mirror. Depending on the era and manufacturing process of the individual mirror, this material may sometimes contain mercury so be sure to wear your mask during this process. Use a HEPA filtered vacuum to clear away the dust once this process is complete.
Dispose of the silvering dust before beginning. Contact your local trash department before dumping to make sure you follow the correct protocol for disposing of a substance like this, as it is hazardous to humans and wildlife.
Prepare the resilvering formula according to the manufacturer's instructions. Apply a thin layer of this formula to the back of the mirror, allowing to dry thoroughly. Be very careful to create a smooth application by using the application tool provided in most resilvering kits; otherwise you'll be left with a repair job that looks clearly botched when the mirror is in use again.
Allow the resilvering formula to dry completely. Keep the room you are working in well ventilated, and continue wearing your mask throughout the process to ensure that you do not subject yourself to any harmful chemicals.
Re-affix the mirror to the original furniture or frame and examine the work once installed. The mirror should have renewed lustre and sheen with no noticeable bare spots.