The Right Way to Clean a Mirror Moisture is the No. 1 enemy of mirrors. If a wet cleaner is sprayed into the joints, it can puddle, invade the protective coating and eventually deteriorate the reflective silver beneath. That's what causes those ugly black spots on old mirrors. Instead:
Use a lint-free paper towel or a clean, soft cotton cloth. Old diapers and
T-shirts are great.
Spray a nonabrasive, low-ammonia cleaner on the cloth, not the mirror, so it doesn't seep into seams. Or, moisten the cloth in 1 gal. of water mixed with
1 cup of rubbing alcohol or 3/4 cup of distilled white vinegar.
Finish by thoroughly drying the mirror, especially around joints and edges, with a soft, grit-free cloth.