Sometimes, you’ll notice mirrors with “black edge”. This is the result of the edges being exposed to moisture, oils, or chemicals that have corrupted the edge and separated either the layers from the glass, or the layers from one another. Does it happen with one brief exposure? Usually it is caused by repeated and prolonged exposure which can cause this damage.
Ammonia is a common – and extremely harsh – cleaning additive that can accelerate the degenerative process even faster. Hotels and other institutions often use these harsh cleaners with their maid services, and so this separation is sometimes referred to as “housekeeper’s mark”. Efficient cleaning professionals will sometimes spray the cleaner onto the mirror and other surfaces while cleaning a room, but this leads to the cleaner dripping down the face of the mirror and pooling at the edge. This is the reason why we only recommend spraying cleaners on a rag, then gently wiping the surface clean. Never directly spray a mirror with cleaner to prevent overspray or pooling at the edge.
Focus on these 5 things when caring for your mirror:
• Keep bathrooms well-ventilated during showers to avoid condensation that can run and pool at the edge
• Never use ammonia-inclusive cleaners on your mirrors
• Never spray cleaners directly on a mirror. Spray a rag first, then wipe
• Always protect the edge from excessive moisture. If you design the mirror to meet a countertop, be mindful to keep that countertop dry, or seal it with a silicone that is safe for use on mirrors.
• When in doubt, gentler is better. A clean cloth damp with water can actually clean a mirror exceedingly well. But even water should not be allowed to pool at the edge.
• An old photographer’s trick is to wipe a mirror with newsprint to avoid lint. It’s a nice finish.
To find a REALLY detailed account on how to clean mirror s from the Glass Association of North America, download the glass informational bulletin “Proper Procedures for Cleaning Flat Glass Mirrors” at the GANA website. (scroll down to the mirror division portion for all the mirror-specific bulletins).