If you have been noticing dark spots on mirrors in your home that appear to be behind the mirror, and not on the surface of the glass, take a look at how you clean the mirror. Your diligent scrubbing could actually contribute to the spot formation if you're not careful. Custom glass companies can resilver the back of the mirror, but prevention is the better route to take. Here are tips on how to care for mirrors so that you don't end up with unsightly brown or black spots destroying the way the mirror looks.
Cleaning the mirror seems like a simple thing -- spray cleaner on the mirror and scrub. But that is not a good idea, because the cleaner can run down to the bottom edge of the mirror, and the fine spray that you get from the cleaner bottle can hit the edges as well. The drips and droplets can work their way behind the mirror, where they can cause the backing, or silvering, to flake off.
Instead, spray the cleaner directly onto the rag or paper towel that you're using. That gives you better control over the spray and prevents dripping. Obviously, you don't want to saturate the cloth or paper towel, because excess cleaner can then drip off that and down the glass when you try to clean. Just spray enough to get the cloth or towel noticeably damp.
Watch out for the Edges
If you have to clean the very edge of the mirror, you can try using cotton swabs dipped in cleaner, but these can easily release excess cleaner when you press the cotton bud onto the glass. You might want to try spraying the rag or towel and wrapping part of it around your fingers, and then moving your hand around the edge of the mirror gently.
For multiple panes of glass that form one larger mirror, use the wrapped-hand method to clean the areas where the panes meet. Don't simply swipe a soaked cloth over the edges as cleaner can get squeezed out into the joints between the mirror panes.
Keep Humidity Low
Ensure the mirror's environment isn't too moist. Extra moisture can seep behind the mirror and damage the backing. This can be a difficult situation in a bathroom, which is going to have excess moisture in it regularly. Ensure the room has adequate ventilation -- use the bathroom fan if you have one, or open a window. Leave the door to the bathroom open after you've finished taking a shower or bath.
For the rest of the house, use dehumidifiers to remove excess moisture from the air. Watch plant placement; you can have some really nice decorative arrangements where plants frame a mirror, but then you risk water splashing up onto the mirror when you water or mist the plants. Then, there's the risk that the water will seep behind one of the mirror's edges.
If you'd like to know more about preventing dark spots on mirrors, or if it's too late and you want to have a mirror resilvered, contact a custom glass company, like Wildwood Glass Company Inc, that works with mirrors. They can give you more ideas for cleaning and caring for the mirrors so that each one continues to look clear and bright.