TL;DR
Never spray a mirror directly. The liquid runs down, pools at the bottom edge, and wicks in behind the glass where it attacks the reflective backing -- producing the black or cloudy fringe that shows up on old bathroom mirrors and cannot be repaired. Spray a cloth instead, wipe, and buff dry with a second cloth while the surface is still slightly damp.
What is actually behind a mirror
A mirror is a sheet of glass with a very thin metallic coating on the back, protected by a layer of paint or sealant. Everything you see reflected depends on that coating staying intact.
The coating is durable from the front, where the glass protects it, and defenseless at the edges, where it is exposed. Moisture that reaches it lifts and corrodes the metal, and the result is the dark, spidery, cloudy fringe that people call desilvering or black edge. It is permanent -- no cleaner, polish, or technique brings it back, and the only fix is replacing the mirror.
Source: glass and mirror manufacturing guidance on backing protection.
The method
Dust the frame first, dry, so nothing falls onto the glass while you are working.
Lightly dampen a microfiber cloth -- spray the cloth, over a sink or a trash can, never the mirror. Wipe the glass in overlapping passes, working from the top down, keeping the cloth an inch away from the very edge.
While the surface is still slightly damp, buff with a second completely dry microfiber cloth. Air drying is what sets residue into visible streaks, so the timing matters more than the product.
For the last inch around the perimeter and any grime right at the frame, use a barely damp cotton swab and dry it immediately. That is the only thing that should ever approach a mirror edge with moisture on it.
What to clean with
| Option | Best for | Notes |
|---|---|---|
| Distilled water on a cloth | Everyday dust and fingerprints | No minerals, so no water spotting |
| Warm water with a drop of dish soap | General film in a bathroom | Follow with a plain-water pass |
| Diluted isopropyl alcohol | Hairspray and product overspray | Effective on bare glass; keep it off frames and coated panels |
| Commercial glass cleaner | Heavy grease | Apply to the cloth only, sparingly |
| Dry microfiber cloth alone | Between real cleanings | Zero streak risk |
Do not mix products. An ammonia-based glass cleaner combined with a bleach product releases toxic gas, and the same is true of bleach with any acid such as vinegar or a descaler. Use one product, ventilate the room, and rinse tools between jobs.
Alcohol is fine on plain mirror glass and wrong on anything with a coating. Anti-fog mirrors, backlit vanity mirrors with treated surfaces, and screens all have layers that alcohol degrades -- the display case is covered in glass cleaner on screens.
Bathroom mirrors specifically
Steam is the mirror's enemy, and a bathroom delivers it daily. Humidity condenses on the glass, runs down, and collects exactly where the backing is exposed. That is why bathroom mirrors are the ones that go black at the bottom edge first.
Run the exhaust fan during and after showers, and wipe the mirror dry rather than letting condensation sit. If a mirror is mounted directly to drywall in a wet bathroom, moisture can also reach the back through the wall, which is why some old mirrors deteriorate from behind with no obvious front-side cause.
Toothpaste flecks are the other bathroom special. Let a damp cloth sit on the spot for ten seconds to soften it rather than scraping, then wipe. Scraping dried toothpaste with a fingernail or a blade puts scratches in the glass.
What ruins a mirror
Never use abrasives -- scouring powder, melamine sponges, or steel wool -- on mirror glass. They scratch, and scratches in a mirror are highly visible because the reflection exaggerates them.
Never use a razor blade to remove paint or adhesive from a mirror. It works on plain window glass and it scores mirror glass, and the mark is permanent.
Never let cleaner sit and soak. On a mirror the entire risk is time plus liquid at the edge, so speed is protection.
Never clean a frame and a mirror with the same wet cloth. Wood and gilded frames take water badly, and a soaked cloth carries liquid straight to the joint where frame meets glass.
Frames and surrounds
Wood frames get dusted dry and wiped barely damp if needed, then dried immediately. Gilded and gesso frames get dusted only, with a soft brush, and nothing wet at all.
Metal frames wipe clean easily, but if they are chrome or a plated finish, skip abrasives and acids, which pit the plating. That care routine is in cleaning chrome fixtures.
Framed art follows all the same edge rules as a mirror, and for the same reason -- see cleaning glass tabletops and frames.
Full-length and closet-door mirrors
Large mirrors are harder mostly because of scale: a big surface dries at different rates and shows streaks readily. Work in horizontal bands of about two feet, cleaning and buffing each band before moving to the next.
Sliding closet-door mirrors also collect grime in the track below, which throws dust back onto the glass every time the door moves. The track method is the same as for a patio door, covered in cleaning a sliding glass door.
For very large glass surfaces, a squeegee technique borrowed from window cleaning gives a better result than cloths alone -- see streak-free window technique -- but on a mirror you still have to keep liquid away from the edges, which limits how wet you can work.
FAQ
What is the best way to clean a mirror without streaks?
Spray a microfiber cloth lightly, wipe the mirror in overlapping passes, and buff with a second dry cloth while the surface is still slightly damp. Use less product than feels right, and wash your cloths without fabric softener, which leaves a smearing film.
Why does my mirror have black edges?
Moisture has reached the reflective backing at the exposed edge and corroded it. It is called desilvering, and it is permanent -- no cleaner reverses it. It comes from spraying directly at the mirror, from bathroom humidity, or from water reaching the back through the wall.
How do you get toothpaste off a mirror?
Hold a warm damp cloth against the spot for about ten seconds to soften it, then wipe it away and buff dry. Do not scrape it with a fingernail, a blade, or an abrasive sponge, all of which leave scratches that are very visible in a mirror.
Why does my bathroom mirror fog and how do I stop it?
Warm humid air condenses on the cooler glass. Running the exhaust fan during and after a shower is the practical fix, along with wiping the mirror dry afterward. Letting condensation sit and run to the bottom edge is what eventually damages the backing.
Can a desilvered mirror be repaired?
Not realistically at home. The damaged area is corroded metal under the glass, and resilvering is a specialist service that usually costs more than replacement for a standard mirror. Antique and decorative mirrors are the exception, where resilvering can be worth it.
This sits inside the broader whole-home work covered by house cleaning services.
Mirrors are easy to keep perfect and easy to ruin, and the difference is entirely about where the liquid goes. Every home is different, so what a full clean covers depends on size, condition, and what you want included. Get a quote and we will walk you through it.