The short answer: black spots, dark edges and grey, cloudy patches on a mirror almost always start at the edge or on the back, not on the glass you see. Moisture gets under the protective backing, attacks the thin reflective coating and the damage creeps inwards. Once the coating is gone it cannot be polished away, so the realistic choices are to stop the damage spreading while it is small, or to replace the mirror.
What is actually happening
A mirror is a sheet of glass with a very thin reflective metal layer on its back, sealed with protective paint. The glass itself does not stain or rot. What goes wrong is the coating behind it: if water, steam or a cleaning liquid reaches it, most often at the cut edge where it is least protected, the metal oxidises and lifts. The first sign is a dark rim or a few black dots near the edge. Later come grey clouds or see-through patches where the mirror no longer reflects at all.
The usual causes
- Constant humidity. Bathrooms and kitchens without good ventilation are the classic case, because steam condenses on and behind the mirror every day.
- Water standing at the bottom edge. A mirror above a basin, or one leaning on a damp floor, keeps its lower edge wet for hours.
- Cleaner running behind the edge. Spraying liquid straight onto the glass lets it run down and soak in at the lower edge. Acidic or ammonia-based products are the worst offenders.
- No air behind the mirror. Hung flat against a cold or damp outside wall, the back can stay moist for weeks.
- A chipped or knocked edge. A small chip opens a direct path to the coating.
What you see and what it means
| What you see | Likely cause | What to do |
|---|---|---|
| Dark line or dots along the edge | Moisture has reached the coating at the cut edge | Dry the edge, ventilate, stop spraying the glass; check whether it grows |
| Black spots in the middle of the glass | Backing damaged by a knock, a scratch or moisture | No lasting repair; replace if it bothers you |
| Grey cloudy patches that seem to sit behind the glass | Coating oxidised | Cleaning cannot remove it; replace |
| Spots that wipe away | Dried water, limescale or cleaner residue on the surface | Clean with warm water and a soft cloth |
| Marks only on the lowest edge | Splashes or standing water | Wipe dry after use; move or raise the mirror |
Can black spots be repaired?
Not in any way that lasts. Spots on the surface are only dirt and come off with cleaning, but spots caused by a damaged coating are gone for good. Keeping the edge dry can slow a small edge mark down, and that is worth doing, but there is no reliable home fix. Re-silvering exists, mostly for antique mirrors, and for a modern mirror it is rarely worth the trouble. If the spots spread or spoil the reflection, replacing the mirror is the honest answer.
How to keep a mirror from spotting
- Dry the edges. After cleaning or after a splash, wipe the lower edge and the frame dry.
- Put the cleaner on the cloth, not on the mirror. That way nothing runs behind the edge. Our guide to cleaning a mirror without streaks explains why warm water beats vinegar.
- Let air reach the back. Hang the mirror so the wall behind can breathe, and avoid sealing it against a damp surface. How to hang a mirror safely covers fixings and how to check a mirror before it goes on the wall.
- Ventilate wet rooms. In a bathroom, hang the mirror away from direct splashes and open a window or run the fan after showering.
- Look at the edges now and then. A torch held at an angle shows the first dark line long before it reaches the middle.
Three mirrors to start from
- Solaro — round, brushed gold aluminium, eight diameters from 60 to 200 cm.
- Grand Arcadian — arch, brushed gold aluminium, nine formats from 160 × 80 to 200 × 140 cm.
- Golden Majesty — rectangular, hand-carved wood, 15 formats from 50 × 100 to 100 × 180 cm.
If your wall needs a size we do not list, see made-to-measure mirrors.
Production
- Production: every mirror is made to order from 4 mm Optiwhite glass in our own workshop — the production time is stated in our shipping policy.
- On arrival: open the crate while the courier is still there and check the glass and the edges before you hang it. Transport damage is only accepted with a damage report signed by you and the driver.
Frequently asked questions
Why does my mirror have black spots?
Almost always because moisture reached the reflective coating on the back, usually at the edge. Humid rooms, water standing at the lower edge and cleaner running behind the glass are the common causes.
Can black spots on a mirror be removed?
Only if they are dirt on the surface. Spots caused by a damaged coating cannot be cleaned or polished away, and there is no reliable home repair. Keeping the edge dry can slow a small mark down.
Is it safe to keep using a mirror with black edges?
Yes, the marks are cosmetic. Replace the mirror when the spots spread into the reflection, or if an edge is chipped, since a chipped edge can be sharp and lets in more moisture.
Can I hang a mirror in a bathroom?
Yes, if the room is ventilated, the mirror is away from direct splashes and you wipe the lower edge dry. The risk comes from constant dampness, not from the room itself.
Does vinegar damage a mirror?
It is acidic, and any liquid that runs behind the edge can harm the coating. Use warm water on a cloth, as described in our cleaning guide.