Why Does a Mirror Go Black Around the Edges?
And What Replacing One Actually Involves

A mirror is glass with a thin metal coating on the back, and that coating is what you are actually looking at. Sealed away from air and water it lasts for decades. The one place it isn't sealed is the cut edge — which is exactly where the black starts.

In a bathroom there is moisture in the air every day, and it settles along that edge and works its way in behind the glass. The coating corrodes, lifts and goes dark, and because it is under the glass there is nothing to clean. People polish the front of a mirror like this for months before someone tells them the problem is on the other side.

It Doesn't Stop, and It Can't Be Repaired

This is the part worth being straight about: once the backing has started to go, it keeps going. There is no product that puts the silvering back. Resealing the edge slows it at best, and only if you catch it very early. A mirror at this stage gets replaced.

The good news is that the removal is the easy half. With the old one off, you are left with a plain wall and a set of holes — and that is the moment to look at what you are fixing into, because it decides everything that follows.

Measure the Back, Not the Wall

The mirror goes face down first. Whatever it hangs on — brackets, a rail, keyhole plates — sits on the back, and the spacing between those points is the measurement that matters. Mark it on the back, transfer it to the wall, and the mirror lands where you meant it to. Measure the mirror's outside edges instead and you will be adjusting holes afterwards.

Two things to settle before anything is drilled: the height, and level. Height is not a rule out of a book — it is where the people using this bathroom actually want to see themselves, so it is worth asking rather than assuming. Level is unforgiving; a mirror an inch out of true is the first thing any visitor notices, and it is the one mistake you cannot hide.

The Fixings Are the Whole Job

A mirror is heavy, it hangs over a hard floor, and if it comes down it breaks into something dangerous. So the fixing has to suit what is behind the lining. Into a stud you can screw directly. Into plasterboard on its own you need an anchor rated to carry the weight — a plain screw into board will hold for a while and then quietly pull through.

Each fixing goes in on the marked line and gets checked before the mirror goes anywhere near it. The old holes rarely line up with the new mirror, and forcing the new one onto them is how people end up with a mirror hung off whatever happened to be there already.

A Frame Buys You Time

The replacement here is framed in black. A frame is not only a look — it covers and shelters the edge, which is the part that failed on the old one. In a room that is steamy every morning, that is the difference between a mirror that ages well and one that starts going dark again.

Whatever is on the wall, the same habit helps: run the fan or open the window while the bathroom dries out, and wipe the mirror's bottom edge where water sits after a shower. It is the edge that goes first, every time.

What It Cost

Two hours, $220 — the old mirror down and taken away, the new one set out, fixed and left level. Nearly all of that time went on the measuring and the fixings, which is as it should be. The minutes you save by eyeballing a mirror onto the wall are the ones you spend filling holes later.