You should be able to purchase a carbide scribe at most large hardware stores or home-improvement stores. It costs less than $10 USD.
You can purchase a diamond scribe through large online retailers or at some craft-supply stores. Diamond tipped scribes are about twice as expensive as the carbide tipped option. They’ll cost about $20 USD.
Be aware that using a rough steel edge (like a file) to cut glass may result in an imprecise cut and a sloppy break. A carbide scribe will produce a sharper, more clean and accurate cut.
The flat surface needs to support the entirety of the mirror. Do not place the mirror over 2 sawhorses, for example, or you’ll risk breaking it in half.
You can buy both glass cleaner and microfiber cloths at a large supermarket or hardware store.
If you’re cutting the mirror to fit in a frame, measure so that the cut mirror will be 2–4 millimetres (0. 079–0. 157 in) smaller than the interior of the frame. This will give it a nice secure fit.
If you don’t already own work gloves and protective eyewear, you can purchase both at any hardware store or home-improvement store.
You can purchase glass cutting oil at a hardware store or home-improvement store. You could also use an all-purpose oil.
Do not stop scoring the mirror once you’ve begun. If you stop scoring partway through the cut, it’ll be very hard to re-begin scoring at the same place. If you’re scoring the glass with a steel file, you may need to make 2-3 passes before the glass is adequately scored.
If you don’t already have a dowel handy, you can buy one at a hardware store.
If the mirror doesn’t break at first, try pressing down in different spots. For example, press once at the top, middle, and bottom of the mirror. Always keep your hands opposite one another when you’re pressing down.
Avoid touching the edges of the mirror until they’ve been sanded. The raw edges will be sharp and possibly jagged.
