Here are the steps to cut tempered glass safely:
1. Wear gloves and protective eyewear.
2. Score the glass with a diamond cutter or abrasive wheel.
3. Place the scored glass on a stable surface.
4. Apply even pressure to both sides of the scored line.
5. Use a wet saw or other cutting tool to finish cutting along the scored line.
Alternatively, you can anneal the glass by heating it up in a kiln and allowing it to cool off over an extended amount of time. At that point, you will be able to cut the glass by scoring and snapping it or by using a glass cutter.
