Crack while drilling? Is it still usable?

[Ulu]

Thin glass heats up quickly at localized spots and cracks.

Go slow, let it cool down, then start again. Don't try to do it in one pass!

The glass must rest a bit.

 

[Guinness]

Thanks, will do. The one that cracked was the first hole I ever drilled. The next 3 went well. Good learning experience.