In article 4e9d672e-18b7-494d-a0a9-e25fe4d06734
@googlegroups.com, says...

I am trying drill some holes in glass tile to allow the screws from a GFI receptical cover to seat properly. Purchased a 1/4" ceramic and glass bit and drilled a test hole in an extra tile. All went well.
Left it on the workbench and returned 1/2 hour later to find the corner had cracked off.
What went wrong ? Why would it do that ?
Thanks

Screwless wall plates https://www.google.com/search?
client=firefox-b-1-d&q=screwless+wall+plates