I think you're supposed to build a circular wall around the hole using plasticine (or similar) to contain some coolant - white spirit rings a bell. I think that's for ordinary float glass though - I don't know if borosilicate glass is stress-free. I'd be very nervous if I had to do it.
Edited 1 time(s). Last edit at 04/16/2015 06:41AM by David J.
