I'm a very poor knapper so I'm still grinding glass.
when i find a good bottle bottom I have the feeling that I could try to knap more than one point from it but usually break it badly when trying to split.
Today I tried to trace a diameter line and scratch it with a glass point (as you do with a diamond cutter) then placing a little elevation underneath and tappin with an hammerstone the line
It broke almost perfectly along the line.
no more waste !!