HI all... I don't know how much time I wasted scoring and shattering wine bottles, champagne bottles, scotch bottles (I have a few of those) and the like, after watching the miscellaneous youtube videos on bottle cutting. They all look so easy....
What I discovered, finally, at the end of my rope, and what works 99% of the time (for real) is;
1) Score the bottle with a glass cutter ( I made a roller fixture out of plywood to hold the bottle on it's side ).
2) Heat a pot of water to boiling, or very near boiling. I use an old 14" deep stew pot that I got at Salvation Army.
3) Immerse the bottle into the boiling water only up to the scored line
, and hold for about a minute ( + or - ). The "end" of the bottle to be cut off is the end to submerge ... in other words... the end of the bottle that you wish to use should remain a air temperature.
IMPORTANT: ONLY UP TO THE SCORED LINE - NO MORE!
4) Remove from the boiling water and immediately dip the hot end of the bottle into cool water again, only UP TO THE SCORED LINE
5) Tink.. ... .. .
My theory... the boiling water is heating the glass at a faster rate than the end of the bottle that is at air temperature. Quenching it in cool water contracts the glass, stressing it, and causes the break.
... you've probably all seen this video> http://youtu.be/t6g5-AdJxJI
I'd add that it's easy to get "perfect" results when filming a video... you just edit out the ten or twenty bottles that failed to separate cleanly...