I’m wanting to cut the bottom off a glass bottle to make a candle holder. Initially I thought I could do this by cutting very slowly with a water-cooled abrasive cut-off wheel. Turns out I can’t.
Baden-Powell’s Scouting for Boys indicates that you can cut bottles by filling them with water to the desired level and placing them in the ashes of a bonfire, whereupon they crack at the waterline as a result of thermal stresses. Not having a bonfire handy, I tried filling the bottle with cold water and immersing it in boiling water. Didn’t work. I tried again, chilling the water and the bottle in the refrigerator. Didn’t work. Tried a third time, this time placing the bottle of chilled water in a pre-heated oven. Bottle sat there uncracked, water inside boiling happily, mocking me.
An appendix of a US Army manual states that you can cut the neck off a bottle as follows. Wrap a fuel-soaked string around it, ignite the string, and holding the bottle horizontal, rotate it to create a ring of hot glass. Then plunge the bottle in cold water and knock off the neck on a hard object. Before I start playing with burning string and buckets of water, does anyone know an easier way to do this?