I do hope you enjoy and stay safe! as this can be quite dangerous!
Step 1: Gather Materials
1 Glass bottle (the thinner the glass bottles wall the better)
Acetone (Most commonly found in nail polish remover
Some form of abrasive paper (I used emery board)
Sink filled with cold water (the colder the better. I used ice which helped)
Step 2: Prepare the Bottle
Gather your string and wrap a portion of it around the circumference of the bottle. Tie the string together and cut off the excess.
Take the string off the bottle and submerge it into a volume of nail polish remover.
Put the string back around the the bottle and prepare to ignite! So keep the bottle of nail polish away and be prepared for accidental fires.
Step 3: The Big Dunk!
What is done now is to ignite the string soaked in acetone and rotate the bottle as the flames lick around the bottle. This increases the temperature around that portion of the glass, inducing stress in the material. Glass is one of the materials which doesn't like being heated and chilled quickly! This property is used to our advantage in this process.
Once the bottle has been adequately heated it is quickly, sharply and abruptly dunked into the volume of cold water. This massive change in temperature at the strings location on the glass causes a thermal shock, rippling a crack around the glass and splitting it in two!
I found out however that one run with the string wasn't enough to heat the glass so once the flame extinguished itself from lack of fuel, I replenished the fuel by dripping nail polish remover over the string then re-igniting. In order to get enough heat I had to do this three times, so expect to replenish the fuel.
On the contrary, the idea of the experiment was to create a massive difference in temperature so if you can't get the bottle hot enough, make the water colder! I found out that this was almost necessary for my experiment so a dozen or so ice cubes helped to bring the temperature of the water down.
Once the glass had split in two, I ran several emery board strips against the inside and outside rim of both portions, removing the hazardously sharp edge of the bottle. Now I am left with two containers of which aren't effected by most chemicals, transparent, strong and above all, fascinating!
Step 4: Final Thoughts
Stay safe and enjoy! :D