Things You'll Need
Bucket of cold water
Cutting a glass bottle or other piece of glass using nothing more than a string is a fun trick to show your friends. Watch their faces as you light the kerosene-soaked string wrapped around a bottle, submerge it into cold water and break the glass along the line of the string. This trick never fails to impress most people who have not seen it before, and it is also a great way to safely cut glass.
Wrap the string around the bottle you wish to cut and tie it off snugly to the surface of the glass.
Remove the tied string loop. Soak it in kerosene then place it back onto the bottle.
Light the string and allow the flame to burn evenly around the bottle until the flame burns out.
Submerge the bottle into the bucket of cold water just after the flame has finished burning. The drastic temperature difference between the hot glass and the cold water will cause the glass bottle to break only along the line on which the burning string sat.
This can also be done with non-bottle glasses, such as glass panes, but both sides need to be heated simultaneously. Make you own drinking glasses by cutting the tops off of wine or beer bottles, Smooth the cut edges using some fine-grit emery cloth.
Always be careful with kerosene, fire and broken glass as they could be harmful.