Not sure.. but heard of a experiment in child hood..!! Take a thin thread and dip it in petrol and make round on the gass you want to cut..!! then lit the thread with fire and let it burn for some time.. put that in water till the level of the thread and just try to move it..you will find the place the thread tied separating from the bottom part. Its done just by expansion of glass when its heated up theory..!!
Lovd it..!! Ha ha aha...!!