For the beginning it is necessary to determine the place of the cut. To make it even take a piece of paper and wrap the bottle with it. Align the edges of the sheet to a smooth line. Then take a marker or marker and circle the edge of the piece of paper. Now you can remove the sheet.
Next, you need to take a piece of nichrome wire with a diameter of 0.5 mm, attach one end to a fixed object. For these purposes, I use a black weight. Immediately attach to it one wire from the battery.
Make a coil around the bottle. And we align them on the trail of the marker.
In order not to get burned, take the wire with pliers.We stretch quite a bit so that the wire is aligned. We apply voltage to the second end of the wire.
It can be seen that the wire is heated. In places of contact with the bottle, the wire does not quite turn red as the bottle takes heat away.
We are waiting without moving the wire and keeping it in tension for about 30 seconds. Then quickly remove the wire and sprinkle the heating point with water. You can also prepare a bucket of water and dip the bottle there.
You will hear a peculiar click of the glass and the bottle will burst exactly along the line where the wire of the nichrome passed.
Everything is explained simply: during the heating of a certain place in the glass, internal stress occurs. After a sharp cooling, the surface of the glass is sharply cooled, and its inner part remains heated.As a result of such a sharp change, microcracks appear, which instantly turn into a split.
This trick can be done not only with round bottles, but also square, oval, etc.
If the bottle does not break away after water, then just hold the bottle and press a little. Everything should fall away.
All irregularities and sharp edges after cutting can be treated with fine emery paper. When working with glass, be very careful not to cut yourself. Be especially wary of small fragments, take all necessary measures to avoid their spreading.