I work with glass as a hobby. I make wind chimes and sun catchers. I have a glass bottle cutting jig that I purchased of Amazon. They are not super expensive but not supper cheap ($40 and up). They work well. I have found the ones that lay the bottle down an you just turn the bottle work better than the ones that clamp around the bottle. It is hard to hold the bottle and the clamp at the same time and ensure an even score line.
You need to make sure that your cleaning the outside of the bottle well. Remove label and residue and then clean the bottle well. The glass cutter won’t cut well if you don’t. Once you score the along the base of the bottle you can take the bottle from cold (ice bath) to hot (pouring boiling water) along the score line. This will cause the score line to deepen through the bottle until the bottom falls off.
Side Notes:
Make sure there is not lid on the bottle because that can cause pressure to build up and can be very dangerous.
The thicker the walls of the bottle the longer it takes to cut.
Square bottles are much harder to cut
Use wet glass sanding paper to get a smooth edge. It takes time but is worth in the end.
