I've seen plenty of glass bottles cut into cups online and have been thinking that, as a college student, I needed some of these. I spent time looking at different methods of glass cutting and decided that they all had flaws in their procedures. So, I combined several of the methods together to get what I think is a lot better method of doing it.
Excuse some of the blurry close up photos, the camera I used doesn't take good close ups.
Step 1: Materials
The materials are pretty straight forward.
Scissors or a utility knife
A bucket of cold water
Fine grit sand paper
The glass bottles you wish to cut
Step 2: Scratching the Glass
As you can see in the picture, I used a clamp to clamp the glass cutter to a bunch of scrap wood pieces to the height I wanted to cut on the glass. Using plenty of pressure and keeping the bottom of the glass on the ground, I turned the glass against the cutter to create a scratch around the glass.
Step 3: Cutting the Glass
Once scratched, the glass must be cut. To do this, start by taking a string and tying it around the bottle at the height that the glass is scratched. I then found it best to cut off the extra hanging pieces as best as you can. You should then remove the string and submerge it into the alcohol. Then replace the string around the bottle along the scratch. At this point you will take the lighter and light the string. I found that once lit, it works well to rotate the bottle so the flames evenly around the glass. Once the flames are mostly extinguished, submerge the glass into the cold water bucket. You will hear the glass break, and you should be able to gently pull the glass apart.
As you can see in the pictures, you may not always get the greatest glass break. It seems that this occurs at the knot and i'm still trying to figure out exactly what to do about that problem. For some reason, all of the Heineken bottles i tried didn't break very nicely and neither did a few of the corona glasses. The last picture broke because I tried a higher grit sand paper, and the glass had a small hairline fracture. This is why I recommend a fine grit sandpaper.
I started with 6 Corona bottles, 3 Heineken bottles, 2 Miller Lite bottles, 2 Absolut bottles, and a Black Velvet bottle. In the end I got 3 finished Corona glasses, 2 Absolut glasses, and a Black Velvet tumbler glass. The glasses I lost were due to trial and error and now that I have a good system down, I plan to make a bunch of other glasses, and shouldn't have such a high loss.
Step 4: Sanding the Edges
You will now need to sand the sharp edges of the glasses. I read online that you should do it in a circular motion, though It didn't seem like it mattered to much for me. Some of the edges didn't break perfectly, so first I focused on these. Then I moved to the edges. These are the most important, due to the fact that you will be drinking from it. To sand the edges I just took the sand paper and went at it until the edges were no longer sharp to the touch.
I would recommend using a glove when sanding, because you have to remember that you are sanding off glass shards. I would also recommend washing the glasses before use.
Step 5: Finished!
You now have some cut glasses with which you can enjoy your beverages.