Step 1: Tools and supplies
Standard size hacksaw (A coping saw may work fine as well)
Carbide saw blade (Glass is harder than steel, so a regular blade won't work)
Leather work gloves
source of water
At least three different pieces of sand paper of various grit (I used 220, 100, and 60)
Roll of masking tape
A base to set your bottle on while you saw. I used a 9X9 Casserole dish turned upside-down.
Home Made Jig
While I would like for everyone to use my instructable, you may skip it if you can get your hands on a Tile saw such as this one:
Still be safe, wear protective gear, and use step four to help smooth out the edges.