Here are the steps to cut a wine bottle in half:

1. Wrap a strong cotton string 5 or 6 times around the bottle and tie a knot.
2. Cut off the loose ends with a pair of scissors.
3. Soak the string in acetone and put it back on the bottle.
4. Light the string on fire and let it burn for 20-30 seconds.
5. Dunk the bottle in a sink filled with cold water.
6. The bottle should break along the line where the string was wrapped.

Alternatively, you can use a cordless rotary tool with a diamond cutting disk to cut the bottle.