Glass is very similiar to flint or obsidian in the way that it flakes and chips. Because of this, and because its a lot easier to obtain, a lot of flint knappers practiced and learned to knap with glass first.
Warning! Be very careful, Glass is sharp. If you didnt know that get out of here. Im not going to be responsible for any harm you do to yourself, eh?
For the arrow that I made, I used glass as the arrowhead.
First take a bottle or plate glass and break it up in a bag. With bottles, usually, the bottom piece is the only thing thick enough to use for an arrowhead. Find a piece that is pretty straight and big enough to be shaped.
Then, with a metal tool, just chip away at it. It takes a while but pretty soon, you get good enough to control the chips and make whatever shape you need. To get sharp edges you have to be careful to hit hard enough to flake the glass, but not so hard that you ruin the edge you just made.
Ive read that you can also take a metal point and push flakes off the edge, but all that did for me was get me a bloody finger.
More practice is needed, and maybe Im doing this all wrong, but I got a couple pretty servicible points to use for my arrows.
