Nice points GL.
When I first started knapping I used a lot of Glass, mostly "frosted" glass, from bottle bottoms, found on the sandbanks along larger rivers. Its a lot of fun, during the summer to float the river "prospecting" for knapping glass. The frosting on the glass actually makes the flaking "run" a lot farther on your initial flakes. If you haven't tried it yet you should. I have also found, if you have access to it, a deer antler tine, "grips" glass a lot better then a nail, which will let you "push" the flakes a lot farther.
Keep
posting pictures
3creeks
Copper grabs even better and your tool lasts longer as well.I built a little jig that makes every flake goe across if the grain is right