Glass is cheap and easy. If you want to learn to pressure flake, then get some glass...empty your flakes out from your pad OFTEN or you WILL get cut...it will happen anyway, but not emptying the flakes will make it a lot more often.
As far as knappable materials. The best thing to do is watch as many people as possible in person, and check out the various videos (Jamie posted some good ones) available on the net.
If I had it to do over, I would get several basic tools (couple different size boppers and pressure flakers), and spend the money and buy some good material online. Dacite is cheap and will tell you exactly what you're doing wrong. Texas stuff can be had pretty cheap, but get good, doesnt have to be GREAT (save that stuff for later), material.
Work it down until it stumps you or you feel like you're making mistakes.
Put it aside
Pick up another piece, and repeat the process.
Put it aside
Repeat until you've went through all the material you have.
Start back again with the ones (by this time they should all be worked to a degree) you put down and work a little more. By now, the "problems" should be a little easier to work out.
Just repeat the process over and over and over stage by stage. Dont try to get a point right off the bat. First work at maybe getting the cortex off, if that allows in the first stage....sometimes there are places that dip into the rock that need to be left until later.
Work all of your rock down, one stage at a time...Not one piece stage by stage, but all of your rock to the same stage...then to the next, then to the next. If you try to work on from start to finish, then you'll only get more frustrated and break more and forget what you may have learned from each flake.
I may be a little long winded, and different things work for different people, but I can promise, more have benefited from worked stage to stage, with all lot of different pieces, than trying to go start to finish, one rock at a time.
Say you have rock A,B,C and D...
Take rock A go to stage 1
rock b to stage 1
rock c to stage 1
rock d to stage1
rock a to stage 2
rock b to stage 2
rock b to stage 2
rock c to stage 2
and so forth.
Hope this makes since...
P.S...learn from each flake. Why did it detach the way it did? Where was my point of impact on my platform? Why did the biface break? Why did it hinge? Too many possibilities to go over in one reply. I'm no expert, but my light bulb just clicked a little while back thanks to a lot of help from members here and from breaking a lot of rock. Post more questions as you have them.
Also, no, coal crumbles.
