I had a blast learning from Bob for 4 days. I never attempted discharge because I'm a hands on person, and I learn best that way. Bob is the nicest guy, and a great teacher! I highly recommend his class if you have the opportunity.
One of Bob's pieces
Bob showed us how he used styrofoam from the Home Depot, and a hot tool, to carve stamps for applying different chemicals for discharge. I got a little too excited about this and after making one in class that day, went home and made about 10 more. I'll make more for applying paint and fiber reactive dye as well.
Seriously, these are just a few that I made after class in the evening. I really went ape---t. :)
This is the result on one piece, and I really like the look you get from fabric that you dye black, and then discharge. You never know what colors will come through. I added no additional color on this, and used thickened bleach (which came out greenish) and Thiox (yellow/gold).