Fungus amungus has a good instructable on using discharge paste for t-shirt designs – “Where bleach is incerdibly thin and can destroy natural fibers if you’re not careful, discharge paste is the opposite. It’s gooey so it doesn’t spill easily and can be used with silkscreens. It’s also nice to natural fibers, which is good as well. It removes most fiber reactives, direct dyes and acid dyes (more info) and typically leaves a light golden color when it’s done.” – Link.
Controlled bleaching with discharge paste