metis wrote:we'd do better to make a resist with some 1" marine ply clamp it on to the shirts, dye them with a good dye and then iron onto that.
Why use plywood? I've done a lot of t-shirt dyeing; summer camp & stuff, y'know. Just treat it like a really simple tie-dye with those good-quality fiber-reactive dyes.
Soak the whole shirt in the soda ash pre-treat solution, then wrap the area that you don't want dyed with a plastic bag, and seal it up with rubber bands. Apply dye, bag it, and let it sit for however long it takes the dye chemicals to bond (some hours; overnight is good, when practical). Then, unbag, rinse like hell, then wash (preferably with an after-dye detergent).
These procedures & materials work VERY well, and the colors stay vivid permanently (on natural fibers, especially cotton).