I know that most "professional" tie dying is done using a dye called Procion. I had really good luck with Dylon, which I got at JoAnn's a few years ago.
Just to add - I highly recommend you do not use RIT dye to dye cotton t shirts. RIT is a blend of dyes that targets both natural and synthetic fibers, resulting in fading after washings and less intense colors. For dyeing cotton shirts use a fiber reactive dye (I use Tulip or Rainbow brand dyes found at Joann Fabrics or other major craft retailers. This will ensure you can enjoy your tie dye many washes to come!
Here is the BEST site I have come across. It helped me learn how to tie dye, now I do it for craft shows!
I was going to respond step-by-step, but this is much simpler! This site has everything you'll need to know. Tie-dyeing is simple and fun, but if you have an attachment to these shirts you want to do, practice your designs on some other things first. Rit dye works the best, it is inexpensive and very available. Good luck and have fun!
Add your voice to the conversation. Click here to answer this question.