I use Decoart SoSoft fabric paint and it work well and stands up to washing. This is a product I am happy with. Don't mess with fabric medium and constantly having to mix it.
Select as Best AnswerUndo Best Answer
Tee shirt paint or if you can't find that, try Artist Acrylic paint. Once it's dry it's waterproof. I don't know how many times it can go thru the washer though. Dry on cool if possible or line dry.
There is a Fabric Medium that can be added to regular artist's acrylics which helps them stand up to washing. Available at the same craft stores as the previously mentioned fabric paints. The advantage to using the fabric medium with regular acrylics as opposed to fabric paint proper is that regular acrylics come in a much wider range of colors.
This isn't an answer to your question, just an idea. You can buy 12 hour glow-in-the-dark powder from GloNation.com. You could make some big bucks if you made a completely glow in the dark T-shirt with this high quality powder...
I've seen some good work with acrylic paints. L
And of course silkscreen inks work. I've also seen folks airbrush onto shirts, though generally that's just for coloring after having silkscreened the outlines. There's also the technique of bleaching the design out of a dark fabric rather than painting it onto a light one; at least one instructable exists on that topic.
Fabric paints (both flat and textured) are available at many craft supply stores.