Bleach is a handy way to mark fabrics, and it turns out that combining bleach with a 3D-printed design is an awfully quick-working and effective way to stamp a design onto a shirt. Plain PLA stamp ...
Companies like Cafepress do this - for t-shirts, mugs, mouse pads, you name it. I have no idea who they contract with, but they get their prices through, as you said, volume. Making it easy for ...