I silkscreened a shirt once for a middle school art class. It was an intensive, smelly process that didn't come out very well. That's why I'm intrigued by the Lumi Process, a water-based printing method for textiles that uses sunlight to develop the prints.
The Inkodye used in the process was developed from a nearly-forgotten dye formula from the 1950s that has some useful light-sensitive photographic properties.
Here's the system. Take a photo. A free Lumi app turns smartphone images into black-and-white negatives, or you can use your own photo-editing software. Print the negative on transparent film.
Apply a layer of Inkodye onto a shirt or other piece of fabric. Pin the negative on top of that. Set it out in the sun and wait 10 minutes for the color to develop. The last step is washing the cloth with textile detergent to clean off the unexposed dye.
The Lumi Process works best with natural fibers like cotton, wool, and silk. It can also be used on suede and wood. The inks are available in red, orange, and blue. The results are permanent and able to hold up to repeated washings. In case you were wondering, the process will still work under cloudy skies, but it takes twice as long.
Lumi is currently offering kits through Kickstarter. The most basic Lumi Process starter kit with dyes and instructions comes at the $35 pledge level, but $70 will get you 20 copier films and a special bottle of textile detergent on top of that.