My next novel, Little Brother, is coming out in a couple weeks — it's a young adult novel about hackers who use technology to challenge authority. The folks from Instructables saw an early copy of the book and were really inspired by all the ingenuity demonstrated by the book's heroes, so they've made a series of HOWTOs in the voice of M1k3y, the techno-guerrilla who tells the story in Little Brother.
The first one has just gone live: Photo-Emulsion Screen Printing, a HOWTO for making t-shirts for your movement's wardrobe needs.
The general idea: After stretching fine-mesh cloth over a wooden frame, you spread a thin layer of photosensitive emulsion on the screen and let it dry. You then take a black image on transparent or translucent surface, place it against the screen, and then expose the screen to light. The light causes the emulsion to harden and bind to the fabric. Where the light strikes the screen, the emulsion will bind, making a solid layer. Where the light is blocked (ie where your black image is placed) the emulsion remains water-soluble. After exposing the screen, you spray down the screen with water, washing off the emulsion only where your image was placed; this clear area is where ink will be pressed through the screen when you print. Finally, you lay the screen on your t-shirt, other fabric, or paper, spread ink on the inside of the screen, and press the ink through the screen. If you use textile ink, you can heat-set the ink after it dries, and it'll be permanent and washable.