Piece of cardboard
Pen or pencil
Spray-adhesive tack (optional)
Put on gloves and safety goggles. Mix up a batch of 50/50 bleach to water solution in a spray bottle. Label it, and draw a skull and crossbones on the bottle so nobody mistakenly thinks it contains water. Then put a piece of cardboard inside the shirt so the bleach doesnt bleed through.
Draw a stencil design on paper and cut it out. Just remember that its going to be a stencil, so it should be designed so it can be filled in with color (or bleach). Bleach can bleed into the shirt, so keep it simple and be bold. When youre done, place the design on the shirt. I put some spray-adhesive tack on the back of the stencil so it would stick to the shirt a bit.
Set your sprayer to a fine mist and spray the bleach solution over the stencil. Watch the color disappear before your eyes.
If you leave the bleach on too long, itll make the fabric disintegrate, so when its getting close to the right color, dunk the shirt in a sink full of water and rinse until it doesnt smell like bleach. Dry it out, and youre good to go your T-shirt design is done!