A while ago I stumbled upon a tutorial for this on A Beautiful Mess. Naturally, I loved it and decided to give it a go. Here is my take on bleach dying, with a Harry Potter nerd twist.
You Will Need:
A dark coloured shirt or singlet (mine is a men's singlet from Kmart)
A thin, synthetic paintbrush
Chalk or fabric marker
Lay your shirt out on a flat workspace, preferably outside (for ventilation reasons) and insert the piece of cardboard between the layers of the shirt to prevent the bleach from going through. Thick cardboard works best.
Draw, using a fabric marker or chalk, your desired design. I chose the Deathly hallows symbol from Harry Potter, but you could draw or write anything you like. I recommend that you keep it simple though, and try to keep things centred and even.
Now, dip your paintbrush into the bleach, and begin tracing over your design. You will need to refill your brush every few centimetres, and will need to be nice and heavy with the bleach so that it sinks in nice and even. Go slow, there is no rush, and you should start to see your design appear before your eyes!
Leave your shirt in the sun for about 10-15 minutes if you used regular bleach, or one hour if you used fabric safe bleach for it to process and lighten. Rinse your shirt out and hang it up to dry. Your design will lighten a little once it has dried. The shade your design turns out will depend on the dye in your shirt and various other conditions. It could end up brown, or could end up stark white. Mine turned out tan and I love it.
*Hermione Granger hair in photoshoot is optional