So in the middle of this project I actually had to leave to go purchase more bleach. Our small amount wasn't doing the trick. All you need to do this project is a spray bottle, a barrier for the inside of the shirt, some bleach, a t-shirt and a stencil that you can make yourself out of card stock.
First off you will need to find a silhouette of something you want to be on your shirt. You could do any kind of shapes or words you would like. You probably want to choose something without much detail. If the shape is hard to cut out- it probably won't turn out so well on the shirt. Print your shape (or draw) onto card stock and cut it out.
Make sure you put something between the front and back of the shirt. We just used a rolled up piece of craft paper. Put some bleach in a spray bottle. We used 2 parts bleach, 1 part water. Place the stencil where you want it on the shirt and start spraying all around, and on top of, the stencil. It will take a while for the bleach to start changing the color of the shirt.
If you had your shirt turned to the side like we did, you will want to turn it back around the front to fix the spread of the bleach. As you can see, on our shirt there was a hard edge on the left side. Spray the bleach to fix the edges. We also removed the stencil in this step because it was too hard to move the shirt without moving the horse.
When your shirt has turned a color you like, rinse the shirt out with just water. Make sure you rinse it out a looooooootttttttt. Let your shirt dry completely and it's ready to wear! After it has dried completely, it is safe to wash it regularly.