Wash and dry the sweatshirt before beginning. Also, tear a few paper towels into four pieces each. You will need these to wipe paint off the sides of the paper mache letters.
Use masking tape to mark where you will stamp the letters.
Mix 2 parts paint with 1 part textile medium. Paint one side of the letter "O". Use a piece of paper towel to wipe excess paint off the sides of the letter, even the inside.
Place the "O" down on the sweatshirt, using it like a stamp. Press firmly for a few seconds, then remove the letter.
Stamp again in the same place to darken the letter until you are happy with how it looks. Remember to wipe excess paint from the sides of the letter each time.
Continue until you have stamped the entire design. Use a paper towel to blot any extra paint.
Allow paint to dry completely, about one hour. Then heat set the paint by covering the shirt with a thin cloth and ironing each letter for 20 seconds with a hot dry iron.
Wait 24 hours before washing and turn the shirt inside out before washing. Drying in a dryer is just fine.