These turned out really good and were fun to make!
What you need:
Fine point sharpie permanent markers
How to make them:
Put the rubbing alcohol in the spray bottle.
Place the cardboard between the front and back of the shirt to prevent bleed through.
Draw on the shirts with the markers.
Spray all over with the alcohol.
Wait five minutes. If the colors aren’t running enough spray again and let dry for 30-60 minutes.