Wash and dry T-shirt. Insert a piece of cardboard into T-shirt to prevent ink from bleeding through to other side.
Using desired marker colors, make a preliminary design on T-shirt. (Note: For a flower pattern, make a large dot of ink in one color, then surround in many smaller dots of a complementary color.)
Remove cardboard and stretch T-shirt over a baking pan, securing with binder clips. Be sure shirt is taut enough that it is not touching the bottom of the pan. (Tip: Individual sections of shirt can also be stretched over the mouth of a glass or plastic container and secured in place with a rubber band.)
Using an eyedropper, slowly drip desired number of drops of rubbing alcohol into center of ink design. The more drops of alcohol used, the further the ink will spread and the larger the design will be. (Note: Avoid flooding design with alcohol all at once.)
Once desired design is achieved, let T-shirt dry completely. Set color into shirt by applying a hot iron for 5 minutes or placing shirt in clothes drier on high for 15 minutes. (Tip: Be sure your iron is on the highest heat possible when setting the ink. Wash shirts separately on the delicate cycle and in cold water.)