Color a design with fabric crayons on a sheet of white paper. Press firmly while drawing to ensure dark, bold, solid colors. Since the design transfers backwards, draw numbers and letters backwards.
Lay a light-colored garment flat on an ironing board. Iron out any wrinkles if necessary. Place a piece of cardboard or newspaper inside or under the fabric to prevent the design from transferring to the opposite side or onto the ironing table.
Position the design on the fabric wherever you want it to transfer. Place it with the colored side down.
Set the iron to the synthetic fabric setting and press the iron over your design, moving it constantly and evenly. Stop ironing when the design shows through the paper.
Peel the paper off the shirt to reveal your design.