I made a quilt for my mom with Crayola school crayons.
When I heat set, I put a brown paper sack on my ironing board.
Then I lay my block (crayon on unwashed, unbleached muslin) on the sack,
WITH THE CRAYON SIDE UP, then a paper towel on top of the block.
PRESS WITH A HOT, DRY IRON. (Remember PRESS not iron)
When the towel shows crayon color wax, lay on a clean paper towel and press again.
If you lay the crayon side down on a towel it melts the color wax down into the towel and away from the fabric.