Shred the crayons using an old cheese grater and separate the shavings into piles according to color.
Cut a piece of brown packing paper (or a grocery bag) that is 2 1/2 times the width and 1 1/2 times the height of one piece of mat board.
Lay one piece of mat board face up on the sheet of packing paper.
Sprinkle the shredded crayons on the mat board in the design of your choice.
Lay the second piece of mat board face down on top of the first piece.
Fold the packing paper so that it wraps around both pieces of mat board. You are folding the paper over like you would fold a book.
Press a hot iron against the top of the paper and move the iron around for one minute (just as you would if you were ironing a piece of clothing) to melt all the crayons.
Set the iron aside, unfold the paper and lift the top piece of mat board away from the bottom piece. You will have two pieces of crayon art, one on each board.