Gather together your crayons, you can use old or broken ones for this.
Take a loaf baking tin and cut the crayons down to size, so that they will fit in the tin. Make sure to cut the pointy drawing side flat.
Take a square of tin foil and lay the crayons on top.
Wrap up the crayons neatly in the tinfoil.
Place back in the loaf tin and melt in the oven for 20 minutes. It's really important that you allow the crayon to cool for at least 10 minutes after baking so that it can set.
When it has cooled, peel off the tinfoil and use a chopping knife to cut of the top of the crayons, leaving you with a nice straight edge for drawing.