Just pick up a canvas and glue crayons to the top. You can group them together in color families but I liked the random look.Lean it up on something (I used the inside of the oven door) and cover the floor with newspaper. Run a heat gun (I've heard a blow dryer on high works well too) back and forth letting the crayons melt and drip.
You can let them drip just slightly or let them run down the canvas. I decided to let the sides drip more than the middle.