I know you probably have seen this or maybe have even done it, but we had to give it a try.
I didn't want to buy a canvas, because as much as I like the end result's look, we don't have any wall space to put it. My walls are covered with family pictures, which I love and we don't have an art or play room. So... I just covered a cereal box with white paper and hot glued the crayons (I had to add 5 or 6 more to complete the row).
Then we went outside with the hair dryer because I was told that this could be messy and I'm glad we did it out there because it did get a little messy.
And this our melted crayon art: