You will need:
a blank canvas
crayons, new or old (I needed about 60-70 for my 16" x 20" canvas)
a utility or exacto knife (optional, for peeling the crayons)
hot glue gun
heat tool or a hair dryer with a diffuser or low blower setting
Step 1: Prep the Canvas
Then decide what kind of color spectrum you are going to do. Remember you don't have to do just a rainbow. You could do only cool colors, only warm colors, a random assortment, big stripes, etc.
Take the wrappers off all the crayons you're going to use. A quick and easy way to do this is to slit each wrapper with a utility knife. It will then just peel right off.
Next lay out your crayons along the top edge of your canvas until you like how the sequence of colors looks.
Then hot glue each one down right next to one another with the tops flush to the top of the canvas.