As you may know, I really like rainbows... Like a lot! So I saw this thing on the internet. Hot glue a bunch of crayons (sans paper sleeves) onto a painted canvas. You can use a bigger canvas and a whole box of crayons but I only had this one.
Then take a heat gun or hair dryer to the crayons. Prop up one end so the drips are a bit more controlled.
To get the drips layered you can let it cool and do some more.
Make sure to have something underneath though because I found a lot of the melted crayon dripped right off the canvas.