Got some old crayons laying around? Turn them into masterpieces!
Heat rocks from your garden in the oven at 325 degrees for 15 minutes. (Smooth rocks work best.) The rocks will be hot to the touch, but not dangerously so. Use hot pads just in case, to protect your kitchen table.
Then color with old crayons. The wax will melt on contact, producing a beautiful paint-like effect.