Check out the amazing dirty car art work of Scott Wade, who does art on the rear windscreens of his very dirty car.
Wade says that the images drawn in the dust are "obviously quite impermanent."
One of the cool things about them is how they change over time. More dust accumulates as the car is driven down the road. Early morning dew streaks and dots the image, creating a patina. A light shower creates a deeper patina
Whilst these are very cool, Scott Wade needs to get a real job.