We humans make things really dirty. One might even say that our biggest contribution to the earth is grime. That being said, some see a reason to play in that dirt. Fast Company just did a wonderful story on Paul Curtis aka Moose, and how he transforms dirty tunnels and walls in to art, using just stencils, water, and brushes.
His art is full of looping, organic forms all set with a backdrop of dirt and grime.
The most powerful image from the article for me, however, was not the photos (although they are wonderful) but the thought that in only a few weeks, the art would be reclaimed by grime and no longer visible.
What a waste.