Painting With Pollution
Alexandre Orion paints with pollution. He finds walls and tunnels that are encrusted with layers of black soot and selectively cleans the surfaces creating art. You can read about his angry encounters with police who think he's spray painting over at Wired.
His art process is called reverse graffiti. At first I wasn't sure that his work should be associated with graffiti because of the associated destructive connotations. Then I guess that's the point and why it is a true reversal.
Orion is a true artist. He's using a visual medium to create awareness. His message is unpopular with the government and is just washed away in the end, literally.