"Dr. Dirt" makes art by cleaning shapes into filthy urban surfaces

From Grist: Street artist Moose Benjamin Curtis doesn't use spray paint or wallpaper paste -- the usual tools of this trade. Instead, he wields scrub brushes, old socks, cleaning fluid, and, when he's living large, a high-pressure hose. He creates images by cleaning shapes into filthy urban surfaces such as retaining walls, signs, and tunnels. People have called it "reverse graffiti," "clean graffiti," and "negative space." Moose prefers "grime writing." He has called himself "a professor of dirt." For more: http://www.grist.org/cities/2011-11-04-dr.-dirt-street-artist-scrubs-images-into-the-urban-landscape

Moose's work at the Broadway Tunnel in San Francisco in 2009