From NPR: "A British street artist known as Moose creates graffiti by cleaning dirt from sidewalks and tunnels."
There's something almost steganographic about the process--as though the visual language were already there, just concealed beneath the impasto of urban grime. Moose's reverse graffiti reminds me of Blake working his copper plate, "melting apparent surfaces away, and displaying the infinite which was hid" (Marriage of Heaven and Hell).