Alexandre Orion: "Ossario", 2006 - is a non-pollutant graffiti, which is the partial removal of surface dirt that has accumulated pollution. Needless to say the work is monochrome, and relatively temporary.
Alexandre Orion is a Brazilian graffiti artist has the distinction of having expressed his talent with a tunnel cleaned blackened by pollution in Sao Paolo. Skulls were designed for about 160 meters, and Alexandre Orion was not arrested because his creations were not painted, but made with a simple cloth. In the end, the city of Sao Paolo had to clean the tunnel to clear the skulls.