the soap thing this guy is doing is a natural extension of "wash me" on a dirty car or truck. He just changed tools and added scale.. In 1987 I stenciled a relatively clean building. returning to that town in 2004 the dirt buildup from the air had brought out the original stencil as a ghost artifact. similar to cleaning around the dirt, they over zealously blasted off the paint from the cement the cement surrounding the paint got eaten away incrementally more than the painted area. the difference was visually apparent only years later when the deeper crevices held the dirt buildup more than the raised surfaces of the original painted area. this was a situation where cleaning an already clean wall disturbed the eventual buildup on the wall. a sort of time based thing.. infinitely more interesting..but not something with controled parameters. .. maybe it could be called "the art of post-graff removal decay?"