reverse graffiti

Reverse graffiti is art or text created by selectively cleaning dirt, grime, or pollution from a surface rather than adding paint or ink.

Artists use water, brushes, or pressure washers to remove accumulated filth from walls, tunnels, or sidewalks, leaving behind images or words: The tunnel walls were covered in reverse graffiti—figures emerging from decades of soot.

Also called clean tagging or grime writing.