Reverse Gaffiti is also known as clean tagging, grime writing, clean graffiti, green graffiti or clean advertising. It is a method of creating temporary images on surfaces by removing dirt. The easiest way to be done is to remove dirt with the fingertip from a dirty surface like a window. The first artist who discovered the technique by a dishwashing job, was Paul Curtis aka MOOSE.
Cologne based artist Tim Ossege aka SEILEISE uses a small portable sand blaster to remove patina from surfaces. SEILEISE at work