Check out this artist, deemed a "reverse graffiti artist" he creates his art by cleaning. Creating stencils and then power washing through them, he creates a design on a wall, building, or other relatively grimy surface.

I have been working on a technique utilizing Nitric Acid on Copper to create some trees, but this is a bit different process, one of cleaning rather than oxidizing. Which lead me to think of what some other applications for this type of technique might be.

Recently all workplaces in Fargo, ND went smoke free. And perhaps this would have been a better campaign for  prior to the passing of that resolution, but you could do the same thing here as well. Work with a bar owner create a stencil of an ad, and then apply to the wall which has been covered with years of smoking residue, and then clean. This would likely work in restaurants where the use of deep fat fryers was used, removing the grease to better illustrate what you are breathing in.

I cities with a lot of pollution, perhaps you could take a plain white board, and apply white vinyl or a polyurethane over your image and then sit back and watch as the image appears due to the discoloration of the board. 

Any other thoughts? How else could the use of cleaning or the illustration of dirt in the environment be used to create art? Watch the video of this artist on Creativity.com.