For the Use the City Festival in Kosice, a steelmaking hub that is Slovakia's second-biggest city, Curtis erased years of industrial grime. | Photographs by Franco Pagetti

EnlargeWorking in Slovakia "was a bit more interesting than I would have liked," says Curtis. For one thing, there were the homemade ladders the locals provided. They also equipped him with firehoses that sprayed sand along with the water, making it difficult to see. In the end, he scaled back his ambitious designs. "I'm a big believer in keeping things simple," he says. | Photographs by Franco Pagetti

EnlargeBefore hitting the streets of Kosice with his crew, Curtis spent hours cutting stencils in an old army barracks. "You can still feel the former communism," he says. You can also see it on the filthy walls that became Curtis's canvases. | Photographs by Franco Pagetti

If there is a lesson in the work of the British artist Paul Curtis (aka "Moose"), it would be that the world is a mess. Curtis's signature technique is cleaning. He strips away years of accumulated soot, dust, dirt, and atmospheric detritus to make pieces like these, which were part of a celebration of street art. He also creates promotions for not-for-profits like Greenpeace and commissions for brands such as Xbox and Clorox's GreenWorks.

Curtis often wonders if his corporate clients see the grim humor in hiring him. "You're encouraging commercialism using a process that reminds people of pollution, which is partly the result of overconsumerism," he says. He adds that he recently rejected an oil company, thinking it was too ironic "that people would ask me to write their name in the dirt they made."

When Curtis puts his brush down, his commentary has only begun: Within days, the patterns begin to fade as the pollution reclaims its territory, a statement about how hard it is to clean things up and how easy it is to mess them up again.