Biocleaning

now listen to part of a lecture on this topic from an art history class. Okay, so this happens a lot with statues. Stone statues often stand outside in public spaces, and some of these statues date back centuries to the Renaissance or even the Middle Ages. So as you can imagine, after hundreds of years of standing outside in all kinds of weather, they don't look too good. One thing that happens is that pollutants in the air, such as sulfates, combine with other pollutants and mix with water, this causes a black crust to form on the surfaces of stone statues and makes it hard to see the details of the statue beneath. Now, one way to remove this black crust involves using a harsh chemical solution, but that can end up weakening the stone that the statue is made of and causing fragments to break off, which, of course, would ruin the statue. So a method that's shown a lot of promise is to use special bacteria instead. These bacteria reduce the sulfates that the black crust is made of when a substance containing these bacteria is applied to the statue, the bacteria. To interact with the sulfates in the black crust, softening it, and then the softened black crust can just be wiped right off, restoring the statue to its original look and leaving behind no broken stone.