Some choose to have their films cleaned prior to transfer. We use a specific solution for cleaning movie films and an anti-static cloth to clean them. We run the film on a different projector so that it does the winding and rewinding for us. A cloth with the solution is held against both sides of the film while the projector winds the film. When we are finished the cloth does have a dark area of crud that was removed from the film but when comparing film when transferred before and after cleaning the difference is not visible. For that reason we don’t really encourage the extra cleaning step. See the attached video of some extremely dirty films that we cleaned up. These were so bad that we wouldn’t transfer them without cleaning them first.