The drill used to be to use finer and finer sandpaper until you get to about 1500 -2000 grit or so, then using a polish (toothpaste makes an acceptable polish, and removes well with soap and water). The discovery of the magic effects of future, however, make it a lot easier. Just sand it with 600, maybe a quick cleanup with 1000, then carefully brush future over the transparencies. That should clean them up pretty well.