The Edge Grinding Rubber, or "gummy stone," is one of my most utilized and thought-about pieces of tuning equipment. A gummy stone can be used to remove rust. (But if you use it on your base edge, do so sparingly). Base edges are easily affected and shouldn’t be meddled with). A gummy can also be used to take the spiky-ness off of a particularly bad burr (but a file and diamond stones will do the actual fixing).