I my work I have to remove scrapes, scratches, and scuff marks from steel, cast iron, and acrylic tubs. Henry in MI is right about the hierarchy of scratches! I found that you can go right up to 1000, 1500, 2000, and 3000 (wet) grit paper in removing a blemish before beginning to use a polishing compound. The benefit of this extra-fine sanding is that the polishing part of the job is over practically before it begins. In general, it's best to start with a grade that is too fine than to harsh: removing scratches YOU'VE put in can be a bit humiliating as well as time consuming... Good Luck with you repairs!