Polishing is a process of progressively finer abrasion. I will use an extreme example. When I got the bulldog hitch lock that is a sand cast aluminum I wanted to polish it up. I first used progressively finer sanding disks in my 7" variable speed sander/polisher and ended up using a buffing wheel with polishing compound. The result
You can take even this beyond what that polishing compound with progressively finer polishing compound to a mirror finish. I would start trying a polishing compound and if that will not do the job a VERY fine sand paper then polishing compound. One thing to remember this removes some surface finish!