It depends if it's bead blasted or polished. If bead blasted than it needs to be rebead blasted. If polished sand it with a corse wet and dry sand paper (I wouldn't go any less than 400) and work your way up to 3000. Then you need to buff it with with compound and preferably a greaseless compound to leave the shines surface. But be warned both of these techniques remove material so if it's plated or to deep it's better off trying something different. And a pic would help.