[Doug D.]

400 grit will not cause a problem as long as confined to already polish ground cooking surfaces. It is fine enough so as not to leave swirl marks on those areas. It is sometimes useful on stubborn stains on those areas. Going with the direction of the original polishing is still a good idea. Using sandpaper or other metal-removing abrasives on "as cast" surfaces, however, will burnish the high spots undesirably, causing a change in the original texture and also diminishing collectible value.