I have a friend in the metals business. He now works at a place that processes scrap titanium into 30,000 lb. ingots. Before that, he worked at a chrome plant. They took in various car parts, (a LOT of hotrod and restoration people used the place) and other things to get chromed. Eventually, the environmentalists shut the place down. (The chemicals are NASTY)
Contrary to popular belief, chromium is NOT shiny. It’s actually a transparent hard coat layer that’s the final layer to get added. The shiny surface you see is actually the nickel underneath it. The nickel is bonded to the copper that’s laid on before that. The underlying metal has to be perfect before the choming is done too, or it won’t have a mirror finish. Parts have to be buffed to a mirror finish before any chemical process is started or the completed chromed part is NOT mirror like.
The chromed plastic is actually like anything else chromed, other than they figured out how to make that ‘’magic’’ black layer that binds the first copper layer to the plastic. It will fracture if the plastic is bent, and the chromed finish starts to peel away. Or, a rock or something gets kicked up, bends the plastic leaving a dent underneath the chroming, and the chrome layers start breaking away from that point on.
Both metal and plastic chrome parts suffer the same problem with repeated polishing. The hard cap chromium layer wears away, then you’re shining up the nickel layer instead, and much more often since the chromium’s gone. As mentioned above, you then quickly wear away the nickel, and you see the ‘’gold’’ of the copper layer. Think of the chrome like the enamel on your teeth. People who over-whiten their teeth, (especially in the late 1800’s with acids and the like) wore away the enamel, and their now softened teeth quickly disappeared down to stumps.
Therefore, AVOID using metal polish unless you’re preparing the part to actually get rechromed.
You just want to CLEAN the chrome parts. Metal polish contains fine abrasive particles, and that’s why it polishes as it does. It may take a while, but that abrasive is removing your chrome hard cap.
As for aluminum. A lot of wheels are mirror buffed, then hard coated, usually with lacquer. (synthetic versions of it anyway) You use polish, and that layer wears off. Then, you’re in for repolishing the wheels every other month. If the wheels have a ‘’gun metal’’ finish, that’s usually a glass beading finish. (Like sand blasting) That’s also clear coated. If you mess up the coating on those, you’re really in for it later since you can’t clean up the micro-pitted surface very easy.
Some aluminum wheels like the Alcoa’s on my motorcoach are non-coated. (Alcoa does make a coated version) Those need maintenance about four times a year. [removed] A good buffing compound (red rouge) will put on a somewhat protective layer that keeps them looking like a mirror longer, but they need constant repolishing. The coach’s 22.5 inch wheels are mostly smooth with only the vent holes to add more polishing work. (Think your basic Kenworth or Peterbilt truck wheel) The shiny lug nuts are just chromed covers.
The Commander’s wheels would be a major Pain [edited] to repolish every three months, so I’d be careful to NOT polish away that clear coat finish.