The following article was written for motorcycle enthusiasts and is presented for what it is worth. In particular, I, for one, would not spray anything intended for metal on my boat.
You do not polish chrome, you clean it. Unlike aluminum and stainless, chrome does not oxidize much, it is inert, very hard, and usually pretty thin. People have tried a bunch of polishes, including the expensive ones, and have found nothing that will remove scratches from chrome. You live with a scratch in chrome, or replace the part.
If you are very careful not to scratch it, all you have to do is remove the schmutz and the shiny chrome will be (somewhere) underneath. Use soaps and solvents, but keep abrasives far away from chrome. Be very careful to use clean, soft rags. One imbedded metal chip will ruin your day.
There are hundreds of alloys of both, but all share the fact that they oxidize at the surface. In fact, the oxidize layer is what protects the metal from further corrosion. All you have to do is remove the oxidization and get it smooth enough and it will rival chrome in shine.
If the part is just oxidized and gray, but smooth, skip on down to "Buffing"; however, if it is pitted or scratched, it must be smoothed. You cannot polish pits.
Wet-sand the part with #600 wet-dry paper using a little liquid dish soap in the water. Sand for a while, then wipe off the dreck, and look closely. If you can still see the pits or scratches through the dark, dull gray, you are not done. When you have a uniform, dull gray, you are ready to buff. Do not worry too much about screw recesses and other hard to reach places. They do not show in the finished job if the edges are smooth.
The final polish on metal is achieved by buffing it with a rotating wheel that has been loaded with a buffing compound. These compounds are very fine abrasives, usually combined with wax in a bar form. From the coarsest to the finest, they are:
Many people lean towards using just emery and rouge. Emery is good for a first cut on stainless, or on aluminum followed by rouge. Usually you can go directly from wet sanding to rouge.
Buffing is a "feel" thing. Keep the wheel moving and you will see when it is polishing effectively. Wipe off the wax schmutz now and then and have a look. Different alloys require different compounds, speeds, and pressure. You cannot really hurt anything, so experiment. If you want to get anal, do a final hand polish (see "Maintenance" below).
Use only cloth wheels.Sisal is too aggressive, and felt does not conform to the odd shapes of boat parts. Look at the side of a buffing wheel and note the ring(s) of stitching. Fewer rings mean softer (for polishing), more rings mean harder (for cutting). A 6" wheel can have from one to seven rings. Use a harder buff with emery, a softer buff with rouge. Speed depends on wheel size. For a 6" max. 3500 RPM, 4" about 6000 RPM, 2" about 12000 RPM, and the little sub-1" wheels can be turned up to 15000 RPM. Go by the wheel manufacturer's specifications.
Wheels come with a bunch of different hole sizes, so get the right mandrel or bushings. An unbalanced wheel at 6000 RPM will get your attention! The mandrel is the Steel shaft that holds the wheel, and is turned by the tool. You can get sets for use in an electric drill at the hardware store, but you need a drill that turns up to about 2000 RPM.
Start at slower speeds and work up. You can be too fast as well as too slow.
Use the buff so that it rotates off the edge of the piece. If it rotates toward the edge, well, let us just say you will learn quickly after it throws a couple of pieces at you.
Load the wheel by arranging it so the top is turning away from you, then apply the bar of compound for a few seconds. You will see it melt in. After you load a few times, you will see clumps of compound build up in the wheel. Again, have the top of the wheel turning away from you while you "rake" the wheel. They sell wheel rakes, but I just use an old "Sawsall" blade. Rake between different compounds, too, but it is best to have one wheel dedicated to one compound. Mark the wheel with a magic marker. WEAR EYE PROTECTION! Read that last sentence again.
Ah, the Tim Allen moment (argh!). Listed below in order of purchase.
These are sister companies, and they have just about everything for metal polishing. Call and ask for whatever you need at (903)509-4500.
Oxidization protects the metal, so as soon as you are finished polishing, the metal starts to oxidize again. I have not found anything good to protect it.
Waxes tend to "gray" the sheen, and do not last long in any case. "Harley Spray" from the dealer seems to do as well as the wax, and is quick to apply. You can do the whole bike with it once a week.
About once a month I do the following, which takes about 90 minutes for the entire bike. Use the L-1000 polish you got from Southwest Metal (above). It is liquid rouge. Shake Hell out of the bottle, upside down (careful!), until there is no residue at the bottom. Soak a 6" square piece of clean terry or sweatshirt cloth, then squeeze it as dry as you can. That one rag will do all the aluminum on my whole bike. It turns really black and gritty, but it seems to keep polishing.
Polish by hand, rubbing in a circular pattern as much as possible, until the area turns black. Allow to dry and buff off with another perfectly clean rag. If you drop the rouge rag, throw it away and start another. For me, this works better than "Mothers", and is a hell of a lot cheaper.
So far, this seems to be all that is required to keep the polish bright, but I expect that I will have to touch-up the aluminum by machine buffing lightly about every six months.