There are a number of ways of doing this. First you could try one of any number of metal polishes. If that doesn't produce the desired result, you could try a more aggressive abrasive such as the kind of rubbing compound that's used on cars with oxidized finishes. If that still isn't enough, you could try using a buffing wheel and some jeweller's rouge. And if you need to go futher, then replating may be the only option.
Great advice above. With auto polishes, I'd recommend starting with a chemical one as opposed to an abrasive. You'll find the effort very similar to using a metal polish. If that doesn't work, certainly go with an abrasive, but I'd start very mild. If the finish is just a bit hazed, you should see good results. Some options from the automotive world... Chemical: (sometimes called paint cleansers) Poorboy's Professional Polish Klasse All-In-One Four Star Ultimate Paint Cleanser Abrasive: Poorboy's SSR1 (or 2) Meguiar's Scratch-X (you can find this at just about any auto care section) Meguiar's #82 Swirl Free Polish
I like this, usually we see someone asking how to make their shiny stuff look old. Back in the days before music stole my soul, I was a gearhead. We used a product called semichrome on our wheel rims and metal trim. That stuff made anything shine like crazy. It's probably still available and might work. It's worth a try. If it's too bad, you have to replate.
Any chance you actually mean Simichrome? If so, it's definitely still available and is a great metal polish. Motorcycle guys love it, so OTC you can probably find it at a dealer's parts counter. In my brief experience with it, it's best on bare metal finishes and multi-dipped coatings (i.e. chrome wheels, fenders, etc.). Nonetheless, it's certainly worth a shot.
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