Kinds of clarinet key work:
Many older clarinet keys are 100% “German silver,” typical on clarinets from before the 20th century through the 1930s. German silver has no sterling silver in it, but is an alloy of something like 88% brass and 12% nickel. These are the dull colored keys that never get really bright looking, but they still look nice when shined up. Typically keys of the early period are not as sturdy as keys made later. The longer keys can bend easily. So if you have a vintage clarinet, assemble and disassemble with care.
Somewhat newer clarinets have German silver base metal (which can be thicker and harder than the older keys above), then a coating of pure brass, followed by a coating of high grade nickel plating. (Nickel is also called “nickel silver,” but there is no sterling silver in it.) These are the keys that shine up nicely. The nickel coating can wear away to reveal the brass underneath. When a clarinet is stored away for long periods in a damp case, the nickel layer can be somehow eaten away. This often occurs on the underside of keys and on the main places where the keys are in contact with the case.
Another variation on high quality instruments is to have German silver base metal, then a coating of brass, followed by sterling silver plating.
Another variation on instruments starting around the later 1940s is to have German silver base metal and a chrome plating. Long storage in a damp case can cause pitting of these keys.
Some clarinets were made around the 1950s and after that were molded out of what is called “pot metal.” Such keys often have a chrome plating that easily flakes away or that is heavily pitted. These keys are often very brittle. They tend to break rather than bend. And they resist being soldered with silver solder. Such keys are a sure sign of a table-lamp clarinet.
Newer Chinese clarinet keys and some other lesser known student model instrument makers often use a softer base metal, but they have made the key work very thick, so that the keys are normally still sturdy enough. Such keys are always chrome plated.