low-pressure sandblasted raw brass ("glass bead" blasted, to be more precise) and then silver plated (no fingerprints - just as with plating a gloss-polished brass surface).
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VERY RARE exception:
I've encountered some VERY old King sousaphone bells whereby the silver plating was SO VERY THICK (old-old) that the bells (outside raw brass surfaces) weren't even "half-@$$" polished, and it was obvious that the silver plating ITSELF (again SUPER-thick silver plating...actually: "clad") was sandblasted AFTER the silver was plated on to the bell. I'm guessing that they also bright-polished (buffed) the bell INTERIOR after it was plated.
NOT KNOWING what we were getting into, we BUFFED
all of the silver from one of those bells (as we needed it to go with a lacquered-brass body). It took
f------o------r------e------v------e------r......and THEN (since the brass underneath was never polished) we had to heavily polish the brass ITSELF.
I believe there were ounce
S of silver on that bell...
Assuming 1930's or 1940's, just ONE ounce of silver would buy (remarkably consistent!) just about what it would today, which is about (2023) $22 bucks worth.
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I've also seen a 1960's Holton 345 bell that was so thickly silver plated that (when re-blasted for a new finish) some of the original silver fell off in thick sheets (almost as if plaster, etc.)