But I don't beleive the bronze guns were polished. I also don't believe there we just allow to tarnish. How were they finished?
That's an area that could use more research. My comments have to do with "what to avoid" as a collector, to preserve the maximum value of an old bronze gun for the majority of collectors. Unless it has bright green, powdery bronze disease, which requires special means to stop, generally today one should only clean the dust off and keep it waxed with something like bowling alley wax. That's all I do with my bronze barrels, keep 'em waxed. That helps keep them from getting bronze disease.
Back when, in military organizations where they were used, the matter of the care of a bronze gun was sometimes addressed in regulations manuals. I've read one USN manual ca. Civil War that forbids "brightening" of bronze barrels.
Beyond that, it probably varied with the country and the branch of service.
If anyone has documented evidence one way or the other, I'd like to be educated, I don't mind admitting I don't know.