I do a bit of amateur silversmithing and sometimes use copper and brass. After polishing a rub with a product called Renaissance Wax works well to stop oxidising and tarnishing. Developed by the British Museum, or similar, so not snake oil
That's interesting Candide!
I used to use a clear lacquer (yeah yeah - OK everyone, it was a cheap cheat), but gave up several years ago as we inherited all Mrs Growster's Mum's brasses etc., and we wanted them to look special!
One trick I did have success with, was to buy special cleaning brushes for an electric screwdiver, and they worked a treat with proper metal polish, especially on an antique brass coal scuttle which I bought from the local charity shop last Spring! I'd still be doing it by hand without that bit of kit!
(Growster-tip - don't use the screwdriver on top speed - the whole shed got spattered at the start - and so did I)!