On 11/07/18 18:13, rick wrote:
I have several door handles .. and interior side is OK ... but exterior
has dulled badly.
https://flic.kr/p/27WZ4dC

These are presumably brass (can't be 100% certain) at least look & feel
like.

It will take some effort to polish back up ..... are there any good
finishes that will protect them.
I remember doing this on a previous house - bought spray on clear cote
lacquer - didn't last 1 winter.
Speaking from the POV of guitar parts and brass instruments, the problem
is that oxidisation of the brass begins from the moment you've finished
cleaning so the finish is being attacked from behind as well as on top.
If you really want immaculate brassware I'm afraid you've got to polish
it regularly. Ask the caretaker at No.10

Nick