I have always used Brasso but this article might be helpful since it goes into details of different issues:
Hi Rose: I use Barkeepers Friend in the dry form on my copper bottom pots. It doesn't scratch and works quickly. Just put it on with a wet sponge, wipe lightly and then rinse off. Be careful not to use anything that will scratch your brass.
found this info for you, Rose
Use ketchup or Brasso.
Try covering it with ketchup and letting it sit for 10 minutes. Then wipe off and and clean it with windex.
Brasso is the best cleaner.
Hi Rose, hope this helps you out,
Here's a post that might help https://www.handles4doors.co.uk/advice/cleaning-tarnished-metal#:~:text=Take%20a%20bowl%20and%20measure,off%20with%20hot%20soapy%20water.
I use a basic commercial metal polish, but ketchup will do the trick too!
Hello. They are dedicated brass cleaners but I find bar keepers friend to be quite an extraordinary cleanser to have on hand for multiple surfaces.
here’s a link that might be helpful.
Is this assuming that your brass is totally unsealed?
Or is it partially there and worn off? Sometimes it’s good to know exactly what you have there has to do you know for there as to do no further harm.
Use" Brasso" Metal Polish, or soak it in Coca Cola overnight.
Is it real brass?
If they are brass and look like real brass chances are they have a lacquer on it. The reason I say this is that brass will tarnish fairly quickly and can turn black. What keeps the brass from tarnishing so fast(and keeps it shiny and gold-ish) is the lacquer which keeps the air from tarnishing.
Eventually (takes years), that brass shine will tarnish even underneath the lacquer though. The way to deal with that is stripping the lacquer... then shine up with a brass cleaner once that lacquer is off, and then re-lacquer.
Sometimes something will look like it is solid brass but is actually brass plated. I think you could still try the above method though, and you will eventually figure out what metal is all the way through. In either case, you could try shining it up with a brass cleaner, if nothing happens to make them look better, you will need to strip it. That means there is lacquer that needs to be stripped to get to the brass. Then try to brass cleaner it again. (TRY BRASSO cleaner) If still nothing looks better, then the metal is probably a cheap metal that has been painted to look like brass and can just be repainted and finished off with another lacquer or polycrilic finisher.
This may help:
Take a bowl and measure in one tablespoon of flour, one of salt, and one of vinegar. Mix it thoroughly until it turns to a paste, and then rub it on to the surface of the brass or copper. Leave it for a couple of minutes, and then wash it off with hot soapy water.
Brasso or another related brass cleaner should handle that easily.