How to clean a really bad tarnished brass barometer?

Esther,. Buy some top of the line brass cleaner, and go to work. Aloha!

Ok, thank you

You can use white toothpaste and a damp toothbrush. A dab of toothpaste on a damp cloth for larger areas. Brass cleaner can remove some of the metal.

Try brasso cream cleaner it’s good I got it on eBay

If your barometer was once sealed with lacquer you will see uneven tarnishing. In order to clean it you will need to remove the lacquer. You can use nail polish remover to disolve the old lacquer. Once that is done you can get the metal clean with a metal polish. In order to keep future tarnish at bay you can re-lacquer the piece.

Thank you V. Smith. I did not even think it was varnished. Getting to work on it. 😊