Cleaning brass requires no harsh chemicals or special cleaners. In fact, everything you need to clean your tarnished or dull brass is most likely in your kitchen already. Before cleaning, make sure the brass is not lacquered. If the brass is dirty, but not dull and shows no sign of tarnish -- if it's still a golden brass color -- it's most likely lacquered, and the dirt should wipe away with nothing but a damp sponge. Doorknobs, door knockers and brass mailboxes are usually lacquered. Unlacquered brass does tarnish and will require deeper cleaning.
Combine the salt, flour and vinegar into a paste. Stir for one minute, until the salt dissolves and the ingredients combine.
Rub the paste on the brass with a sponge.
Allow the paste to dry.
Rinse the paste from the brass thoroughly. Wipe the brass dry with a microfiber cloth.