A problem with old brass is that much of it is actually brass plate over a base-metal casting. The "grungy" remnants seen after multiple attempts to clean it using metal polishes may be only the base metal showing through where the brass has been completely removed.

Additionally, most "polished brass" is lacquered, to slow down tarnishing, and it can be difficult to remove the lacquer completely. Any remnants of the protective coating will prevent the "polish" from having any effect on the brass tarnish, and will result in uneven cleaning.

Penetration of the brass layer, and revealing base metal locally is often a result of removing all of the brass in areas where it is exposed without getting past the lacquer to start cleaning the rest of the brass.

The more-or-less standard method for cleaning small brass parts is to "tumble" it in a rotating can of the kind used for cleaning brass cartridges for reloading, or the kind used for polishing "gem stones." Small tumblers of either kind can be found for around $30 - $50 (US) in my area, quite easily. A tumbling/polishing medium must be used, and for polishing and cleaning brass a common medium is crushed black walnut shells. Corn cobs and rice hulls or similar materials may also be used for "fine polishing," but will usually work rather too slowly for removing "serious tarnish" within a reasonable time.

With this method, you can fill up the can, set it on the rollers, and turn it on. Go back in a few (usually many) hours or after a couple of weeks. If there's any brass left, it should be shiny. If not, you may have run it a bit too long - or may have not had much real brass to start with.

John