Thomarse wrote:

Does anybody know of any good methods for cleaning the surface to make
it shine again?

Soak it in cheap pickling vinegar for a couple of days. Don't add salt,
as that causes corrosion afterwards.

For a mechanical scrubber, use the plastic Webrax / 3M Scotch / Machine
Mart pads in varying grades, right down to abrasive-less green kitchen
scouring pads.

Don't use Brasso on cast brass. It polishes the highlights, but you
can't get the white deposit out of the crevices afterwards. Although
Brasso itself isn't too bad for this, the liquids are much worse.

To age cast brass, use the sawdust and ammonia process (posted to
rec.woodworking)

If youy expect it to stay remotely shiny then you're going to have to
lacquer it. This requires the right lacquer, as brass is fussy stuff.
Use Rustin's metal lacquer, which is a methacrylate.