On 21 Sep, 19:52, Thomarse wrote:

Basically I have what I think is a brass letter box on my front door
and it is tarnished and no longer shiney.

Ideally take it off to work on - saves scratching the wood, leaving
deposits behind and allows soaking.

Start out with Nitromors, because any paint splashes there happen to
be will retard other cleaning and look very obvious afterwards.

Salt and vinegar. Make a paste of the two, then leave it to soak for
a day or two. Salt acts as a scouring agent, but the chemistry is
important too. Be careful using this on bronze though (vinegar is OK,
chlorides are the problem). Rinse well afterwards. I'd also remove any
steel springs or bolts beforehand.

If it's cast, then it's time for either Nitromors (easiest source of
dichloromethane) or citrus engine degreaser in an ultrasonic bath to
get the nooks and crannies out. Otherwise move in with a dental
hygienist, as they positively relish this sort of task!

If it's big, smooth and a thick cast section then bring the big guns
out and simply repolish the lot with a couple of Garryflex abrasive
blocks. Dead handy, but you are removing metal.

For a final polish, you can use Brasso (tripoli in a carrier) but be
wary of this if you're going to lacquer afterwards. The ammonia can be
a problem and lead to splotching - personally I'd just use bare
tripoli wetted with a bit of meths and white spirit.

For lacquering afterwards, yoiu really need to use the right stuff -
Brass is a pig for adhesion with any paint or lacquer. The right stuff
is a methacrylate solution lacquer, which you can get from Rustins via
Axminster.