hi i found brown sauce works or coca cola .vinegar.why not try a bit of each depends how bad it is but be patient im sure it will be ok.good luck.

Unless its been laquered? I think you will find Brasso will do it if you do it this way. Its the friction/heat that cleans the brass so apply a very small amount and rub really well the less Brasso you use the better.

thanks guys for your advice i will try them all and see what happens and let you know how i get on:)))

I got this formula from enameling on copper:
soak a rag in white vinegar, and sprinkle it with salt just before rubbing the rag on the metal. Re-salt as needed. This may leave the brass looking pinkish, but it should return to its normal yellow with handling.

If it has actually gone black rather than just dull you can use a very fine grade steel wool on it. I cleaned a pair of tympani that way very satisfactorily - the finest grade doesn't seem to scratch the metal. Only try this if the other methods fail though.