My cleaning lady cleaned a very old and lovely brass lamp that belonged to
my mother. Whatever she did, it looked fine at first, but now green stuff
is gathered in the creases of the embossing. In one or two places, it is
starting to turn black. I managed to rub away most of the black and some of
the green with a toothbrush, but not all, and it is tedious.

Any ideas welcome. Would vinegar and salt help?