I also trumble lots of chains (other things too). I use a small vibratory tumbler with about 7#s of assorted shapes of shot.
Dave - I use a rotating tumbler with steel shot (asst. shapes and
sizes), would that make a difference? I will certainly give it a
try. Also, the burnishing soap was purchased and is specified for
silver and another for gold. I was told to use about 1 tablespoon.
It really foams up, but has not overflowed the tumbler. Any
suggestions? It seemed to do the trick on an oxydized silver piece
piece I did. I have not finished my gold piece yet… still working
on my clasp.