I was producing some rather ornate leather treasure pouches a few
years ago with sterling silver beads in the fringe and on the
necklace. I had put the pouches into ziplock bags to protect the soft
buckskin leather, but left the beaded necklace strands out of the
bag. The sterling beads inside the bag reacted to the leather and
turned pure black while the beads on the outside of the bag didn't
tarnish a bit. It was very difficult to clean those beads! If the
finish of the jewelry would allow it, a vibratory tumbler should
save you a lot of time. Luckily for me the bali beads look their best
with oxidation so complete removal was not necessary.
The cool thing is that now I know how to get a really nice oxidized
finish in no-time flat without using chemicals out of a bottle.
Coffee beans are good for that too.
If it wasn't something in the tray itself when it was shipped that
did the tarnishing, I'm wondering if the rep was remiss in taking
care of it. Maybe he left the tray in a hot, humid, closed area (like
a car) for too long.