pearls and shiny things, like metals, are hard to photograph..
try putting your subject inside a...damn i forgot how it's called..
it's like a small box tent that's open only on the front side, with white cloth as walls,
and with lights inside it that lights up your subject from almost all angles.
that way, glare and hotspots on your subject is reduced to a minimum.
sorry i just forgot what it's called.

now i remember, it's called light tent..
http://www.ezcube.com/documents/ezcube_features.htm