[Tom Edgerton]

Sure, Michele--

Don't overmodel them. Sometimes they have more luster if you let the brush do the work, and don't overblend. See Sargent. Keep them loose and goosey and you'll have more fun; turn them into an anal rendering exercise and you'll have hand cramps and feel like it's a season in purgatory. Less is more.

You can basically knock in the whole pearl with a medium gray, contour slightly with a reflected light near the bottom that has a cast of the local color they're resting on, and finish with a dab of off white for the highlight. Don't over-contrast values within them. And don't forget some hint of adjacent cast shadow to ground them.

See, I told you it's a Guilty Pleasure.