[Caitlin]

What is the best temperature and humidity for keeping pearls? Can it get too humid for pearls? Can pearls be preserved for long periods in water? Or oil of some kind?

I would imagine that the dryness of the winters in the southwestern desert where I live is detrimental to them. I run a swamp box cooler in the summer so there is some humidity in the summer.

Maybe I should keep the ones I wear in a box in the bathroom where it gets humid a couple of times a day?

[jshepherd]

I would not worry too much about that. You do not want to leave pearls in an air tight environment, of course, but you do not want the environment to be too humid either. This will speed the process of the stretching of the thread.
As for leaving in water or oil, I would definitely not do this, especially with oil.
When pearls are stored (depending on the pearls, actually), they are typically stored within a case that has cups of water. This water ads needed humidity to the air within the case.
One thing to be careful with, however, is Akoya pearls. If the Akoya pearls have been heat treated you do not want too much humidity, and you do not want to clean them with water. The heat treatment takes the moisture out of the pearls, and adding the moisture back can make the nacre brittle. So if you are unsure (and it is very difficult to be sure unless you are sure about your source), do not use liquid on Akoyas.