I got the answer from an expert from Fire Mountain Gems.
Wash the mother-of-pearl beads or shell with water and a gentle soap, like Ivory Soap. Do not scrub the beads, as you could damage the porous outer layers. Use your fingers or a soft cloth to remove stubborn areas of dirt. Jewel Brite is a liquid cleaner that is safe for most stones and contains no ammonia, acid or alcohol. Always test a small area first to watch for any reactions. A soft cloth can be used to clean the beads or shells if the piece cannot be submerged.
- Maura Buckner, Jewelry-Making Expert