How do I clean ivory jewelry which has turned dark?

I wonder if a pencil eraser would help. Try a little (gently) on a surface you normally don't see (e. g. the back) and see how it goes.

Here are some hints that suggest how to care for ivory jewelry. Follow this link:

http://www.ehow.com/how_4853179_clean-ivory-jewelry.html

A white vinyl eraser can be used to clean the dirt. but i would suggest you to Take your ivory jewelry to a professional jeweler to clean.

If u want to clean your ivory jewellery at home then you should do it by the help of lemon and cotton easily.

u can try lemon juice to remove its darkness

Use the following steps to clear your jewellery-
Take a brand new high-quality pen eraser and try to erase the yellowish marks on your jewellery.
Take two parts of water and three part of lemon, use a clean cloth to apply and rub this mixture.
Keep it away from oil, corroded metals, humidly and things colored that may harm and damage it badly.

There are many points out of one is you can make use of -
Lemon Juice or Dry Mango Powder