Hydrogen Peroxide and UV is also used to whiten old ivory piano keys - but you need to use "industrial strength" peroxide, not the watered down stuff from the drug store.
This is what you use with the Retr0Bright process. It will turn your hands white if you don't wear gloves, and burn your eyes and nostrils if you don't have good ventilation. It's a thick cream so it stays put on the walls. Hairdressers use it too.