Recently the topic of whitening old ivory keytops was showing up in the
Digest.  Let me tell you how it was done some 40 years ago:

Get to the drugstore, buy some hydrogen-oxide (35 %), as well as
rubber gloves.  Wait for a sunny day, remove the ivory keys from the
piano, expose them to the sun.

Don't forget, if not yet done, to number them from the left to the
right, all of them!  Otherwise you will have to spend quite much time
to reconstruct their layout, if by accident you did drop them.

Take a brush, and "paint" the keytops with the hydrogen-oxide.  Wait a
little, clean them up, and repeat.  The hydrogen-oxide will bleach the
ivory, and after carefully polishing those bleached keytops you will be
amazed about the result of this non-destructive method.

But be careful: 35 % hydrogen-oxide is quite aggressive to your skin
(and eyes).  Keep it stored in a save place.

Jan Kijlstra

 [ I'm pretty sure that Jan is referring to what's referred to in the
 [ U.S. as hydrogen peroxide, H2O2.  It is an oxidizer.  I can't recall
 [ seeing hydrogen peroxide sold at the pharmacy at any concentration
 [ greater than 3%, and I have it stuck in my mind that stronger
 [ concentrations can spontaneously give off _lots_ of oxygen, making
 [ it a hazard to store.  I'd love to know more about this bleaching
 [ agent for this application.   -- Jody