In the MMD (27 Jan 97) John A. Tuttle wrote about grinding ivory keytops.
Here is an alternative for that method.

In my younger days I worked at an old-fashioned piano shop, where I
learned a lot about restoring old pianos.  We restored them thoroughly,
and as a result we were able to offer the customer a pre-war German brand
piano at a post-war price.

The advantage was that the customer got a better piano for his money,
especially regarding the quality of the sound (larger soundboard, longer
bass strings, and so on) . We often stripped the piano completely and
rebuilt it from scratch, including the mechanics.  Remember, in those
days wages were still low.  Nowadays that kind of operation has become
unprofitable.

We also restored the keyboard . Many times we had to get rid of the
ivory -- too many pieces missing, too much damage.  But we also, many
times, could complete an old keyboard from our stock of old ivory
keyboard salvage.  What we never did was grind the ivory!

There is a better way to get the ivory in a better shape:  clean it,
removing the dirt from the surface, by scratching carefully with a
knife, if necessary.

Bleach it with hydrogen-peroxide (30% -- put gloves on!) in the sunlight.
You will have to repeat this two or three times.  After bleaching all you
have to do is to polish the ivory again. The results will surprise you.

Jan Kijlstra