Anyone who's ever dealt with old celluloid keytops knows how
difficult they can be to remove.  At work, we have a supply of
celluloid keytops we've salvaged off of pianos and organs, to use
to replace damaged originals, particularly on reed organs.  We had
been using the cement used for assembling plastic models, and began
wondering what was originally used.  After all, this modeling cement
wasn't around a hundred years ago.

I happened to recall the story of how celluloid was discovered.
A scientist had been attempting to make a glue, and when a bottle
containing various elements in a solvent fell off the table it
didn't break as expected, thus leading to the new material.

I reasoned that therefore there must be some readily available
chemical that would dissolve celluloid.  As it turned out, that solvent
was methanol [methyl alcohol].  A few pieces of scrap celluloid dropped
into a canning jar not only readily dissolved, but when the cloudy
mixture that resulted was brushed onto the underside of a celluloid
keytop, it was attached with the same tenacity one encounters with
those put on in the factories a century ago.  What's more, when I did,
finally, manage to remove it, it peeled up the same way: with small
bits of the wood firmly attached to the underside.

I'm pretty sure, therefore, that this method is the same method used
a century ago in reed organ and piano factories to attach celluloid
keytops.  Around here, its now the method we use as well.

Bryan Cather - Piano World
Alton, Illinois