Here is an old article I give to people that have ivory keyboards.
It was written by Kelso Davis, Vice-President of Pratt, Read & Co.,
Inc., and was reproduced in January 1961 Piano Technician's Journal
at the beginning of an article by Edith Ann Davis entitled "Ivories
and Synthetic Key Coverings".

Earl Hennagir

 - - -

  "It was in June of 1958 that we stopped cutting ivory for the first
time since the founding of the company in 1798.  We did this for
several reasons.  First, because the use of ivory in keyboards had
diminished greatly and second because we could find no way of
labor-saving devices to cut out the man-hours necessary to prepare
a set of key covering.  Presently, we recover very few keys with ivory
and we procure the ivory that we do use from England, already cut.
When we receive it here, there is very little processing left to make
it ready for our presses.

  "Presently, we are using two types of plastic or synthetic key
covering.  One is a resin acrylic which is known as Implex, and which
is made from powder supplied by the Rohm & Haas Company.  This material
comes molded to us in octaves and then with additional molds for the
wide end keys.  It is applied with the same adhesive that we use on the
cellulose nitrate that we still use on a decreasing percentage of our
keys.  The cellulose nitrate comes to us in sheet stock and we die-cut
this material into ones, twos, threes, and fours, for laying on the
boards.  The cellulose nitrate comes in .052 thickness, and the Implex
in .060 and we have a thicker material which is .100"

 [ Histories and photos of the Ivoryton keyboard companies are
 [ presented at http://www.essexct.gov/history/ivtn/ivtn.html and
 [ http://ivoryton.com/articles.htm  -- Robbie