Page "Steinway & Sons" Paragraph 74

The surface of the white keys is today made of polymer, but was earlier made of elephant ivory.

In 1975, an international treaty outlawed the use of ivory for commercial purposes making it illegal to use ivory for keys.

Steinway, however, voluntarily instituted this change already in the 1950s, because polymer surfaces are more durable, do not yellow over time, nor do they crack as easily as ivory, and are easier to replace than their ivory predecessors.

The surface of the black keys is neither polymer nor ivory, but black wood stain.