The Key is the Key

Pretty shiny keys
The keytops, the finish and the name decal on
this piano are all polymers.
Key tops used to be made from ivory, a polymer made of hard
proteins. Ivory, which comes from elephant tusks, has a nice smooth feel and looks pretty, but now it is illegal to use it. So most new key tops are some kind of hard plastic like polystyrene. The same goes for the black keys, which were traditionally made of wood (namely ebony), but now are most often black plastic. The key itself, which is basically a long lever that goes far back into the piano to push the action is made of some sort of lightweight wood.