How to tell ivory from plastic

Ivory has a grain, like wood. Also ivory, being a commodity, was cut into rectangular pieces before installation: a long skinny rectangle (the tail) to go in between the black keys and a short fat one (the head) at the front of the key.

With ivory key tops, you can almost always see the line that separates them going straight across the keyboard

Also be aware that if you are unhappy with the condition of the key tops, they can be replaced with new plastic key tops.

Turn this...
...into this:
oooh, now that's better