When I was about 8 or 10 years old, (that makes it about sixty years ago). we had an old organ with "ivory" keys. It seems like my Mother and Sister thought it would make a good desk and book case, so they renovated the old organ, threw away all the keys and the rest of the innards, brass reeds and pedals, bellows, etc.. Strange thing was my Brother and I found out that the white "ivory" keys, if you held a match to them would burn almost as good as gun powder, I mean it would hiss and burn fast with a yellow flame and almost no residue left, so we came to the conclusion they were not ivory, but someone said they were probably celluloid, but we never found out for sure.. I don't know if the black keys were ebony or not, guess it was possible they could have been..