>>2754390>>2754394The white keys are usually grained celluloid, though I have seen some that are ivory veneered. I believe some were veneered with galalith too, which is actually a milk protein based plastic, we use it as an ivory substitute for bridge pins and tuner buttons, it's fairly convincing.
The piano I found had legit ebony black keys, but grained celluloid veneer over maple for the white keys. The ebony was pretty weathered though. Ebonizing woods with that tannic acid stain is pretty cool, I do it a lot with walnut on my instruments. On some woods, it just makes them look weathered and dirty, but walnut has such a high tannic acid content that it's almost indistinguishable from ebony, especially once you get some finish on there. Here's a pic of the neck of a parlor guitar I'm building right now, the fingerboard on the right is Indian Ebony, and the peghead veneer is ebonized black Walnut.