Well, unless you can come up with a cheap, accurate, carbon-14 dating machine, its impossible to tell “new” ivory from old ivory. Ive seen a lot of “old” ivory WINK WINK sold in souvenir shops when on vacation. Needless to say, I didn’t buy any. I have very mixed feeling about such a law (NOTE: I SAID, LAW). Not what passes for a law these days.
The galling part of this, is that for Westerners, anyway, the value of ivory is not in the material, but the craftsmanship of the work that went into carving it. I believe that the Japanese came up with a material YEARS AGO that duplicates perfectly the carving and material properties of ivory (they did large aquatic mammal teeth for scrimshaw, too). There is no good reason for anyone to make anything whatsoever anymore out of the real materials, period.
I’d envision some sort of lab that would take samples of the kind that could be scraped off a hidden area with a knife, if it had to be done.
If it’s part of an antique then it’s reasonable to presume it’s antique itself.
I learned piano on a piano that had actual ivories. There is something to be said for the touch. The porosity tends to absorb small amounts of moisture. Sweaty pianist fingers on a modern plastic keyed instrument can build up to a slippery, grimy problem.