Right, done the needle test.
They ain't ivory. The nearest thing I can identify from the late 1800's is an early type of cellulose.
''In 1862 Cellulose was first made artificially from gun-cotton by A.Parkes, of Birmingham UK. Called "Parkesine", it could simulate ivory.
In 1869 John & Isaiah Hyatt (1837 - 1920), of New York, produced Celluloid from camphor and pyroxlin (cellulose nitrate), and in 1870 Hyatt was granted a patent in the USA.
Cellulose has been used for the key coverings on the cheaper pianos since then''
In a way, I'm glad they're not ivory.