Yeah, ivory can be thicker and you can see lines from different angles so I don't think those are reliable standards to go by. They look like ivory to me.
Too bad more ivory scales were not cut thicker. They wouldn't crack as easy.
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I am leaning towards calling them ivory.
The thickest ivory that I have is on a Henkel 71.
The best way to expose the grain pattern,
is to illuminate at a shallow angle, along the grain.