How do I tell tortoise shell kanzashi from plastic look a likes?

Question:

Is it not usually darker in appearance and less uniform?

Answer:

Yes, fake tortoise shell tends to be more yellow, and more evenly yellow all over, than real tortoise shell. That said, I have been told that while some new tortoise shell pieces are being manufactured in Japan, they are from shells that had been stockpiled before the ban on killing turtles for their shells was put in place. I have no idea if that is true or not but if you're concerned you might want to look into it.