Under magnification, it's easy to see the grain and irregularities of the bone. Having handled thousands of knives, I can see those are bone from the pictures. Looking at a lot of knives is the only way to train your eye!!
A simple test for plastic is to lay a very sharp knife on the "bone" (like you were going to cut a salami in half!) and with some light pressure, try to "scrape" the surface sideways. The blade will "skate" over the bone because it's so hard, but it will "bite" the plastic and stick.
Try at your own risk!!
Upnorth is right on. Big surprise there! He has been doing this awhile. His comment about handling a lot of knives is exactly how one learns to tell the difference rather quickly. A GOOD jewelers loop is invaluable for this reason alone. If you look very closely, you can see the specs in the bone that carried blood. Just compare a delrin to the bone under the glass and you say OHHHHHHHH!!!!! now I get it. Pearl of course you rub on your teeth. Real pearl is rough, pearloid or fake is far to smooth. Again, test the two and you will feel the difference. Just a couple of tricks of the trade.
Upnorth, I liked you method for bone too. I tried it and no doubt it works. Thanks
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Author of "Great Eastern Cutlery:An American Tradition,The History of the Northfield & Tidioute Brands" & "Tidioute: A Town With an Edge" “The Chronicles of Cooper Cutlery”
I agree that, lacking the ability to detect the pores that carried the blood in the bone (old eyes , no magnification , poor feeling in the hands ), upnorth's method of a "Sliding Scale"...as it were...is the best I've tried. Thank you for that great bit of information Charlie.