Anyone old enough to have seen The Graduate will remember the advice Benjamin received about plastics.

Not all plastics are created equal, but if the plastic is cast phenolic, aka Catalin (often described as Bakelite which is something else entirely) the advice about plastics was sound.

The napkin rings above sell for around $15-40 apiece these days. But look at what you could have gotten them for in the late 1930s.