An elderly Chinese scholar once asked me to cut a seal for him from a stone he had purchased in Taiwan. It had a pretty color and one of the finest carved lions on top that I had seen up to that time. When I began to cut the seal into the base I was surprised to find that it was, in fact, made of plastic. The “stone” had been created from a mold, probably in the hundreds or thousands. It was easy to cut, almost too easy, and made a good, usable seal. I never told the owner that it was not stone as he had thought.
Many years ago I attended a lecture given by an expert on jade. Among other topics he discussed the many ways in which the Chinese have, for centuries, created fake jade and some of the ways to detect it. He said the Chinese attitude is that if you are not knowledgeable enough to tell the difference then it is your problem and not that of the person who sells it to you—it is your responsibility to gain more knowledge and experience.
So if you buy a stone that turns out to be plastic I hope you didn’t pay too much for it. And if, like me, you are asked to cut a seal from a stone that is, in reality, plastic then take it as an educational opportunity, carve the seal, and don’t tell the owner.