Thank you Pernula!
I've got some reading to do. I really prefer the idea of tissue nucleation. I just purchased a freshwater pearl bracelet from Pearlparadise.com, and I'm hoping that these are solid nacre. I looked on their site for that information, but I couldn't find it. I'm thinking that if they are farmed in China, that they will be tissue nucleated?
I've got lots to learn. Thank you both for your information.