I really hate to be the bearer of bad news, but the black pearl is dyed. There are factories in Japan and now (primarily) in China that insert those pearls into the mollusks. After they insert the pearls, the shells are dropped into a chemical solution that causes them to constrict and close, and then preserve them until they make their way to their "pearl-in-an-oyster" destination. A lot of the factories will even insert freshwater pearls into akoya pearl oysters. You know this is what you are dealing with when pearls come out in freshwater colors like peach and lavender, and some of the pearls are slightly egg-shaped.
I am very familiar with the operation because I was approached by Budweiser years ago to assist in getting akoya shell for their pearl-in-a-shell operation. I brought in a few hundred shells and they weren't happy at all - not all the pearls were perfectly formed, they were different sizes, etc. They responded with a spread sheet detailing exactly what they wanted in every shell; the pearl sizes, the pearl colors, the number of pearls per shell, etc. That, of course, is impossible. That is when I started doing research and found out the real story behind the pearl-in-a-shell operations. One of the companies that does it in Guangzhou is the Fukui shell factory.
