I am sharing a video that I took at the Ha Long Pearl Farm in Vietnam of a worker implanting an oyster so it will "grow" a pearl.

Notice in the video that the woman inserts a piece of mantle tissue from a donation oyster first. The mantle tissue is the outer ring of the mollusk's body. The whole ring is cut out and then slivered into tiny 3.03mm pieces. This length is a Japanese measurement of length called the Bu. Only one piece is needed for each oyster implantation. After the mantle tissue, a round ball called a nucleus is inserted next to the mantle tissue, with the epithelial cells facing the nucleus. The mantle tissue and the nucleus are inserted into the gonad organs of the oyster. 

The nucleus material used for these beaded cultured pearls is traditionally from freshwater Mississippi mussels.

After this surgical operation is completed, the oyster is once again attached to a labyrinth of netting and reintroduced into the water. 

The epithelial cells are the activator in the pearl sac. The pearl sac grows around the nucleus and starts to produce nacre over the nucleus. Layers and layers of a brick-like structure of nacre are laid on the nucleus. The nacre is the pearl. 

The more layers of nacre, the more intense the glow of the luster of the pearl.