Most black pearls are between 8-12mm. Anything over 12mm is considered to be large. Oysters are like people, they come in all different sizes, colours, and strengths. A nucleus is inserted into the gonad of the oyster where it will secrete it’s nacre to create a pearl. Some oysters secrete nacre at a higher rate than others thus producing a larger pearl. However, there is a technique used called a reoperation to create larger pearls. After harvesting the first pearl from the oyster, the technician will assess the pearl’s quality and health of the oyster to determine if he will insert a second nucleus. During the time the first pearl has grown in the oyster, the gonad has become larger as the pearl has become larger. Thus, during the reoperation, the technician is able to insert a bigger nucleus to produce a bigger pearl. This is the main technique for producing big pearls over 12mm.