Freshwater cultured pearls are produced using a specific method that differs from the process used for saltwater cultured pearls. Here’s how freshwater cultured pearls are made:
- Selection of Mussels: Freshwater cultured pearls are typically produced using freshwater mussels, such as species of the genera Hyriopsis and Cristaria. These mussels are native to rivers, lakes, and ponds in regions like China, Japan, and the United States.
- Incision and Grafting: The process begins by selecting healthy freshwater mussels. A small incision is made in the mantle tissue of the mussel without harming its internal organs. Unlike saltwater pearls that use a bead nucleus, freshwater pearls often use a small piece of mantle tissue (graft) from another mollusk as the nucleus.
- Nucleation: The incised mussel is then inserted with multiple pieces of mantle tissue (or occasionally a small bead) into each incision. This stimulates the mussel to begin the process of coating the nucleus with layers of nacre.
- Placement in Water: After nucleation, the mussels are returned to their natural freshwater environment—rivers, lakes, or specialized pearl farms. Here, they are suspended or anchored in mesh bags or nets to protect them and allow them to grow undisturbed.
- Pearl Formation: Over time, typically ranging from 2 to 6 years, the freshwater mussels secrete layers of nacre around the inserted nuclei. The nacre layers build up gradually, forming the pearl.
- Harvesting: Once the pearls have reached the desired size and quality, which is determined by periodic inspection, the mussels are harvested. Harvesting involves carefully opening the mussel shell and extracting the pearls. This process is usually done manually to ensure the pearls and mussels are not damaged.
- Sorting and Grading: After harvesting, the freshwater pearls are cleaned, sorted, and graded based on various criteria such as size, shape, luster, surface quality, and color.
- Processing and Market: The graded pearls may undergo additional treatments like polishing or bleaching to enhance their appearance. They are then ready to be sold in the market as freshwater cultured pearls.
Freshwater cultured pearls are known for their variety of shapes, sizes, and colors, and they are a sustainable alternative to natural pearls due to their controlled cultivation process.