Unique Agriculture Commodities: Pearls

A few weeks ago, I was looking for inspiration for a #FridayFarmFact. I was trying to find something that was out of the ordinary and branched beyond the corn and soybean field. This led me to thinking about my time in Muscatine, Iowa. Muscatine used to be a hub for harvesting mussels from the Mississippi River to create pearl buttons. It was a whole town affair with pop-up button factories, and you can still find remains of the pearl button industry as you dig down into the soil. Though pearl buttons aren’t pearls (they are actually created out of the shells of mussels), it got me wondering, where do pearls come from, and are they truly as rare as people say they are?

What is a Pearl?

Pearls are biological gemstones that develop into a wide variety of colors (e.g., black, gray, silver, green, purple, blue, etc.). They form in freshwater and saltwater bivalve-mollusks such as oysters, clams, and mussels. These gemstones can develop naturally as an irritant enters the mollusk. In response to the irritant, the mollusk secretes enzymes and calcium byproducts to form a tissue known as nacre around the irritant that is resemblant to its inner shell, much like when we form a scar. Over the next 3-5 years the tissue continues to grow and deposits calcium carbonate in smooth layers creating what we know as a pearl. To simplify this, think of a pebble that might get into your shoe. Overtime, your body might develop a blister to help protect your foot from the pebble. Eventually, the skin of your foot would toughen up to prevent the pebble from hurting you. In the case of an oyster something as small as a piece of sand might be the irritant that gets in and causes the mollusk to start forming the nacre. Natural pearls are rare and finding a “perfect” pearl is even rarer. This rarity, and the demand for pearls, has sparked a market for the cultivated, or human induced, pearl.  

White and pink pearls
(photo courtesy of James St. John)

How are pearls cultivated?

As in most cultivation, pearl farmers do not reinvent the wheel; rather, they utilize and optimize what occurs when Mother Nature is left alone. Thus, the pearl forms in the same way that a natural pearl would, however, specialized tools and growing conditions are used in cultivation farms to develop the “perfect” pearl. Most pearl cultivation farms can be found in Japan, China, and Indonesia. These locations are ideal for cultivation because of the water quality, temperature, and nutrient availability. The cultivation of pearls can be broken down into six main steps (watch this VIDEO to see them in detail):

Step 1: Grow host oysters or mussels

Oyster or mussel sperm is placed in a tank with eggs (oyster or mussel) for fertilization and the development of a larvae. These tanks are carefully monitored for temperature, minerals, and acidity to make sure the mollusk will have the best conditions for growth. The late larval stage of the mollusk will cling onto the hanging mesh in the tanks. Feeding these mollusks 2-3 times a day allows them to reach the proper maturity to be transferred to open calm waters within a month. Here, the mollusks will grow until they are the proper size for seeding.

Life cycle of an oyster
(graphic courtesy of Wallace et al, 2008)

Step 2: Seeding

The first step of seeding is to create the seed, or nucleus bead. No, the seed won’t sprout a pearl, it’s not like a plant seed. In this process, a donor mollusk is cut open and a round nucleus bead is made from the shell. This little piece of shell (or seed) is surgically placed inside the mollusk with a piece of donor tissue (called a graft) and will serve as the irritant to start the pearl. This process takes steady hands and careful precision, so the mollusk isn’t harmed. The bead’s size will help determine the overall size of the pearl. I like to think of this process like priming a wall with paint, you prepare the wall so that the color in the end comes out the way you want it.  Same with seeding the mollusk.

Placing a seed and donor tissue into an oyster for pearl cultivation
(photo courtesy of Shawn Harguail)

Step 3: Rest and Recover

After seed surgery, the mollusks are placed in containers and back into calm open waters of the ocean or lake. As their wound heals, farm workers use technology to x-ray the mollusks to determine if the seed was accepted, and to determine the progression of the pearl. If the seeding was accepted, the mollusks are then hung either by a rope through their shells or laid in baskets for the remainder of the pearl making process.

Creation of the nucleus seed of an oyster (left) and pearl formation (right)
(illustration courtesy of C. Montagnani)

Step 4: Grow Pearl

As the pearl continues to grow, the mollusks are moved from cooler waters to warmer waters to ensure that the animal doesn’t die, and optimal pearl growth occurs. Throughout the growth process the mollusks are collected and cleaned to get rid of parasites that could damage the animals. This stage of pearl production can take anywhere from 10 months to 3 years depending on the size of pearl.

Hanging of mollusks for growing pearls in baskets (A) and on a line (B)
(photo courtesy of Simon-Colin et al, 2015)

Step 5: Harvest 

Mollusks are cut in half and the pearl is extracted from the meat. If it is an oyster, part of the meat may be conserved and sold as Ise-Shima, a delicacy in Japan. The pearls are washed and rinsed and sorted through to find the perfect pearls. It may take up to 10,000 pearls to find enough desired pearls to make a 16” necklace.

Harvesting of oysters
(photo courtesy of Asian Development Bank)

Step 6: Develop Product

Pearls require no polishing or shaping. After they are washed and sorted, they are exported to factories and shops where they are used to create a wide variety of jewelry such as rings, earrings, necklaces, and more.   

Example of a pearl necklace, a possible end product for cultivated pearls
(photo courtesy of HarshLight)

Pearls in the United States

Though most pearls are cultivated in Asia, we do have one freshwater pearl cultivation farm in the United States. Located in Camden, Tennessee, the Tennessee River Freshwater Pearl Farm was started by John Latendresse (1925-2000). Latendresse utilized the Washboard mussel, an indigenous freshwater mussel in the Tennessee river, and culturing techniques from Japan to cultivate the pearls. Through years of research and trial and error, Latendresse and his family perfected cultivating techniques and developed new ones to create pearls of varying shapes such as coins and duck wings. They started a business for their pearls, American Pearl Company, to branch across markets and industry. At the farms peak it was worth roughly $50 million. Today the farm is owned by Bob Keast, and though it is still an operational farm, most of the farm’s income is acquired through agritourism.  You can visit the farm and stay in one of their cabins along the bay, go on boat tours, hunt for pearls, or view and purchase pearls in their onsite museum.

My Takeaways

Natural pearls are still a rare find, however, the need to search the ocean and riverbeds for mollusks bearing gems has declined (and is illegal in some areas). The farming and cultivation of pearls has tremendously changed the market and rarity of the once sought-after pearl. Through the advancement of technology and biological understanding we are now able to meet the demand for such a valuable commodity in a more sustainable way. And though pearls may not be as rare as they once were, a perfect high-quality pearl still is.

~Cathryn

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s