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Pearls! Natural and Cultured: What’s the Difference?

The birthstone for June is the lusciously gorgeous Pearl. Freshwater pearls have been treasured since at least the 13th century in China. They have been believed to provide protection, strengthen relationships, bring joy, and symbolize generosity and integrity. Let’s take some time to explore and get to know this beauty a bit better!

Today, I’ll share a bit about the differences between Natural Pearls and Cultured Pearls. In later posts, we will explore Pearls further. I LOVE sharing about them, have studied and learned quite a bit, and will happily wax poetic and scientific about these whenever the opportunity permits…like here for example. :)

What distinguishes a natural pearl from a cultured pearl? It’s centre. Also, and perhaps most importantly: how said centre is introduced to the mollusk’s insides to start the process. Natural pearls have been around as long as mollusks, but cultured pearls as we know them today only came about as an industry in 1916 thanks to the works of Mikimoto, Nishikawa, and Mise.


You can see a beaded pearls centre in an x-ray. This is only way you can see the internal pearl structure for assessment without damaging the pearl. It is used on all pearls (aside from imitation)to determine whether a pearl is bead cultured.

With natural pearls, a parasite of some sort(not a grain of sand as lore tells us) becomes an irritant and manages to slip into the mantle lining and get lodged there. To protect itself, the mollusk begins to surround the irritant with a fluid called “nacre”(NAY-kur). Nacre is made up microscopic crystals of calcium carbonate and a gluey substance called “conchiolin” which is an organic protein secreted during the initial phases of pearl formation. This combination makes nacre a very strong substance. The nacre covers the irritant with a multitude of layers. The thickness and quality of each layer is determined greatly by water temperature and quality, as well as available nutrients for the mollusk. Colder temperatures slow the nacre production, producing the highest luster sheen, which is coveted. For this reason, it can take 4 years to grow a gorgeous gem quality pearl. Smaller pearls can be harvested as early as 6 months.

For cultured saltwater pearls, a slit is surgically made into the mollusk’s gonad and then a bead nucleus and a piece of donor mantle tissue from another mollusk(of the same type as the mollusk being used as a host) are inserted into the slit. The implantations are performed by experienced technicians with a high level of skill, and can be completed in less than a minute. The number of nuclei implanted depends on the type of mollusk and the size of the pearl desired. Nowadays, nuclei are commonly made of the shells of freshwater mussels which come from the Mississippi River, and while round is the most popular shape, they can be anything from coins to hearts to cubes and beyond. After the insertion, the donor mantle grows into a pearl sac that surrounds the bead and deposits layers of nacre, growing a pearl over time.

If you are looking for a vast array of natural colours and interesting shapes, then a freshwater pearl is probably right up your street. For cultured freshwater pearls, there are two different ways to culture, and they lead to dramatically different pearls. Dr. Fujita had worked with Mikimoto with cultured saltwater pearls. In the 1920s, he began experimenting with the same surgical bead implantation method using freshwater mollusks in Japan’s Lake Biwa. After a successful harvest, he noticed there tiny “extra” pearls that had formed. He realized that freshwater mollusks could form pearls without a beaded centre, and non-bead nucleus pearls came into being, soon becoming the traditional form of cultured freshwater pearl. With non-bead nucleus pearls, the mollusk determines the pearl’s shape, in a pastel rainbow of colours and variety of sizes typically ranging from 1mm to 10 mm, but on rare occasions they can be greater than 50mm. These pearls still come from a surgical procedure, but it is a tissue graft inserted into the mantle of the mollusk. This creates a pearl that is composed of solid nacre. Since the mantle is quite large in comparison to the gonad, multiple grafts can be performed on the inside layer of both shells, making it possible for single mollusk to host the development of dozens of pearls – potentially. It still depends on the size of the mollusk and the size of pearls desired. In a fun turn of events, two pearl farmers in the 1960s – Yanase and Sakai – devised a new method of culturing freshwater pearls with a bead. They used a needle to insert small mother-of-pearl nuclei with donor tissues, and this led to Lake Kasumi ga ura’s first beaded freshwater pearls. These new beaded pearls came with greater size options. Remember how the non-beaded ones were most frequently 1-10mm in size? Nowadays, beaded cultured freshwater pearls are considered to be small at around 12mm, and they can reach sizes greater than 20mm by 40mm. This leaves lots of room for fun experimental shapes and greater variances for sizing.

Pearls are truly lovely. Knowing more about their formation helps us appreciate their beauty and originality even more. From natural to cultured and saltwater to freshwater, these lovelies have withstood the test of time and will hopefully continue to beautify the world for generations to come.

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