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What is it that makes Pearls so Expensive?

Posted April 8, 2019

For millennia, pearls have been a symbol of elegance and class, typically worn by rulers and nobility across the world, and judging from the attire of current celebrities attending red carpet events ­– the allure of such expensive jewellery is alive and well to this day.

The most expensive piece of jewellery ever sold was Marie Antoinette‘s pearl, comprising a part of a diamond-studded pendant, sold for $32 million during an auction which took place back in 2018.

While the price of it, in this case, is surely determined – at least in part – by its ambience of historical significance, this is by no means a satisfying explanation. What other factors could be identified as significant when assessing the value of these gems?

According to the gemologist Tom Moses from the Gemological Institute of America, the key determinant of the value of pearls is whether they are natural or artificial.

In the wild, pearls are formed when a foreign body enters the shell of a mollusc, such an oyster or a mussel, by accident and becomes covered in nacre (the same material lining the inner layer of the shell) as a result of the organism‘s defence response.

Natural pearls can be distinguished from artificial ones (produced by humans inserting foreign bodies into shells themselves) by using an X-ray machine and looking for concentric layers, which typify natural gems.

Pearls are both rare in nature and difficult to fashion by artificial means, making them a highly prized gem for celebrities and nobility alike. Image:, CC BY-SA 3.0

Most pearls on the market today are artificial. But growing them is a difficult task, which can take anywhere from six months to two years, and even then results often vary by a large margin, partly determined by the type of mollusc chosen for farming.

An important aspect of such variation is size, because “the larger the pearl, the more valuable, just like any other gem,” explained Moses.

Colour is another important consideration and here, too, “the main reason for the color difference is the species of the mollusk. Another very interesting influence is when a pearl is cultured, there is a donor tissue used from another living mollusk, and depending on the color of that tissue, it will influence the color of the final cultured pearl”, said Moses.

Last, but not least, the price of pearls also depends on the most elusive of qualities – luster, or the way the pearl reflects light, mostly determined by the amount of nacre deposited in layers on the foreign body inside the shell.

With all of these considerations in mind, it isn’t much of an exaggeration to call pearl farming an art, made even more difficult by the hard-to-predict processes taking place inside a live animal.


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