Susan Miller

·Master of Fine Arts in Jewelry Design, Pratt Institute, 2012

·Bachelor of Arts in Gemology, University of California, Los Angeles, May 2005

·Editor-in-Chief, White Victoria (2018 - present)

·Write and research feature articles and profiles for print and online publication

·Contributing Writer, Modern Jeweler and Ornament

·Write and publish freelance articles for IGS and WSJ Magazine

·Jewelry Appraiser (2012 - 2020)

No one knows where or when pearls were first discovered, but these lustrous gems have been treasured worldwide. So what gives pearls their value? In part, it's because of the unique way they're formed. Nacre — also known as mother-of-pearl — is a thin layer that coats the inside of pearl oysters and other mollusks. It's this iridescent coating that gives pearls their signature sheen and luster! In this blog post, learn more about the nacre and how it impacts the value of pearls.

What is nacre?


Nacre is the material that forms the bulk of pearls. It is a beautiful, robust, radiant substance that gives pearls their beloved and enduring luster. The term nacre comes from the Arabic word "nacreous," which means "cloudy." In ancient Rome, mother-of-pearl was valued no less than pearls, and in the 12th century, it was very popular with the nobility. However, it is not a precious or semi-precious stone. By the way, gemologists (scientists who study minerals) do not even consider it a gem, but in terms of beauty, it is not inferior to it.

How is nacre formed?


Nacre comprises tiny crystals of calcium carbonate (CaCO3), which oysters and other mollusks secrete. The nacreous layer of pearls is typically about 0.5 to 2 millimeters thick. It is perspired by the cells of mollusks, including oysters, abalone, and conch. These creatures secrete nacre to line their shells and protect themselves from predators and parasites.

What factors affect the quality of mother-of-pearl?

This high-quality material in pearls has a lustrous sheen and a smooth surface. The factors that affect the quality of the nacre are thickness, uniformity, and shine! The luster of a pearl is directly related to the thickness of this radiant substance. Notably, such accessories are more durable than lower-quality ones, meaning they will last longer without losing their shine.


Dimensionality & depth of luster


The thickness of the nacre affects the body color of a pearl. It also impacts how light is reflected within the pearl, affecting its luster. The iridescence of a pearl is created by light interference. When light waves reflect off the surface of a pearl and then off the nacreous layer beneath, they create an interference pattern. It is what gives pearls their unique glow. 


Luster is determined by the quality of surface reflection and the depth of light penetrating the pearl. Thus, the more light penetrates, the deeper the luster will be. Therefore, the ideal pearl will have a high-quality surface reflection and deep luster. As a result, accessories with thicker nacre have more dimensionality and depth to their luster.


When it comes to pearls, there are three main types: Akoya, Tahitian, and South Sea. Each type of pearl has its own unique set of characteristics, including differences in luster.

The Luster of Akoya Pearls


Akoya pearls are grown in bivalve oysters, which belong to the genus Pinctada and are called Akoya-kai in Japanese. Hence the name of this type of pearl. They gained worldwide popularity thanks to the famous Japanese explorer Kokichi Mikimoto. He was the first in the world at the beginning of the 20th century to grow a natural pearl in natural conditions. 

 

Compared to other types of sea pearls, the Akoya core is covered with a thinner layer of mother-of-pearl. The latter grows faster in the warm season, forming thicker layers. During the cool months, the metabolic processes inside the oyster are slower, and the layers become thinner. The thinner the layers and the greater their number, the stronger the brilliance of the pearl. The time after the cold months is considered the best for harvesting because it is at this time that pearls have a bright, strong, and deep luster.

 

Akoya pearls have the strongest and brightest luster of all other sea pearls. As a result, jewelers worldwide recognize it as a quality standard. Due to their unique parameters, these pearls are used for the production of high-quality jewelry all over the world.

The Luster of Tahitian Pearls


Tahitian pearls are world-renowned for their unique beauty. These lustrous gems are found in the waters around Tahiti, a French Polynesian island group in the South Pacific. Tahitian pearls come in various colors, from black to green to pink. They are also larger than other pearls, with an average diameter of 10mm.

 

Tahitian pearls are grown in the black-lipped oyster Pinctada margaritifera. These oysters can only be found in the warm waters of the South Pacific. The Tahitian islands are home to some of the world's largest and most valuable black-lipped oysters.

 

Tahitian pearls are highly prized for their unique colors and lustrous surface. Different minerals create their shades in the water where they are grown. For example, black Tahitian pearls get their color from the presence of magnesium in the water.

 

Tahitian pearls are typically more expensive than other types of pearls. This is due to their rarity and the fact that they are only found in one place worldwide. Tahitian pearls are a perfect choice if you're looking for a truly unique and beautiful piece of jewelry.

The Luster of South Sea Pearls


South Sea pearls are among the most lustrous and beautiful in the world. Their glow is created by the thick layers of nacre that make up the pearl. South Sea pearls are the most expensive of all cultured pearls due to their size and color, which can be white, white-pink, silver, and cream, and they also have golden hues or rich golden shades.

 

This variety of colors depends on the type of mollusk, Pinctada Maxima. Oysters with silver lips (edges) produce white, silver, and bluish overtones. In contrast, oysters with golden lips (edges) have pearls of cream, vanilla, and champagne tones.

 

The history of South Sea pearls began over a thousand years ago when the locals started to use shells and the pearls found in them to adorn their tribal outfits and as a currency to exchange for food and tools. With the advent of European explorers in the 16th and 17th centuries, South Sea pearls became a precious global commodity.

What color is nacre?


Nacre is a natural iridescent material produced by some mollusks as an inner shell layer. The colors of the nacre vary depending on the type of mollusk it comes from, but it can be white, cream, yellow, pink, orange, or even black. The shades are created by the interference of light reflecting off the different layers of the nacre.

 

Nacre comprises microscopic hexagonal platelets of aragonite (a form of calcium carbonate) stacked together with a thin layer of conchiolin between each platelet. The aragonite is transparent, but the impurities in the conchiolin give nacre its coloration, which can range from white to black.


The nacre inside a clamshell is usually white but can be tinted with other colors. Different minerals create these tints in the water where the clam lives. For example, if there is a lot of iron in the water, the nacre can have a pink or red tint. Likewise, the nacre can be green or blue if there is a lot of magnesium in the water.

How does the color of the nacre affect the price of pearls?

One of the most important features that influence pearl price is nacre coloration. Inherited nacre color has been demonstrated in selection studies, with yellow being the most prominent. It has been proposed that Akoya pearl oysters without yellow nacre in their shells would be better resources of mantle tissue for producing non-yellow pearls, which are more valuable. However, the color of the nacre is not a reliable indicator of oyster quality because yellow pigments are found in the nacre of most oysters. 

Can nacre be cultured?


It is a question that has puzzled scientists for years. Nacre, also known as the mother of pearl, is an iridescent material produced by certain mollusks as a defense mechanism against predators. It comprises layers of calcite (a type of calcium carbonate) and conchiolin (a protein).

 

Nacre is solid and resilient, making it ideal for jewelry, watches, and other decorative items. However, its beauty is also a curse, as harvesting wild nacre has depleted many mollusk populations. To protect these creatures and provide a sustainable source of nacre, scientists have been trying to culture it in laboratories. So far, they have had mixed results.

What are the obstacles to nacre cultivation?


Some mollusks, such as the pearl oyster, can be successfully cultured for nacre production. However, others, such as the abalone, have proven much more challenging to cultivate. The primary obstacle to culturing nacre is that it is produced by living cells. To create an artificial environment where these cells can thrive, scientists must first understand the precise conditions under which they operate.

 

It is a complex and time-consuming process, but it could ultimately create a sustainable nacre industry. In the meantime, we can only hope that the wild populations of mollusks that produce this fantastic material can be protected from extinction.

Bottom Line

So, what is nacre? It is the organic material that makes up the lustrous layer on the surface of a pearl. This substance is composed of calcium carbonate and proteins and has an iridescent sheen that can vary in color from white to black. Many factors determine the value of a pearl, but the quality of the nacre is one of the most important. Pearls with high-quality nacre are more valuable because they are rarer and more beautiful. So, if you're looking for a pearl with fantastic luster, choose one with thick, lustrous nacre.