All About Pearls: Nacre and Color

Cultured pearl, turquoise and diamond earrings, Orb Collection

South Sea cultured pearl, turquoise and diamond earrings, Orb Collection, Yael Designs

The factors of size, shape, color, luster, surface quality, nacre and matching all have very strong effects on the look of a pearl and how well it will hold up to wear and tear over time. Nacre and color are just two of these seven factors that ought to be considered when choosing cultured pearls for yourself. Size and shape were discussed in our previous blog post, and we will be discussing luster, surface quality and matching in the next blog post.

To the naked eye, pearls look like delicate smooth globes of soft light. But under magnification, it’s a different story. Pearls have a texture closer to fine grit sandpaper; which is why you can feel their texture against your teeth, and partially why a lightly textured substance such as fish scales and varnish makes such a good coating for imitation pearls.


Electron microscopy image of a fractured surface of nacre, By Fabian Heinemann

Electron microscopy image of a fractured surface of nacre, By Fabian Heinemann

Under magnification, the two substances that compose nacre become visible. One is platelets of aragonite, a crystallized form of calcium carbonate, and the other is conchiolin, the binding agent that holds the platelets of aragonite together, rather like bricks held in place by cement. And, in fact, when viewed in cross-section, this is exactly what nacre looks like! Each layer is semi-transparent, allowing light to pass through them and create that soft glow that pearls are so well known and loved for. Nacre and mother-of-pearl are made of the same substance, but have different names dependent on where they are found.

Growing time within the oyster strongly affects how much nacre forms on the pearl. And more nacre generally means better luster and that the cultured pearl will wear and last better. But the longer the cultured pearl is left in the oyster, the more likely it is to become off-round; and round is a very important shape for pearls. Growing time, generally 6 months to 6 years, is usually kept to an optimal length to maintain this round shape; usually between 6 months to 3 years. This is one of the reasons that natural pearls are favored over cultured pearls: Because they are entirely formed from nacre, unlike cultured pearls which are started from beads, they are said to have better luster and wear for generations if well cared for. But they are seldom round.


Pinctada Maxima by Line1

Pinctada Maxima shell, photo by Line1

Color is another important and obvious factor upon which pearls are judged. Pearls come in a variety of colors. The strongest factor as to what color a pearl will form in is the color of the “lip” of the oyster – the color of the mother-of-pearl already there. The color of the lip of the oyster that donates mantle tissue during the nucleation process can also affect the color of the pearl, but usually, these are both the same breed of oyster with the same color lip. Color can also be affected by any pollutants in the water.


Baroque freshwater cultured pearl and diamond necklace

Baroque freshwater cultured pearl and diamond one-of-a-kind pendant, Yael Designs

It is more difficult to breed for certain colors of freshwater cultured pearls than it is for salt water cultured pearls because many of the mussels used to grow pearls have lips of multiple colors. Also, there are some pearl farmers who are experimenting with adding small amounts of "pollutants" directly into the mussels to see what color these chemicals influence the cultured pearls into becoming.


Freshwater cultured pearl and diamond necklace, Custom Collection

Freshwater cultured pearl and diamond pendant, Custom Collection, Yael Designs

But body color is only the tip of the color iceberg for pearls. Some pearls also have overtone and/or orient. Overtone is defined as "one or more translucent colors that lie over a pearl's body color". It is believed that overtone might be caused by diffraction of light around the edges where nacre crystals overlap. These pearls have an additional glow of rose, green, blue, etc. over their main color. Rose is the most prized for Akoya grown cultured pearls. On dark green-grey Tahitian cultured pearls, the addition of rose to purple overtones create the prized "peacock" color.


Tahitian cultured pearl and diamond ring, Orb Collection

Tahitian cultured pearl and diamond ring, Orb Collection, Yael Designs

In our next blog, we'll touch on the last three major concerns when choosing out a pearl: luster, surface quality and matching.



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