Color Treatments for Pearls

Those new to the world of pearls often marvel at the marvelous colors pearls come in these days. Yes, pearls come in colors. Here's how they get that way.

A good thing

Let me say, first, that color treatment for pearls is not a bad thing. No longer do we buy pearls as the color they come, straight out of the clam. When a mollusk makes a pearl, it has a mind of its own, making most pearls with less perfect coloration than we require from them.

Human beings have developed methods to improve upon nature. If you want to wait for those bivalves to produce the rare perfect white pearl, be my guest. I'll ask you next year whether you're still waiting.

Eosin

Before WWII, the Japanese employed the first coloration technique using eosin, a vegetable dye. After bleaching with regular hydrogen peroxide, they soaked the white pearls with eosin in vats exposed to sunlight. This imparted the desirable pinkish to the pearls. This was far better than the beached white look or even the yellow, gray, or dull beige of naturally colored pearls.

Mother knows best

I can vouch for the desirable pink hue of the first colored pearls. I received my first strand well after World War II, presented by my Mom who said about them, "Notice they're pink."

What does it mean to be pink? I wondered about that before she replied, "They're better." And if my Mom said it, it had to be right. She knew about such things.

Black pearls

Also before the war, the same Japanese folks dyed Akoya pearls to a dark color with solutions of silver nitrate, chemically AgNO₃. Silver from this silver salt would incorporate into the nacreous layers as the pearl formed in saltwater oysters. Dark coloration became part of the pearl as it grew.

The nucleus, however, does not uptake the silver but remains white. The ordinary person, of course, cannot see what's inside. But a pearl so treated and cut in half for analysis will display a white center.

Any color as long as it's white or black

For decades after the war, pearls came in variations of color as long as the color was white or black. I can vouch for this too.

After showing my strand of high quality pinkish pearls, my college friend produced her strand, ahem, of decidedly more desirable black pearls. Without saying they were better than mine, I knew she knew about such things without even saying.

What everyone these days should know without saying is that Tahitian black pearls are the only pearls that are naturally black. Pinctada margaritifera, the saltwater black-lipped oyster, produces black pearls without any help from people. Any freshwater pearl that is black got that way from the inorganic salt method of coloration.

Enter freshwater pearls

More recently and starting in the 1980s, the Chinese developed chemical treatments for coloring freshwater pearls. They started the industry in earnest, producing pearls from freshwater mollusks instead of their saltwater cousins.

Because freshwater mollusks produce more than one pearl at a time, the availability of pearls increased dramatically. At the same time, the Chinese developed ways to treat them for color. Both constituted remarkable achievements from which women all over the world would benefit.

No-coat color

Let it be known that color treatments for freshwater pearls are not coatings. The mollusks themselves incorporate coloring agents into the pearl nacre as it's made within the shell. In processes similar to the silver nitrate salts, salts of cobalt and other inorganics are added to waters in which the mollusks grow and produce.

Inorganic lab

Different salts produce different colors. I can vouch for this too. Inorganic Chem. Lab 101 forced color experiments, requiring students like me to equate color with inorganic ions. Cobalt produced blue; manganese produced purple; iron begot red; and so on through the periodic table of the elements. Chemistry students got to know such things.

Salt solutions

While the Chinese don't disclose their methods, the pearl coloration technique is some variation of a salt solution wherein mollusks produce the pearls. Sitting in the stuff for up to two years, what comes out of each freshwater mollusk is a small batch of freshwater pearls in color.

The last word

Let it be known-and known well-that a colored pearl does not make a pearl manmade. Colored pearls are products of mollusks, not men. Men made the means to achieve color for pearls in ways the mollusks could not do themselves.

I can vouch for this. I'm a woman who seeks desirably colored pearls to match my wardrobe. I care less that some guys in China threw some inorganic salts in the water to get them that way than I care about getting my pearls that way-in color!

Sources: http://www.pearls.com/Education/PEARL_TREATMENT/TREATMENT_PEARLS.asp

http://www.gia.edu