This time we will examine the “opposite” colored pearl group: we’ll move from “white pearls” to “black pearls” and we’ll have a totally different experience in the pearl’s fluorescence. If last time you ended up believing that all pearls glow with a blue color under a long-wave UV light, then you’ll be surprised. But I don’t want to get ahead of myself, let us go out and play in the field.
What is the source for “Black Pearls”?
Authentic "black pearls" –both from the natural & cultured pearls varieties- have been mainly produced by two species of pearl oysters that belong to the "mother-of-pearl" or “Pinctadine” oyster group that mainly includes: the "Black-lip Pearl Oyster" (Pinctada margaritifera and its many varieties or sub-species) and the “Madreperla Panámica” or "Panamic Mother-of-Pearl Oyster" (Pinctada mazatlanica). Some of the characteristics of these Pearl Oysters is their large size (up to 25 cm/9.8” in diameter for the the first one, and up to 20 cm/7.9” for the second one) and they have a beautiful metallic-looking shell whose coloration may range from white to smoky-grey, with flashes of emerald green and violets; once the the shell is polished it displays a beautiful wavy pattern that makes it just perfect for a collector as well as being used to make buttons and all kinds of shell hand-crafts.
These many species of "black lip oysters" have a very wide distribution througout the Pacific Ocean, and you can find them from the Persian Gulf (with the variety Pinctada margaritifera persica) to the islands of Hawaii (with the variety P.margaritifera galstoffi), but it is variety cummingi which stands out for its beauty and large size, and it is in the Islands and atolls of the South Pacific where this oyster is grown for the mass production of cultured black pearls.
Then we also have the “American” variety that we know as the “Panamic Black LIp Oyster” (Pinctada mazatlanica) which was considered as yet another variety of P. margaritifera for many years, but then the many anatomical differences (including the “anal flap”: talk about “dark discoveries”) made scientists conclude this species was unique. This variety is found from the Gulf of California in Mexico, all the way down to Peru and including the Galápagos archipielago and Easter Islands. Below you’ll find a distribution map of several species of Pearl Oysters based on Sohehi Shirahi’s book (Shohei Shirai. 1994. Pearls & Pearl Oysters of the World. Kousoku Printing Co. Ltd. Okinawa, Japan. ISBN: 4-9900287-1-6)
The Third Group
There is still another group of marine mollusks that produce “black pearls” and this one is also a group of animals related to the “Pinctadine” group, but different enough: the Black Pen Shell (Atrina maura) and the “Concha Nácar” or “Rainbow Lip Oyster” (Pteria sterna). Since there is no cultured pearl production on Pen shells we will only talk about the “Rainbow Lip” oyster.
The “Rainbow Lip Oyster” is a uniquely different organism: it is related to the “Pinctadines” (they belong to the same family so they are…second cousins!) but this species is much smaller (the largest specimen we have recorded is just 14 cm/5.5”, but on average the “large” individuals measure about 12 cm/4.7”), the shell being less flattened (more concave) and having a very unique anatomy (more on this in a future post): smaller and more muscular. It also has a unique metallic looking shell, and the color range is somewhat more impressive than that of the “black-lips”: it also ranges from a blueish light-gray color to a smoky-dark color with many beautiful color reflections, including green, golden, violet, purple and blue. A photo here can be more helpful.
How we’ve been Trained to See “Black Pearls”
Now, when most people think of "black pearls" they really picture “black orbs” in their minds, but the black pearl is so much more since it can display a enormous variety of colors, from white, to light-gray to an obsidian black color, but they also display beautiful overtones, mainly in green and violet. For the most part you can say that Tahitian pearls display darker colors (black), while the Cook Islands pearl have a more greenish color (pistachio), and "Kamoka Pearls" (from our friend Josh Hubert) and pearls from Fijii have a wide range of rich dark colors. To say "Black Pearl" is almost the equivalent of sayin "Not a White Pearl", but even with all the recent awareness and knowledge about pearls in forums, websites and specialized books there is still confusion surrounding the use of the "Black Pearl" term.
Now, there are many people that talk about black pearls from Japan and China… and the truth is that the vast majority (not to say all) of these so called "black pearls" are actually artificially colored pearls; these have been “blackened” by means of chemical processes (staining/dyes) and/or physical (heating, radiation). Then, these pearls are not black pearls at all and have not been grown in any of the species we’ve discussed on this entry, and it doesn’t matter how much those selling them say they are. In the near future we’’ll show you a way –quite dramatic- to “discover” these crypto-black pearls.
Anyway, today we decided to differentiate several groups of “black pearls” from Pinctada margaritifera (from Tahiti, Kamoka and the Cook Islands), of Pinctada mazatlanica (from Guaymas, Mexico) and of Pteria sterna (again from Guaymas), but also a group of artificially blackened pearls (some Pinctada imbricata from Japan and also some freshwater pearls from China); and something that can be easily appreciated is how these pearls are so different among themselves and this is something that truly distinguishes them from the "white pearls" group that we saw in the previous post.
When we compare these groups we can see that margaritifera pearls are much darker, almost black but with overtones in green and violet (the best quality, as seen in the above image), mazatlanica pearls are more of a dark grey color with some olive green, and that those from Pteria sterna they are very different: highly iridescent. On the other hand we see that artificially colored pearls also display a highly variable appereance (the “Black Akoya” are… just jet-black) and that their Chinese counterparts can be very iridescent, but this is in a “static way”, not “dynamic” in their appearance (will try to explain this in the future).
Here are a few examples:
Panamic Mother-of-Pearl Oyster – Pinctada mazatlanica -Guaymas, Sonora, Mexico.
These include white, light gray and a dark grey-green colors.
Rainbow-LIp Oyster – Pteria sterna – Guaymas, Sonora, Mexico
I see pearls like these every day… and I still find them breathtaking! No need to explain their colors, since it is also difficult to do so.
Artificially Colored Pearls – Akoya and Freshwater pearls.
The Akoya pearl is the one located to the left-front side of the photo below, the other three pearls are all Chinese freshwater pearls and they have been dyed. The colors are static… you can say they are "painted" or “burnt-in” and thus the colors simply remain in place.
Now, let’s see how all these pearls look when they are exposed to a long-wave ultraviolet light… what kind of fluorescence will we see?
Black Pearls under UV
Let’s start with the first group, the "Tahitian" pearls. In the previous post we saw that white pearls glow with an intense blue color, so I will use a white pearl to help us to compare the fluorescence between these two different groups of pearls. This little white pearl –let’s call it the “blank pearl”- is the same for all pearl groups.
As you can see in the above photo, “black pearls” from Tahiti and the Cook Islands and all those that are produced in the Pinctada margaritifera pearl oyster do not possess any kind of fluorescence. Unlike “white pearls” they are inert under this radiation and therefore this test cannot be used to distinguish them from fake pearls or artificially colored pearls.
Will the other “black pearls” behave like this group? Let’s us see…
American Black Pearls
This group of pearls includes those produced by the “Panamic Black Lip” (PInctada mazatlanica) and this oyster produces both light and dark colored pearls so we might see something very interesting: the light colored pearls display the typical white pearl fluorescence, and the dark ones do not show this phenomenon. Somehow this special pearl group is between both the “white” and “black” pearl groups. I wish I had a light colored Tahitian pearl to see if it also displays a similar fluorescence. Obviously the pearls black possess something that does not allow the pearl’s fluorescence.
Sea of Cortez Pearls – Pteria sterna
Now let us move on to the group that is remarkeably different from all other black pearls: pearls from the "Rainbow-lip Oyster" or Pteria sterna. This Oyster has an enormous capacity to produce colors including a “Rainbow” color effect within the pearl (see previous image of the three pearls from this species). Will these pearls behave in a similar way to the fluorescence of “black pearls”? Let’s us see again…
We definitely see something completely out of place in this case. Definitely: these pearls are NOT inert, but neither do the they glow blue… but, instead they glow RED. And this is something diametrically opposite to what we had expected. These pearls are unique in a way that it is possible to use this test to identify them among any other cultured pearl in production currently.
Artificially Colored Black Pearls
Now let us see how fake pearls will behave under UV light. Will they try to imitate the black pearl? Will they glow like the pearls they originally come from (the “white pearl” group)??? Will they glow like Cortez Pearls??? Let us dive into the results:
As you can see there is no fluorescence. All these pearls are inert (except the white we use to compare with). In this sense we see that they behave more like the natural colored black pearl. For those who imagine seeing a small red-pink pearl of the far right: this is actually a “Hot Pink” colored pearl and whe are not seeing any glow from it…just is current color, there is no inner glow. What do these pearls have in them that prevents their fluorescencent glow?
Questions that we will need answers later, but for now I would like to close with a comparison between all these varieties of pearls.
Comparing between black pearls
We see a group photo of these "classmates" and we can easily detect a wide variety of sub-colors, something that we could not observe easily in the previous group (white pearls) and to the extent that we can easily identify the species of oyster that produced it, if you have a bit of experience and you know what to look for.
To the left we can see a large drop shaped “Kamoka pearl” from Tahiti, just in front of it we see a round Japanese Akoya, with a couple of dyed Chinese pearls to its righ, and on the far right a beautiful drop shaped pearl from the Gulf of California. I Just have to add that I somehow forgot to add a Pinctada mazatlanica pearl… a small detail that I hope does not affect you.
Now, let’s look at the reaction of these same pearls under a long wave UV light:
And again we see that only two pearls are glowing here: the little white pearl which is used as blank, and the Pteria sterna pearl with its unusual red colored glow.
We hope that this entry about black pearls has aroused a greater interest in the subject and on the methods used for pearl identification. Next month we will have more evidence and more exotic specimens, so continue learning in this free Gemology course that we are happy to have prepared for our avid readers.
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