Q&A: Pearlfacts For Not-Pearlologists

[katbran]

On Keshi - the accidental pearls, not nucleated, that form randomly in farmed molluscs are not natural in that they are a product from a farm. Humans are involved in the process if not the formation. Only Keshi or pearls from Wild molluscs are 'natural' - no human involvement at all.

That said... it can be extremely difficult to tell if pearls sold as Keshi are, in fact, true Keshi. X Ray will tell but frankly no one really does that it seems. A few years ago there were a lot of GSS Keshi that were small sort of oval shapes that in fact were not Keshi ... they were sold as Keshi as that gave them a higher value that just little GSS.

When I buy Keshi now I often am told " these are Keshi but have not been X Rayed." Some have the obvious lumpy bumpy organic shapes but then there might be a few that are suspect. I suppose I could take a hammer to one...

 

[Daisys and Diamonds]

On Keshi - the accidental pearls, not nucleated, that form randomly in farmed molluscs are not natural in that they are a product from a farm. Humans are involved in the process if not the formation. Only Keshi or pearls from Wild molluscs are 'natural' - no human involvement at all.

That said... it can be extremely difficult to tell if pearls sold as Keshi are, in fact, true Keshi. X Ray will tell but frankly no one really does that it seems. A few years ago there were a lot of GSS Keshi that were small sort of oval shapes that in fact were not Keshi ... they were sold as Keshi as that gave them a higher value that just little GSS.

When I buy Keshi now I often am told " these are Keshi but have not been X Rayed." Some have the obvious lumpy bumpy organic shapes but then there might be a few that are suspect. I suppose I could take a hammer to one...

That could be a tax right off as trainng or research & development or something ?

 

[MrsBlue]

On Keshi - the accidental pearls, not nucleated, that form randomly in farmed molluscs are not natural in that they are a product from a farm. Humans are involved in the process if not the formation. Only Keshi or pearls from Wild molluscs are 'natural' - no human involvement at all.

That said... it can be extremely difficult to tell if pearls sold as Keshi are, in fact, true Keshi. X Ray will tell but frankly no one really does that it seems. A few years ago there were a lot of GSS Keshi that were small sort of oval shapes that in fact were not Keshi ... they were sold as Keshi as that gave them a higher value that just little GSS.

When I buy Keshi now I often am told " these are Keshi but have not been X Rayed." Some have the obvious lumpy bumpy organic shapes but then there might be a few that are suspect. I suppose I could take a hammer to one...

Thank you so much! This is exactly what I was looking for. Any lazy and disorganized mollusc might decide to create a keshi look-alike around a bead nucleus.

I would imagine that x-rays are saved for larger and more valuable specimens rather than the bitty babies often sold online. Still, at least I'll know what to ask if I'm ever in the market for something special.

This thread is awesome!!!

 

[Pearlescence]

That would be clear at harvest because of where the pearl was

 

[MrsBlue]

That would be clear at harvest because of where the pearl was

How much sorting happens at harvest and are those processes similar across farms?

Also, do white akoya keshi get processed (washed and dyed) as do the round pearls or can we reasonably assume that they are always natural in color?

 

[yssie]

As I read the article, the ratio they mention is the ratio of the refractive indices. (This is explicitly stated in the supporting information - top of last page.) A higher ratio of refractive indices gives stronger reflections at each interface, so the light doesn't penetrate as far into the nacre. That said, I have trouble seeing why the refractive index of the conchiolin would vary.

Well that nominal brainwave went nowhere but at least it failed fast And then actual work got in the way, gosh darn it

Thank you for posting here Starstruck!! Because I'm rereading... I read Fan et. al. as talking mostly about the effects of the "aggregate" double layer of conchiolin and aragonite. Since both materials are translucent, but aragonite has higher RI than conchiolin, the refractive index of the totality of each nacre double layer changing thanks to the amount of aragonite vs. conchiolin changing. But I was reading and taking notes on about six papers at the same time and I goobered the citation!

So, um, yeah, back to *this* paper. I'm attaching it (and the supplemental info) to this post for folks who don't want to go searching.


Re. Higher conchiolin index of refraction yielding lower iridescence saturation:

Assuming aragonite RI doesn't change, and assuming conchiolin RI never exceeds aragonite RI, which are two assumptions that the authors do make -

Given n1 is constant and n1>n2,

They go into a whole thing about light decay in the supplemental info but I really think the rationale for why higher conchiolin RI => light impinges deeper into the pearl can be boiled down to Because Fresnel Said So. At normal light incidence:

Reflectance = abs[(n1-n2)/(n1+n2)]^2

Higher conchiolin RI brings it closer to aragonite RI, which makes (non-reflected) incident light bend less from the normal per transmission through consecutive aragonite and conchiolin layers. Fresnel's equation states that higher conchiolin RI yields lower reflectance; lower reflectance means less light is reflected from the surface of the aragonite-to-conchiolin boundary; less light reflected off the surface means more light transmitted into each consecutive conchiolin layer...

On the other hand, an increase in n2 also reduces amplitude of the superposition, as the result of decrease in individual amplitude

And then they suggest that the more passes that light makes through multiple alternating layers of aragonite and conchiolin, the more likely wavelengths are to become out-of-phase and destructively interfere with each other. Which, yeah, kinda handwavey, but I buy it.

a greater conchiolin index means slower energy decay of light when it impinges in the repetitive double layers, so higher proportion of incident light could reflect back from deeper layers. The longer the light waves travel, the more likely they become out of coherent length. As wavelength-independent reflection mainly adds lightness to the color, a greater conchiolin index possibly results a less saturated color.

Re. Thicker conchiolin layer yielding stronger iridescence (brighter colours):

I feel like this explanation is wayyy more complicated than it needs to be. The real-world point of evaluating optical path distance is pretty much always to figure out how out-of-phase two rays exiting the non-opaque material at in same place at the same time will be - whether or not those light waves are going to interfere constructively or destructively. Constructive interference = combine to produce higher-amplitude = higher-energy coloured light = bolder iridescence colours. Destructive interference, the opposite. So far so good.

The formulae in the second section of the supporting documentation aren't specific to pearls - they're pretty common derivatives of Bragg's law for two non-homogenous media. Three things worth highlighting though, IMO:
A) One of the authors' assumptions is that only primary reflections count. Secondary and tertiary reflections - just ignore those.
B) When light passes from lower-RI to higher-RI medium, (air into aragonite layer, or air into conchiolin layer, or conchiolin layer into aragonite layer), the reflected portion of incident light is phase-inverted (by π, or 180degrees), and the refracted portion sees no phase change.
C) When light passes from a higher-RI to lower-RI medium (aragonite to conchiolin, conchiolin into air, aragonite into air), neither reflected nor refracted portions of incident light see any phase change.

This pic grabbed from the article shows light going (top to bottom) from air into aragonite into conchiolin into aragonite:


So... The canonical thin film example is a soap bubble, right? When the soap bubble's soap wall approaches infinitely thin - as the depth of the film itself approaches zero - OPD is minimal, so at a given point on the bubble at any given time there are reflected rays (from air onto bubble surface and back off bubble surface) and refracted rays (from air into bubble thin film then back out to air) that are almost perfectly out-of-phase. Thanks to the phase of light from air reflecting off the surface of higher-RI soap, vs. no phase change of light from the soap bubble surface refracting out into air, at the same place/time. So the bubble surface looks grey/black rather than iridescent.

So from that perspective I can see why the authors would contend that overly thin conchiolin layers aren't going to do any pearl iridescence any favours. But in order for constructive interference to occur and amplify wavelengths the emitted wave fronts need to be *in phase*...
My highlighting -

In this equation λ is wavelength (of a colour) in a vaccuum and Λ is OPD, and d2 is the thickness/depth of the thin film. The statement that a decrease in d2 results in a decrease in amplitude of the superposition is predicated on the fact that OPD represents the path length difference between light that reflects off a surface and light that penetrates into that layer and refracts back out, where the layer (conchiolin) always has a lower RI than the medium below it. If the surface being penetrated has depth of 0, then the path difference is 0, and the two waves (reflected and refracted at the same place and time) have a phase difference of either π - 0 or π + 0, and a π phase difference is perfectly destructive. Back to that black/grey soap bubble.

Increasing the thickness of the surface that's being penetrated from zero will increase OPD, which will increase the 2π/λ(Λ) component. Which in turn reduces the difference between the (2π/λ)(Λ) component and π (or 2π).

If we set d1 = 350 nm, n2 = 1.3, and d2 = 25 nm based on previous studies of nacre, then OPD can be calculated as 1244.5 nm.

BUT three (IMO pretty major) gotchas here!!
1. Right up to the point where the (2π/λ)(Λ) component of the equation equals π (for a given wavelength), increasing the conchiolin layer thickness will increase superimposition amplitude just like the paper says. Once you reach the point of the abs[(2π/λ)(Λ)] component equalling π, though, increasing the conchiolin layer thickness further will decrease superimposition amplitude. The paper doesn't discuss this bound. Possibly because reaching this condition would require the conchiolin layer thickness to be much thicker than ever seen in nature? (Again for reference - conchiolin is said to be about 25nm thick, whereas aragonite layer is defaulted to 350nm). But I still think this boundary condition should be stated explicitly. It just says "thicker conchiolin is probably better", but you don't benefit from increasing conchiolin layer thickness indefinitely, only until a phase shift inflection point!
2. This is all a mathematical presumption. From rereading this paper - it doesn't look like they ever cut a bunch of pearls open to scan and verify this behaviour, even if by inference only. So I'd sprinkle a little salt on it, personally, until something more examination-based turns up.
3. Why would conchiolin RI change at all? After all this @Starstruck8 I still haven't a clue.

 

[yssie]

Any lazy and disorganized mollusc might decide to create a keshi look-alike around a bead nucleus.

So much mollusc judgment here

 

[yssie]

Also, do white akoya keshi get processed (washed and dyed) as do the round pearls or can we reasonably assume that they are always natural in color?

Curious too…
And can I add the same question for baroque white akoya too…

 

[Pearlescence]

I can only write about the harvests I have been at, at which there were expert eyes on every pearl as they were collected. It is easy to distinguish a keishi from a nucleated pearl because the keishi is simply not in the area of the gonad, where the nucleus and graft were placed. They will nearly always be around the mantle. And very small most of the time.
Larger keishi happen when a mollusc is re-grafted because the shell is not opened so the keishi is not retrieved until final harvest.
Akoya keishi are collected and washed with all the other pearls. Also non-rounds. You only see them rarely because mainstream suppliers tend only to offer round white pearls.
This is the harvest from one grafter on one day.
Pic 2 is some of the weirder pearls I picked out from a day's harvest on a vietnam farm.

 

[MrsBlue]

Thanks for the interesting photos. Especially love the blue peeking out at 3 o'clock and the pale gray drop just to the left of 6 o'clock.

My intent wasn't to question whether the farmers know the difference between keshi and nucleated pearls but rather whether these pearl types are separated at the start and kept separated throughout the process up to point of sale.

I think the earlier point made was key and in line with other purchasing advise given on the board. Ask questions about origin and expect clear answers especially when buying a higher priced item.

 

[Pearlescence]

Ah, misunderstood. No. There are too many pearls going through every day on an average farm. They are more interested in looking at the results of each grafters work.
Initially the whole harvest will be tumble washed and rinsed to get rid of all the goo and stuff and then it will be sorted either for auction or sale. So types in terms of size, shape, colour, etc etc will be sorted, often the same day or within a day or two. Then pearls will go to a factory. There they will be mixed in with other pearls from other farms to be made into strands or left loose.
Realistically pearl sellers can't normally guarantee provenance. I have some I can provenance down to farm, date and time but that is because I did the harvesting. And they aren't for sale. I can't even bring myself to drill them.

 

[lissyflo]

As to pearl colour...how the colour happens is scientifically known and straightforward.
The real question is why? Why do molluscs make shells (and therefore pearls) with coloured insides. No mates, no light..no point. But they do. I've asked evolutionary scientists and they say that it is still a puzzle.

Some things are just beautiful, unintended consequences. Water droplets in the air don’t mean to refract light and cause rainbows for us to marvel at, they just do because of the laws of physics.

The benefit of nacre (irrespective of colour) to the mollusc might be limited to physical protection from irritants; the colours we humans perceive being just indirect, but fortuitous, consequences of the nacre’s molecular structure. I agree with @Daisys and Diamonds : not everything needs a reason, some things just are. Or that’s what I tell myself when I’m stumped by something seemingly simple

 

[Pearlescence]

Nacre doesn't need colour. But it has it. Darwin says there has to be an evolutionary advantage.
So colour in nacre does need a reason.

 

[Daisys and Diamonds]

Nacre doesn't need colour. But it has it. Darwin says there has to be an evolutionary advantage.
So colour in nacre does need a reason.

How old were you when you stopped beleaving in Father Christmas.?

 

[oceanblue]

Nacre doesn't need colour. But it has it. Darwin says there has to be an evolutionary advantage.
So colour in nacre does need a reason.

I am so glad others are pondering this most interesting question. Back when I used to spend my free time here:




I would sit and ponder the shells and just wonder how the lowly mollusk could make make something so perfect , colorful, complex and symmetrical. They really are amazing and beautiful.

Here is is an interesting article with insight into why shells have colors and patterns. Maybe it is the same for pearl formation. The theory is that the mollusk is making a pattern for rebuilding purposes. This may also explain why the pearl has layers of different colors so it can be duplicated and repaired if necessary.

https://massivesci.com/articles/sea-shell-pattern-formation-mollusks-turing-meinhardt-ocean-mussel/

 

[lissyflo]

I found this interesting: deeper water = darker (in this specific research anyway), driven by changes to both pigmentation (biological coloring mechanisms) and iridescence (physical coloring mechanisms based on the differential organization of biomineral crystals). Can you tell I prefer biology to physics - an interest in genes over light return!

(Environmentally Driven Color Variation in the Pearl Oyster Pinctada margaritifera var. cumingii (Linnaeus, 175 Is Associated With Differential Methylation of CpGs in Pigment- and Biomineralization-Related Genes​

Pierre-Louis Stenger1,2,

Chin-Long Ky1,2, Céline M. O. Reisser1,3,

Céline Cosseau4, Christoph Grunau4,

Mickaël Mege1,5,

Serge Planes6and Jeremie Vidal-Dupiol2*)

 

[yssie]

I am so glad others are pondering this most interesting question. Back when I used to spend my free time here:




I would sit and ponder the shells and just wonder how the lowly mollusk could make make something so perfect , colorful, complex and symmetrical. They really are amazing and beautiful.

Here is is an interesting article with insight into why shells have colors and patterns. Maybe it is the same for pearl formation. The theory is that the mollusk is making a pattern for rebuilding purposes. This may also explain why the pearl has layers of different colors so it can be duplicated and repaired if necessary.

https://massivesci.com/articles/sea-shell-pattern-formation-mollusks-turing-meinhardt-ocean-mussel/

I'm reading this and anthropomorphizing like a lunatic Y'know, imagine what it must be like to never be able to bury memories of our own past oopsies - to have my whole life of decisions laid out in shell, an ever-present retrospective - I’m really feeling quite sorry for oysters at the moment

 

[Pearlescence]

I am so glad others are pondering this most interesting question. Back when I used to spend my free time here:




I would sit and ponder the shells and just wonder how the lowly mollusk could make make something so perfect , colorful, complex and symmetrical. They really are amazing and beautiful.

Here is is an interesting article with insight into why shells have colors and patterns. Maybe it is the same for pearl formation. The theory is that the mollusk is making a pattern for rebuilding purposes. This may also explain why the pearl has layers of different colors so it can be duplicated and repaired if necessary.

https://massivesci.com/articles/sea-shell-pattern-formation-mollusks-turing-meinhardt-ocean-mussel/

Shell making is all in the maths - Mostly Fibonacci. And for all you need to know on that there's this series of lectures by my very dear friend Ian Stewart for the Royal Institution

The magical maze – Sunflowers and snowflakes (1997)

Ian Stewart explains how mathematics is the magic thread that binds our universe.

www.rigb.org

(which I am so delighted to be reminded of. That's the weekend's box set!)

 

[Pearlescence]

How old were you when you stopped beleaving in Father Christmas.?

I am perfectly content to see the wonder in evolution, thanks.

 

[Pearlescence]

I found this interesting: deeper water = darker (in this specific research anyway), driven by changes to both pigmentation (biological coloring mechanisms) and iridescence (physical coloring mechanisms based on the differential organization of biomineral crystals). Can you tell I prefer biology to physics - an interest in genes over light return!

(Environmentally Driven Color Variation in the Pearl Oyster Pinctada margaritifera var. cumingii (Linnaeus, 175 Is Associated With Differential Methylation of CpGs in Pigment- and Biomineralization-Related Genes​

Pierre-Louis Stenger1,2,

Chin-Long Ky1,2, Céline M. O. Reisser1,3,

Céline Cosseau4, Christoph Grunau4,

Mickaël Mege1,5,

Serge Planes6and Jeremie Vidal-Dupiol2*)

It's all mathematics deep down.

 

[Starstruck8]

BUT three (IMO pretty major) gotchas here!!
1. Right up to the point where the (2π/λ)(Λ) component of the equation equals π (for a given wavelength), increasing the conchiolin layer thickness will increase superimposition amplitude just like the paper says. Once you reach the point of the abs[(2π/λ)(Λ)] component equalling π, though, increasing the conchiolin layer thickness further will decrease superimposition amplitude. The paper doesn't discuss this bound. Possibly because reaching this condition would require the conchiolin layer thickness to be much thicker than ever seen in nature? (Again for reference - conchiolin is said to be about 25nm thick, whereas aragonite layer is defaulted to 350nm). But I still think this boundary condition should be stated explicitly. It just says "thicker conchiolin is probably better", but you don't benefit from increasing conchiolin layer thickness indefinitely, only until a phase shift inflection point!
2. This is all a mathematical presumption. From rereading this paper - it doesn't look like they ever cut a bunch of pearls open to scan and verify this behaviour, even if by inference only. So I'd sprinkle a little salt on it, personally, until something more examination-based turns up.
3. Why would conchiolin RI change at all? After all this @Starstruck8 I still haven't a clue.

1. I agree with your story (and theirs) on conchiolin thickness and RI. To be fair, all the figures I have seen for conchiolin thickness are in the range they use, so I don’t really blame them for not explicitly stating an upper limit.

2. The paper is not entirely mathematical presumption. They did cut their (one) pearl in half and scan the sections at three points (figure 4b). Their scans show the layering, with average repeat thickness (i.e. d1 +d2) of about 330nm at location 1, 385nm at 2 and 320nm at 3 (by my counting, and using the scale bars). They present figure 3d, which show actual colours at least in the ballpark of what their interference model predicts. But certainly, you would want to see the same thing done with a whole range of pearls.

What puzzles me is how to reconcile the ‘interference enhanced’ pictures (figure 3d) with the normally lit ones (figure 3a). For the round pearl (figures 2a and 2b), it’s easy to see that the bluish and greenish outer zones in the normally lit pictures correspond to those of the ‘interference enhanced’ ones. But I’m having trouble seeing any sort of circular zoning in 3a. If the effect is there, it is being masked by the blue and green surface pattern. And that needs explaining.

It may amuse you to hear that I went to Paspaley (here in Brisbane, not their HQ), meaning to check out some iridescent dark pearls. But the SA informed me (very politely, I have to say) that as a proud Australian producer, they usually retail only their own lighter toned Australian pearls. Still, I did get to see some very nice pearls... So I haven’t actually studied a good iridescent dark pearl in real life.

3. As I understand it, conchiolin is not a specific substance, just a cover-all name for whatever organic material holds the aragonite plates together. So it could vary in composition, and hence in RI. But other relevant properties could also vary, e.g. the absorption or the scattering. It would be good if someone could directly measure these things.

There is another possibility. Look at figure 4b. The scan taken at point 3 shows less regular layering than at points 1 and 2. This could plausibly be washing out the interference colours. I’m also wondering about the white spots: are they defects in the nacre, or are they just artifacts of the preparation?

So altogether, ‘a little salt’ is certainly in order. But figures 2b and 3c do seem to support an interference-based story.

 

[oceanblue]

Shell making is all in the maths - Mostly Fibonacci. And for all you need to know on that there's this series of lectures by my very dear friend Ian Stewart for the Royal Institution

The magical maze – Sunflowers and snowflakes (1997)

Ian Stewart explains how mathematics is the magic thread that binds our universe.

www.rigb.org

(which I am so delighted to be reminded of. That's the weekend's box set!)

So you disagree with the article/theory that I posted?

No higher math please, a "beach read" version is fine

 

[Cinders]

Nacre doesn't need colour. But it has it. Darwin says there has to be an evolutionary advantage.
So colour in nacre does need a reason.

Perhaps Darwin was wrong.

 

[yssie]

1. I agree with your story (and theirs) on conchiolin thickness and RI. To be fair, all the figures I have seen for conchiolin thickness are in the range they use, so I don’t really blame them for not explicitly stating an upper limit.

Yeah, I've never seen the conchiolin layers listed at more than ~50nm thick. Significantly less than even the thinnest aragonite.

2. The paper is not entirely mathematical presumption. They did cut their (one) pearl in half and scan the sections at three points (figure 4b). Their scans show the layering, with average repeat thickness (i.e. d1 +d2) of about 330nm at location 1, 385nm at 2 and 320nm at 3 (by my counting, and using the scale bars). They present figure 3d, which show actual colours at least in the ballpark of what their interference model predicts. But certainly, you would want to see the same thing done with a whole range of pearls.

I actually think this is one of the best papers out there The authors attribute the interference colours primarily to aragonite layer thickness and IMO they've done a really good job of modelling this. My statement re. mostly mathematical presumption was intended strictly for the assertion that conchiolin layer thickness impacts interference brightness! The authors explain that the conchiolin is too thin to actually measure, but I would have liked to see more simulation and comparison with real-world examples - same as they did for the aragonite model. In the grand scheme of things it's a mini nit to pick

What puzzles me is how to reconcile the ‘interference enhanced’ pictures (figure 3d) with the normally lit ones (figure 3a). For the round pearl (figures 2a and 2b), it’s easy to see that the bluish and greenish outer zones in the normally lit pictures correspond to those of the ‘interference enhanced’ ones. But I’m having trouble seeing any sort of circular zoning in 3a. If the effect is there, it is being masked by the blue and green surface pattern. And that needs explaining.

Let me make sure I'm following - d'you mean these pics?


I think the enhanced interference pics are using the angle of the normally-lit pics as face-up - the Area II pics match up with the red, and assuming they did the same thing for Area III. Although I don't see nearly as much green in the normally lit pearl at area III. Is this what you're referring to though?

It may amuse you to hear that I went to Paspaley (here in Brisbane, not their HQ), meaning to check out some iridescent dark pearls. But the SA informed me (very politely, I have to say) that as a proud Australian producer, they usually retail only their own lighter toned Australian pearls. Still, I did get to see some very nice pearls... So I haven’t actually studied a good iridescent dark pearl in real life.

Oh dear. Well, yeah, I guess Australia really isn't known for their black pearls! The "Fiji pearls" come from the same oyster as normal French Polynesia Tahitian pearls, Pinctada margaritifera, but for whatever reasons the Fiji pearl oysters tend to be a bit smaller. Same species, just evolved a bit differently, I guess. Fiji and Australia aren't that far apart!! But Paspaley does have the absolute best WSS in the world, I'm convinced of that.

I used to live in Brisbane too, actually. When I was a child. Gotta laugh about the fact that *now*, as an adult, I want Australian black opal, Australian South Sea pearls, and Australian pink diamonds, from quite literally across the globe

3. As I understand it, conchiolin is not a specific substance, just a cover-all name for whatever organic material holds the aragonite plates together. So it could vary in composition, and hence in RI. But other relevant properties could also vary, e.g. the absorption or the scattering. It would be good if someone could directly measure these things.

There is another possibility. Look at figure 4b. The scan taken at point 3 shows less regular layering than at points 1 and 2. This could plausibly be washing out the interference colours. I’m also wondering about the white spots: are they defects in the nacre, or are they just artifacts of the preparation?

So altogether, ‘a little salt’ is certainly in order. But figures 2b and 3c do seem to support an interference-based story.

Agreed. And a number of other studies support this as well. And to your point about less regular layering - seems to be ubiquitously accepted that less evenness in aragonite tablet shape, structure, arrangement, and layer thickness yields both lower interference brightness and fewer interference colours. Meaning that aragonite is driving the interference. That makes sense to me. And guess that makes conchiolin the backseat bl*ghter

It's just odd that noone else seems to even discuss conchiolin refractive index - or even conchiolin composition, I had the same thought - as variable. I've not seen a single thing about why it might differ for different oysters or different conditions! Maybe it all goes back to why nacre exists at all, and how the protein matrix best protects the oyster..? Also - I'm mentally assuming that the nacre that's secreted to form a pearl has exactly the same composition as the nacre that the oyster creates its shell with, because both depend on the host - host health and environment and genomics - but I've not got substantiation for that.

Nicole Fan's GIA email is listed on this article. I don't want to be the rando weirdo who emails out of nowhere but I might call GIA NY and see if she's contactable. There must be something somewhere.

 

[katbran]

Paspaley's Flagship in Sydney did have a case ( small ish) that had beautiful Tahitian earrings - studs - and I believe a strand or two. But obviously there just to cover some bases... there are no Tahitian farms here . There is an Akoya farm just North of Sydney - Broken Bay Pearl Farm ( now a joint venture with Cygnet Bay in Broome. )

Back to Keshi - the farmers certainly know which are Keshi . It's once they head out into the rest of the pearl chain that small baroque may be added in to swell the numbers and profit.

 

[bright&shiny]

@yssie , thanks for such a great thread, information, analysis and discussion. This is fantastic- I’m dedicating next week to reading the papers!

 

[pearlsngems]

Regarding Fijian pearls, this information is from the CPAA Pearls As One course:
https://www.pearlsasone.org/courses/84220/lectures/1438698

"Seven varieties of black lips are native to different parts of the world. French Polynesia hosts the most common variety, Pinctada margaritifera cumingii, which is used almost exclusively in the production of Tahitian pearls. Fiji is primarily populated with the Pinctada margaritifera typica variety. The typica is a smaller pearl mollusk with distinctly different coloration around the lip of its shell, often a striking orange rather than the dark colors of the cumingii. By selectively breeding the native typica black lip, Mr. Hunter succeeded in producing a new type of black pearl."

 

[yssie]

Regarding Fijian pearls, this information is from the CPAA Pearls As One course:
https://www.pearlsasone.org/courses/84220/lectures/1438698

"Seven varieties of black lips are native to different parts of the world. French Polynesia hosts the most common variety, Pinctada margaritifera cumingii, which is used almost exclusively in the production of Tahitian pearls. Fiji is primarily populated with the Pinctada margaritifera typica variety. The typica is a smaller pearl mollusk with distinctly different coloration around the lip of its shell, often a striking orange rather than the dark colors of the cumingii. By selectively breeding the native typica black lip, Mr. Hunter succeeded in producing a new type of black pearl."

Thank you!! This is great to know!

 

[yssie]

Regarding Fijian pearls, this information is from the CPAA Pearls As One course:
https://www.pearlsasone.org/courses/84220/lectures/1438698

"Seven varieties of black lips are native to different parts of the world. French Polynesia hosts the most common variety, Pinctada margaritifera cumingii, which is used almost exclusively in the production of Tahitian pearls. Fiji is primarily populated with the Pinctada margaritifera typica variety. The typica is a smaller pearl mollusk with distinctly different coloration around the lip of its shell, often a striking orange rather than the dark colors of the cumingii. By selectively breeding the native typica black lip, Mr. Hunter succeeded in producing a new type of black pearl."

Okay confession, I had to look up what a “variety” is. I, unlike @lissyflo, have no genetics knowledge whatsoever Apparently animals within the same species can interbreed and produce fertile offspring. The term “variety” seems to be reserved for plants, and the fauna equivalent is “subspecies” - so both normal Tahitians and Fiji pearls are the same genus (Pinctada) and species (margaritifera), but are different subspecies… Subspecies have evolved differently for different ecosystems and seems like they can look pretty dang different, too!

Here’s one definition. Prob not the best out there but first one I found that made sense to me.
http://museum2.utep.edu/mammalogy/species.htm

Edit: About subspecies and humans. TLDR: Different human races shouldn’t be thought of as subspecies.

Biological Races in Humans - PMC

Races may exist in humans in a cultural sense, but biological concepts of race are needed to access their reality in a non-species-specific manner and to see if cultural categories correspond to biological categories within humans. Modern biological ...

www.ncbi.nlm.nih.gov

 

[Starstruck8]

Let me make sure I'm following - d'you mean these pics?


I think the enhanced interference pics are using the angle of the normally-lit pics as face-up - the Area II pics match up with the red, and assuming they did the same thing for Area III. Although I don't see nearly as much green in the normally lit pearl at area III. Is this what you're referring to though?

Yes, that's what I meant. But I wasn't thinking or looking hard enough. (That happens quite often...) What worried me was the greenish zone that seems to run right around the pearl (II below):


This differs from the bullseye pattern of their model. The 'interference enhanced' picture does not cover enough area to give a good comparison.

But, thinking about it a bit more, it would make sense if the aragonite plates were thicker in area II than in the rest of the pearl. This is consistent with the scans shown in figure 4b, which show wider spacing at point 2 than at point 1. So the model in the paper still seems plausible.