Tom Stern's natural pearls

[pearl guide]

Re: Arco Valley pearl. I just remembered, it was taken off the block before the auction due to a death or illness in the family that owns it.

 

[DrTKStern]

Are Tridacna Pearls? GIA says so.

Are Tridacna Pearls? GIA says so.

A number of members stress that the Pearl of Allah is not a pearl but instead a simple concretion of material from inside a Tridacna gigas. This object below is a perfectly spherical, 50+ carat, high gloss, porcelaneous material certified by GIA as a natural pearl, saltwater, no treatment, mollusk T. gigas. Is GIA taking a different position from Pearl-Guide by calling a T. gigas product a pearl? Who is right?

Tom Stern, MD

 

[SteveM]

While the photo is missing, the description is surely of a gem quality piece.

The comments to which you refer primarily defend the official definition of 'pearl' as being composed of concentric nacre and conchiolin deposits, produced by a bivalve. Non-nacreous 'concretions' tend more towards the family of bezoars (kidney stones, etc), although they can rise above their calling in the case of highly-mirrored, symmetrical and spectacularly colored and flamed items such as conch, melo melo, quahog, and your round, huge, lustrous T. gigas.

Then there is nacreous abalone, from a gastropod, the baroque shapes from the intestinal tract very much in the manner of bezoar stones.

The Pearl of Allah is simply an insult to the world of pearls for its dire ugliness, rising above nothing from an aesthetic standpoint.

CIBJO has things pretty well defined for themselves. Perhaps Jeremy can speak officially for GIA.

 

[Valeria101]

By the current definition of a pearl (calling for 'concentric layers of nacre') that odd Tridacna concretion does not qualify, does it?

 

[DrTKStern]

While the photo is missing, the description is surely of a gem quality piece.

The comments to which you refer primarily defend the official definition of 'pearl' as being composed of concentric nacre and conchiolin deposits, produced by a bivalve. Non-nacreous 'concretions' tend more towards the family of bezoars (kidney stones, etc), although they can rise above their calling in the case of highly-mirrored, symmetrical and spectacularly colored and flamed items such as conch, melo melo, quahog, and your round, huge, lustrous T. gigas.

Then there is nacreous abalone, from a gastropod, the baroque shapes from the intestinal tract very much in the manner of bezoar stones.

The Pearl of Allah is simply an insult to the world of pearls for its dire ugliness, rising above nothing from an aesthetic standpoint.

CIBJO has things pretty well defined for themselves. Perhaps Jeremy can speak officially for GIA.

Thanks, that is great information. Can you direct me to the CIBJO definition. I looked through their website but cannot find their precise wording.
Tom Stern,MD

 

[SteveM]

Thanks, that is great information. Can you direct me to the CIBJO definition. I looked through their website but cannot find their precise wording.
Tom Stern,MD

CIBJO Pearl Book, pdf version. Doublechecking, both nacreous and non-nacreous pearls are recognized and defined, so indeed Allah is a pearl, albeit an extremely ugly one!

 

[Caitlin]

Hi Steve
Thanks for the CIBJO answer on the Pearl of Allah. I'll concede that it is a pearl, but it is also a calcareous concretion that looks like a porcelain brain.

BTW, the Pearl of Allah has not been authenticated since 1939- so it could be a porcelianious copy. Many copies are known to exist in various museums and were apparently passed out to donors of the pearl of peace foundation, or maybe it is the pearl for peace. Those two names belong to the original buyer, Hoffman, and to a secondary buyer Barbish and I forget which is which.

 

[SteveM]

BTW, the Pearl of Allah…could be a porcelianious copy.

That's the thing about calcareous concretions. We all have them in our bathrooms, by Modern Masters such as K?hler and American Standard (and Roca, for those Spaniards among us!). The Chinese, then Medieval European alchemists such as those near Meissen, Saxony improved upon nature.

I was on the verge of proclaiming the non-violability of nacre/aragonite's iridescent qualities, but then remembered the quite effective use of fish scales by the likes of Majorica. And returning to porcelain—there are the iridescent glazes developed in the late 19th century by Tiffany and contemporaries to mimick antique glass. Here is a period tea cup by Upper Silesia's Ohme we came across quite recently in a second-hand store outside of Seattle.

I have no idea where I'm going (or where I went) with this. Consider it recreative diversion…

 

[Valeria101]

I was on the verge of proclaiming the non-violability of nacre/aragonite's iridescent qualities, but then remembered [...]
I have no idea where I'm going (or where I went) with this. Consider it recreative diversion?

There was a thread about 'iridescence' with a horde of other gems showing iridencence of some kind... somewhere 'round here. No shortage! Pearl keep the property pleasantly mysterious and hold the lead, I'd say (this is a pearl forum after all!)

 

[SteveM]

Pearl keep the property pleasantly mysterious and hold the lead, I'd say

In like manner to the husband of Antoinette Matlin (from her intro), pearls are unique among gems in holding my attention?perhaps for the mystery as you suggest?

?but your opal sure has some 'orient'!

 

[Valeria101]

If it wasn't for pearls and the endless discussion of what 'orient' is and what is it worth in them... I am quite sure I would have missed much of the special interest iridescence holds in other ornamental / precious stones. Opal isn't easy to overlook, of course, but THESE?

It took one outstanding example though to send the message - and even how! (mid of second row HERE, of course)


Still not pearls! Wouldn't even call that 'orient'...

... however, in Other Mineral's Cases similarities go down to the structure along with The Looks.

Iris Agate - Horse Mountain, Tennessee

The property is always interesting and a sales point. Makes it harder to concede that orient could ever be 'denied' recognition as the crucial quality of pearls, when similar qualities manages to sell otherwise relatively base materials indeed

 

[SteveM]

Thanks so much?that agate is truly amazing.

Brings us all the way back to non-nacreous calcareous concretions, in which iridescence ('orient') is an impossibility?pending discovery of an image to the contrary!

 

[Valeria101]

...that agate is truly amazing.

Yeah... Too bad the effect is so subtle; barely shows when the stones are worn: you need a thin slice getting light from the back The orient of pearls is very obvious by comparison. What I like in the rainbow of agates is that the effect has depth - as it does on pearls and MOP, not just a thin layer as in the 'rainbow' fractures in crystalline quartzes, etc.

GIA has published some striking pictures of transparent, colorless agate slices with relatively strong rainbow effect. I have never found such material on offer (those might have been just very thin slices of the usual pale yellow - just dunno.)

 

[DrTKStern]

Iridescence

Iridescence

If it wasn't for pearls and the endless discussion of what 'orient' is and what is it worth in them... I am quite sure I would have missed much of the special interest iridescence holds in other ornamental / precious stones. Opal isn't easy to overlook, of course, but THESE?

It took one outstanding example though to send the message - and even how! (mid of second row HERE, of course)


Still not pearls! Wouldn't even call that 'orient'...

... however, in Other Mineral's Cases similarities go down to the structure along with The Looks.

Iris Agate - Horse Mountain, Tennessee

The property is always interesting and a sales point. Makes it harder to concede that orient could ever be 'denied' recognition as the crucial quality of pearls, when similar qualities manages to sell otherwise relatively base materials indeed

Yes, for me in grading pearls, orient must be present to a striking degree for a natural to be AAA. Without it, at best only an A. The color of that agate was one of the most pleasing colors I have ever seen, in my whole life. Thank you for that.

The phenomenon of orient stems from prismatic physics, but it seems as if irridescence is light that comes from within, deeper.
Tom Sterm, M.D.

 

[SteveM]

The phenomenon of orient stems from prismatic physics, but it seems as if irridescence is light that comes from within, deeper.

Thanks so much. Not sure if the concept is any clearer (in the near total absence of concrete examples), but a discussion of orient vs. iridescence is clearly at home on this thread. The term 'orient' has its origin in natural pearls from exotic (Eastern) waters, and orient in classical times was reputedly the rarest of attributes.

Either modern pearling technology has improved upon nature to such a degree that what was formerly rare is now commonplace, or the term has been degraded by the industry for purely commercial reasons.

I'm just asking the questions?don't mean to be an irritant (at risk of nacre coating!).

 

[GemGeek]

I'm just asking the questions?don't mean to be an irritant (at risk of nacre coating!).

Thanks for making me snort!

 

[J Marcus]

Having never understood the term "orient," I spent a few hours last week reading and re-reading and trying to come to an understanding of what has been written about orient on the Pearl Guide. I think that there is a fairly complete discussion of orient in this thread:

https://www.pearl-guide.com/forum/cultured-pearls/1604-orient-color.html

The high point of this thread, I believe is to be found in a post on pg. 3 by valeria, complete with illustrations, graphs, etc.:

https://www.pearl-guide.com/forum/cultured-pearls/1604-orient-color-3.html

I must timidly and respectfully submit, not being an expert in pearls myelf, but having a good grasp of science in general and also a fair grasp of the area of semantics, that the term orient is one lacking any real value and probably causing far more trouble than it is worth in the field of pearls. Although it is not too unusual for the same term to have different meanings in very different areas of knowledge, I simply cannot see "orient" serving any real purpose when used within the limited world of pearls when it is supposed to mean different things for different types of pearls. In the end, I believe that it can in general only serve to dis-inform and confuse the pearl marketplace. When a consumer learns a definition for the term in regards to one kind of pearl and then finds out that it refers to a different quality in another kind of pearl, it may, will and probably has contributed to distrust and negative feelings towards even very ethical pearl vendors. With the huge headaches coming from such problems as dishonest vendors touting their cultured pearls as "natural." (among other issues) I think that those of us who adhere to standards of honesty and full disclosure risk loosing the trust of customers who, having come to think of us as trustworthy find us using terms whose definition is maleable or, in their eyes perhaps, "slippery." I propose that a good, possible solution to this quandry would be to either 1. Eliminate the use of the term "orient" in the commerce of pearls, or 2. Expand the definition of "orient" to be the equivalent only of irridescence whether coming from under the surface of pearls or coming from the surface only. If we need to discuss a difference, we will be better off using a more descriptive approach such as referring to irridescence from the surface or irridescence from below the surface. If we continue to use a changeable definition of "orient," then it is my opinion it will ultimately only cause us harm.

Respectfully,
Marc

 

[Valeria101]

The phenomenon of orient stems from prismatic physics, but it seems as if iridescence is light that comes from within, deeper.
Tom Sterm, M.D.

Some gemology papers explain iridescence through thin film interference - it is the case for rainbow agates and garnet.

I have found similar models developed to explain pearl color (science goes where cash comes from...no surprise there). THIS appears to be going the whole hog (haven't looked into it yet).

 

[Valeria101]

... a discussion of orient vs. iridescence is clearly at home on this thread.

Love both terms to death

... did anyone care to define the difference between these? I'd think it might fit something from real life: the 'directional' vs. 'non-directional' nature of that rainbow display. Those agates make the point beautifully. And if we were talking about opals, that difference would be crystal clear (HIC!) and well accepted. Since the surface of pearls is always convex, the distinction is rather trickier for them.... Hm....

What good would it do to separate 'orient' fro 'iridescence' as technical terms?

 

[SteveM]

What good would it do to separate 'orient' fro 'iridescence' as technical terms?

That orient should not be equated with iridescence, as Aragonite platelets are inherently iridescent (.5 micrometers avg thickness roughly equivalent to visible light wavelength, resulting in diffraction). So it is believable to me that orient originally must have meant something else (and still does for some purists), even if orient is coincident in many if not most cases with iridescent qualities!