[DrTKStern]

Originally Posted by DrTKStern

Hello, All,

I would like to reopen discussion of the topic of non-bead nucleated pearls now that GIA has issued a monograph on them.

Here is part of the issue. I have a 20mm white round that was reported by one major lab as natural. I sent it to another lab and was told it is non-bead nucleated cultured pearl. It went to a third lab which could not make a call.

When it comes to very large pearls, to believe in the theory of non-bead nucleated, we must believe the following:

1. At a pearl farm, an oyster was implanted with a bead or piece of tissue.
2. Sometime before harvest, that oyster spit out the bead or digested the piece of tissue, so the pearl sac collapsed, but the irritation of the process continued to be enough to cause the oyster to continue making the pearl.
3. That the rejection of any bead occurred before nacre enclosed the center of the pearl with a hard layer...which must take place very early on.
4. That the rejecting oyster escaped detection by xray, etc. at the pearl farm.
5. That the oyster escaped the standard racks of the pearl farm and fell to the bottom in shallow water. Or that the pearl farmer moved it to some other location, anticipating a harvest in many, many years of an oyster not fed except by natural processes.
6. That for the next 15 years the pearl grew in that oyster just below the cultured racks and was never noticed or investigated by the SCUBA divers that are always in the water. Little pearls might be just 3-6 years, but great big ones are MANY years.
7. That 15-20 years after rejecting the man-placed irritant, the divers decided to harvest this oyster.
8. That after harvesting, the pearl farmer decided to try his luck by putting the pearl on the market as a natural.
9. That the resulting Non Bead Nucleated pearl is so nearly natural in its interior make-up that laboratories have difficulty being sure.
10. That although no one admits to using tissue to culture saltwater pearls, it must be done.
11. That the laboratories can be sure that some tiny tissue nucleation creates a wholly different xray appearance than non-human intrusion by a small parasite. I am reminded of one pearl I have that has the skeleton of a fish inside it and is the subject of a GIA report.


I would really appreciate criticism of this flow scheme to correct any errors of assumption.

Sincerely,
Tom

Dear All,

Now I want to further refine the category of pearls that confuse me in that I do not understand how they can be called cultured.

Let's consider 2 very large pearls, say 20 mm. The first has an interior void that occupies 25% of more of the pearl by volume, with several mm. of nacre. On xray, the finding is a very large black hole surrounded by nacre. This type of pearl I do not want to talk about now.

The second type of 20mm is 99% nacre. On xray no black void can be seen, only the finest of central lines which sometimes can require 20 or more views to detect. It is this type of pearl I would like to have someone explain in detail as to its formation and why it is cultured, i.e. at what stage did the hand of man become involved, and answer my questions above. I know the theory that the fine line represents the residuals of a collapsed pearl sac. Now, considering the realities I posted above, how can one call such pearls cultured?
Please, all of you scientists, explain why the laboratories who see this fine line believe it is proof of culture.

Tom

[DrTKStern]

Hi Tom,
thanks for your e-mail.
actualy the lab are not sure 100% when they get a pearl
without some evidence of structure looking like a natural
pearl. So they will not give the cert. What I understand is
when they look at old pearls they always find nice structure. This must be a good reason to think that new
pearls are probably originated differently than old one....
In any case the lab prefer not taking the responsability in
case of doubt....
best regards

This answer came from a highly respected pearl trader in Europe. From experience, I know that labs, when in doubt, usually call the pearl cultured...not INDETERMINATE. After all, we have paid up to $600 per pearl for analysis, so that getting an indeterminate answer raises doubts about why we paid in the first place.

This man says that unless there is internal structure like that seen in old pearls, new pearls are assumed to be coming from some non-natural process; and the labs therefore back into calling it cultured if they cannot see "OLD STYLE" findings.

To this argument, which fails to explain any of the serious questions I raise, I would counter in addition that we have recently had the opportunity to study some very old pearls. With aging, splits occur in the layers of the pearl, which may not be found in fresh pearls that have their 3-5% moisture content. A fresh pearl may not show the characteristics of an aged pearl.

Best to all,
Tom

[GemGeek]

The trader is right about the labs. I have seen and discussed microradiographs with lab staff. They are saying if there is any evidence of a line or pear-shaped void, there is evidence of expellation, so they will call it cultured. What is to say that the oyster did not expel natural foreign matter and therefore would be a natural pearl?

Certainly, it would be preferable to see the call of indeterminate, rather than cultured, if it really is indeterminable. For natural pearl dealers, this is frustrating beyond belief, as a pearl must be submitted to multiple labs. How can someone market an expensive natural pearl without a lab report and realize a decent profit?

Labs are concerned with liability, a legitimate concern.

[Pearlgully]

I have a question. Using the above example of the 20mm pearl that is 99% nacre; if the pearl is accidently dropped, can the "shock" (for lack of a better word) of hitting a hard floor, cause a line in the inner nacre, assuming there was no line prior to dropping the pearl?


Gail

[DrTKStern]

Originally Posted by Pearlgully

I have a question. Using the above example of the 20mm pearl that is 99% nacre; if the pearl is accidently dropped, can the "shock" (for lack of a better word) of hitting a hard floor, cause a line in the inner nacre, assuming there was no line prior to dropping the pearl?


Gail

Hi, Gail,

The type of cracking would be unlikely I think.

Tom

[DrTKStern]

Originally Posted by GemGeek

The trader is right about the labs. I have seen and discussed microradiographs with lab staff. They are saying if there is any evidence of a line or pear-shaped void, there is evidence of expellation, so they will call it cultured. What is to say that the oyster did not expel natural foreign matter and therefore would be a natural pearl?

Certainly, it would be preferable to see the call of indeterminate, rather than cultured, if it really is indeterminable. For natural pearl dealers, this is frustrating beyond belief, as a pearl must be submitted to multiple labs. How can someone market an expensive natural pearl without a lab report and realize a decent profit?

Labs are concerned with liability, a legitimate concern.

Hi...Expellation...how does that happen and then grow a 20mm pearl? For now, I'm just talking about pearls that are almost entirely nacre, no void visible...multiple views to see any line. By what process is such a pearl cultured? See my logic above. I want someone to explain to me in what particulars my thinking is incorrect.

Thanks for comments.

Tom

[GemGeek]

Personally, I can't see how such a pearl could be cultured, without leaving a telltale void.

[Caitlin]

Originally Posted by Pearlgully

I have a question. Using the above example of the 20mm pearl that is 99% nacre; if the pearl is accidently dropped, can the "shock" (for lack of a better word) of hitting a hard floor, cause a line in the inner nacre, assuming there was no line prior to dropping the pearl?


Gail

My daughter's Bahraini pearl ring has a line under the surface like that. It is natural to the pearl as far as I know. I've posted the ring before but I'll go back and see what other pictures I have of it.

Remember Douglas's bashing test? Where he took Cortez pearls and banged them on the floor repeatedly? Pearls are resistent to banging but can be damaged through abrasion and scratching.

That line is small in width and depth and only seems to affect a couple of layers of the pearl, so maybe the oyster jiggled enough to change the refraction from that point on?

[Lagoon Island Pearls]

Originally Posted by Caitlin

My daughter's Bahraini pearl ring has a line under the surface like that. It is natural to the pearl as far as I know. I've posted the ring before but I'll go back and see what other pictures I have of it.

Remember Douglas's bashing test? Where he took Cortez pearls and banged them on the floor repeatedly? Pearls are resistent to banging but can be damaged through abrasion and scratching.

That line is small in width and depth and only seems to affect a couple of layers of the pearl, so maybe the oyster jiggled enough to change the refraction from that point on?

A lovely piece, Caitlin.

It appears to be an interruption, as opposed to a "jiggle". The edge of the layer has a distinct, thicker and rounded margin as opposed to a crack or fracture.

I've observed this in several of my naturals too.

[GemGeek]

I was thinking of the line that shows up in the center of the pearl in microradiography, but that internal line is an interesting feature. Tell your daughter any time she gets tired of that ring, I'm ready for adoption into the clan!

[Caitlin]

I was making up what I was saying to describe what I see, so thanks for the proper term. How does an "interruption" happen? From a jiggle?

[Lagoon Island Pearls]

Originally Posted by Caitlin

How does an "interruption" happen? From a jiggle?

Haha, perhaps.

Actually, any environmental stress can cause an interruption. Storms, siltation, pollution, relocation, algae blooms... to name a few. In the case of your photo, it's quite apparent the seasonal growth during that one year was incomplete. Likely, the pearl sac never fully formed, or was occluded by gas or pressure.

Seasonal growth in pearls is much like trees, which have wider summer growth rings next to narrower recessive growth. The thicker brigher nacre over top of the lighter, finer nacre certainly indicates a "high season" interruption of some kind.

[Lagoon Island Pearls]

Originally Posted by DrTKStern

By what process is such a pearl cultured? ........ I want someone to explain to me in what particulars my thinking is incorrect.

1- Percentages of nacre or voids are not primarily conclusive factors.

2- Hatchery conditioned, spawned and spatted bivalves are cultural events, even before a pearl is formed.

Too often, the scientific value of an object is greatly reduced when it's no longer "in situ". The same basic rules apply to biology, as they do in archaeology and paleantology (among others).

Collectors greatly increase value, when there is provenance, but scientists often ignore provenance, unless they gathered the specimens themselves, under specific terms of reference.

[smetzler]

Originally Posted by Lagoon Island Pearls

Seasonal growth in pearls is much like trees, which have wider summer growth rings next to narrower recessive growth. The thicker brigher nacre over top of the lighter, finer nacre certainly indicates a "high season" interruption of some kind.

Perlus Interruptus

(A thousand apologies, but someone had to say it.)


Add: Another example, a small oval pearl offered to me as Nautilus but far more likely Tridacna, showing a similar phenomenon.

[gtown]

what do you have and do you have a price list?