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  1. #1
    perlas
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    Default South Sea Pearls' Nacre Thickness

    Just some questions...

    1) I understand that the minimum nacre thickness for akoyas is .25mm and .8mm for tahitians. What is the minimum for south sea pearls? Anything official? Whati s currently being applied in the industry?

    2) Thick nacre makes good luster. However, I recently saw a thin nacre coating in a small baroque south sea pearl (it's in a strand) through the drill hole (I'm estimating about .5-.8mm) but the luster of the pearl is great. If I'm not mistaken, good luster also may be produced by good nacre quality aside from nacre thickness. I'm assuming the pearls were still untreated as the strand is composed of bi-colored pearls and the overtone was a bit greenish to greyish but the luster is great and looks natural. Not sure though if there is a nice polishing agent that's been applied. Any thoughts?

    3) Is Indonesia still producing much of the indicator pearls?

  2. #2
    Super Moderator Senior Pearl-Guide.com Pearl Expert jshepherd's Avatar
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    There are no standards for nacre thickness in South Sea pearl production, at least not in the way there is in French Polynesia. But the nacre is typically very thick (2-4mm), at least when not dealing with indicator pearls, which I have not seen around in a while.

    If the pearl is baroque it could definitely have thinner nacre on one side than the other, and thinner nacre does not mean the luster will always be bad (think akoya). This is a problem in Tahiti right now, with so much production going to waste because of thin areas (of baroques), even though the nacre is thick everywhere else around the pearl.

  3. #3
    perlas
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    The south sea that I saw was around 8.5mm. What's the smallest nucleus typically used in south seas? 6mm?

    In akoyas, it is plausible to attribute the luster to treatment for thin- nacred pearls. I understand that a thinner side than the other is typical in pearls esp. baroques, but the current lack of standard for nacre thickness in south seas concerns me about the durability of the product.

  4. #4
    perlas
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    May I also add that why is thick nacre associated with luster? Isn't it a reasonable assumption that luster depends on the nacre quality, not the nacre thickness?

    Think of freshwater pearls. They are almost all nacre yet there are a lot of freshwater pearls that are not lustrous at all.

  5. #5
    Valeria101
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    Quote Originally Posted by perlas
    May I also add that why is thick nacre associated with luster? Isn't it a reasonable assumption that luster depends on the nacre quality, not the nacre thickness?


    Both... I think. Structure and thickness - as you say with the example.

    And treatment is obviously more reliable way to get lustre than scouring for natural quality.

    I don't think there is any natural counterpart to the mirror shine of fake or (some) inexpensive treated pearls. Not sure how to 'show' what I am talking about here, but I am quite sure everyone has seen such examples somewhere. Think cheap!

    Anyway, just an opinion (the same as yours, I guess).

    Would add a question:

    It seems reasonable to think that a lower limit for nacre thickness that may produce the very same visual effect as on an all-nacre pearl could be determined - it should be a matter of how deep through the nacre does reasonably strong light get into the pearl. Which can't be all that deep... no matter how much more desirable all-nacre pearls might be

    Does anyone know what this thickness is for any type of pearl? (would imagine that candling half a pearl would give such result; Don't have a microscope with darkfield at hand...).

  6. #6
    perlas
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    This is the only relation I see in nacre thickness and luster --- the bead nucleus maybe seen in thin-nacred pearls. And since a thin nacre is translucent/transparent, the pearl may have a chalky appearance.

    On the other hand, I've smashed a chalky south sea with good nacre thickness!

    A lot of written resources always say good luster is indicative of thick nacre.

    However, if we think of good nacre quality/structure, maybe a thin-nacred pearl is possible to have great luster even without treatment. Doesn't great luster hide blemishes? Why can it hide a nucleus?

    Also, as I've seen in fwps, in some pearls (they're usually in the multi-colored strands), there can be that mirror-like shine when placed in incandescent/ pearl lights.. they can have that metallic mirror shine (but in daylight, you can see some depth unlike in overly treated and fake pearls).
    Last edited by perlas; 06-27-2007 at 09:31 AM.

  7. #7
    Valeria101
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    Quote Originally Posted by perlas
    ... if we think of good nacre quality/structure, maybe a thin-nacred pearl is possible to have great luster even without treatment. Doesn't great luster hide blemishes? Why can it hide a nucleus?"
    Haven't yet found any measure of what is 'too thin' to allow lustre naturally... in mm, for any type of pearl (= nacre structure) or quality. That's where the question in the previous post comes from. Since nacre is translucent... it should have different properties from different thickness. Anyone knows how this works exactly?



    Quote Originally Posted by perlas
    Also, as I've seen in fwps, in some pearls (they're usually in the multi-colored strands), there can be that mirror-like shine when placed in incandescent/ pearl lights.. they can have that metallic mirror shine (but in daylight, you can see some depth unlike in overly treated and fake pearls).
    Yes Sir! That's why we love them to death

  8. #8
    The Pearl Outlet
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    The south sea that I saw was around 8.5mm. What's the smallest nucleus typically used in south seas? 6mm?
    The smallest nucleus I've seen used in South Sea pearls is 5mm.

  9. #9
    CortezPearls
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    Quote Originally Posted by Valeria101
    Haven't yet found any measure of what is 'too thin' to allow lustre naturally... in mm, for any type of pearl (= nacre structure) or quality. That's where the question in the previous post comes from. Since nacre is translucent... it should have different properties from different thickness. Anyone knows how this works exactly?
    Maybe this link can help...at least I hope this is what you meant to ask:
    http://www.perlas.com.mx/english/orient.html

  10. #10
    Valeria101
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    Quote Originally Posted by CortezPearls
    Maybe this link can help...at least I hope this is what you meant to ask:
    http://www.perlas.com.mx/english/orient.html
    Exactly.

    I was however wondering whether there is a quantitative model/measure of the effect explained on the page down your ling... fully recognizing that it would be a rather 'hot' if not controversial thing (depending on where it came from).

    Love the 'deep lustre' wording; new to me. It sounds suggestive in the right way, appreciate the relation with the nature of the phenomenon, clear as two words can get, etc...

    Thanks for the reference !
    Last edited by Valeria101; 07-06-2007 at 03:26 PM.

  11. #11
    CortezPearls
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    Valeria,

    It wuld be extremely complex to find an equation to describe the relationship between nacre thicknes and luster. In the case of thinly coated pearls it is a no-brainer: just surface luster, mainly due to polishing.

    But when we talk about thick-coated pearls (Cortez, SSP, FWP) then we have to take into account too many variables. Each animal is said to deposit some 1-3 nacre layers per day. The amount depends on: the environment (food availability, temperature=metabolic rate, stress, etc.), the oyster's health (also influenced by the environment, but also having to do with parasites, predators, handling, etc.) and the organism's genetic make-up.
    If we were to cut a pearl in half, and inspect the nacre layers you can find all sorts of interesting data...just as dendrochronologists (the people that can "read" tree-rings) use tress and old logs-wood at archaelogical sites. Each pearl can tell a story of good times and times of sorrow. The longer the pearl was grown, the more complete its story can be.
    The pearl layers can also be of different substances, not only nacre (aragonite), but also chalky calcite, brown conquiolin, and all these will interact with each other...so every pearl bearing mollusk will have a personal story to tell, the story unfolds in its pearl and we can see that each pearl is unique...

  12. #12
    Valeria101
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    Quote Originally Posted by CortezPearls

    If we were to cut a pearl in half, and inspect the nacre layers you can find all sorts of interesting data...just as dendrochronologists use tress and old logs-wood at archaeological sites.

    ...so every pearl bearing mollusk will have a personal story to tell, the story unfolds in its pearl and we can see that each pearl is unique...

    Leaving any cold judgement aside, what you describe is so .... beautiful! All self-respecting pearls should feel flattered.

    Sure there's no exact science here, just like the one scientific method you mentioned (dendrochonology) isn't working with the same concepts of 'precision' as material science or whatever.

  13. #13
    tacy_cc
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    Smile

    From my scientist-pearl-farmer friend, she harvests her pearls in the cool months of December-Feb (Philippines). The oysters coat the pearls with a thinner layer of calcium carbonate which is shinier than a thicker coating. So whether your nucleus is big or small then that accounts for the luster, unless its treated or coated artificially.And the smallest nucleus that can be used is 2mm. I know of a philippine farm that uses 2-6mm for their virgin oysters. When they are inserted, the oysters are held in baskets where they are held upright (as in with the lips looking up) so that the oysters do not spit out or reject the nucleus. There is also a 50% mortality rate among spats in the pearl farm, so in culturing, one must really pick the spats which display the best "healthy" attributes. This assures for better genes the next time it's their turn to produce their own spat. Veddy veddy interesting huh? You should really visit a pearl farm and see for yourself..

  14. #14
    Pearling Technologies
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    My understanding was that a greater number of thinner layers refract light better than fewer thicker layers and as such, lustre is vastly improved. Some farmers have been known to drop their oysters to deeper (colder) depths just prior to harvest to partly achieve this.

    Re nuclei size, I would doubt anything smaller than about 6mm is used regularly.

  15. #15
    tacy_cc
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    Perhaps...but when i buy from this reputable farm they insist on this fact. They use it regularly because their oysters are virgin and cannot accommodate bigger nuclei..i believe they have a high mortality rate and actually produce smaller-sized specimen. This is actually due to shabby management..and also accounts for a lot of their oysters being stolen from right under their noses...