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  1. #16
    First-graft Pearl Senior Member Lugana's Avatar
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    Another question. Why they don't grow thicker nacre in akoyas? I mean if keeping some part of the harvest, say, 3 times longer - will it reach 1mm nacre thickness or will it be destroyed/ deformed/ spoilt etc with "overripe"?..

  2. #17
    Super Moderator Senior Pearl-Guide.com Pearl Expert jshepherd's Avatar
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    I measured a fragment and it is 0.52 mm thick. Anything thicker than 0.4 mm is considered thick and should last a lifetime of normal wear.

    Most Tahitian pearls are just slightly thicker at 0.8 mm with the only exception I've consistently seen coming from Rikitea.

    Akoya could be left in the water longer to grow 2-3 times thicker nacre but it wouldn't make sense for the farmer. Every month the shells are in the water there is some level of natural attrition, and a pearl with 1.5 mm of nacre will not sell for more than a pearl with 0.5 mm if similar quality.

  3. #18
    First-graft Pearl Senior Member Lugana's Avatar
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    Thanks Jeremy.. then I don't understand (but still worried with ) the statement about the money going into the drain if spent on akoyas.. Was it an expressive exaggeration, Cees?.. I was going to get a strand of "aurora effect" certified akoyas.. But I don't want to think it would be a waste of money or that the pearls won't last..

  4. #19
    Rare Pearl Senior Pearl-Guide.com Pearl Expert JerseyPearl's Avatar
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    Lugana, I think if you buy a quality strand, it should last a lifetime. But like anything, know your source before you buy.

    Jeremy, on your comment about Tahitians from Rikitea, you are consistently seeing much THICKER nacre, correct?
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  5. #20
    Third-graft Pearl Senior Pearl-Guide.com Pearl Expert
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    Quote Originally Posted by jshepherd View Post
    I measured a fragment and it is 0.52 mm thick. Anything thicker than 0.4 mm is considered thick and should last a lifetime of normal wear.

    Most Tahitian pearls are just slightly thicker at 0.8 mm with the only exception I've consistently seen coming from Rikitea.

    Akoya could be left in the water longer to grow 2-3 times thicker nacre but it wouldn't make sense for the farmer. Every month the shells are in the water there is some level of natural attrition, and a pearl with 1.5 mm of nacre will not sell for more than a pearl with 0.5 mm if similar quality.
    Jeremy, how thick is the nacre of Vietnamese akoya pearls? They look really beautiful and the overtones are stunning but I'm also afraid the nacre will wear out quickly when they're worn in a hot and humid climate often.
    And how do you measure the thickness of the nacre? as far as I can remember from reading the info on PG, the nacre is measured like this: for instance a thickness of 0.8mm is the total nacre which coats the nucleus diametrically. It measures like 0.4mm nacre, then the nucleus, then 0.4mm nacre again. Is this correct?

  6. #21
    Rare Pearl Senior Pearl-Guide.com Pearl Expert
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    I live in a hot, humid climate and wear my pearls everyday, as did my mother and my grandmother. I've only had my grandmother's pearls wear out, and she bought cheap pearls. And to be honest, even my grandmother's are still wearable, they just were cheap to begin with and don't look as nice as my other pearls.

    Has anyone here had akoyas wear out during their own lifetime, because I haven't?

  7. #22
    Super Moderator Senior Pearl-Guide.com Pearl Expert jshepherd's Avatar
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    the statement about the money going into the drain if spent on akoyas.. Was it an expressive exaggeration, Cees?
    Yes, it absolutely was. That is the case if you buy short-cultured, thin-skinned akoya pearls. But you can spot this easily and if you're at a show spending $30 to $50 for a strand of akoya, that's what you're buying. If the nacre is adequate, there is no reason the pearls should not last just as long as freshwater - or even longer because the nacre is not as porous.

    Jeremy, on your comment about Tahitians from Rikitea, you are consistently seeing much THICKER nacre, correct?
    Yes, much thicker. It's rare to slice something with less than 2 mm. I haven't seen this from anywhere else in Tahiti. The only pearls Hisano will slice now are from Rikitea. She hasn't been successful slicing any other Tahitians. She was successful in slicing a few pearls from Fiji though.

    Jeremy, how thick is the nacre of Vietnamese akoya pearls? They look really beautiful and the overtones are stunning but I'm also afraid the nacre will wear out quickly when they're worn in a hot and humid climate often.
    And how do you measure the thickness of the nacre? as far as I can remember from reading the info on PG, the nacre is measured like this: for instance a thickness of 0.8mm is the total nacre which coats the nucleus diametrically. It measures like 0.4mm nacre, then the nucleus, then 0.4mm nacre again. Is this correct?
    On average, Vietnamese nacre is very thick. Nacre deposition is much faster in Vietnam where the water is a lot warmer. That doesn't mean all Vietnamese akoya will last forever. The baroques with sort of "nacre splotches" that clump in thick areas but leave bead or razor-thin nacre in other areas will peel. Again, they are easy to spot and if you're at the show spending $50 on a strand of Vietnamese akoya, you know what you're buying.

    For Tahitian nacre thickness it's 0.8 mm on either side for a total nacre thickness of 1.6 mm.

    Has anyone here had akoyas wear out during their own lifetime, because I haven't?
    In 20 of selling akoya pearls, I have never heard from a client that a strand of our akoyas wore out.

  8. #23
    Natural Pearl Sciences Senior Pearl-Guide.com Pearl Expert Lagoon Island Pearls's Avatar
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    Quote Originally Posted by jshepherd View Post
    Akoya could be left in the water longer to grow 2-3 times thicker nacre but it wouldn't make sense for the farmer. Every month the shells are in the water there is some level of natural attrition, and a pearl with 1.5 mm of nacre will not sell for more than a pearl with 0.5 mm if similar quality.
    Also, the longer a pearl remains in the host there's a higher risk of losing roundness, developing bumps or dimples or the worse factor of all.... calcite. All of those will devalue what otherwise would have been perfectly round and more lustrous finishes.

    The finest pearls are borne of juvenile growth, much like children have finer skin than adults.

    Some of you might ask, why do some larger, older pearls appear lustrous? The answer is simple. Very often oversized pearls will burst from the sack. If the pearl isn't displaced too far from the original sac, it will regrow around the pearl. Although the pearl may be several years old, the newly formed sac is technically juvenile growth.

    Even the time of year is critical for harvesting. Late winter/early spring is the preferred time, because e-cells are not tired (for lack of a better term). After long summer growth periods, epithelial cells become somewhat calcitic. During winter, new cells and new growth cycles begin to produce fresher, tighter oriented, more lustrous nacre.

    For this very reason, I have suspended harvesting natural pearls during late summer months.

    One thing that's not well known is a natural process called "reversion". All living things need calcium. During times of low salinity, storms or cold weather, food sources for mollusks become reduced. When mollusks need calcium and cannot obtain it from food, they'll modify their behavior to gather calcium from their shells. This will actually remove calcitic layers from the previous summer.

    I could go on for days how this is an "indicator" for ocean acidification and climate change, but I'll save that for another thread and occasion.

    Many people believe "circle pearls" rotate in the sac, but I have more substantiated reasons to believe that's not necessarily the case. I'm certain circle pearls are partially protruded from the sac more than one time during their life in the oyster. You'll rarely see calcitic circle pearls, even if you're a discerning farmer. They're almost always highly lustrous.

  9. #24
    Pearl Enthusiast Senior Pearl-Guide.com Pearl Expert Pearl Dreams's Avatar
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    David, your posts are always informative!

  10. #25
    Super Moderator Senior Pearl-Guide.com Pearl Expert jshepherd's Avatar
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    Quote Originally Posted by Lagoon Island Pearls View Post
    Many people believe "circle pearls" rotate in the sac, but I have more substantiated reasons to believe that's not necessarily the case. I'm certain circle pearls are partially protruded from the sac more than one time during their life in the oyster. You'll rarely see calcitic circle pearls, even if you're a discerning farmer. They're almost always highly lustrous.
    Pearl rotation was a theory promoted in Hubert Bari and David Lam's book. I spoke with Mr. Bari about this just two weeks ago in Munich. He told me that his theory had been proven and that it had been filmed. This was over dinner with a group of people so we weren't able to discuss it much further, but I would expect to see something published if an experiment like he described was actually conducted.

  11. #26
    First-graft Pearl Senior Guide Member moneymeister's Avatar
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    I love this site. Learning so much and appreciate the time to teach about the pearl industry.

    I have an Akoya strand that I believe to be at least 40-60 year old and are still wonderful (another for the record). My mother's strand is 50 and going strong.

  12. #27
    Natural Pearl Sciences Senior Pearl-Guide.com Pearl Expert Lagoon Island Pearls's Avatar
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    Quote Originally Posted by jshepherd View Post
    Pearl rotation was a theory promoted in Hubert Bari and David Lam's book. I spoke with Mr. Bari about this just two weeks ago in Munich. He told me that his theory had been proven and that it had been filmed. This was over dinner with a group of people so we weren't able to discuss it much further, but I would expect to see something published if an experiment like he described was actually conducted.
    I'm not disputing rotation, merely stating not all pearls rotate on all three axis. With round pearls, rotation is observed when longitudinal and lateral growth fronts are present. Circle pearls, baroque etc. are something yet again. Rotation is the exception, not the rule.

    Pearls Are Self-Organized Natural Ratchets

    Julyan H. E. Cartwright, Antonio G. Checa, Mar, Rousseau

    Pearls, the most flawless and highly prized of them, are perhaps the most perfectly spherical macroscopic bodies in the biological world. How are they so round? Why are other pearls solids of revolution (off-round, drop, ringed), and yet others have no symmetry (baroque)? We find that with a spherical pearl the growth fronts of nacre are spirals and target patterns distributed across its surface, and this is true for a baroque pearl, too, but that in pearls with rotational symmetry spirals and target patterns are found only in the vicinity of the poles; elsewhere the growth fronts are arrayed in ratchet fashion around the equator. We demonstrate that pearl rotation is a self-organized phenomenon caused and sustained by physical forces from the growth fronts, and that rotating pearls are a - perhaps unique - example of a natural ratchet.
    Last edited by Lagoon Island Pearls; 03-12-2017 at 09:50 PM. Reason: edited to add "on all three axis"

  13. #28
    Natural Pearl Sciences Senior Pearl-Guide.com Pearl Expert Lagoon Island Pearls's Avatar
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    A good example of equatorial rotation are coin pearls or in nature any pearl in the mantle pressed against the adjacent shell. Mantle pearls are notorious for presenting with flat spots.

    While some circle pearls may rotate, it's not necessarily the cause insomuch as an effect of another scenario. A perforated pearl sac will limit or prohibit rotation on the axis of the prolapse while otherwise healthy growth is observed adjacent to remaining pearl sac.

  14. #29
    Rare Pearl Senior Pearl-Guide.com Pearl Expert CathyKeshi's Avatar
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    Fascinating! Thanks, Jeremy & Dave!
    Cathy

    CathyKeshi

  15. #30
    Rare Pearl Senior Pearl-Guide.com Pearl Expert JerseyPearl's Avatar
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    Yes, really fascinating.
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