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Thread: Cracking pearls

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  1. #1
    TahitiPearlImport Guest

    Default Cracking pearls

    I just received a 500 momme lot of Tahitians from a dealer in Shenzhen. I have been drilling them like I do all others but have been having a difficult time, especially using a .9 bit. Sometimes I hit the nucleus and it is like a rock. Sometimes the pearls basically explodes. When it is too hard and I flip it for the other side I end up with a double drill-hole. Those that explode and completely worthless.

    I have never had this problem before. I keep my bits very sharp and have been drilling for several years. The company that sold me the pearls told me that I am using an incorrect bit for Tahitian pearls. But as I said, I have never had this problem before. Can someone shed some light on this problem for me? Has anyone else experienced this before? The pearls look great! Very clean, high luster, great color. The price was great too, but I am starting to think I will be losing a large percentage.

  2. #2


    I have forwarded this question to three different pearl farms in French Polynesia. Hopefully one will answer soon. I suspect this has something to do with the nuclei described by senior member jshepherd. But I would like to hear what a farmer has to say...

  3. #3 Guest

    Default Response from Tahiti

    I also think that it has something to do with the nucleus. I will transmit
    your question to the administration département of research in Tahiti.

    Hinerava Amaru

  4. #4 Guest


    If you want that the administration département answer to your question, you should send them more information about the pearl that you buy in Hong kong. Or at least sample. Nothing can be sure. Where does your wholesaler buy the pearls. What kind of pearls it is ?
    The mail département of research is :
    I send her your mail, but you can also send her a mail.

  5. #5 Guest

    Default Answer from Research department

    Quality of the nuclei .(anglais) 0704

    Answers :

    As French Polynesia Pearl culture office we are totally concerned by your problem. Actually, several cases of broken pearls after drilling have been reported to our administration. The problem is known and most of the time due to the use of unsuitable quality of nuclei, especially nuclei made with Giant clams shell from China.
    These nuclei are harder than usual Mississippi mussel nuclei and when you drill the pearl it may cause some over heating that can lead to the pearl destruction.
    The research department is actually developing with some experts an instrument to detect the origin of the nuclei (mussel, giant clam, Bironite…). These detectors will be used to stop giant clam nuclei importation to French Polynesia as wished by the Government.

  6. #6
    jwong Guest

    Default giant clam as pearl nuclei

    Although the post was nearly two years ago, I believe that pearls cracking at the processing of drilling still exist. It is possible that the cracking is caused by incorrect drill bit. However, if you are an experience driller, the chances of cracking should be well within a small percentage. Most likely, it has to do with the nuclei.

    In fact, giant clams used as pearl nuclei will cause pearls to crack at a much greater chance than the traditional Mississippi shells. Giant clams grow at a faster rate, bigger size and thickness. Hence, one clam produce many difference sizes of nuclei, but at a lower density than Mississippi shells.

    I am very concern with this problem because my company sells pearls and manufactures our own nuclei. We are well experienced in the area and we do not have this problem because our nuclei is strictly made out of Mississippi shell.

    Although the pearls have good luster, color, quality and price, please be careful.

  7. #7
    Join Date
    Dec 2004
    near Tucson AZ


    Even though this thread is old, this is great information to bring forward occasionally. It is interesting to get a follow up post.

    What is it about Mississippi shell that is better than the equivalent from China? Aren't they all mussels?

  8. #8
    jwong Guest

    Default Cracking pearls and correction

    Quote Originally Posted by jwong
    Hence, one clam produce many difference sizes of nuclei, but at a lower density than Mississippi shells.
    I would like to correct myself from the previous post on this thread. I'm uncertain about the difference in density between the Mississippi shells and the giant clam shells. But I know from the industry that the giant clam shells are a lot cheaper than the Mississippi shells, and can produce bigger nuclei and larger amount of nuclei from one single clam than one single Mississippi shell.

    We hear from the industry that when you drill through pearls having giant clam shell as the nucleus, the pearls will crack. We have tested it out ourselves, and found that this is true. The pearl will crack from the inside, hence it will have no value.

    Giant clams from the industry mainly come from China and Vietnam, and other South Sea area.

    I'm uncertain of what the effects giant clam nuclei have on shells and pearl farms, all i know is it devalues any good pearl. This is well-known in the industry. However, some bad suppliers might mix the two different kinds of nuclei together to lower their cost without telling buyers.

  9. #9
    Join Date
    Dec 2004
    near Tucson AZ

  10. #10
    Amy M Guest


    we have had recently lots which have the cheaper nuclei. we are currently experimenting with different drill bits to see if a harder bit will fix the problem. i will post again if we find a solution but has anyone tried using other bits with any success?

  11. #11
    Join Date
    Jun 2004
    Manhattan Beach, CA


    It is not the bit that will crack the pearl, it is the heat and the pressure. If you are buying a mixed lot from a co-op(from more than a single farm) you are bound to run into 1-2 that drill like rocks. Even if you have more than 2mm coating on either side you will crack it if you do not wait for the pearl to cool and switch dull bits with fresh ones. Yes, the bits will cost you $3, but the pearl is more expensive.

    I am really unsure what causes this. I have personally examined a lot of different cracked pearls. It is not always a Tridacnae or byronite problem. I really do not know what causes it. I have found, however, that the darkest pearls have a higher ratio of "rock nuclei", and if anyone could shed light on that I would love to hear it! We have learned how to get through them but we occasionally lose one...

  12. #12
    Pearling Technologies Guest

    Default Nuclei

    I know this thread is a little old but if anyone is interested I can probably give a little more information on nuclei - clam, mussel and Bironite. The company I work for was/is a manufacturer of all these items and more.

  13. #13
    Slraep Guest


    Quote Originally Posted by Pearling Technologies

    I know this thread is a little old but if anyone is interested I can probably give a little more information on nuclei - clam, mussel and Bironite. The company I work for was/is a manufacturer of all these items and more.
    Hi PT,

    Oh yes please! Tell us more! Do you also have info about composite nuclei? Who uses them?


  14. #14
    Join Date
    Jun 2007
    Portland, Oregon. Ahe, Tuamotus.


    George is that you?
    I've used Bironite but don't like it because it's porous, not a clean finish like shell. Slraep that's not what you mean by composite huh? You're talking about glued nuclei aren't you?
    Just yesterday we drilled a strand that had giant clam (bad, bad, bad) nuclei. It's easy to spot because it's hard as hell and really opaque white. We broke 5 drill bits and cracked two pearls. That stuff really sucks.
    Josh Humbert
    Pearl farmer and Tahitian pearl farming consultant.

  15. #15
    Pearling Technologies Guest

    Default composites

    Hi Josh.....yes it's George.

    We've seen a lot of different nucleus material that have been tried. When we did a lot of grinding of reject pearls back into nuclei, we saw some weird stuff. As far as composites are concerned, I think you are right Josh. It is quite difficult to compose a material with a view to transform it into a sphere that is perfectly smooth. Even harder to try and mould a spherical shape!

    There is a company in Germany (I think) producing some pretty good quality glued MOP nuclei - mainly in larger sizes. These have been copied (or at least tried) by some Asian manufacturers with limited results. If the layers are not glued properly, other than splitting, there will be a bump or gap at the edge of each join and this can affect the layering of nacre.

    Bironite is not a composite but a natural material that is altered to improve various characteristics. Some of the stuff that you tried Josh was a little off but technology has and did get better.

    Re drilling, in all testing we did, we did find quite a variation in drilling difficulty even for mussel shell. If you drilled along the layers in the mussel shell nuclei as against into the layer, there was a difference in drilling - even on a 45 degree angle to the layers there was a difference.

    In some clam we worked with, it even drilled a little easier than mussel!

    By far and away, the best material to work with from a manufacturers point of view is clam. Many companies did use it and perhaps still do. It was just more consistent and easier to work with on our machines. Yes it was harder to drill and is a protected species but you know.....

    Of course we are really talking about the larger sizes for these alternative nuclei as the smaller sizes are fairly readily available.

    Chinese versus USA shell.....some but marginal difference. Historically all shell was from USA and prices were high. Some time ago there was even an auction held for larger sizes of nuclei due to their scarceness. This proved somewhat false and over the past 15 years, prices for nuclei have dropped considerably.

    Naturally you get what you pay for and we have always pushed the quality aspect with any of our contacts. You would be amazed what some farmers stick in their oysters!

    Hope some of this is of interest and not too much dribble!!

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