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Thread: Cracking pearls

  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
    julianner Guest



    Based on what I learned in Tahiti recently, I'll throw in my two cents worth here.

    I don't know if the clam shell is a darker colour than the Mississippi shell - if it is, and it's cheaper, it could explain the greater frequency in black pearls as, unlike for lighter coloured pearls, the nucleus for a black pearl does not have to be as light in colour so the farmers may think they are economising, without realising that they are causing a problem further along the chain.

    I am attaching a photo of shell nucleii that were used on the farm I visited. Any comments about whether they are clam shell or Mississippi would be appreciated by more than just me, I'm sure.

    I'll also say that I have had pearls drilled that I bought from that farm and they've been fine.

    Note, the pic shows a plastic bag of nucleii in the background and a few loose ones in my hand.
    Attached Images Attached Images  
    Last edited by julianner; 08-19-2006 at 01:22 PM.

  13. #13
    Zeide Erskine Guest


    Hi Julianne,

    Those are regular mussel shell nuclei, albeit with dark striations. Nuclei like that are considered unacceptable for white pearls, but for black ones they are fine. These mussel shell nuclei have nothing to do with the ones from tridacna gigas that are thought to cause the cracking problem.


  14. #14
    julianner Guest


    Thanks Zeide. That's exactly what I needed to know.


  15. #15
    CortezPearls Guest


    The photo of the Nuclei does seem to be from a Chinese Unionid...our experience with these beads is that they -sometimes- just "separate" at any of the brown-white bands, hence we do not use them anymore.

    The American Mussel Beads do seem to be denser and devoid of such striations (banding), probably due to lesser protein content. Maybe Gina Lattendresse could shed her opinion on the matter.

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