What is a Pearl Nucleus?

The pearl nucleus is the core of the cultured pearls.

There are three products that we offer to our clients:

  • Pearl nucleus - regular products with the freshwater mussel shells as the raw materials
  • Biocoat - pearl nuclei coated with a medical layer that improves the healing process of the nucleated shells
  • Metakaku - technological enabler that impacts a unique identity to each pearl


Anything can be used as the raw material for the pearl nucleus as long as the pearl oysters do not reject, get sick or die.  As the purpose of pearl cultivation is to produce pearls that resemble closest to natural pearls, only a certain type of material is accepted.  By the industry standard, the freshwater mussel shells are the main ingredients. Freshwater mussel shells have the closest resemblance as the natural pearls and the best stability in the molecular structure.


There are four qualities that determine the acceptance of a pearl nucleus.  Each pearl farmers have different preferences on what kind of qualities they wish to receive.


The pearl sizes vary depending on the location of the cultivation site and the type of shells the pearl farmers use.  There are two measurement units that are being used - bu and gram.  "Bu" is the traditional Japanese unit for a pearl's diameter.  1 bu equals 3.03 mm.  We have produced sizes as small as 1 mm and all the way to 20 mm.


By standard, only round is accepted.  Round pearls have the highest values and they are all wanted by all pearl farmers.  In order to increase the chances of yielding perfectly round pearls, the pearl nuclei must also be perfectly round.


Stain is a natural marking on the shells.  The acceptance of stain on pearl nuclei vary between pearl farmers.  For the pearl farmers who produce Japanese Akoya and White South Sea Pearls, they ony accept white and clear pearl nuclei.  For those pearl farmers from Philippines and French Polynesia, they have a varied acceptance level for stained pearl nuclei. 


While the pearl nuclei are generally white, there maybe hints of yellow or brown due to the raw materials.  While stain occurs on a portion of the pearl nucleus, the colour itself is the general colour of the whole pearl nucleus.  Just as the acceptance for stain, the acceptance of colour follows similarly.


In here, blemish refers to any physical and irreversible deformity that occurs on the pearl nucleus regardless of causes.  In general, no pearl farmers would accept such, because any form of blemish would lower the chance of yielding beautiful round pearls.


Grading of a pearl nucleus vary between nations and clients.  Nevertheless, in general, they would grade the pearl nuclei based on the above criteria in the Quality section.  On a side note, while we encourage the adoption of an international standard for simplifying the communication, we are accustomed to the various standards that our different clients follow.  It is also possible for us to provide recommendations on what to use as well.

How to Order?

If you are interested in ordering our pearl nuclei, please provide the following information:

  • company information
  • pearl farm location
  • size
  • grade

We will return you with a quotation based on your request.

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