The standard criteria
|Following the same benchmarks as those for natural pearls, cultured pearls are evaluated by two main criteria.
- The shape :
There is a large range of shapes but the four most common shapes are as follows:
- The size :
Pearl sizes are measured in millimetres by an instrument called palmer.
For pearls of high value that are not perfectly round their minimum and maximum size is indicated within a 100th of a millimetre. The size of Tahiti’s cultured pearls are usually understood to be between 8 and 13 mm, the pearls that are larger than 15 mm are extremely rare, but the truly exceptional ones can reach 20 mm. To this day the largest cultured pearl harvested is one of 23 mm!
- The weight :
The weight of pearls is most often indicated within a 10th of a gram. In the past the unit of weight used to be the grain which represents ? carat (0.2 gr). Therefore 20 grains make a gram. The momme is a Japanese unit of weight that equals to 3.75 grams; it is often used as an industry standard.
- The thickness of the mother of pearl :
This criteria which is invisible to the naked eye needs to be measured by an X ray machine. Law in French Polynesia imposes a minimum thickness of mother pearl.
- The surface quality :
Being a natural product cultured pearls are always subject to imperfections.
These imperfections might be spots, grooves, pin pricks or blisters which are more or less visible. Depending on the quantity and the position of these imperfections they are classified in 4 categories :
Two other categories exist that are at the extremes :
- Pearls known as Top Gem :
These extremely rare pearls are faultless and have exceptional surface quality.
- Pearls classified as discards :
These pearls don’t conform to the minimum requirements even to be classified as D quality. These pearls don’t have a layer of mother of pearl over the minimum 20% of the surface and so it is illegal to sell or export them.
|- The colour :
Compared to other pearls produced the world over that are usually white, Tahiti’s cultured pearls offer an extremely wide variety of colours.
Though these pearls are generally grey or dark green, which is the reason why this pearl has often been called “Tahitian Black Pearl”, they can often be bronze, aubergine, steel grey, blue, pastel or peacock. Peacock is the colour that is the most sought after, a shade of grey-green with iridescent pink overtones that remind us of peacock feathers.
- The lustre :
Difficult to define, it is the refraction of light on the surface of the pearl. It is this quality that gives the pearl its luminous aspect.
- The orient :
This quality is even harder to define, it is the refraction of light not on the surface of the pearl but though the layers of the pearl. It is the reflection of the light within the crystals which make up the layers of the pearl that mean that light seems to be emanating from the pearl.