Pearl Grading | Luster
Pearl Grading System
Pearl grading is very similar to the 4C's of diamond grading in that it takes into consideration several categories of qualitative comparisons. The pearl grading system consists of five main parts. They are:
5. Pearl Size
Generally speaking, the larger the size of the pearl, the greater its value. Large pearls not only require larger oysters to produce them, but they require much more time to develop inside the oyster. An average sized pearl can take 2 to 3 years to develop. Significantly larger pearls can take twice as long to grow. Additionally, it is very difficult to maintain a perfectly spherical shape while the pearl develops. This is why very large round pearls are extremely rare and valuable.
A pearl's size is measured by its diameter in millimeters. Sizes range from 1 millimeter or less, to 20 millimeters or 3/4 of an inch for the largest black Tahitian pearls. The largest black pearl ever found was about 25 millimeters (1 inch) in diameter.
The most common size range for pearls is from 7 to 7.5-millimeters in diameter. Akoya pearls greater than 8 millimeters are considered extremely rare and valuable. The largest pearl an Akoya oyster can produce is around 9 or 10 millimeters in diameter. Pearls larger than 10 millimeters are generally black Tahitian pearls, white South Sea pearls, or freshwater pearls.
Each of the main types of pearls has a common range of sizes:
- Freshwater pearls typically range from 3mm up to 12mm
- South Sea or Tahitian Pearls range from 8mm up to 18mm or larger
- Akoya pearls range from 4mm to 10mm
Pearls that are in strands are rarely uniform in size. Akoya pearls will always have a .5mm differential within an individual strand according to international standards. Freshwater pearls have an allowable size variance of a full millimeter per strand. A strand of 8mm freshwater pearls may be measured between 7mm and 8mm in size.
Tahitian and South Sea pearls are typically measured individually. To be considered a "uniform" strand there may still be up to a 1mm differential from the smallest pearl near the clasp to the largest pearl at the center of the necklace. A 9mm to 10mm strand of Tahitian pearls is considered a uniform strand, but an 8mm to 10mm strand is considered slightly graduated.
Per industry standards, a strand measuring 7.5mm, will actually be composed of pearls measuring 7mm to 7.5mm. This size variance should be noted in any good appraisal or accurate description of the pearl strand.
Pearls of the same quality ranging in size from 5.5mm to 6mm do not vary greatly in price. It might only be a 10% to 20% increase for the next 0.5mm to 1mm in size. An increase in size to 8mm or 9mm will cause the price to increase by 50% to as much as 100%.
Pearl Necklace Styles
While most other necklaces are simply referred to by their physical measurement, strings of pearls have their own set of names that characterize the pearls based on where they hang when worn around the neck. The names for pearl necklaces are:
- Choker - Nestles at the base of the neck
- Collar - Rests directly against the throat - can be multiple strands
- Princess - Comes down to or just below the collarbone
- Matinee - Falls just above the breasts
- Opera - Long enough to reach the breastbone or sternum
- Rope - Any length that falls down further than an opera
Necklaces can also be classified as uniform, where all the pearls are the same size, graduated, where the pearls are arranged in size from large in the centre to smaller at the ends, or tin cup, where pearls are generally the same size, but separated by lengths of chain.
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