Pearl Grading Criteria

Luster
Luster is the shine, or brilliance of reflected light from the pearl’s surface.  A pearl with high luster will have a crisp, mirror-like reflection as well as a certain glow.  Pearls with high-quality luster also have brilliant orient, or iridescence, which cannot be replicated. 

Cleanliness
Pearls that are clean have minimal blemishes on the surface of the pearl and are graded higher than pearls that are “spotted”.  While some pearls may have minor surface spots, many times they can be concealed when stringing the pearls or setting them in a jewelry design. 

Shape
Pearls come in a variety of naturally-formed shapes, including off-round, drop-shaped, button-shaped, baroque, semi-baroque, and circlé.  Because round pearls are valued for their perfect symmetry, they are generally graded higher than other shapes. Depending on preferences, other shapes may be more desirable for their unique appearance.

Size
Because large pearls are rare, any pearl in excess of the average size for each specific type of pearl commands a high price.  For example, Akoya pearls that are larger than 8mm are considered rare, as are South Sea pearls and Tahitian pearls that are larger than 15m.  A pearl's value appreciates with size, if all other factors are equal.

Color
While there is no specific grading scale pertaining to color, Tahitian and South Sea pearls with rarer hues are generally sought out and can command a higher price.  For example, golden South Sea pearls that have a deeper golden color are are more expensive than those with a fainter shade of gold.

Nacre 
Refers to the thickness of the coating covering the pearl. Nacre is the creamy, crystalline substance which the oyster secretes to protect itself from foreign debris. This is what hardens around the nucleus or foreign object inside the oyster’s body to form a pearl (see Pearl Cultivation).  The thicker the nacre, the better the quality of the pearl.

Grading System
Pearls are graded into categories primarily based on their luster and cleanliness, although all of the above-listed factors effect the value of the pearl.  We use the Tahitian grading system (based on French Polynesian government standards) using the letters A-D to denote quality, “A” being the highest grade. Other retailers may choose to use the A-AAA nomenclature, used for primarily grading akoya pearls.

A quality: Top grade, excellent luster, little or no visible imperfections on the surface of the pearl. On average, only about 5-10% of harvested pearls will be classified as A-quality pearls.  

B quality: Very good luster, more visible surface spotting, but limited to 30% of the body of the pearl
C quality: Average luster with surface imperfections on the pearl covering less than 60% of the surface area

D quality: Many imperfections on the majority of the pearl’s surface. Pearls that are lower than grade D are not marketable. 

While luster and cleanliness are the major factors affecting price, round shapes, bigger sizes and rare hues are more valuable and priced accordingly.  

      Pearl Fact

• The government of French Polynesia has set a minimum nacre thickness of 0.8 millimeters for Tahitian pearls. Pearls that do not meet this standard are not allowed to be sold.