GIA Updates Pearl Classification System The lab has adjusted the scale it uses for nacre grading.

he Gemological Institute of America has updated its pearl classification system, adjusting the scale it uses for nacre grading on its pearl reports. 

The lab will evaluate the nacre of a pearl, strand, or other item based on the degree of eye-visible movement—or nacre variation—found on either the surface or sub-surface layers of nacre, in addition to the post-harvest condition, including wear, damage, modifications and treatments, and trade standards for thickness.  

The nacre will be classified as “excellent,” “very good,” “good,” “fair,” or “poor,” and the new scale will be listed on all GIA pearl reports. 

Previously, GIA classified nacre as “acceptable” or “unacceptable.”  

"Acceptable” denoted expected commercial nacre quality in terms of thickness, layering, and condition, the lab said, while “unacceptable” indicated poor quality nacre that may impact durability, such as thinness, chalkiness, or damage.

In developing the new scale, GIA examined an assortment of pearl samples with varied surface and sub-surface features that can indicate differences in nacre layering and continuity during a pearl’s growth. 

“Nacre formation plays a critical role during a pearl’s growth, as its structure influences other value factors such as size, shape, luster, and surface quality. Nacre thickness and continuity also affect the pearl’s durability,” said Tom Moses, executive vice president and chief laboratory and research officer at GIA. 

“This update on the nacre quality scale provides improvement to the existing nacre quality description for the GIA 7 Pearl Value Factors [size, shape, color, nacre, luster, surface, and matching] classification system that better serves our clients.”

Due to the update, the lab said most pearls submitted will now be classified as having “good,” rather than “acceptable,” nacre.

The new scale was prompted by observations and requests from members of the global pearl trade, GIA said.