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Founded in 1998, GemEx pioneered the concept of scientifically measuring diamonds for light performance. Using a unique lighting technology developed by engineers called the imaging Spectrophotometer, GemEx can determine and quantify the brilliance, fire, and sparkle of every diamond they certify.

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GemEx, Fire & Sparkle Certification

GemEx Diamond Light Performance Certification

A diamond is comprised of many facets that act like mirrors. One of the ways diamonds are beautiful is the way they play with light. The more light a diamond is able to reflect with those facets, the brighter it shines. GemEx uses their patented BrillianceScope to measure how much light is returned to the eye from a diamond. The BrillianceScope takes five measurements that measure white light (brilliance), colored light (fire), and scintillation (sparkle), as well as a view that reveals the craftsmanship and symmetry of the diamond. Only diamonds that measure Very High in brilliance, fire, and sparkle on the GemEx Diamond Light Performance scale are fine enough to be Astor by Blue Nile™ diamonds.

Graded and Certified

Each Astor by Blue Nile™ diamond arrives with a brochure that includes grading information from GIA, as well as a GemEx Diamond Light Performance certificate. Full reports from both laboratories are available online for each Astor by Blue Nile™ diamond.

Diamond Characteristics Documented in the GemEx Report


Measures the percentage of bright, white light being returned to the observer.

White light passing through a diamond


Measures the percentage of bright, colored light being returned to the observer.

Colored light passing through a diamond


Measures the number of light points being returned to the observer, and how they change as the light moves.

Top view of diamond sparkle