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GCAL & GemEx

GCAL is a globally recognized gemmological authority offering a wide range of services such as premium, Guaranteed Diamond Grading Certification, Gemprint Fingerprinting, Light Performance Analysis, Appraisals, and Forensic Analysis.

GemEx, founded in 1998, 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.

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. Light Performance Certification labs measure how much light is returned to the eye from a diamond to determine brilliance (light), fire (colored light), and sparkle (scintillations, 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 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 either a GCAL or GemEx Diamond Light Performance certificate. Full reports from laboratories certificates are available online for each Astor by Blue Nile™ diamond.

Diamond Characteristics Documented In The Light Performance Report


The overall return of white light to the viewer. It is measured to thee thousandth decimal place. The white areas indicate light return/brilliance, and the dark-blue areas indicate light loss.

White light passing through a diamond


Results when white light travels through a diamond and is dispersed into its rainbow of spectral colours. These flashes of colour contribute. To sparkle and are best viewed as the diamond moves.

Coloured light passing through a diamond


The flashes of white light, or scintillation, produced when light is reflected from a diamond as it moves. This image shows the light returned from a single beam of light when your diamond is rotated in nine positions.

Top view of diamond sparkle