Diamond Light Performance Certification

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. 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.

GCAL is a globally recognized gemological 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.

The signature aspect of a diamond? Its captivating sparkle. The world’s most famous gemstone has entranced people for thousands of years with its radiant and colourful reflections. This is a diamond’s light return.

Light return is measured in three categories, Optical Brilliance, Fire and Scintillation. Each of these aspects is evaluated on a scale of Poor, Fair, Good, Very Good and Excellent. Diamonds that are graded Excellent in all three of these categories provide the highest levels of light return.

What Makes a Diamond Shine?
It’s a combination of the outstanding physical properties unique to a diamond: its incredible hardness gives it an outstanding lustre and ability to shine. Precise faceting lets some diamonds shine brighter and more brilliantly than others. All diamonds start rough—cutting and polishing determines how much one reflects, refracts and releases its inner beauty.

The most true-to-life way of determining the quality of a diamond’s light return is through direct assessment. GCAL and GemEx examine how a diamond appears to the eye and the way each diamond performs in the real world, rather than relying solely on a theoretical model and mathematical analysis. Every shape of diamond can be evaluated this way.

This means that if your diamond comes with a GCAL or GemEx light performance certificate, it was evaluated independently in their lab by expert technicians who capture a series of measurements and analyzed the quantity of light return. These measurements are recorded by the images included on the certificate and the videos on the digital verification webpage.

Each is unique and specific to only one diamond: every image on a GCAL or GemEx certificate is an actual image of that diamond. No generic “sample” photos are ever used.

Fire describes the captivating, colourful sparkle that diamonds are known and loved for. It is the result of white light traveling through a diamond and being dispersed into a rainbow of spectral colours by its facets. These flashes of colour contribute to a diamond’s overall sparkle and are easiest to see as it moves.

Because of this, your GCAL diamond certificate verification page includes a video that showcases its fire. Each video is composed of 200 frames that are processed to analyse the quantity and size of coloured light return as your diamond is tipped and turned. A GemEx certificate will show multiple images at different angles illustrating the diamond’s fire.

Scintillation describes the bright flashes— “sparkle”—that are produced when a moving diamond reflects light. Our 3rd party labs measure scintillation using technology which shines a single beam of light into the centre of a diamond and captures the light return pattern as the diamond is rotated. The total number of points of light that a diamond reflects back is then calculated and compared on a scale against other diamonds of the same shape and faceting style. The more points of light refracted and reflected out of your diamond, the greater the measured scintillation.

On a GCAL certificate, the scintillation animation shows the light returned from a single beam of light when your diamond is rotated in nine positions. The scintillating images are all captured and evaluated in full on a square background and then cropped to the shape outline on the certificate and in the thumbnails.