What is a Certified Diamond?

A certified diamond is one that has been put through a series of tests and undergone quality analysis by an established laboratory dedicated to performing diamond verification and grading (as opposed to non-certified diamonds). There are many laboratories around the world that provide these services and produce documentation commonly referred to as a diamond certificate, or in the trade simply as a “cert”. Certain laboratories cater to select markets, regions or even specific countries. A few laboratories have a global reputation and the focus of this article will be on two of these – GIA (Gemological Institute of America) and AGS (American Gem Society Laboratories). These two labs are arguably the most important in the world, but for very different reasons.
The primary purposes of diamond certification are to identify the diamond, revealing any treatments or enhancements that might have been applied to it, and to grade different aspects of the diamond in a way that an understanding of its overall quality is achieved. Most high quality laboratories that are regarded as reputable in the industry conduct similar types of analyses, but there are important differences. Depending on the level of understanding a customer is seeking, some labs are far superior to others, especially in the area of cut quality analysis.
Today, with true synthetic diamonds on the market as well as diamonds treated by high temperature and high pressure techniques, the first order of business of any reputable diamond lab is to verify natural origin and detect treatment. A laboratory that does not have the equipment or expertise to provide this service should not be relied upon.
AGS Diamond Certificate
GIA Diamond Certificate
AGS and GIA Diamond Certificates (click to enlarge)
The basic functions of the lab begin with detailed weights and measurements. The diamond is carefully weighed on a regularly calibrated digital scale, and measurements are taken by a sophisticated non-contact digital measuring device that records angles and dimensions of all the facets on the diamond. Reporting is done on averages of multiple facet measurements, and labs do that in different ways.
GIA is the most well known gemological lab in the world. They literally wrote the book on color and clarity grading of diamonds, having created the systems used today by most labs. Clarity grading involves careful study of the diamond under magnification to observe and record internal characteristics and surface blemishes. The grade is determined by how apparent the inclusions are, and that depends on a number of factors including size, type and location of the features. The GIA clarity scale starts at Flawless and progresses down in small increments to the Imperfect grade. Color grading is done by comparison to a master set of diamonds that the lab maintains for accuracy and consistency. The GIA color scale begins at D and progresses in small increments through the alphabet. DEF are considered “colorless”, GHIJ “near colorless”. Diamonds past ‘J’ begin to show tints of yellow and browns that become progressively more obvious towards the bottom of the alphabet. Diamonds past ‘Z’ have color so distinct that they are considered rare “fancy colors” and are graded on a different scale altogether.
AGS, GIA and EGL Certificates
AGS, GIA and EGL Certificates
While color and clarity grading, as well as screening for synthetics and treated diamonds, is done in a very similar manner at both GIA and AGS, the two labs differ significantly in the area of diamond cut grading. AGS has developed a sophisticated light performance based cut grading system that is the only scientifically vetted system in existence. This system represents the most comprehensive and critical cut grade analysis done by any lab in the world. AGS is able to use their system to grade diamonds of many shapes, whereas the GIA system is limited to the round brilliant shape. In addition, the GIA cut grade system is more forgiving and lenient. Their top grade of Excellent includes diamonds that would receive the second and third grades at AGS. It is for this reason that buyers seeking the ultimate understanding of the light handling properties of diamonds they are considering for purchase show a strong preference for AGS certified diamonds. It is also why elite brands like A CUT ABOVE® Super Ideal Diamonds feature an AGS Triple Ideal certificate as a baseline requirement.
Another aspect of diamond cut quality that is important to many modern shoppers looking for certified diamonds is Hearts and Arrows patterning. The presence of a precise pattern of arrows visible from the top and hearts visible from the bottom indicates perfect symmetry of the diamond in three dimensions. Unfortunately, GIA does not provide any information on this aspect of diamond cut quality. The AGS system, on the other hand, provides for the generation of light maps including both ASET view and Hearts view. Both views are included on AGS platinum dual light map reports. The AGS system also provides for the availability of other cut related reports and light maps that can be included for a certified diamond such as the new scintillation reports just hitting the market. This report provides understanding of the diamond’s capacity for sparkle, arguably the most important aspect of diamond light performance for most diamond shoppers. In the AGS vs GIA debate it is clear that AGS is far superior in terms of diamond cut grading.
Certified Diamond
A CUT ABOVE® H&A Diamond
It is important to keep in mind that just because a diamond has undergone analysis at a major lab making it a “Certified Diamond”, that fact alone does not in any way attest to the beauty or value of the diamond itself. As they say, “the devil is in the details”. Certified diamonds whose reports contain details that are troubling or are simply lacking in detail, have to be seen for what they are. Diamonds can be sent to labs regardless of their overall quality, light performance, beauty, or value. It is highly recommended that anyone considering purchase of a certified diamond should consult with a credentialed diamond expert, such as a GIA Graduate Gemologist or AGS Certified Gemologist, who can read the report much like a doctor might read your x-ray film. Things that would not seem remarkable to a lay person can be highly significant to a highly trained professional. It is likewise highly recommended that shoppers seeking ideal diamonds with maximum fire, brilliance, and scintillation look for diamonds with light performance based certificates from the AGS Laboratories.
A final point about diamond certification relates to conflict diamonds. A diamond certificate from a lab is not the same thing as the documentation required by the Kimberly Process Certification Scheme. The “KP” is a system that documents the movement of rough, uncut diamonds as they travel from the mining areas to the cutting houses. Socially responsible shoppers seeking conflict free diamonds should get assurances and guarantees from their jewelers in order to gain peace of mind about their purchase.

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