A certified diamond means that a diamond was sent to a gemological laboratory for grading. Diamond grading consists of color and clarity as well as an evaluation of the physical proportions of the stone so there an understanding of how the stone was cut. Diamond certification not only standardizes the industry by providing irrefutable evidence of the nature of a diamond, it also provides all the information necessary for the consumer to make an informed purchase. When I am working on a diamond search for a customer, they typically ask to see the certificate. I always wonder if they truly know how to interpret all the information or if they just want to see the certificate “because they are supposed to”. Below is the breakdown of the most important parts to look at when reviewing a GIA certificate.
On a GIA certificate, the date the certificate was issued will always be at the top on the left hand side, followed by the certificate number. Depending on the date, it can give you some insight as to if the diamond is relatively new or not. Although a diamond does not age, the older the certificate, the more likely the stone was being used by someone else and could have some wear and tear. The next thing listed is the certificate number which is unique to every certified diamond. If a diamond is laser inscribed, it means that the same unique report number is inscribed on the girdle of the stone. Laser inscriptions have contributed tremendously to the integrity of the diamond business; I consider this an asset to any diamond. Any stone that is laser inscribed can be easily identified and reported if stolen. To see if the diamond you are considering is laser inscribed, you need to look at the bottom of the certificate under “additional grading information” to see if there is an inscription listed. To be clear, every certified diamond has a certificate number but it is not necessarily laser inscribed on the girdle. This is an extra feature that is a common practice but not required when a diamond is graded at the GIA.
The “grading results” section on the certificate should state the color and clarity and a cut grade only if you are considering a round brilliant cut diamond. No fancy cut diamond will ever receive a cut grade from any gemological laboratory so this is important to recognize if you are considering a fancy cut diamond.
The most difficult and possibly important part of a GIA certificate is the second column which features the profile of a diamond with all of its exact proportions as a means of a percentage of the entire stone. The two most important numbers to consider are the depth% and table % for those are key indicators of how well the diamond is cut and how well it is likely to sparkle. The depth % is the number (typically in the 60’s) placed in the middle of the diagram represented by a line extending from bottom of the girdle to the culet. The table % is the number (typically in late 50’s to early 60’s) at the top of the stone extending from one side of the facet to the other. Every diamond cut has a range of depth % and table % that is considered ideal and being able to find and interpret these numbers is important so you know the diamond was cut well, especially when it is a fancy cut diamond. These numbers are not listed independently so knowing which numbers to pay attention to can be helpful when comparing multiple certificates.
The last portion of the GIA certificate is the plot. The plot identifies the top grade setting inclusions. Many people are surprised to find out that their diamond has more inclusions than what might be listed on the certificate, this is because it is very possible to have inclusions so small that they do not affect the clarity (unless they were the only inclusions). The GIA will typically list the largest and or most prominent inclusions because those are what the clarity is judged on. The most helpful part of the plot is that it can guide you into locating the inclusions in your diamond if you ever needed to identify it.