This is a great article is from the Hearts on Fire website explaining the diamond grading process…
When purchasing certified diamonds, it is important to understand how your diamond is graded so you can clearly assess the value. However, this can be much harder than it would seem.
Why? Let’s take a minute to break it all down and explain.
Diamond grading covers numerous aspects of each individual diamond’s qualities, but there are four grades which are critical to understand in the process: cut, color, clarity, and carat weight (otherwise known as the 4 C’s). There are additional ratings and measurements noted on a diamond certificate, but they generally fall under the diamond’s grade in one of the 4 Cs.
There are many diamond labs that issue certificates, but the Gemological Institute of America (GIA) and the American Gem Society (AGS) are the two most widely regarded and recognized diamond grading labs in the world. Another name you might see or hear is EGL (European Gemological Laboratory), another popular lab worldwide even though it generally falls second to GIA and AGS.
The tricky part begins when you determine which lab grading system to trust over another. Many diamond grading labs have different grading standards and produce their own grading reports (including EGL), and, therefore, some labs will be more lenient with their standards than others. However, GIA or AGS certified diamonds have earned high reputations for consistently demonstrating their commitment to high standards and stricter guidelines across the board.
For example, each GIA diamond is carefully evaluated by at least four expert gemologists who are chosen at random to guarantee an unbiased evaluation, while EGL’s grading standards are more lenient and vary among the EGL locations. As a general rule, an EGL certified diamond will compare equally in quality to a GIA certified diamond that is graded two color grades and one clarity grade lower.
As a result, while EGL diamonds may be less expensive due to their grading, GIA certified diamonds are considered more valuable and provide the consumer with more confidence in the product they are purchasing. However, this is not necessarily true, as a GIA certificate does not guarantee that a diamond is more brilliant or even priced correctly, as there are as many undesirable GIA diamonds as there are EGL.
The most important thing to remember? Not all diamond certificates are created equal. If you do opt to buy non GIA or AGS certified diamonds, always ask for credentials of the certifying lab. Brilliance and value should always be your key priorities when selecting a diamond and even the GIA makes no comment on these two most important considerations.