Diamonds Education

How to Certify Diamonds

The loose diamond certification process is an easy way to boost buyers’ confidence during the shopping process. When diamond certification is conducted by a reputable organization, such as the Gemological Institute of America (GIA), buyers can rest assured that the diamond is a genuine, natural diamond, rather than grown in the lab as a synthetic diamond. It also reveals whether or not a loose diamond has been treated.

Since no two diamonds are alike, the certification process assigns value to each individual stone. For example, the GIA uses an internationally recognized grading system to compare common attributes. This system, known as the “four C’s”, determines each certified diamond’s value by grading its color, clarity, cut, and carat weight.

Diamond Color

To determine the color of a diamond, a gemologist compares the stone to a color classification chart ranging from D (colorless) to Z (light yellow or brown). The loose diamond is compared to a set of master stones representing the colors on the chart.

Certified diamonds classified as “D” are colorless, while those graded “Z” are light yellow or brown. Since truly colorless diamonds are extremely rare, the majority of diamonds used in jewelry are designated as “H” or “I” and have a slightly yellow tint—described by gemologists as “nearly colorless”.

Diamond Clarity

Natural diamonds are formed under considerable heat and pressure, giving most of them internal or external inclusions that can impact diamond clarity. There are eleven grades of diamond clarity, ranging from flawless (no inclusions visible under a magnifying glass) to I3 (inclusions visible to the naked eye).

Much like the human fingerprint, inclusions are markings that distinguish one loose diamond from the next. During certification, gemologists plot a diamond’s inclusions on a diagram to indicate its distinctive features—those that no other diamond has—which then get added to the certification paper. This diagram helps match each diamond to the proper certification, so buyers can be sure the diamond they’re evaluating is the same one on the report.

Clarity tests also reveal authenticity, helping gemologists determine whether a diamond has been treated. Inclusions verify that a diamond is natural, rather than a synthetic look-alike. If it is determined that a diamond has been treated, that will be noted on the certification report.

Diamond Cut

While people often think of cut as indicating the shape of a diamond (i.e. square or round), the term is used during certification to describe the stone’s sparkle and brilliance on a range from “Excellent” to “Poor”. To assist with cut grading, gemologists place each loose diamond in a machine, rotating the stone 360 degrees and capturing every one of its facets to generate a sophisticated 3D model. Many factors are considered to determine the stone’s grade, including proportions, girdle thickness, culet size, polish, and symmetry.

Diamond Carat Weight

As counter-intuitive as it might seem, bigger isn’t always better when it comes to diamonds. Value is determined by all four of the “C’s”, not just its weight.

To determine carat size, certified diamonds are placed in high-tech, sealed-chamber electronic scales. The weights, which measure how close a diamond is to one carat (200 milligrams), round each stone to a second decimal place to arrive at a standard carat size measurement.

Upon completion of the rigorous certification process, a certified diamond is given a report indicating its grading for each of the four C’s, along with other pertinent information. Buyers can ask to see this report before purchasing a certified diamond; some grading agencies also allow them to check the information online.

Want to learn more about how to certify diamonds? Watch the video below, which chronicles one diamond’s certification journey at the Gemological Institute of America (GIA).