Measuring Diamond Brilliance, Fire, and Scintillation

When shopping for a diamond, you will experience an overwhelming amount of gemological terms that can be used to describe a diamond’s beauty. Sparkle, fire, brilliance; sometimes these words can appear to be a sales tactic because people often forget to explain what each term means. As a gemologist, I clarify these terms and explain to my customers how they apply to evaluating the beauty of a diamond.

The most important thing to look for when buying a loose diamond is that the proportions are ideal for maximum light return. The proportions of a diamond refer to the angles and measurements that will either enhance or deter the diamond from being able to return light to the viewer. This is why you will always hear a gemologist refer to the pavilion depth percentage and table percentage for any diamond. These numbers provide important information as to whether the diamond is well cut and worth buying. For a round brilliant, it is these measurements that differentiate between a cut grades since round diamonds are the only diamond cut that the GIA assigns an official cut grade to. Proportions are also the main reason why many people are comfortable buying a diamond with lower color (J, K, and L). A well portioned, lower color diamond will have more light return (brilliance & fire) than a whiter diamond with a poor cut grade.

Fire is the term used to describe all the rainbow colors that are visible in a diamond when rocked back and forth. The rainbow colors reflect the spectral colors (red, orange, yellow, green, blue, violet), the colors the human eye can see. Fire can provide a lot of information about the quality of a diamond’s proportions. Certain proportions such as a high crown and small table typically make for more fiery diamonds. Gemological laboratories also pay attention to specific colors within the diamond, the more flashes of red you see in a round brilliant, the better the suggested cut. This is because red is the hardest color to get since it has the highest wave length in the visible spectrum. A diamond that bends light enough to make red visible is a well portioned, excellent cut diamond.

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