A diamond looks the way it does because of three optical effects: white light reflections called brightness, flashes of color called fire, and patterns of light and darkness called scintillation. Together, these factors give the diamond life and determine its visual appeal.

Brightness – often called brilliance in the trade – is the effect of all the diamond’s internal and external reflections of white light. Well-cut diamonds are brighter than poorly fashioned ones, even if they’re of equivalent size, color, and clarity. In general, the brighter a diamond, the higher its cut grade.

The proportions that play the biggest role in determining a diamond’s brightness are table percentage, crown angle, and pavilion angle. These proportions, in a variety of combinations, can produce high levels of brightness in a round brilliant diamond.

Fire results when white light traveling through the diamond is dispersed into a rainbow of spectral colors. It’s the most difficult of a diamond’s optical qualities to evaluate, and is especially challenging to assess in diamonds under 0.50 ct.

Scintillation is a combination of sparkle and pattern. Sparkle is the spots of light that flash as the diamond, the observer, or the light source moves. In an attractive diamond, the flashes should appear even and balanced in size.

Pattern is the relative size, arrangement, and contrast of the bright and dark areas that result from a diamond’s internal and external reflections. The pattern of bright and dark areas should be well balanced, and there must be enough contrast to give the pattern a crisp, sharp look.

GIA Education teaches students the two stages needed to arrive at the final estimated cut grade of a standard round brilliant diamond. During the first stage, students use the diamond’s appearance to assign a visual estimate of the cut grade. They do this by judging the quality of its optical attributes – brightness, fire, and scintillation. Students then use the diamond’s proportions, polish, and symmetry to assign a final estimated cut grade.

When assessing a diamond’s appearance in the first stage, the lowest assigned grade for brightness, fire, and scintillation sets the cut grade estimate. For example, a diamond with Very Good brightness, Very Good fire, and a Good pattern would get an initial estimated cut grade of Good.