Performance resulting from cut quality has been studied and developed since the 1800s. Traditional components include brightness (all light returning to the eye), dispersion (“fire” seen as white light is broken into spectral colors) contrast (the pattern of dark and light areas) and scintillation (sparkle seen as the diamond, the light source or the observer move).
Angular Spectrum Evaluation Technology® (ASET) was developed to demonstrate – in red, green, and blue – how the diamond is performing – in other words, how the diamond is handling and returning light to our eyes. With a small amount of study even a novice can learn how to judge Cut Performance with this tool.
Light entering a diamond will (a) reflect from the pavilion and return to the viewer’s eye or (b) ‘leak’ through the pavilion.
The ASET, when placed over a diamond, allows a viewer to see where light is returning to the eye and where it is leaking, as well as a “contrast pattern” which is critical to scintillation.
RED is Direct Light (drawn from 45-75 degrees). Red will be the brightest and most intense areas of the diamond – areas that attract the brightest light from above.
GREEN is Reflected Light (drawn from 0-45 degrees). Green has less intensity. It is light reflected from walls, the environment, etc.
BLUE represents light Obscured by the observer (your head blocks this light from reaching the diamond). These areas will light up when the diamond is tilted and other areas will become shaded. The blue indicates a contrast pattern of dark reflections giving the diamond its personality.
WHITE (if the diamond is backlit, as above) or BLACK (if not) is Leakage. These areas show where pavilion facets are acting as windows rather than mirrors. You see white because those windows allow you to look through the diamond and see the light underneath. White should be minimized.
In general RED should be maximized. Some BLUE is necessary. Too much GREEN is undesirable. The distribution of the three colors is important. WHITE should be minimized.
Each cut has its own set of light performance standards. Fancy cuts are not held to the same standards as Round Brilliants, which are the best at returning an abundance of RED direct light.
Round Brilliant Examples
Brightness and Dispersion
Abundant RED indicates abundant light return, which most people find appealing. The balance of dispersion or “fire” seen will depend on the diamond’s configuration or “make.” Large tables and shallow crowns have more whiteness than fire. Small tables and high crowns have more fire than whiteness. Middle combinations are balanced.
BLUE creates the contrast pattern in a round diamond. These areas are obscured by the observer in the face-up position. Tilt the diamond slightly and those areas erupt in light as others go dark. Tilt it more and they swap again. Keep tilting and the on-off sparkle you see is scintillation. In high performance diamonds the character of scintillation is influenced by the table and lower halves. Short lower halves result in fewer, broader flashes. Long lower halves create more numerous, smaller flashes. Middle combinations are balanced.
Princess Cut Examples
Brightness and Dispersion
RED rarely reaches the corners in a princess. When it does that edge-to-edge brightness makes the diamond appear larger. Like rounds, abundant RED indicates abundant light return, which most people find appealing. Also like rounds the balance of dispersion or “fire” seen depends on the diamond’s configuration. Large tables and shallow crowns have more whiteness than fire, which is the way most princess cuts are produced (large tables and shallow crowns) since it follows the shape of rough which many cutters find suitable for princess cuts. Designing a middle combination can balance fire and whiteness.
RED, GREEN and small areas of BLUE are equally important to the contrast pattern in a princess cut. The pattern is less defined than the round brilliant so princess cuts rely strongly on movement to create the on-off fireworks you see as scintillation. The distribution of colors is extremely important in this shape. WHITE leakage can be present but should be minimized.