Brilliancy / Light return = Brightness
Scintillation / Sparkle = Contrast
by David Atlas
I hear so many people asking for the "most brilliant" diamond or the one that "sparkles the most." I know what they want, but their understanding of it is very different than my own. Below is a demonstration that shows that a beautiful diamond is a perfect combination of brilliancy and scintillation, not a maximum of either component. It takes the proper combination of sufficient brightness and adequate contrast to arrive at the perfect image of a diamond. When you want a beautiful diamond you want the correct combination of these elements, not the "maximum" of either one or both.
The upper left photo is the "ideal"...Would you even consider one of the others as equally pleasing or beautiful? While all are extreme examples, I believe this proves the point I am attempting to make about the proper balance of brilliancy and scintillation required to make the best looking diamond. I hope you agree and have learned from this.
Light Behavior, The Imagem Definitions, both simple and more complex
Three simple definitions:
Brilliance: a measure of a stone's overall strength of light return that represents its average light return in the face-up position. This measure is arrived at by computing the mean gray-scale value of all pixels within the girdle portion of a diamond.
Sparkle: a measure of those spangle-like flashes of reflected and refracted light that gives diamonds what might be called "kick". The greater the number of these flashes, the higher a stone's sparkle. This measure is arrived at by measuring the standard deviation in the gray-scale value of the light return within the girdle image. (Note: Do not confuse sparkle, which is observed when the diamond is held stationary, with scintillation, which is observed when a diamond is moved about.)
Intensity: a measure of the number and strength of contrasting light-dark areas in the girdle portion of a diamond that give it vitality and character. The greater the stone's symmetry the higher its intensity will be. .This measure is arrived at by calculating a ratio of bright pixels to the total number of pixels within the girdle.
The more technical definitions:
- ImaGem uses direct measurement of light returned from a diamond. Measurements are repeatable within margins of error.
- Three measures of light behavior are used to represent the beauty and the quality of a diamond. These are: Brilliance, Sparkle, and Intensity. Combinations of these measures represent levels of beauty in diamonds.
Brilliance represents "average light return." It is measured as the average of gray scale values of pixels within the girdle area. This value can range from 0 to 255 as a property of the measuring device. For the standard lighting level used this value is purposely kept low to prevent saturation. Higher value on Brilliance represents: more brilliant, brighter, excellent cut stone, more efficient stone returning more of the incident light back.
Sparkle represents "variation" in light return. It is measured as a variation in the gray scale values of pixels within the girdle area. Theoretical maximum standard deviation for 40 pixels is about 129. Sparkle represents the degree to which a diamond is lively, dynamic, and responsive to kinetic behavior. Higher the value, more lively, more dynamic a stone is likely to appear to a viewer.
Intensity is measured as a ratio of pixel areas with high levels of light return to the total area within a girdle. In theory this value can be as high as 1000, but under selected lighting condition the value has not exceeded 500 yet. Intensity level represents well defined areas of contrast and pattern and hence gives a stone a "pleasing visual definition", "interest" and "mystique." Stones with high levels of optical symmetry score very high on this scale. But other types of cut may score well on this scale as well.