Diamond Performance – Basics
Learn what makes some diamonds dazzling and others dull.
Diamond Performance Described
Did you know that “fire” and “scintillation” are not the same thing? “Contrast” and “leakage” also differ from each other. Learn these terms to have intelligent, detailed conversations about diamond performance with others.
Positive Performance Components
- Brightness: All reflections of white light (photos below).
- Contrast: Areas which are temporarily dark due to your head’s shadow (photos below).
- Fire: Dispersed light your eyes see as spectral colored flashes (photos below).
- Scintillation: The on-off pattern of brightness, contrast, and colored flashes seen when the diamond, observer or light source are in motion (video coming).
Negative Performance Components
- Leakage: Dark or dead areas where light escapes through the bottom of the stone (photos below).
- Over-Obstruction: The presence of any observer creates darkness (shallow diamonds)
- Haze: Clouds, graining or other characteristics dense enough to interfere with transparency.
- Dirt: (temporary) Dullness caused by grease, dirt or detritus on the diamond’s surface.
Intermediate Diamond Performance
Brightness and Leakage
Depending on the main facet angles, light entering a diamond will either reflect and shoot up to the viewer’s eyes (as brightness) or escape through the bottom (as leakage or windowing). In general terms, brightness is desirable, leakage is to be avoided – with exceptions.
Store lighting disguises leakage
Stone A is bright in all lighting. Stone B is not. Under normal lighting, areas of leakage cause it to appear smaller and darker than Stone A. Jewelry store spotlights can be used to over-brighten stones, disguising leakage.
Ideal Scope reveals leakage
Pro tip: An Ideal Scope image will reveal dark or dead areas where light exits through the bottom of the stone. Partial leakage is light pink. Blatant leakage is white.
Brightness photos by PriceScope members
Superior, Average and Poor brightness examples in Ideal Scope
- Brightness is red.
- Leakage is white. Partial leakage is light pink.
Leakage photos by PriceScope members
Some light above the diamond will be blocked (obstructed) by the head of a viewer. This creates a pattern of areas which are temporarily dark.
Contrast photos by PriceScope members
A symmetrical, balanced pattern of contrast helps bright areas appear brighter. This works like a chess board, which has only 1/2 the brightness of a sheet of white paper, but appears brighter by comparison. The brighter the bright areas and the darker the dark areas, the more contrast the diamond has.
When moving, a diamond’s contrast becomes a dramatic component of scintillation.
Light from high above usually illuminates the lowest facets on the diamond (the pavilion mains on a round brilliant). When a diamond is being photographed the camera itself blocks light from the highest angles and the lowest facets are darkened, reflecting the black of the camera lens. This creates a contrast pattern which can be useful for assessment.
Contrast pattern seen in Ideal Scope
Ideal Scope codes light from directly above the diamond black. This simulates the amount of light obstruction caused by the average person’s head at a distance of 25cm (10 inches).
Round diamonds cut to have more brightness than fire (Shallow-Ideal and 60-60) typically have narrow pavilion mains, so you will see red than black in the contrast pattern.
Round diamonds cut for balanced brightness and fire (Tolkowksky-Ideal and Super-Ideal) typically have a balanced, symmetrical pattern of red and black in the contrast pattern.
Round diamonds cut for abundant fire (Steep-Shallow and Antique cuts) typically have wide pavilion mains designed to create larger dispersive-fans, reducing brightness but increasing the potential for a viewer to see fire.
Round diamonds produced long ago, or fashioned from oddly shaped rough, may have chaotic, asymmetrical contrast patterns where negative leakage becomes a contrast component.
Some leakage can create positive contrast effects in a diamond, particularly in fancy shapes, antique diamonds and cuts which don’t prioritize brightness. Contrast-leakage may reveal colors underneath the diamond or gather reflections from the environment, creating an aesthetic unique and specific to each stone.
Advanced Diamond Performance
Dispersion is one of diamond’s most appealing attributes. Visible light is composed of fast wavelengths near infrared to slow wavelengths near ultraviolet. When light enters a diamond those wavelengths start to ‘disperse’ from each other, separating into their component colors.
Fire is human perception of dispersion.
If dispersed light arrives to your eye and the dispersive fan is large enough that only one color enters your pupil your brain sees a flash of that color (example A). If the entire dispersive fan is smaller than the size of your pupil your brain recombines all the colors, and your brain sees a flash of white light instead (example B), which counts as brightness rather than fire.
Learn why you see more colored flashes when your pupils constrict on our Diamond Fire and Dispersion page.
Fire photos by PriceScope members
The camera lens works like your eye’s pupil. If the dispersive fan is large enough that only one color enters the diaphragm the camera captures that spectral color.
Does Ideal Scope show fire?
No. You can draw conclusions about a diamond’s likely dispersion potential based on its proportions, but whether you see a specific diamond’s dispersion as fire depends on your own physiology and the specific lighting environment as much as the diamond’s proportions and cutting details.
Can fire be measured?
Not practically. Dispersion is a physical constant, so it’s possible to estimate a diamond’s dispersive output potential, based on how it was cut. Any measurement of fire is only relevant to the specific environment in which it was measured, at the time it was measured, according to the eyes of whomever did the measuring.
Diamond Cutting and Fire
Diamond experts have known for a long time that high crowns and small tables (like antique diamonds) promote more visible fire because rays of light travel through more diamond material and disperse more. But this combination also produces less light return, therefore less brightness. The reduction in brightness actually makes it easier to see small fire events that might otherwise be overwhelmed by white light return.
Lighting Environments and Fire
A number of small bright light sources overhead will help you see fire in any diamond. You may also see it more readily in a low-lit environment like a restaurant with just a few lights or candles.
Scintillation is the on-off pattern of brightness, contrast, and colored flashes seen when the diamond, observer or light source are in motion. It’s the diamond performance combo-platter.
- On-off Brightness √
- On-off Fire √
- On-off Contrast √
Does Ideal Scope show scintillation?
No. You can draw conclusions about likely scintillation intensity based on the diamond’s static brightness and contrast pattern, but scintillation is seen in motion. It will also be different, environment to environment and, as with fire, your specific physiology will determine the amount of on-off colored flashes you see.
Can scintillation be measured?
No. Like fire, any measurement of scintillation is only relevant to the specific environment in which it was measured, at the time it was measured, according to the eyes of whomever did the measuring – and is further confined to the movement choices of that diamond, observer or light source.
Lighting Environments and Scintillation
Bright spotlights above the diamond promote more intense scintillation, which is why jewelry stores use that scheme. The best store setups have small but powerful LEDs situated above the diamond counter, white ceilings and a single dark colored wall to provide contrast.
Sunlight promotes vivid colored scintillation thanks to your physiology (your pupils constrict and see more fire), but the inside of the diamond may seem dark. This is due to environment. The sun sub-tends light at only about one-half a degree in a 180-degree hemisphere, so it occupies only 1/360 of the total area a diamond “looks” to gather light. So, while you see the (very) vivid sparkles that single (very) bright source creates, the constriction of your pupils makes the surrounding areas effectively dark.
Filtered sunlight, standing underneath a tree where the leaves permit sunlight to filter down to the diamond, is a great way to enjoy scintillation. Ambient light reaches down to the horizon, promoting edge to edge brightness, while the leaves break up the cascading sunlight, creating abundant scintillation events. Meanwhile, your pupils have constricted (because your brain registers the sunlight) and in that state they clip abundant dispersive fans, causing your optic nerve to perceive far more colored flashes than you do in other illumination scenarios.
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