I have mentioned virtual facets several times before in my previous tutorials and so if you’ve been following my tutorials, you should already know that they are simply what we call the reflections of real facets. The real facets being the table, crown, pavilion, star, upper and lower girdle facets, girdle, and the culet. Virtual facets are ‘virtual’ because when we look at one, it appears as though they are individual facets handling light differently from its neighboring virtual and real facets.
An example of a virtual facet are the arrows in a hearts and arrows diamond. From my hearts and arrow formation tutorial, you know that the arrows are created using the reflection of the pavilion mains. This means we have already been using virtual facets to identify certain characteristics of a diamond.
The interesting thing about virtual facets is that they change when you tilt the diamond. If you pick up a diamond ring in a jewelry store and you start tilting it, a diamond that we would normally call steep-deep may still return a great deal of fire. This is because as you tilt the diamond, the angles of the crown and pavilion facets relative to the observer and the light source changes so instead of leaking, the virtual facets will return light to the observer.
What’s more is that steeper facets are often larger so that their virtual facets are also larger. A larger virtual facet will give off a larger flash of light or fire. This means steep-deep diamonds that look bad outside of spotlights are actually enhanced under jewelry store lighting! So the take away is that the tilt angle that you view the diamond is important. Diamonds that appear dead face up under fluorescent lights can still have excellent sparkle scintillation under spot lights.
Apart from the size of the virtual facet, we also want to know the total number of virtual facets. The reason is because more virtual facets means more sparkle scintillation. Mathematically, there is an inverse relationship between the number and size of virtual facets for any given diamond. The cut of the diamond will change the number and therefore the size of its virtual facets.
An important point is that more scintillation isn’t necessarily better. In diamond light performance terminology, a single flash of light or fire is referred to as an ‘event’. In order for an event to be beneficial to light performance, it has to be visible to the observer.
Virtual facets are kind of like the mirrors in a house or mirrors. They keep reflecting each other and get smaller and smaller until eventually they cannot be seen anymore. Remember the larger the virtual facet, the bolder the flash and small events are known as pin-flash. In my experience most people tend to prefer bold flashes to pin flashes.
Another thing to consider is the pattern of the virtual facets. In previous tutorials we looked at the contrast pattern of the diamond focusing on the bright and dark areas. Dark areas could be either virtual facets that are reflecting head shadow/body obstruction or alternatively are leaking light with a dark background. A well-cut diamond will have a well-balanced distribution of dark and bright reflections as well as a good balance between giving off large and small events of flash and fire.
Virtual Facets in Hearts and Arrows Diamonds
In theory, a diamond with perfect H&A optical symmetry will give off the most balanced fire and scintillation. A proponent of H&A would argue that H&A is actually very important to light performance, in particular for fire and scintillation. This is because hearts and arrows produce the least number of virtual facets in a standard 57-facet modern round brilliant cut. The small number of virtual facets in an H&A mean that the size of the virtual facets are larger.
Apart from being a matter of preference, there are advantages to having larger virtual facets. For example, in a large diamond, you may notice more large and small events that all register as a flash to your eyes. However, in smaller diamonds, you may only get a few large events and the others are small or are events that do not even register as a flash to your eyes. A virtual facet that returns a flash that registers to your eyes is what is called an effective virtual facet. Conversely, a virtual facet that doesn’t register a flash is known as an ineffective virtual facet.
Ineffective virtual facets are the reason why melee diamonds that have a full cut do not have a lot of sparkle to them. The entirety of the diamond appears bright for reasons that I will come to when we talk about cones below. However, there is no sparkle because the virtual facets are too small to produce a flash.
This is why if you want a pavé ring with small melee diamonds to sparkle, it may be better to find melees are eight-cut. An eight-cut diamond has fewer real facets and produces fewer numbers of virtual facets that are consequently larger. Just bear in mind that diamonds that are optimized for fire rarely photograph well.
Sometimes, a diamond is designed to have a large number of virtual facets. The perfect example is a crushed-ice look cushion cut. The crushed-ice appearance is a result of a chaotic patterning of many virtual facets that are created by cutting in a way to increase the internal reflections within a diamond. We have previously discussed that increasing internal reflections increases color entrapment and that is why color diamonds are more often than not cut into fancy shapes such as radiant cuts that have a large number of virtual facets.
When a diamond has a chaotic patterning of virtual facets, there is no easy way to predict whether these virtual facets are returning light or are leaking light without using Diamcalc to model the entire diamond, which also has its limitations. That is why I would consider a diamond that has more virtual facets such as a crushed-iced cushion at a higher risk of having more light leakage. On the other hand, a diamond with more virtual facets can have a chance of being brighter than the background in darker situations because the diamond gathers light from more different places.
Because fancy shapes are not cut to maximize performance, they typically have larger numbers of virtual facets compared to round diamonds. They also have more types of facets and therefore a more complicated patterning of virtual facets. In other words, fancy shape diamonds tend to have more internal reflections and this explains why they are less brilliant than the modern round brilliant diamond.
For this same reason, fancy shapes are better for color retention. Also, because of the chaotic patterning, the only way to properly assess a colored diamond is by visual inspection. Fortunately, an ASET viewer can make this task easier by helping us discern the patterning and distribution of light and also tell us how the diamond handles light.
Now the reason why virtual facets can become ineffective is because of how dispersion works. We have talked about dispersion before and how larger facets can increase the dispersion in any particular diamond. The same is true for virtual facets. A small virtual facet has less dispersion and this means that when white light is dispersed into the spectrum colors, it fans out more narrowly as it leaves the diamond.
We’re now entering the complex field of optics so I will try to keep it simple.
When we see white light, the reason is because our eyes can recombine the colors of the spectrum as it enters through our pupils. When we see a flash of color, it is because the light is fanned out so large that our pupils ‘clip’ the light. When our pupils do this, it means we cannot see the entire spectrum of light that is necessary in order for our eyes to recombine the white light. We therefore only see a part of the spectrum that we perceive as color.
This is why when we look at a diamond in a bright room, we are more likely to see color in a diamond because our pupils are contracted. Conversely, in the dark when our pupils dilate, we are less likely to see the color in a diamond. However, this is only one of the reasons why we perceive color better in bright conditions.
(The above images are courtesy of John Pollard, used with permission.)
Our eyes have two kinds of color receptors, rods and cones. Rods are the receptors that detect black and whites and cones are the receptors that detect color. When it is dark, our brains tell our eyes to switch to using more rods than cones because cones require a lot of light in order to function. It is the combination of using fewer cones and clipping less light that we perceive less of a diamond’s color in dimmer conditions.
A virtual facet is a reflection that behaves just like a real facet. Virtual facets can leak light, return white light, or return fire. An effective virtual facet is one that produces an event that your eyes can register as a flash of light or an ‘event’. Ineffective virtual facets produce events so small that the light being dispersed from the diamond recombines into white light before entering your eyes. Low lighting conditions negatively affects the number of virtual facets that we can observe so that we see less fire in dim lighting conditions.
A true-H&A diamond optimizes the large events in a diamond and produces a better distribution of large and small events. Melee diamonds that are eight-cut have fewer virtual facets that increase the number of effective virtual facets increasing both fire and sparkle. However, melee diamonds that are full-cut have a better balance of smaller virtual facets and coupled with ideal proportions will generally be brighter than the eight-cut.