Virtual Facets

Introduction to Virtual Facets
This is the penultimate tutorial in Prosumer Level 3 and today we are going to be discussing the topic of virtual facets, which is what I consider to be the current pinnacle of diamond optics. I will explain what they are, how we have been using them, and how they affect the appearance of diamond.

I have mentioned the concept of virtual facets several times in my previous tutorials and so you should already know that it is simply a term given to the reflections of real facets. They are called ‘virtual’ because when we look at them, they appear as though they are individual facets handling light differently from its neighbouring virtual and real facets.

The best-known virtual facets are the arrows in a hearts and arrows diamond. We now know that the patterning of the arrows is created using the reflection of the pavilion mains. We have been utilising virtual facets and how they behave, face-up in a well-cut diamond, to identify certain features in light performance images. The point of this is to get you to familiarise yourself with what we are talking about and to show you that you already know a bit about virtual facets. The only difference now is that we are not only going to be considering the face-up view because the virtual facets of a diamond change when you tilt a diamond.

Now virtual facets affect the diamond’s optics because they are what we see at any given time. If the real facet is leaking, then the virtual facet will leak light, but the virtual facet can be leaking light even when the real facet is returning light. Understanding virtual facets will allow you to evaluate a diamond not just from the face-up view, but also through all the tilt angles. If you pick up a diamond ring in a jewelry store and you start tilting it, a diamond that we would normally call a steep-deep would seem to be returning a great deal of fire. This is because as you tilt the diamond, the angles of the crown and pavilion facets change and instead of leaking, it will return light. Whenever a virtual facet is returning colourful flash, they are commonly referred to as giving off an ‘event’. Because steeper facets are often larger, their virtual facets also become larger and you observe an apparently larger event. The point to remember is that the angle at which you view the diamond is important and that this is one of the ways a jewelry store can be designed to enhance the look of certain diamonds we normally reject.

A large virtual facet naturally returns a greater amount of light to your eye, whether you perceive it to be white light or a colourful flash. In terms of fire, it is the larger events that we consider to give off bolder flashes. Apart from the size of the virtual facet, we also want to know the number of virtual facets. Logically, there is an inverse relationship between the number and size of virtual facets for any given area. We can say that a greater number of virtual facets mean that there is in terms of shear quantity, more scintillation.

Other things we want to consider are 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. When we talk about virtual facets, we are going to be talking more about fire and scintillation rather than brightness and contrast. There is some overlap here because in general, we are looking for something that has a well-balanced distribution whether it is a balance between dark and bright reflections, or the balance between large and small flashes of color.

There is however a major difference, which I mentioned at the beginning of the tutorial and that is when we look at fire and scintillation, we want to look at not only the face-up position but through all the tilt angles. Now in theory, a diamond with perfect optical symmetry will give off the most balanced fire and scintillation. But apart from balance, we are looking for that even distribution of fire throughout the diamond. Here is where hearts and arrows come in. Now personally I am not a huge advocate of perfect hearts and arrows or what you would consider a purist, although I appreciate how special a truly perfect H&A is. But many people have told me that light performance is the most important aspect to them yet they fall short of requiring perfect H&A in their diamond search.

Virtual Facets in Hearts and Arrows Diamonds
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. Remember that 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 many 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 events. Many more are events that are so small that they 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 if you look at melee type diamonds that have a full cut, then these diamonds do not really have that much 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 for your personal preference to find melees that have an 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 optimised 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 increase 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-ice looking diamond 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 maximise 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 sometimes be so small that they become ineffective is because of dispersion. We have talked about dispersion before and how larger facets increase 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.

Cones
We now enter the area of optics.

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 so that we cannot see the entire spectrum of light in order to recombine white light. We therefore only see a part of the spectrum that manifests itself as a colourful flash. 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. But this is only one of the reasons why we perceive color better where it is bright.

pupil-dispersion
(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 blacks 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. Remember that the above discussion is independent of the type of light source, which also plays a part in a diamond’s fire so please don’t be confused by thinking that because you notice more fire in your diamond in dim situations, such as under incandescent lighting, that dimmer conditions are more favourable for fire.

Conclusion
To conclude, a virtual facet is a reflection that behaves just like a real facet. Virtual facets can therefore leak light, return white light, or return a colourful flash. Virtual facets can either produce large flashes of lights known as large events or small flashes of light known as small events. A virtual facet that produces an event that your eyes can register as a flash is an effective virtual facet. An ineffective virtual facet means that it is so small that the light being dispersed from the diamond recombines into white light before entering your eyes. An H&A diamond can produce a better pattern in terms of its balance of large and small events. Melee diamonds that are eight-cut have fewer virtual facets that increase the number of effective virtual facets increasing 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.