Brilliance is brightness and contrast.
When you see black arrows in pictures of diamonds, what you’re actually looking at is a reflection of the black camera lens. At normal viewing distances, the arrows reflect light around your head and body so this effect is known as head-body shadow or obstruction.
When there is strong light return under the table and the arrows are black, the arrows stand out giving strong contrast. But if the arrows are light (without obstruction) then weaker light return under the table actually gives a stronger contrast than a diamond with strong light return.
The range of angles where obstruction is visible is dependent on the viewing distance and the particular combinations of facets. This is why you need to know what you’re looking at when making comparisons.
Different types of cuts have different contrast pattern because the pattern is made up of the different combinations of faceting in a diamond. In the modern round brilliant, the contrast pattern of a Hearts & Arrows diamond and a non-H&A are very different.
There are a few reasons of why people might choose an H&A diamond. You may like the fact that it carries a romantic connotation, or you may like it for its artistic value and craftsmanship. For consumers, H&As can also offer proof that the diamond is cut to very tight tolerances.
Most say, you should think about whether you have a preference for the H&A contrast pattern before you think about anything else. Many people have a preference for non-H&As that have more unique and asymmetrical features. The optical symmetry in an H&A produces more balanced light return whereas you get a kind of randomness with non-H&As.
For many, H&A diamonds look nicer in still images. But many people also fall in love with unique diamonds that speak more to them and most can respect that as well.
Even among H&A diamonds, the contrast pattern will be different depending on the table size, crown height, star and lower girdle length, and upper girdle angles.
Brightness vs Fire
In general, for a fixed table percentage, there is a compromise between a diamond giving off more brightness or more fire if you want ideal proportions/light performance. This is known as the cutter’s trade-off.
What I am talking about is the difference between a 34/41 CA/PA, a 34.5/40.8 CA/PA, and a 35/40.6 CA/PA. In theory, the 34/41 can be said to be more optimised for brightness and the 35/40.6 can be said to be more optimised for fire. The 34.5/40.8 CA/PA can then be said to be more balanced in terms of brightness and fire. Please bear in mind that all of these CA/PA combinations produce both bright and fiery diamonds and fall within the Tolkowsky Ideal Cut (TIC) range.
Brilliant Ideal Cut and Fiery Ideal Cut Diamonds
You can take the basic concepts and take it to the extreme. A diamond optimised for fire is known as a Fire Ideal Cut (FIC). These diamonds typically have smaller tables and steeper crown angles with very high crown facets. A diamond optimised for brilliance is known as a Brilliant Ideal Cut (BIC). These diamonds typically have larger tables, shallower crown angles, and shorter crown heights.
If you’re interested in these, you should note that there are limits to how much you can optimise if you want to remain in ideal light performance territory. The BIC and FIC were cuts coined by Gary Holloway and there has been much debate on what the limits are.
Once you know how each facet of the diamond works, you can even optimise the minor facets to achieve a particular look.
I want you to be aware that choosing a FIC or a BIC really does create a trade-off between brightness and fire so think hard before making such a choice. Although there isn’t a big difference between a FIC and a TIC and a BIC and a TIC, FICs have been reported to be much dimmer than BICs as you would expect.
If you’re planning to optimise for fire, you should know that there are other gemstones similar to diamond that actually have more fire than diamond.
Please also remember that regardless of cut, all diamonds react to various lighting conditions in a similar way so you need to be aware of how a diamond should react under diffuse and direct lighting.
Under diffuse lighting, you’re really looking at the brightness and contrast in a diamond. Don’t expect to see fire under these lights, having a FIC or a TIC that is more optimised for fire will not help you see fire under indoor diffuse lights! If you want to see fire, then you should view your diamond under spotlights.
Scintillation is the term given for the frequency of flashes that is given off by the diamond as you move a diamond. In other words, it is the play of light and the on-off effects of the facets that gives a diamond ‘life’.
It is affected by the size, the number of facets, proportions, physical and optical symmetry of the diamond. Scintillation relies on the movement of the diamond relative to the light source or the observer.
Scintillation plays an extremely important part in the character of the diamond because whenever someone says that they want a diamond that “sparkles”, they are referring to scintillation. A static image of a diamond displaying fire is not as inviting as the thousands of flashes or ‘events’ that occur when you observe scintillation.
In general, the larger the diamond the more facets and virtual facets there are. The opposite is also true and that is why the standard 57-facet cutting may not be the most suitable for really small diamonds. In small melee diamonds, an eight-cut will produce noticeably more fire.
You may also prefer the character of branded proprietary cuts like the Solasfera, Eighternity, Leo diamond, and many others that have more facets. These diamonds create more but smaller facets and therefore more scintillation. However, the nature of the scintillation is more ‘pin’ flashes rather than ‘bold’ flashes. If you want to see what bold flashes look like, have a look at older cushion cuts or the August Vintage Cushion (AVC) from Good Old Gold.
In larger diamonds, it has been suggested that some asymmetry may increase the number of smaller virtual facets without increasing the number of real facets. In more typical diamonds, increasing the number of smaller virtual facets is less important. It has also been suggested that having perfect H&A optical symmetry maximises the number of virtual facets for more typical diamonds. The point is that if you want to maximise visible scintillation, then the way you do it depends on the size of the diamond you are looking for.
Finally, the proportions of a diamond obviously impact its scintillation. The most obvious is the impact that the lower girdle facets have. In general, the shorter the lower girdle facets, the fatter are the arrows which are virtual facets of the pavilion mains. As these are some of the facets that generate the bolder flashes, shorter lower girdle lengths produce bolder flashes and longer lower girdle lengths produce more pin flashes.
One of the ways to view scintillation is to tilt the diamond if the light source and the observer are stationary. This means that not only is the face up position important, but all the tilt angles of the diamond.
Every diamond will show some leakage as you tilt it. This is known as ‘windowing’. This is primarily dependent on refractive index but to a large extent also depends on the proportions.
The bottom line is that if you prefer a certain type of scintillation, there are many ways to optimise for it. Most say that the effects of scintillation must be viewed in real life in order to really grasp what you prefer. If you just look at videos, it is very easy to conclude that more flashes, whether pin or bold flashes is good. Most have found that the opposite is true in real life and that many people prefer more bold flashes. If you can’t decide or if you are seeking a balance, most agree that the modern round brilliant cut diamond cut to super-ideal proportions with H&A optical symmetry does a pretty good job at creating this balance.