Elements of Light Return - Scintillation

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What is Scintillation?

Scintillation is defined by GIA as...

• Sparkle: The appearance, or extent, of spots of light seen in a polished diamond when it is viewed face-up that flash as the diamond, observer, or light source moves.

• Pattern: The relative size, arrangement, and contrast of bright and dark areas that result from the internal and external reflections seen in a polished diamond when it is viewed face-up while that diamond is still or moving.

AGS, on the other hand adopts a simpler definition. Scintillation, according to AGS is the combination of white and colored sparkles seen as the diamond and/or the observer and/or the light source(s) move.

Scintillation, in layman's terms is most commonly referred to as "the sparkle factor".  Measuring or determining scintillation is not an easy task as you have now learned how diamonds with different cut proportions perform differently under varying lighting environments.

GIA's first definition under sparkle primarily covers your strong ambient and direct light sources and always involves movement.  The addendum to that definition under pattern primarily covers your hemisphere (outdoor) lighting and includes a static (still) view.

Since GIA has highlighted the importance of pattern when the diamond is still or moving, we will examine "Patterning" within the diamond in what we shall call "static (or still) scintillation" as well as "dynamic (or moving) scintillation".

Patterned Static Scintillation

Let us begin by examining static scintillation in a patterned diamond.

Patterned Static Scintillation

Here is a chart depicting different flavors of patterned Hearts & Arrows type diamonds available on the market. Each exhibiting superior craftsmanship in what we refer to as "optical symmetry".  For all sakes and purposes it would be very possible that each of these have identical or very similar crown angles, pavilion angles, table size and other basic proportions.

As you view each of these patterned round brilliant cuts bear in mind GIA's second definition.

"Pattern: The relative size, arrangement, and contrast of bright and dark areas that result from the internal and external reflections seen in a polished diamond when it is viewed face-up while that diamond is still or moving." 

While the appearances above may only change slightly from one stone to the next, look at how different the appearances change from the first to last stone. These images represent the on/off contrast of bright and dark areas GIA is talking about.  In these hemisphere lighting pictures this static scintillation becomes easily visible.  None of them are best and they all get ideal ratings for GIA's metric for scintillation (AGS does not consider patterning their system). 

The correlating checkerboards have been placed under each diamond to highlight the visual difference.

By altering facet structure amongst lower girdle facets and star facets (refer to article on 'minor facets' we shall present later) we can, make the arrows thinner and add more dark hotspots. Effectively, this is akin to adding more squares to the checkerboard (but reducing the size of each square) and thus altering scintillation. The appearance of the diamond will ultimately be different.

Which is best? In taste, there is no dispute. Only you can answer that question.  More square on the checkerboard may appeal more to some people, while less may appeal to others. If you are buying the diamond for yourself, then you can choose based on your preference. However, if you buying your proposal ring and it is meant to be a surprise, then you will need to find out the taste of your girlfriend.

Patterned Dynamic Scintillation

If "Patterned Static Scintillation" involves the observance of diamonds in a still (static) position, "dynamic scintillation" simply involves observance during movement of either

• the diamond
• the observer
• the light source or
• all of the above

Under the definition where GIA talks about this patterning, the bright and dark areas still exist even when the diamond is tilted, however the patterning is obviously different.  Excellent scintillation no matter the view.  Rocking and tilting the diamond involve movement which changes our definition from static to dynamic.

Face Up View of Diamond	Tilted View of Same Diamond

The diamond above has an excellent contrast of white and dark areas when it is viewed face up and when it is tilted. So, it would have excellent dynamic scintillation. Obviously, a diamond that does not have a good contrast when tilted will tend to be less scintillating.

Let us bring back the 4 diamonds with excellent patterning and subject them to motion. Evidently, all 4 have excellent dynamic scintillation. So, the one that moves your spirit is the best diamond for you.

Patterned Dynamic Scintillation

To Pattern or Not to Pattern?

Up till this point we have been examining patterned diamonds cut to rare levels of optical symmetry as observed in the famed "Hearts & Arrows" type diamonds.  All of these patterned diamonds represent some of the rarest and most highly valued diamonds on the market.  They represent less than 1% of diamonds cut in the world and many connoisseurs seek them out as they generally take up to 4 times the amount of time to cut to attain that level of precision.

Hearts & Arrows Patterned Diamond	Non-Patterned Diamond

Many AGS Ideal Cut or GIA Excellent Cut diamonds however do not have this precise symmetrical patterning as found in the cuts we have been exploring till this point.  Most represent the stone showed to the right in the above illustration.  It is important to note at this point in our presentation that GIA and AGS do not take into account this aspect of "optical symmetry". GIA mentions the patterning present within diamonds but do not acknowledge optical symmetry in their final grade. AGS and GIA would only ensure that the diamonds graded as Ideal or Excellent respectively have good scintillation, but they need not have a pleasing pattern.

It could properly be said that all diamonds have a pattern.  Even the diamond to the right in the above illustration has a pattern which can be identified by a set of numbers. The difference however is that one diamond (left) has an organised, structured pattern which took at least 4x longer to cut (with more loss to the diamond's weight) while the stone on the right has a more chaotic pattern and took less time to cut.  GIA and  AGS are not considering optical symmetry in their grading system so on paper both diamonds may appear to have similar "numbers" yet produce entirely different looking appearances.

Here is a simulation of both stones in various lighting environments:

Lighting	Patterned	Non-Patterned
Dynamic Image (Contrast Brightness AGS)
Dynamic Image (Dispersoin/Fire)
Dynamic Image (Brightness GIA)
Dynamic Image (natural ambient daylight)

Note that both diamonds have similar "sparkle factor". The difference is that one is sparkling with a visible arrows pattern, and the other is more chaotic. If you do not mind the appearance of a non-patterned ideal cut diamond, you can purchase it for a less expensive price because there is a larger supply of these.

The Hearts & Arrows pattern attests to the diamond cutter's high level of craftsmanship. Not to mention that it takes 4 times as long to cut with a higher loss of diamond rough. As such, it will be more expensive.

Again, we will leave the decision to you as it is a matter of taste.

Next, we shall introduce some tools you can help you examine the light return of a diamond. We will show you the lightscope and talk about the new AGS ASET, which is based on a similar reflector technology.