How Dark Arrows in Diamond Photos Reveal Cut Precision and Sparkle

The bottom-most facets on the diamond (the main pavilion facets) draw their light from the highest angles in the hemisphere above the diamond. When a round diamond is photographed from directly overhead, dark arrows in the diamond image will appear as a result of the camera blocking light from the light source. This is known as obstruction or “obscuration”. These dark areas in diamond photos are a reflection of the camera lens in the crown of the diamond. This is also a proxy for the head shadow that an observer casts when looking at the diamond at close range.

Obstruction sounds like a bad thing, and it is if not in the correct amount and distribution. But if designed correctly it creates structured contrast in the diamond which is an essential ingredient in scintillation and our perception of brilliance (brightness plus scintillation). Due to its importance, contrast is one of the four factors measured in the AGS light performance cut grading system. Like salt increasing the perceived sweetness of a slice of watermelon, the sparkle of a diamond is accentuated by positive contrast and the resulting on/off patterns of dark and light!

A lot is made of the black arrows in hearts and arrows diamonds. And diamond photos can give an idea of facet precision, which is very important. But in real life the dark arrows are not an obvious feature. The only way obstruction can be seen as it appears in these diamond images is if you observe the stone face up at close range (10-12”) with the main light source behind your head. Your head shadow is reflecting back in the diamond in the same way the camera lens is in photographs. When diamonds are viewed from greater distances and from other viewing angles the arrows are not as prominent or well defined.

In the first photo below, stones are positioned so the dark arrows are visible in a layout of precision cut diamonds. Photos of the finished piece show different angles and their resultant contrast patterns. All of these diamonds have premium optical symmetry (facet alignment in 3D space), but for the arrows effect to be visible the camera must be directly over the crown, blocking the light source at the correct distance so that all of the pavilion mains go dark simultaneously.

It's important to understand that a dark arrows diamond is not an end in itself. The presence of well defined and symmetrical arrows that are not too thick or too skinny is simply an indication of facet precision, and evidence that the diamond has been cut with the proper amount of structured contrast to produce good brilliance.

Diamonds with premium optical symmetry have precise alignment of pavilion mains with all the other facets in 3D space. Most diamonds today do not exhibit optical precision. Diamonds with different levels of facet precision have different levels of optimization of the facet design, and predictably, different levels of light performance.

Hearts and arrows diamonds feature symmetrical positive contrast as seen in the arrows view, and optical precision as seen in the hearts view, as all the corresponding facets in 3D space are in alignment.