It is commonly and correctly believed that diamonds with steeper crown angles and smaller
tables have enhanced fire. Believing this makes objective observation based study of the
nature undertaken here was somewhat difficult. However the discovery that shallow crown
angled diamonds display enhanced fire challenged the preconditioning notion.
I acknowledge that fire is the most subjective and least reproducible of the four factors
presented here. Never the less we have made many loosely structured comparisons with actual
diamonds in various lighting conditions and a variety of observers.
The first of these two sets of charts show a selection of crown and pavilion proportion
combinations with the virtual fire tool from the MSU / Octonus website
www.cutstudy.com/cut/english/comp/scint1.htm.
The second chart has had a head shadow effect subtracted.
Because HCA is concerned with the face up view, removal of the central section of the image
effectively reproduces the potential for fire should a ray of light fall on the diamond from
the same direction as one of these areas of a firey flash. Many people find this concept rather
difficult to understand, and it is very difficult to explain. It may help to imagine that we are
considering the ray of light to be going in the opposite direction.
Therefore the more firey flashes on the imaginary screen, the more potential fire could be
displayed. However we must always remember that excessive brilliance will drown out potential fire.
Figure 14. These grids show fire returned to a screen placed between diamond and viewer. The virtual diamond is illuminated from a single light source from directly above the diamond. The central area has been removed from the second set, simulating the effect of a 21° head shadow. To use this tool for Consider the reverse situation - if illuminated with a beam of white light from the same direction as a burst of fire, then an observer positioned directly above the stone would see the same burst of fire.
Figure 15. Comparative fire scores estimated for each diamond on grids for crown and pavilion angles.