Because of minerals different refractive indexes, the same faceting design will not yield the same result in all gems. That’s why we always make careful ray-trace study of each design, using special computer programs to analyse how a gemstone pass the light and to get its virtual photorealistic image from different views before cutting.
This process allows us to choose the optimal angles for better brilliance and dispersion of the future gem and to optimize the recovery of the rough with the best aesthetic results.
Examples of simplified ray pass for brilliant cut sphalerites
(images made using GemCad program for ray trace and KeyShot for rendering)
Example of well cut stone with correct proportions and high light return.
If the pavilion is too deep it causes loss of light in the peripheral zone of the stone.
If the pavilion and crown are too shallow it results in practically total loss of light return and brilliance
of the stone.
See also below an example of ray-trace for similar three cases but in lower refractive index material - emerald, 1.57 (click on the picture to enlarge).
For more accurate ray-trace modeling we use Octonus DiamCalc software, taking into account not only the refraction of light but also partially reflected rays and the dispersion of light, very important for sphalerite. Some examples of ray-trace study for a particular faceting design optimized for sphalerite are given below. White arrow shows the position of incident ray in each case.
Examples of visualization of future stone using GemRay program (left -- optimal proportions, right - lower brilliance and dispersion, higher extinction and windowing due to incorrect proportions).
Examples of visualization of future stone using Diamcalc program, with possibility to change angles and proportions and see the changes live in stone.