Mr. Al Gilbertson displayed a multi colored variation of a Fire Scope at the proceedings of the 1999 GIA Symposium. This device uses different colors to indicate the origin of illumination direction in a diamond being viewed. Figure 7 is a diagrammatic interpretation of a virtual GilbertsonScope that is one of the tools available on DiamCalc that was used to generate the images in Figure 2 in the section titled Inverse relationship between Crown and Pavilion Angles.
The DiamCalc scheme is different but effective variation of the inventors lighting environment. (Personal communication with Al Gilbertson, 2000).
If part of a diamond appears blue then the illumination source is from a shallow or oblique angle; red indicates light coming from almost directly above the stone. Leakage of light through the pavilion shows as white the same as seen in an Ideal-Scope.
Figure 8. The lighting model for the virtual GilbertsonScope on the DiamCalc program as displayed on the MSU website.