Оценка качества огранки бриллианта...

	Introduction
	Recent achievements
	Building of cut grading system
	Work with scanned diamond models
	Example with tilted table
	BLResponses
	Analysis of illumination
	GIA's illumination model
	"Brill" software analyses light response
	WLR metric and brilliance
	Example with mirrors
	An observer model
	Understanding of brilliance
	Practical value of the cut grading system
	Acknowledgment
	References

"Brill" software analyses light response

Let us consider the ratio between white and color light using the software "Brill" :

Run Brill software

An infinitely distant light source, such as that used at GIA to analyze fire, which produces parallel rays, creates mainly colored highlights on a screen placed at a distance of 75 mm (the hemisphere radius) from the illuminated diamond. When this distance is longer, white highlights can be produced only by those rays reflecting off the surface of the diamond and not entering it. All the refracted rays are observed as colored.

Clicking at the left picture will run Brill software in this regime.
You can change the diamond parameters and rotate the stone.

Run Brill software

The position of the screen is the same (75 mm from the diamond), while the light source now has a finite angular size (3 degrees). The highlights produced in this case consist of both white and colored portions. It can be seen that the white ones prevail.

Run Brill software

The distance between the screen and the diamond is increased to 0.5 m. One can still observe both white and colored portions in the highlight pattern, the white ones still prevailing. The angular size of the light source is 3 degrees, as before.

Run Brill software

To get rid of white highlights, it is necessary to decrease the angular size of the light source. In this example, the screen-to-diamond distance is 0.5 m and the source size is 0.5 degrees. Only colored highlights are observed on the screen, however their area is small.

Basing on the figures presented and the results yielded by the modeling software, a careful reader may notice that the amount of fire or, more precisely, the overall area of colored highlights is not maximal for a light source with a small angular size. Increasing the angular size causes not only the appearance and intensification of white highlights and the decay of green ones, but also an increase in the overall area of blue and red highlights. So, the optimum angular size of the source can be neither too small nor too large.