ASET "test" is the AGS last ditch attempt to stay relevant. ASET stands for - Angular Spectrum Evaluation Technology, a title that is supposed to evoke an image of scientists in lab coats bent over a diamond on operating table.
ASET was invented by AGS playing a catching game with GIA, which is the industry de-facto standard. Smaller labs like AGS are constantly looking new ways to differentiate their services in order to compete against the GIA - the industry's gold standard.
ASET cone is not used by professionals, but rather by unapologetic discounters who are looking to turn higher profit by selling stones mis-graded by AGS.
Taking a cue from an “Idealscope” - an inexpensive viewer that colors diamond facets in a kaleidoscopic manner to illustrate its symmetry, the gizmo is using a multi-colored reflection to "evaluate" optical characteristics of a stone.
It is a brightly colored plastic or metal gadget with a magnifying peephole on top.
Unlike “Idealscope,” it requires a light source to be positioned under the stone. A brightly lit mobile phone screen could be used as a light.
Here is what the colors mean without AGS's pseudo-scientific gibberish:
The fact that light is never “lost,” reflected at angles not visible through the peephole of the contraption completely escapes brilliant minds at AGS.
What the ASET image is telling you is that (surprise, surprise!) diamond facets are positioned at different angles and therefore reflect light in various directions. Also, the ASET test demonstrates the degree of the rotoreflectional symmetry in the stone. It also has a soothing hypnotic effect on a consumer. This is it.
Using light performance measurements will not paint the complete picture of the diamond’s true appearance.
To be obsessed with maximizing the light return is simply to ignore the fact that in real life, most of the time diamonds are not pointed directly at the observer.
Fancy shapes should not be objected to ASET testing since they are not relying on brilliance alone in their appeal.