The ASET (Angular Spectrum Evaluation Tool) scope was introduced by AGSL in 2005 after 30 years of research by the AGS Diamond Grading Standards Committee. Since then, it has been the foundation of their three-dimensional cut grading system and the AGS Ideal light grading.

ASET scope

The ASET scope is simple to use yet it provides an in-depth understanding of the graphical portions of the sophisticated light performance grading system used by the American Gem Society and its Laboratory. It works similar to the Ideal Scope, but provides additional information in the intensity of a diamond’s light return. When viewing the diamond through the ASET scope, a colour-coded image will be seen, which gives us information about where light is coming from and that if it is returning to the eye.

ASET colour coding

Red - represents light drawn from 45° to 75°, where there is likely to be bright and direct sources of light exposure in most viewing environment. Red will be the most desirable color as it represents intense light return in the particular area of a diamond. In a Super Ideal Cut diamond, Red will be the most dominant color of an ASET scope image as it basically translates to a brighter diamond.

Blue - is commonly referred to as the Head Shadow which is formed when light is obscured by the observer from a 75° to 90° angle. A moderate amount of nicely patterned blue will be the primary factor in a diamond’s contrast patterning. When the diamond is rocked and tilted, these blue will turn out to become some of the most intense fire and scintillation under direct lighting condition. When a diamond is seen under diffused lighting condition, these blue will contribute to both brightness and contrast, often referred to as dynamic scintillation.

Green - produces a lower intensity light return, usually reflected off walls or other objects from the surrounding area (instead of light coming from a direct source). This is usually considered as the weakest sources of light input coming from a 0° to 45° angle. Green areas will have weaker brightness compared to red areas. A Super Ideal Cut diamond will show minimal green around the bezel area of the ASET image.

Brightness and Contrast

Brightness - refers to the amount of white light return to the observer. With a well-proportioned and a well cut diamond, the facets of the diamond act as mirrors and reflect light back to the observer and hence, achieving good brightness. On the other hand, if the cut is too shallow or deep, the facets become windows where light leaks out and causes the diamond to look less bright.

Contrast - is the light and dark patterns seen when observing a faceted diamond. Below is an image to highlight the importance of contrast. Generally, people tend to prefer the image on the right which displays contrast patterning, resulting in a more aesthetically appealing image as compared to the unpatterned white image on the left. In addition, on top of having contrast patterning, it needs to be symmetrically distributed.

Below shows a Super Ideal Cut diamond that is cut to maximum brilliance, striking a fine balance between brightness and contrast. The ASET Scope image shows dominant red areas with minimal light leakages which translate to a bright diamond complemented with 8 symmetrical blue arrows acting as contrast.

Below is an example of a typical triple excellent diamond with light leakages at the centre of the diamond. A white circle (also known as ring of death) is shown at the centre of the ASET Scope image which becomes dark areas on the actual diamond. This reduces the brightness of the diamond as light entering the diamond is escaping through the pavilion. Diamonds that are cut too deep tend to have these severe light leakages.

In addition, this diamond lacks contrast patterning as there are very little blue on the ASET scope. As a result, the 8 black arrows on the diamond would not be visible.

An ASET Scope image can also easily detect dugged girdle. Dugged girdle refers to light leakages at the girdle as shown by the green semi-circle at the edges of the ASET Scope image. These weaker light return at the edges will cause the diamond look less bright and greyish at these areas as shown on the actual diamond image. As a result, the diamond will appear smaller than it is, as the edges of the diamond will be less bright.

Moreover, this diamond lacks contrast patterning which looks messy on the actual diamond, diminishing the brilliance of the diamond.

Fire and Scintillation

Fire or dispersion of light - is the flashes of rainbow colors one observes when viewing a diamond under direct light. When light enters a diamond, the diamond acts as a prism and splits the light into 7 spectrums of coloured lights due to different wavelength. The intensity of fire is dependent of how strong the lighting condition, generally, the more intense light condition for example under direct sunlight, the stronger the fire.

Scintillation - refers to the sparkles and flashes you see as you move the diamond. For a good scintillating diamond, the sparkles and flashes spread evenly throughout the diamond. On the other hand, for a poorly cut diamond with light leakages, dark spots can be seen when you move the diamond which resulted in poor scintillation with uneven spread of sparkles and flashes.  Generally, under the ASET scope, the blue areas act as reflectors which produce very intense fire and scintillation when the diamond is rocked and tilted at a certain angle. While for the green areas which also act as reflectors, display a less intense fire and scintillation.

Below is a comparison of cushion cut diamonds showing Brellia and a normal Cushion Cut diamond.

The cushion Brellia at the top is cut to have minimum light leakages, maximising on light return. It has an ASET scope image similar to that of a Super Ideal with dominant red areas and 8 symmetrical blue arrows. The brilliance of the diamond is optimized with a well balance brightness and contrast. Compared to the typical cushion cut diamond below, it has significantly more light leakages as shown by the white and green areas on the ASET Scope image, making the diamond appear darker and less bright on the actual diamond image. Moreover, it also lacks a contrast patterning on the diamond and hence it looks messy on the actual diamond.

Patterned Scintillation

Patterned scintillation refers to the contrast patterning as you move the diamond. When the diamond is tilted, the bright and dark spots still exist but exhibit a different pattern. A well cut diamond in the case of Super Ideal cut, will show a good distribution of bright and dark spots regardless of how you move your diamond.

The ASET scope image can also tell us if the diamond exhibits good distribution of patterned scintillation. Deep cut diamonds with multiple light leakages and over-contrasted shallow cut diamonds will exhibit poor scintillation when tilted as dark spots will concentrate at an area.

ASET Image and actual image of shallow cut, deep cut, Super Ideal and Solasfera



The ASET Scope images of the Super Ideal and the 91 facets Solasfera above show symmetrical arrows perfectly aligned with minimal light leakages. Both display a nice pattern and a good distribution of scintillation.

However, the Super Ideal and Solasfera exhibit different types of patterned scintillation. By changing the length of the lower girdle facets, the thickness of the arrows is altered and thus altering the scintillation. By having a longer lower girdle, it resulted in thinner arrows which is shown by the Solasfera diamond, exhibiting scintillation of larger number of pin flashes. While having a shorter lower girdle, the arrows will be thicker as shown in the Super Ideal diamond, exhibiting a smaller number of bold flashes.

The video below illustrate the different types of scintillation.