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Angular Spectrum Evaluation Tool

What is ASET?

ASET was developed by The American Gem Society (AGS) as a means for evaluating a diamond’s interaction with light. It is the only diamond cut grading tool endorsed by the scientific community, as it critically examines a stones optics by 3-dimensionally evaluating light performance in all 58 facets.

How does it work?

First a little background: When light passes through the table of a diamond, it is broken down into a rainbow spectrum of colors. Once in, these colors are temporarily trapped, causing them to bounce around several times from facet to facet, generating sparkle. When the light finally has an opportunity to refract out, it can leave through the table as white light, which is what we see as brilliance; or it can leave as separate rays, which reach our eyes in flashes of color.

diamond brilliance and fire

Keeping the physics of light play in mind, ASET generates a color-coded image that identifies the angle from which a diamond is gathering its light, allowing us to see how well or how poorly the diamond is handling the rays. (Stout, P. (n.d.). The American Gem Society An Introduction to ASET ® Theory & Technology. Retrieved March 9, 2015, from

What colors are used in the coded image?

Red: Captures the brightest reflected, represents brilliance. (Strikes the diamond from 45 to 75 degrees to the table)

Green: Captures light that is not as bright; reflected off of indirect angles (Strikes diamond from 0 to 45 degrees)

Blue: Represents contrast; created by light that could have entered the diamond, but was blocked by the observers head (Strikes at 75 to 90 degrees)

Black/White: Both colors represent leakage- or an area from which light is lost.

Click To Learn More About Each Shape's Aset Reading

  • round diamond


  • princess diamond


  • emerald diamond


  • asscher diamond


  • marquise diamond


  • oval diamond


  • radiant diamond


  • pear diamond


  • heart diamond


  • cushion diamond


Types of Aset Images:

There are two types of ASET images:

  • Actual images seen through a device: detailed, three-dimensional
  • Computer generated images: simplified, idealized and two-dimensional

Tips for Evaluation

Ideally you want to see more red than green in a stone; with the exception of the reflection area in the very center of the stone, which can be red, green or a combo of both.Blue should be distributed in a balanced and symmetrical manner because it shows us the pattern of light and dark areas that makes a stone visually pleasing. Since black and white represent light leakage, you should really see very little of these colors. In fancy stones, expect to see more green. American Gem Society

Using Aset Technology

  • Is not limited to round brilliants; it works with all fancies
  • The technology works with both loose and mounted diamonds
  • Can easily evaluate your inventory and select diamonds based on light performance
  • Eliminates any ambiguity regarding a diamond’s cut
  • Does not require backlighting to generate a good visual of the stone
  • Requires more knowledge to decipher what individual colors mean and how they relate to a stone’s optics

Light Performance Rating

ASET images of stones can be rated on a scale of 0-10

  • 0-2 indicates HIGH PERFORMANCE, with 0 limited to being “AGS Ideal”
  • 3-7 indicates MEDIUM PERFORMANCE
  • 8-10 indicates LOW PERFORMANCE

Presentation VS Handheld Aset

Aset Report

An ASET report should be able to tell you about a stone’s

  • Light Performance: Optical Efficiency
  • Optical Symmetry
  • Physical Symmetry
  • The Cutters Expertise

A well cut stone will reflect most of the light striking it, appearing bright and beautiful! But a low quality stone leaks most of the light and looks dimmer to the observer.

clarity bar


1- Stout, P. (n.d.). The American Gem Society An Introduction to ASET ® Theory & Technology. Retrieved March 9, 2015, from

2- Yantzer, P., Caudill, J., & Sasian, D. (n.d.). Foundation, Research Results and Application of the New AGS Cut Grading System. Retrieved March 9, 2015, from

Extraneous Info:

*Physics fact: critical angle for a diamond is 24.4 degrees- resulting in total and repeated internal reflection, giving the diamond its sparkle - Having a small critical angle, light has the tendency to become "trapped" inside of a diamond once it enters. A light ray will typically undergo TIR (total internal reflection) several times before finally refracting out of the diamond. Because the diamond-air boundary has such a small critical angle (due to diamond's large index of refraction), most rays approach the diamond at angles of incidence greater than the critical angle. This gives diamond a tendency to sparkle. The effect can be enhanced by the cutting of a diamond gemstone with a strategically planned shape. The diagram below depicts the total internal reflection within a diamond gemstone with a strategic and a non-strategic cut.

Images to include:

(ASET and rounds, ASET and fancies… + evaluation)