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The AGS Ideal Cut Grade

Some content on this page are contributed by Good Old Gold, with thanks.

The science behind AGS new ideal cut is based on an advanced form of reflector technology called the ASET which is the abbreviation for "Angular Spectrum Evaluation Tool".

Since the ASET is based on reflector technology, its concept is similar to a lightscope we explained earlier. Everything we learned earlier still applies, except that the ASET, being and improvement to the old reflector technology applied by lightscopes, is richer in information.

A lightscope shows light coming from the top as red, but the ASET differentiates the angles that the light comes from, as per the following diagram:


Interpreting Images

Blue areas are the dark contrast areas you observe in a diamond due to obscuration. In the ASET configuration it is intended to represent light coming from 75 degrees to 90 degrees. The amount and distribution of these areas are important. In the AGS metric well made round brilliants have about 18% blue content.

Red is the most desirable color to have in the image. This is intended to be light coming from 45 to 75 degrees: It is not obscured so it is producing brightness via the most direct light.

Green light comes from the horizon to 45 degrees. It is usually reflected light and of lower quality. It should be minimized if possible with this important exclusion: Undesirable in large quantities, green is not altogether bad depending on the size and distribution of the areas in the image. It is one of two vehicles whereby brightness contrast effects are produced - the other is leakage.

Black (or white if using white backlighting) represents areas of non-reflection referred to as leakage. Depending on how you define it, this is ‘escape’ (a better scientific word than leakage) or simply non-returning facets.

The ASET as a Cut Grading Tool

AGS Laboratories consulted the expertise of optical scientist Jose Sasian to determine light performance within diamonds based on the ASET technology. After which, cut grading is determined based on the amount and distribution of blue, red, green and black (or white). The light return is evaluated with the diamond face-up, as well as tilted so that the dynamic scintillation can be checked as well.

The ASET proves to be an excellent tool for evaluating diamond cut quality and light performance since it is based on the actual light return of the diamond.

The AGS Ideal Cut Grade

AGS Ideal Cut Grade must show a certain balance of colors in their ASET Reflector tool. A good distribution of blue, a superior amount of reds and minimal greens are needed in order to meet "Ideal" status for light performance.  In addition, to meet Ideal grade, the diamond must have ideal symmetry, ideal polish and ideal proportion factors (particulary those that affect the structural integrity of the diamond).

What It Does Well

A diamond that receives an AGS Ideal cut grade will most probably be a bright and beautiful diamond. However, you will have to be careful of the limitations of the system.

The major advantages of the AGS cut grading system are

  1. ASET shows a more critical analysis of cut. That is, it is more scientific in its analysis of light return. Therefore, the GIA steep/deep diamond will not make it as a AGS Ideal because of the excessive leakage around the table of the diamond, which we like to call the 'ring-of-death'.
  2. AGS took reflector technologies to a new level by incorporating multiple colors, coding exactly where a diamond is drawing its light from in most circumstances. This is useful to consumers for evaluating the light return of the diamond, and select one according to personal taste.
  3. Their new system does not arrive at its conclusion from a static viewpoint alone but considers tilt factors.
  4. Dug out girdles are properly disqualified from the ideal grade.


Limitations 1: High Tolerance of Girdle Painting

Although AGS does a good job at weeding out diamonds with girdle digging, it has a high tolerance of girdle painting in its Ideal cut grade. If you have gone through the pages on girdle painting, you will realise that the AGS' tolerance for girdle painting is much higher than GIA's. Since GIA's system is based on human observation testing, this shows that the ASET images do not correlate to human observations all the time. Most people agree that highly painted girdles do not look good, but the AGS' ASET technology does not weed these out. However, to be fair, AGS does weed out extreme girdle painting.

Having said that, some people actually prefer diamonds with painted girdles. Perhaps that is why AGS kept the tolerance for painted girdles higher. Since it's a matter of taste, it would be wise to check out this little detail and decide for yourself if you actually like the look of a painted girdle.

As AGS does not provide information on the extent of girdle painting, consumers have to obtain such information from the vendor before making a purchase.

Limitations 2: No Optical Symmetry Grade

Like the GIA cut grading system, the AGS cut grading system also does not grade the optical symmetry of a diamond. The importance of optical symmetry can be found in discussions on scintillation and the key minor facets.

As such, consumers have to rely on a trustworthy vendor to provide such information if optical symmetry is important to them.

Limitations 3: Higher Allowance for Shallower Crown and Pavilion

The AGS cut grading system is not as strict as GIA on the shallow crown and pavilion combinations. This is due to basic weakness in reflector technologies which do not always display how a diamond truly appears in common daylight environments. When angles get too shallow it contributes to greater darkness within a diamond in daylight. Unfortunately, reflectors are not the best tool for picking this up except for extreme shallow combinations.

In Summary

The AGS cut grading system is also an excellent system. The reflector technology it employs is a great tool for weeding out poor performers.

However, there are instances where ASET images do not always correlate to human observation and we have to be wary of them. It is not as if these diamonds are bad looking, but rather, they should not qualify as Ideal. The ideal cut grade should be reserved for the very best. I am sure when you pay top dollars for an ideal cut diamond, you would not want to settle for second best. Therefore do take note of the limitations of each cut grading system and do your due diligence.




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