Final Words on Girdle Painting and Digging

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AGS and GIA Cut Grading on Painting and Digging

The AGS performs ray-tracing analysis on each diamond it cut-grades using the AGS ASET. A diamond of any configuration must return specific numeric values for brightness, dispersion, leakage and contrast to earn the top grade. Painting & digging judgments are incorporated into the overall face-up performance assessment.

Studies have shown that Painting and Digging at the pavilion would lower the cut grade quickly. A change in the lower girdle facet angles by about 3˚ would most likely cause the diamond to lose its Ideal cut grade. This is why Painting and Digging at the pavilion is seldom done. Hence we will focus our discussions on upper girdle facet digging and painting.

AGS ASET is also not tolerant of (crown) girdle digging. Girdle digging increases the girdle facet angles. An increase of about 3˚ would almost surely cause the diamond to lose its Ideal cut grade. The diamond we examined in our discussion on girdle digging would surely not qualify as Ideal.

AGS ASET is fairly tolerant of (crown) girdle painting. This is because it recognises that girdle painting can be used by diamond cutters to achieve a particular optical characteristic called edge-to-edge brightness. We explained earlier when we examined girdle painting that this is done at the expense of contrast brilliance. As contrast brilliance is an important factor in the AGS cut grading, excessing girdle painting would cause the diamond to lose its Ideal cut grade. Typically, if the girdle painting causes the upper girdle facet angles to fall by 6˚ or more, the cut grade would fall. As such, the diamond we examined we examined in the section on girdle painting may just make it into the Ideal cut grade because its girdle facet angles averaged to 36.24˚, which is 5.76˚ shy of 42 ˚. If the girdle facet angles had an average of 36˚ then the diamond would probably not be graded as Ideal.

The GIA scans each diamond and uses the reported proportions to determine cut grade. Metrics obtained from the girdle scan are used to establish a painting & digging value. The same brillianteering judgments are applied to all configurations.

The GIA's grading is based on a database built based on human perception.

Studies have shown that the GIA's assessments of cut grade as affected by girdle painting and digging are quite similar to AGS, even though their methods differ. However, the GIA cut grading system is a little less tolerant of girdle painting compared to AGS.

How do we tell if a diamond has a painted or dug girdle?

The Diamond Scan Report:

The best way to tell if a diamond has a painted or dug girdle is to obtain a diamond scan using a diamond scanning machine such as Sarin, Helium or similar. Below, is an example of a Helium Report. Click on the highlighted areas to see how you can tell if the diamond is painted or dug:

Example of a Helium Report. Click on the highlighted areas.

Lightscope

You can purchase an Idealscope, AGS ASET or a similar device using reflector technology. These can identify painted or dug girdles if used correctly.

To give an example, the image on the left is taken using GoodOldGold's DiamXray using the same diamond as the one in the Helium Report above. The areas around the edge (indicated by the arrows) that are meant to give the diamond contrast are pale red. This means that this diamond is very slightly painted.

However, this diamond's girdle would still qualify as a classical girdle because the painting is slight. Overall, this diamond would be an excellent purchase for someone whose preference leans towards edge-to-edge brightness, but would like to retain the contrast brilliance.

Be warned that some vendor's idealscope images cannot show girdle painting and digging very well. So, we have to interprete with these images with caution. The following show the lightscope images of diamonds with the 3 girdle types taken using the DiamXray and the Idealscope. The images speak for themselves:

	DiamXray	Idealscope
Classic Girdle
Girdle Digging
Girdle Painting

Reliance on AGS or GIA Reports

You also place some reliance on the AGS or GIA diamond reports. If the diamond is graded as GIA Excellent or AGS Ideal for cut, then it is unlikely to have a dug girdle. However, it may have a painted girdle because of the higher tolerance for painted girdles.

Personally, I employ all the above methods. A diamond is an expensive purchase. It is better to be safe than sorry.

Should we buy diamonds with girdle painting or digging?

1. We should avoid diamonds that have the pavilion girdle facets painted or dug because the extra weight only decreases the optical quality of the diamond. Fortunately, this phenomenon is rare.

2. We should avoid diamonds that have girdle digging (at the crown) for the same reason: the extra weight only decreases the optical quality of the diamond.

3. We may consider diamonds that have painted girdles (at the crown) only if we like the optical characteristics of such a diamond. A diamond with crown girdle painting will have edge-to-edge light return, but lower contrast brilliance. Make sure you like the look of such a diamond before you buy it. We would like to suggest that even if you like the look of a painted girdle, make sure that it is within the AGS/GIA tolerance for the Ideal/Excellent cut grade.

What's Next?

If you have followed the articles from the beginning, you would already know which facet measurements make a diamond bright. However, we have not really touched on the measurements that affect a diamond's scintillation. This is what we will attempt to do next.