Girdle Painting

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Once again, girdle digging is described as follows:

Effect of Girdle Painting on Facet Angles

Similar to girdle digging, girdle painting can affect the angles of both the upper girdle facets and lower girdle facets. However, the effect of painting and digging at the pavilion alters the optical quality of the diamond very drastically (which will affect the diamond's cut grading). Which is probably why we observe empirically that most painting and digging are done at the crown, and not the pavilion. Therefore, we shall concentrate on the upper girdle facets in our studies.

Painting (girdle bezels thinner than girdle halves) essentially causes the upper girdle facets to face away from each other. Since the girdle halves have popped up, it is natural that the girdle facets will face away from each other, thus causing the angles of these facets to decrease.

Case Study

To illustrate the point, we will compare 2 diamonds, one with classic girdle and the other with painted girdle, using scans and lightscopes.

First up, we have the graphs from the Helium scan, which measures the thickness of the girdle:

Next, we take the Sarin scans. These are extract of the reports, concentrating on the parts we are interested in:

Classic Girdle	Girdle Painting

Note that the diamond with girdle painting has thicker girdle halves compared with girdle bezels. Also, where the girdles are painted, the upper girdle angles are much lower (Average of 36.24 ˚) compared with that of about 42 ˚ for the classic girdle. The lower girdle angles are also not materially affected by girdle painting once again.

Good lightscope images (using reflector technology) also illustrates this. The following are images taken using GoodOldGold's DiamXray:

Classic Girdle	Girdle Painting

A diamond with painted girdle will have edge-to-edge redness. This means that the diamond will appear bright. However, not allowing some leakage from the edge will decrease the diamond's contrast. It is widely agreed today that a diamond's brilliance depends on both its brightness and contrast. Therefore, achieving edge-to-edge light return at the expense of the diamond's contrast (achieved by painting its girdle) may not be necessary a good thing.

We can use AGS' ASET images to illustrate this as well since it also relies on reflector technology:

Classic Girdle	Girdle Digging

Crown only girdle painting will show up as increased greens along the girdle. The ASET can tolerate a fair amount of painting. Studies have shown that when the upper girdle angles decrease by about 6˚, the green will be too much for the diamond to be graded as Ideal per AGS. So, this diamond here sits on the borderline. There is a good chance that it may not be considered as ideal.

Finally, we present a picture of the 2 diamonds side by side, I'm sure you can tell the difference. Well, some people actually prefer the diamond on the right because they like the edge-to-edge brightness, even though it has less contrast brilliance. However, most people seem to agree that the diamond with the classic girdle looks better.

Left: Diamond with Classic Girdle | Right: Diamond with Girdle Painting

Next, we will conclude on this issue...