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Girdle Digging

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

Once again, girdle digging is described as follows:

Classic Girdle:

The "ideal" classic girdle is cut to a nice evenness throughout from beginning to end around the diamond.
Girdle Digging

Girdle thickness at the halves (bone) are thinner and not consistent like the classic girdle. Conversely, you can say that the girdle bezels are thicker.

Effect of Girdle Digging on Facet Angles

Girdle digging can affect the angles of both the upper girdle facets and lower girdle facets. However, the effect of painting and digging at the pavilion affects the optical quality of the diamond very drastically (which will affect the diamond's cut grading). Which is why we also 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.

Digging (girdle bezels thicker than girdle halves) essentially causes the upper girdle facets to face each other. This will cause the angles of these facets to increase.

Case Study

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

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

Classic Girdle


The "ideal" classic girdle is cut to a nice evenness throughout from beginning to end around the diamond.
Girdle Digging


Girdle thickness at the halves (bone) are thinner and not consistent like the classic girdle. Conversely, you can say that the girdle bezels are thicker.

 

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

Classic Girdle
Girdle Digging

Note that the diamond with girdle digging clearly has thicker girdle bezels compared with girdle halves. Also, where the girdles are dug, the upper girdle angles are much higher (Average of 45.3 ˚) compared with that of about 42 ˚ for the classic girdle. The lower girdle angles are also not materially affected by girdle digging as explained earlier.

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

Classic Girdle
Girdle Digging

Clearly, the area around the girdle facets look paler compared with the classic girdle. This increase in light leakage around the edge. This is bad news, because this will cause the diamond to look smaller!

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

Classic Girdle
Girdle Digging

Here, we see excessive green at the edges, indicating more leakage than necessary. Some greens around the edge like the image corresponding to the Classic Girdle is healthy because it contributes to contrast brilliance, but not to the level of greens per the image on the right.

Finally, we present a picture of the 2 diamonds side by side, I'm sure you can tell the difference.

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

Next, we will observe some diamonds with painted girdles...

 

   

Next: Girdle Painting...