We are going to talk about the part that runs around the diamond and marks its width: The Girdle. We also will delve into how its size may affect or not the setting of a diamond in a solitaire ring.
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The girdle is that section which literally cuts the diamond in half visually, with on one side the crown and the other the pavilion.
It marks the width of a diamond and acts as the diamond’s setting edge. The girdle of a standard round brilliant diamond is actually composed of 16 “hills” and 16 “valleys”, which are formed through the faceting of the upper half facets in the crown area and the lower half facets in the pavilion area.
What are the girdle thicknesses?
The average girdle thickness is actually measured by an optical device in millimetres. To calculate the percentage, you need to divide the average diameter of the stone, by the average thickness and multiply the result by 100.
The grades of girdle thickness as described by GIA range from Extremely Thin, Very Thin, Thin, Medium, Slightly Thick, Thick, Very Thick and Extremely Thick.
When looking at the extremes, we come to two very different conclusions: when the girdle is extremely, very thin, it is fragile and can be damaged quite easily when setting a stone. The opposite, extremely and very thick girdles hide weight, meaning the diamond will be heavier in carats than it looks face-up.
It is important that the girdle is evenly scalloped and that the hills & valleys are regular in size and shape to be given a good grade.
How to discreetly maximise weight yield?
Polishers can use a couple of known techniques in order to maximise the yield of a diamond, these are called Painting and Digging Out. Both essentially consist of tilting the upper or lower facets toward the bezel or pavilion mains or tilting them away and toward each other. Thus creating thickness in some parts of the girdle and increasing slightly the total yield of the stone.
Typically, if the visual impact doesn’t go beyond the minimum thresholds that were created by GIA to deem the impact on the stone and the overall grading reasonable, it is an ok technique to use.
Because strong digging out or painting can clearly modify and hinder the appearance of a diamond so they could lower the grade considerably.
How does the girdle size affect your setting when choosing a solitaire ring?
As mentioned before the girdle does need to be at least thin in order to avoid damaging the stone when setting it into a ring, whether it is a solitaire ring with prongs or a bezel setting as a lot of pressure is applied by the setter in order to ensure the diamond doesn’t fall out of the setting over time.
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