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Is this a stupid question or has it been answered somewhere else?


Not stupid at all.


On a well-made diamond the girdle will have enough thickness to prevent chipping but no so much that it adds weight needlessly.


By AGS/GIA standards, diamonds with thin, medium, or slightly thick girdles meet this criteria. Since girdles are measured in multiple places there may be a range (thin-medium for example). Any combination of thin, med and slightly thick is most desirable, but if one descriptor is outside (vtn-med for example) don’t panic: Further examination of the specific diamond will reveal what the ‘outer’ descriptor implies. It may be enough to disqualify it, or it could be a single position that won't be a problem. It’s a stone by stone call.


Thin, med & slightly thick girdles are all durable and hide no appreciable weight. We suggest the med or stk range for tension settings. A girdle at the thin side of thin gets you a tiny bit more spread.


Remember girdle thickess is a range: A girdle described as “thin†on diamond A may be a micron away from medium, whereas “thin†on diamond B may be closer to very thin. Both are perfectly acceptable, but diamond A’s "thin" would be a better candidate for certain settings. The AGSL range for thin is wider than the ranges for medium & slightly thick combined, so an abundance of well-made diamonds will have “thin†in their girdle description (chart attached)


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The AGSL and GIA judge thickness differently.


On a round brilliant the AGS reports the thinnest/thickest places anywhere on the entire girdle. GIA measures at the 16 valleys only.


Logically, range % figures will appear wider on AGSL graded diamonds.


Edited by JohnQuixote
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Types of Girdles


A faceted girdle is one where the brillianteer polished facets into the diamond's girdle.


An unfaceted, or bruted girdle (aka frosted) is one where the diamond's girdle remains unpolished and has a rough/frosted appearance. Some cutters believe polishing the girdle can cause color to be reflected back inside, so bruted girdles are more common in low near-colorless grades and down, and in small goods, 0.25 and lower. In top near-colorless diamonds it's not the concern that it is with slightly colored and below.


A polished girdle on a diamond is see-through or clear. This is sometimes considered a finishing touch but is not critical. One situation where polish is desirable is when the diamond is a fish-eye, where polishing will reduce the effect of the girdle's reflection in the table.


Some of today's girdling machines are putting a very fine texture on. These girdles are more than bruted but less than polished. We choose to call them finely finished: Not faceted, not completely polished, nor bruted. They're in a cozy place somewhere in-between.

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Range Variations


You can investigate descriptors outside thin, med and stk. Here is a princess with a girdle described as very thin-med. Almost the entire girdle is medium. The vtn on the grading report referred to an indented natural on a corner (arrow). In this case the stonesetter was careful to protect the corner. No problems.


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