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From the experts

Girdle thickness

By John Pollard | Aug 8, 2019

Microns matter

The girdle of a diamond serves several purposes. It needs enough substance to protect adjoining facets in case of accidental impact. It should be thick enough to endure the pressure of setting, including tension-setting. But it should not add unneeded weight to the diamond.

You may not know that girdle thickness happens on a sliding scale. For example, "Thin" is 10X wider than "Very thin."

In fact the AGSL range for thin is the widest of all ranges. You can see below that it's wider than the ranges for medium and slightly thick combined. It's also considered the minimum safe measurement in terms of durability. The world's best made diamonds typically begin with "thin" in their girdle description.

The Crafted by Infinity approach

We craft each diamond so that its minimum girdle description will be "thin" and its maximum will be "medium" or "slightly thick." This is to provide enough girdle for safety without creating excess vertical weight in the diamond.

Diamonds with those minimum and maximum descriptions receive the most favorable grade from every grading laboratory and appraisal institution. This is because a thin minimum ensures enough substance to protect main and half-facet edges, and a medium or slightly-thick maximum provides enough thickness to endure the pressure of any setting application, whether prong, bezel or tension-setting.

A matter of microns

One jeweler asked me to describe how much our girdles can vary. This jeweler had no idea that the ranges for medium and slightly-thick were so small, compared to the wider span of thin. To illustrate how negligible the variance is I provided these illustrations of a Crafted by Infinity with thin to medium girdle (TN-MED) next to one with thin to slightly thick (TN-STK).

Literally, a matter of microns.

Zoomed for detail

Real world context

In the real world the girdle game may be played differently.

The goal of most diamond producers is yield, or maximizing the weight of the finished diamond (described here in diamond cutting basics). One of the easiest ways to increase a diamond's carat weight is by planning a thick girdle. In egregious cases, diamonds with thick, very thick and extremely thick girdles can have significantly less vertical spread than diamonds with girdles in the thin to slightly thick range.


  • A 1.00-carat diamond produced by Crafted by Infinity will always have vertical spread near 6.43 mm
  • A 1.00-carat with Thick girdle might only have a vertical spread of 6.28 mm (like a CBI 0.90ct)
  • A 1.00-carat with Very thick girdle might only have a vertical spread of 6.18 mm (like a CBI 0.85ct)
  • A 1.00-carat with Extremely thick girdle may only have a vertical spread of 6.00 mm (like a CBI 0.80ct)

This becomes even more exaggerated at higher carat weights.


Grading laboratories penalize diamonds by lowering cut grades for overly thin or overly thick diamonds. Nevertheless, there is far more permitted in the real world than in Crafted by Infinity's closed-channel production. For that reason we urge you to consider durability and proper vertical spread, not just carat weight, when buying diamonds on the open market.

Your Crafted by Infinity masterpiece

The girdle is a wonderful area, connecting the performance facets safely and durably, and providing an adamantine tablet upon which your unique Crafted by Infinity AGS report number is laser-inscribed. In every case, the needs of your specific crystal dictated how the girdle finished. And in every case, the girdle is a special part of your Crafted by Infinity masterpiece.

John Pollard

John Pollard

John is the Unites States Director for Crafted by Infinity diamonds. A consultant for manufacturers, grading laboratories and showrooms on three continents, he has lectured for JCK Las Vegas, the American Gem Society in Washington D.C., International Gemological Institute in Beijing, Shanghai, Hong Kong and Europe, the GIA Alumni Association and Polygon symposiums across the nation.

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