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What is Diamond Girdle?

Holding a diamond ring with thick girdle

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The diamond girdle may not be on most people’s priority lists when searching for a diamond, but it’s an important element of the stone’s overall quality. The girdle affects not just the beauty, but also the structural and practical aspects of the stone. As such, the diamond girdle is a very important feature to consider.

Where is the Diamond’s Girdle?

Where diamond girdle is

The girdle refers to the part of the diamond that separates the crown from the pavilion. The girdle is made up of the outermost facets at the widest part of the stone. When mounted into jewelry, it is the girdle that connects to the setting. If you want to get accurate measurements of the loose diamond’s length and width, you’ll have to measure the girdle.

How is the Girdle Graded?

The diamond’s girdle makes up one aspect of its cut and is measured and included in the grading report.

Because a girdle isn’t always the same in width around the diamond, the stone is measured at a few different points and then given two ratings based on its thickest and thinnest points.

But if the stone measures the same at different points, then a single girdle rating is given. The two diamond charts below show this difference.

Like other features of the diamond, the girdle is also given a grading on a scale. Here’s the industry accepted scale:

Diamond girdle thickness scale
  • Extremely Thin – The girdle is almost non-existent. It’s fragile and can chip or break. It needs to be mounted carefully into the setting. Diamond depth can be shallow and cut grade is affected.
  • Very Thin – The girdle is thin and must be set carefully. Risk of chipping and breaking is there.
  • Thin/Medium – This is the best proportion. Low risk of breaking and doesn’t affect the cut grade. Good diamond depth.
  • Slightly Thick – Excellent to ideal proportion, with low risk of chipping. Cut grade is not negatively impacted.
  • Very Thick – The girdle is thick and affects cut grade. Diamond may be too deep.
  • Extremely Thick – The girdle takes up too much of the diamond and can make the diamond look smaller. It’s much thicker than desired.
Medium cut diamond girdle

Medium girdle

Thick cut diamond girdle closeup

Thick girdle

The perfect girdle is Medium to Slightly Thick as these proportions balance out durability with beauty and practicality.

Types of Girdles

There are a few different girdle variations that depend largely on the shape of the diamond:

  1. Faceted Girdle – You’ll see faceted girdles on brilliant cut diamonds, as they enhance sparkle and contribute to the stone’s light performance. These facets are typically triangular in shape.
  2. Polished Girdle – This type of girdles is typically seen on step cut diamonds like emerald or Asscher cut diamonds. Polished girdles are not faceted and fit in with the rest of the facets of step cuts – long, open and transparent.
  3. Rough Girdle – Also known as bruted or frosted, this type of girdle is a rough, unpolished style which gives the girdle a frosted glass look. This type of girdle isn’t very common and while it adds a textured look to the diamond, it tends to reduce brilliance.

Today almost all diamond girdles are either faceted or polished.

How the Girdle Impacts the Diamond

The girdle affects a diamond’s symmetry. If the girdle is too thin or too thick, it gives the diamond an off-balance skewed look.

A too thin girdle compromises the strength and durability of the diamond as it can break when mounting the diamond. Setting the diamond requires pressure and heat – which can be too much for a thin girdle. A setting like bezel or halo will protect the diamond when you wear it. This will keep it from impact and protect the knife-edge of the stone.

Solitaire setting engagement ring

The girdle is clearly visible in prong settings. See this here.

halo setting engagement ring

Girdle is less visible in halo settings. See this here.

A too thick girdle, on the other hand, will have a lot of wasted diamond in the middle and can make the stone look smaller than it is. While it may not impact the light performance of the stone, the thick girdle affects the apparent size.

A thick girdle can be useful in some cases, especially for diamond shapes with sharp points like marquise or pear. If the girdle is thicker at the point, it strengthens the area reducing the likelihood of the diamond chipping.

Sometimes a diamond’s girdle is thickened simply to retain any rough that would be wasted anyway. This makes economic sense because it makes the diamond heavier, which then corresponds to a higher carat weight. And as we all know, higher carat weight means a more expensive diamond.

An undesirable girdle width can affect the price and quality of the diamond, which can offer good value for you. Depending on the setting, the girdle may not be visible at all, in which case paying less for a very thin or very thick girdle can be an excellent option.

Overall, if the diamond is cut to ideal specifications, the width of the girdle shouldn’t affect the stone’s light performance or cut quality.