Diamond Girdle: Learn Why It is Important

The part that separates a diamond's crown from the pavilion is called the girdle. It forms the diamond’s circumference and outermost edge, coming into contact with its setting. A diamond's girdle can be rough (unpolished), polished and faceted, or polished and unfaceted.

The thickness of the girdle is critical because it significantly affects the diamond’s appearance and durability. In short, be mindful of two extremes:

Extremely thick girdles add unnecessary weight, making the diamond appear smaller than it should be.
Extremely thin girdles increase the risk of chipping, especially during setting or regular wear.

The girdle is not a primary consideration when purchasing a diamond, as its thickness generally does not affect the overall appearance of a well-cut diamond. However, symmetry should be evaluated, as excessive variation between the thinnest and thickest parts of the girdle can make the diamond appear disproportioned. Always review the symmetry grade on the diamond certificate before making a purchase.

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Ideal Girdle Ratings

For an ideal cut diamond, a girdle rating between thin and thick is recommended. The most perfectly proportioned diamonds typically have a medium girdle, but other ratings close to medium are also considered acceptable.

Round Brilliant Cut Diamonds: A girdle range of thin – medium – slightly thick is ideal. Diamonds with ranges like thin – slightly thick, thin – medium, or medium – slightly thick are generally good purchases.
Fancy-Shaped Diamonds (e.g., pear, heart, marquise): Girdle thickness should range from thin – medium – slightly thick – very thick. For instance, diamonds with ranges like thin – medium, medium – slightly thick, or slightly thick – very thick are suitable, provided the diamond is well-cut. A very thick girdle can be advantageous in fancy-shaped diamonds, especially at pointed edges, as it adds strength and helps protect against chipping.

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Diamond Girdle Types

Girdle is the edge of a diamond, the widest part of any diamond. It is formed while edging or cutting a diamond and is important for diamond cutters. Since the girdle is the widest part of any diamond, the width of any diamond is measured by measuring its girdle. It is measured lengthwise as 100%. A girdle can be a guideline towards the excellence of a cut and, therefore, the quality of any diamond. Most diamonds have two divisions - crown and pavilion, and the girdle is the meeting point or joint of these two limbs of a diamond.

Laser Inscription Girdle

Most diamonds have their grading report number inscribed on the girdle.

Three main types of girdles are faceted, bruited, and polished. A faceted girdle means rows or waves of small polished sides around the diamond. A brutes diamond girdle means just one row of the unpolished exterior. A polished girdle is a smooth one, as obvious from its name. Interestingly, unlike cut, color, clarity, and carat, these types of girdles in a diamond do not directly influence its value.

Girdle Thickness

Diamond girdles are rated based on their thickness. There are eight grades:

Extremely thin
Very thin
Thin
Medium
Slightly thick
Thick
Very thick
Extremely thick

During diamond grading, various points along the girdle are measured to determine the thinnest and thickest areas. To account for these variations, girdles are often graded in a range, such as "thick to very thick. " However, extreme variations, like "extremely thin to very thick," usually indicate poor cut quality and symmetry, resulting in subpar optical performance. Such diamonds are best avoided.

Function and Importance of the Girdle

The girdle is the part of the diamond that separates the crown (above it) from the pavilion (below it). From a profile view, the girdle is the diamond’s widest part, forming its circumference. When set in jewelry, the girdle is the edge in contact with the setting.

The girdle plays a vital role in protecting the diamond, reducing the risk of damage during handling and setting. It is also essential for measuring the dimensions of loose diamonds, such as length and width in millimeters.

Girdle Variations in Diamond Cuts

The appearance and treatment of girdles vary depending on the diamond cut:

Brilliant cut diamonds typically have faceted girdles. These facets are triangular and contribute to the diamond’s brilliance and transparency.
Step-cut diamonds usually have polished but unfaceted girdles, often featuring elongated rows of facets characteristic of their cut style.

By understanding the girdle’s characteristics, you can better evaluate a diamond’s quality and durability, ensuring an optimal balance between aesthetics and resilience.

Evaluating Girdle Grades

Like many other attributes of a diamond, the girdle also has a grading scale. Different points along the girdle are measured during the diamond grading process to determine its thinnest and thickest areas. The grade of a diamond’s girdle ranges from extremely thin to extremely thick. Most often, girdles are graded as a range, such as "thick to very thick," to account for differences between the thinnest and thickest points. If the measurements fall within the same category, the girdle is given a single rating.

The different grades of a diamond girdle are as follows:

Extremely Thin: This girdle is very small and almost invisible. Extra care is required during setting, as it is more prone to breaking or chipping. Diamonds with this girdle grade often have shallow depth, which can significantly affect their cut grade.
Very Thin: A very thin girdle is proportionate for diamonds but still requires caution during setting due to the risk of chipping. Diamonds with a very thin girdle typically cannot achieve an excellent cut grade and may also have shallow depth.
Thin: This is a good proportion for diamonds. However, it is not ideal for fancy-shaped diamonds, as they are more prone to chipping. Fancy diamonds with this girdle grade must be handled carefully during setting.
Medium: This is an ideal proportion for diamonds. A medium girdle grade does not adversely affect the diamond’s cut grade or depth, and the diamond is not prone to chipping.
Slightly Thick: This is also an ideal girdle proportion. It does not negatively impact the cut grade or increase the diamond’s depth significantly. Diamonds with this girdle grade are structurally sound.
Thick: A thick girdle is slightly thicker than necessary but still good for diamonds. While it may cause a slight increase in the diamond’s depth, it often results in a very good cut grade.
Very Thick: A very thick girdle is much thicker than required, leading to increased diamond depth. This may reduce the cut grade from very good to good and can result in visible girdle reflections within the diamond.
Extremely Thick: An extremely thick girdle is excessive and can make the diamond appear smaller than it should because the girdle takes up more depth. It may affect the diamond’s symmetry and significantly reduce its cut grade. This grade often leads to a “fisheye” effect, where the reflection of the girdle is visible inside the diamond, adversely affecting its brilliance.

Final Thoughts

Evaluating a diamond's girdle is important because it influences symmetry and, hence, the cut proportions.

A medium girdle would be a perfect girdle you may want to have. An extremely thin girdle is always at risk of being chipped. On the other hand, an extremely thick girdle in a diamond is not good because it may enhance the carat weight of a diamond without expanding its outlook. Hence a medium girdle is an ideal one.

While girdle thickness is a factor, it is not the most important aspect of a diamond. The 4Cs—cut, color, clarity, and carat—should remain the primary criteria. The cut is paramount, as it determines the diamond’s quality and light performance.