Diamond Education

What is a Diamond Girdle? Rating Facts You Need To Know!

What is Diamond Girdle

The diamond girdle is a small but very significant part of the anatomy of a polished diamond. It has practical as well as beautiful properties and is an important factor taken into consideration in laboratory grading.

The girdle is the short vertical plane on the edge of the diamond that helps determine its shape and acts as a border between crown and pavilion.

Girdle is the narrow section to the diamond that separates the crown and of the pavilion and serves as occupied edge and blunt surface thereby reducing the risk of damage from a stroke on would reduce that edge. The girdle is measured in relative thickness and type of finish (polished, ground, none).

If the belt is too thin, the diamonds can be sensitive and crack. Diamonds with belts that are too thick will weigh more and will not display the correct proportions.

What is a Diamond Girdle?

The ‘Girdle’ of a Diamond defines the outer edge and division between the Crown and Pavilion of a polished Diamond. The diameter of a Diamond can be found by measuring opposite sides of a Diamond girdle using a Leveridge gauge, or caliper gauge. Under the microscope, the diamond of the girdle can change in color.


The crown of a diamond

Let’s go upstairs. The top portion of a diamond, above the girdle, is the crown. However, the crown is not an even part. It part of the diamond includes 4 additional elements: table, star facets, bezel facets, and upper girdle facets. The table is the top part of the diamond that is completely flat. The table is parallel to the belt but is not part of the crown.

The facets of the star are right next to the table. They have the important job of directing the light that goes into the diamonds. The bezel facets also direct the light. What makes them particularly interesting is that they are shaped like kites. This is last but not least we have the Upper Girdle Facets. As their name suggests, these are next to the belt. It is also the lowest facet in the crown.

The pavilion of a diamond

The pavilion is the part of the diamond below the belt. It part also has its parts. The first part is the lower girdle facets. It is similar to the facets of the upper girdle. But they are below the belt. These facets focus the light entering the diamond back to the crown. Complementing this are pavilion facets. They adjoin the kollet: a facet on the underside of a diamond. Or the 1st, if you happen to be looking at the diamond upside down. The pavilion facets direct the light back to the crown.

When discussing the anatomy of the diamonds, you should also consider some measurements. Starting with the length and width of the diamond. Both are listed in millimeters, but the number of facets isn’t the only thing that matters. Their ratio is also important. This ratio is determined by dividing the length by width.

A diamond with the same length & width (=either an ideal square or round diamond) has an L/W ratio of one. The belt width determines the diamond’s class on a special scale from ‘extremely thin’ to ‘extremely wide’. The kollet is a single point or even a small facet.

The Rating Facts of Diamond Girdle:

When it comes to buying a diamond, the several types of finish on the girdle would not certainly perform a very vital role in the value of the diamond. The choice between a rough, polished, or faceted girdle is one of the individual decisions. What is more significant to note is the thinness or thickness of the girdle that has an influence on the symmetry and proportions of the diamond. Specific ratings can in turn influence the overall cut grade of the stone. The reason? When the diamond includes some major changes it can make the gemstone appear disproportioned.

When a diamond is verified, experts will record the thickness and thinness of the girdle to provide the diamond with a specific rating. Its measurements are represented as a percentage relative to the average width of the diamond. The calculation is: girdle thickness (mm) divided by the average width of the diamond multiplied by 100 same the girdle thickness percent.

Girdle ratings and their facts/properties can come into one or more of the following categories:

Extremely thin:

When a girdle is extremely thin, it might be at risk of cracking or even breaking. It’s great to handle the diamond with care if placed in a setting.

Very thin:

Its range is considered to be a ‘Very Good’ diamond dimension. Once again, it’s essential to take care when placing the diamond in a setting.

Thin, Medium:  

When you are buying a diamond, this is what you require for your girdle. A thin to medium girdle is the perfect gemstone dimension.

Slightly thick, thick:

This range is estimates to be an excellent to ideal dimension of a gemstone.

Very thick:

A very thick girdle of diamond means a good gemstone dimension.

Extremely thick:

With an extremely thick girdle as such, your diamond might look smaller than it is since more depth is taken up by the girdle.

How thick should a Diamond girdle be?

A Diamond girdle should only be deep enough to protect the Diamond during the setting. It will also defend the Diamond to some extent from chips and nicks resulting from everyday wear. Diamonds with a mainly thick girdle often feature in Diamonds cut for weight rather than proportions. A thick girdle will rarely reduce brilliance but in extreme cases, a thick girdle will allow light to reflect around the inside of the diamond. A resulting fish-eyed appearance will reduce important beauty from the Diamond.

Diamond Girdle Thickness

It should be remarked that the GIA (Gemological Institute of America) assessment of girdle thickness is estimated at the narrowest part of the girdle. Under the CIBJO (the World Jewellery Confederation) diamond grading system, by contrast, girdle thickness is assessed at the wider area of the diamond girdle.

Girdle is the short vertical plane on the edge of the diamond, that helps determine its shape and acts as a border between crown and pavilion.


Girdles play a significant role in improving the appearance of diamonds and the cut of diamond girdles also have an impact on the diamond’s grade and price. This is essential to know the value of the girdles of the diamond before buying. The most suitable is the one that is valued and suggested.

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