Diamond Girdle

The diamond girdle, a tiny component of the stone that is typically disregarded, is crucial in the grading of polished diamonds. When viewed from the top of the diamond, it is the circumference, and when viewed from the side, it is the border that divides the crown and the pavilion. The girdle is created during the cutting stage or bruting (for round diamonds). Bruting is a process where two rough diamond stones are brought in contact together for cutting. 

The girdle has two distinct parts - the valley, which is convex part of either the upper or the lower facets creating a depression and forming the thin part of the girdle; and the hill, which is the highest section of the girdle relative to the center of the girdle diameter forming the thick part.  


The girdle is the perimeter of the diamond as seen from the top of a round brilliant diamond:


Why is a Diamond’s Girdle Important?

The girdle is a powerful small object. When a diamond's little component is undervalued, it can have a significant influence on your hard-earned investment. Here are some of the reasons why this small part of the diamond is so important:

  1. It plays an important role in measuring a diamond’s symmetry and proportion. 
  2. The girdle sets the diamond in place in creating jewelry.
  3. It provides added security for the diamond from bumps or damages when coming in contact to a surface or another object. Additionally, it safeguards the stone when it is put in jewelry.
  4. Laser inscriptions that are used to mark a diamond for identification are placed in the girdle for discreet placement without affecting the diamond’s appearance and performance. 



Types of Girdle 

Diamond girdles come in different forms. Depending on how it was created, the girdle can be faceted, polished, or unpolished.  

Faceted Girdle

The faceted girdle, which is more prevalent in the round and oval diamonds with triangular facets, follows the forms of the facets and appears thin and thick from the side. 

Polished Girdle

Polished girdles are flat and cut in a straight line; they are frequently seen on rectilinear forms including princess, emerald, cushion, and asscher. 

Unpolished Girdle

Unpolished girdles, commonly referred to as "bearded" girdles, are rough and still carry the etch marks left behind by the bruting or cutting of the diamond, giving them a frosted appearance. In the early days, unpolished girdles are left the way they are. Modern diamond cutting opened the door to polished and faceted girdles as technology developed.


How a Girdle is Graded

The ideal cut of a diamond is determined on the girdle thickness. The weight of the diamond and its carat weight is relative to the thickness of the girdle. If the girdle is too thin, it increases the risk of chipping that can damage the diamond. On the other hand, if the girdle is excessively thick, the diamond will get heavier yet the sparkle will suffer due to a poor light return.

 The diameter of the diamond and the girdle thickness are taken into account by GIA when grading the girdle at a 10x magnification. An optical device measures the girdle thickness, which is then calculated using the formula below:


Girdle Thickness (%) = (girdle thickness / average diameter) x 100


Here is the girdle grading system established by GIA to classify a diamond girdle:



Considerations for a Diamond's Girdle

There is a lot to consider when it comes to diamond girdles. You can save some money, time, and effort by doing your research and learning what a diamond's girdle is before shopping for the ideal stone.  

  1. Choose a diamond girdle with the thickness ranging from thin to slightly thick girdles when it comes to round diamonds. 
  2. For diamond shapes other than round, a range from thin to very thick is good. Pear, heart, marquise and oval shapes benefit from thick girdles for strength particularly on the pointed edges to avoid damage or chipping.
  3. When in doubt, speak with a reputable jeweler who can advise you on the diamond cut that most closely matches your preferences. You can also schedule a FREE  consultation with us, and we will be happy to help you with the entire process of finding your ideal ring.



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