A polished diamond has a special shape and comprises several parts, each with its own name. The widest feature of the diamond is called a girdle or roundist.
The girdle is the thin perimeter of a diamond, dividing the "crown," the upper part of the diamond from the "pavilion," the lower part of the diamonds.
When viewing a diamond in its setting or from a profile view, the girdle is the widest part (or the circumference) of the polished diamond – the portion of the stone that makes contact with the setting itself.
Creating a diamond's girdle
A rough diamond undergoes several cutting and polishing stages before reaching its final shape. Creating the girdle entails cutting the diamond to determine the maximal size of its circumference. Once the latter has been determined, the other sides of the diamonds are polished and cutters take great care not to damage the girdle during the polishing process.
Determining the girdle's thickness
When polishing the diamond, the cutter can create a wide or narrow girdle. The optimal width ranges from thin to medium, depending on the diamond's desired shape.
Too narrow a girdle may be damaged in certain parts, and disappear during the polishing process, thus losing the diamond's round shape. A narrow girdle is inherently vulnerable and may fracture when the diamond is set in a piece of jewelry, thus diminishing the value of the diamond.
On the other hand, a very wide girdle misuses the rough diamond and even detracts from its beauty, as it casts a gray shadow on diamond's interior. To eliminate this shadow, the girdle is cut using a roundist polishing process.
The girdle in fantasy diamonds
Specialty-cut diamonds also feature a girdle. In small marquise-cut diamonds, for instance, the girdle is cut as if they were round diamonds. In fancy cuts for large diamonds, the girdle is created using the roundist polishing process.
The square fantasy diamond cuts – baguette, cara, princes – feature a straight-edge, facet-like girdle, which is best suited for their setting in jewelry.
The girdle in jewelry
The girdle is the part of the diamond that anchors it into a piece of jewelry.
When the diamond is set, the girdle becomes almost invisible, as it is hidden by the metal that holds the diamond in the jewelry.
In a prongs setting, however, the girdle is visible. In a solitaire ring, for instance, the prongs hold the diamond in place by the girdle, so even when the diamond is set, its shape remains in full view, including the girdle.