A diamond girdle can be bruted or polished. Modern diamonds usually have girdles with small facets giving them better transparency and stronger brilliance. Step-cut diamonds usually have polished girdles that are not faceted.
Bruted girdles were typically left on old cuts before girdle faceting became common. Counterintuitively the bruted girdles are better at masking the diamond tint, which means that once such a stone is repolished and facets are added, the stone might drop a grade or two in color. However, they tend to absorb dirt and oils, requiring periodic cleaning.
Girdle thickness effect
A girdle is the widest part of a gemstone, separating the crown above from the pavilion below. The girdle’s circumference defines the stone face-up measurements. Girdle thickness does not affect a diamond’s brilliance and fire. A diamond with an extremely thin girdle has an elevated risk of chipping along the girdle edge during setting or when worn. However, it does not pose a challenge for a qualified stone setter. A diamond with an extremely thick girdle weighs more and looks smaller than a diamond of the same carat weight and a thinner girdle. Given a choice, diamonds with extreme girdles are less desirable than similar diamonds with moderate girdle thickness.
GIA girdle grades
- Extremely Thin: May be prone to chipping or breaking unless properly set
- Very Thin: Typically a very good cut grade in diamonds
- Thin, Medium: The most desirable girdle thickness
- Slightly Thick, Thick: Typically an excellent cut grade
- Very Thick: Typically a good to a very good cut grade
- Extremely Thick: Makes a diamond to face-up smaller
In the past, girdles were left unpolished after the bruting process, where two diamonds are rotated against each other to give them a round shape. Such girdles with a frosted appearance are called bruted or rough. “Bearded” girdles have microscopic feathers resembling tiny hairs radiating from the girdle’s edge. This is the result of too much pressure applied during the bruting.