Girdle thickness is how thick the girdle is at its thinnest and thickest points. A report gives it as a range of words, such as "Thin to Medium".
In more detail
The eight words are: Extremely Thin, Very Thin, Thin, Medium, Slightly Thick, Thick, Very Thick and Extremely Thick. A round's girdle has 16 valleys and 16 hills. The grader reads it at the valleys, in profile at 10x. Too thin is a chipping risk and too thick adds hidden weight; GIA allows Excellent for Thin to Slightly Thick.
On a grading report
On the proportion diagram as a range of words plus an average percentage, and the girdle finish. IGI's Ideal band is Thin to Slightly Thick.
Related terms
- Girdle: The girdle is the narrow band at the widest part of a cut stone, between the crown and the pavilion. It is the edge that a setting grips.
- Knife-edge girdle: A knife-edge girdle has no girdle band at all: the crown and the pavilion meet in a sharp line.
- Durability (cut grade): Durability is the part of GIA's cut grade that checks for a risk of damage. The risk comes from a very thin girdle or thin points.
- Weight ratio: Weight ratio is the part of GIA's cut grade that compares a diamond's weight with its diameter. A stone can carry too much or too little weight for its width.
- Total depth: Total depth is the height of a stone from table to culet as a percentage of its average diameter. It equals crown height + girdle thickness + pavilion depth.