The girdle is the dividing line between the crown and the pavilion of the diamond. Its function is to protect the edge of the stone from damage and fracture. The girdle should be thin, so that it is just visible to the unaided eye as a light line. A thick girdle can not only adversely affect the color of a cut diamond, but also diminish the light yield and with it reduce the brilliance, as light rays in the region of the girdle width are refracted into the air and not totally reflected. This applies to girdles left in a natural state, as well as to polished or faceted girdle, which only reinforce the perfection of well made stone it is also thin and even. Completely or partially knife sharp girdles are dangerous, as they easily fracture during setting of the stone and can thus produce nicks and cleavage cracks.
As the thickness of the girdles is expressed in percentage of the girdle diameter, it is dependent on the size of the stone, no single size can be given as ideal girdle. The girdle thickness examined by 10X magnification and graded as:
1) Extremely Thin to Very Thin Girdle
2) Thin Girdle
3) Medium to Slightly Thick Girdle (This is the most desirable, or Ideal girdle thickness)
4) Thick Girdle
5) Very Thick to Extremely Thick Girdle
A Culet is the point at the bottom of a diamond’s pavilion which has been cut off to make the stone more durable. The culet of a diamond should be in the center of the stone, i.e. in the middle of the widest part or table. As the light which falls perpendicularly on a stone emerges straight through the culet and thus causes a loss of light, the culet should be as small as possible, for a large on looks, when seen through the table , like a black hole. The size of the culet is visually examined through the table by a 10X magnification and described as:
2) Very Small
5) Very Large
The finish of a diamond consists of two components:
It relates to the exactness of the shape and arrangement of the facets.
It relates to the appearance of the individual facets and how well each is polished.