Girdle Thickness (5.31)
The girdle thickness is judged between the upper and lower girdle facets since this is where the girdle is at its thinnest. The vast majority of stones will have a range of thickness due to the slight (or obvious) inconsistencies in symmetry left by the cutter. A Very Thin to Slightly Thick range on a girdle is fairly common and is not unattractive. Girdle thickness can be judged under 10x magnification. The following are girdle thickness terms that are applicable in understanding and communicating to other dealers or clientele:
Extremely Thick: Very obvious and unattractive to the naked eye. Very negative value effect. (0.40+mm)
Very Thick: Very obvious and unattractive to the naked eye. Very negative value effect. About 2/3s the thickness of the Extremely Thick. (0.33-0.40mm)
Thick: Still very visible to the naked eye, but not nearly as negative as Very or Extremely Thick. Still an undesirable characteristic. (0.23mm-0.33)
Slightly Thick: Very common in finer makes. “Thin to Slightly Thick” or “Medium to Slightly Thick” is a neutral characteristic. Difficult to detect the detail of the Slightly Thick girdle with your naked eye, but quite obvious under 10x. (0.20-0.23mm)
Medium: A positive characteristic when “Medium” or “Thin to Medium”. Girdle looks very thin to the naked eye and has an attractive appearance under 10x. (0.15-0.20mm)
Thin: A positive characteristic when “Thin” or “Thin to Medium”. A very fine line with your naked eye and attractive under 10x. (Less than 0.15mm)
Very Thin: A negative characteristic, but not as negative as “Thick”, “Very Thick”, “Extremely Thick” or “Extremely Thin”. This begins to pose a risk of breakage. Very difficult to see with the naked eye and a very thin line under 10x.
Extremely Thin: A very negative characteristic, but not as negative as “Very Thick” or Extremely Thick”. Sometimes this may occur on a very small section of the girdle of the diamond when a report reads “Extremely Thin to Medium” for example. But even when the extremely-thin (knife-edge) section is short, the likelihood of damage is almost inevitable. Extremely thin girdles occur when the cutter has polished the upper and lower girdle facets into each other. Besides the obvious risk of damage, a knife-edge girdle also shows a straight edge or flat spot when viewed from the top.
