Our cut tutorial would not be complete if we do not give proper attention to this vital subject of girdle cutting which was first featured in GIA's Gems and Gemology and released online in Feb of 2004. Painting and digging, while relatively new terms to the retail trade are quite common in the world of diamond cutters and there is a certain degree of it that is done on many diamonds being cut that are on the market. Super ideal cuts (ie. Hearts and Arrows type diamonds) are no exception as the results of painting and digging help the cutter maintain extra weight on the finished product thus increasing price.
This would not be so terrible were it not for the optical effects it has on a diamonds appearance, generally decreasing brightness, fire & scintillation which we will demonstrate in photography (and soon after video) taken under GIA's Diamond Dock and also through dynamic images and modeling of stones we have scanned in.
What makes this article intriguing is that the diamonds used in this study have what would be considered "ideal proportions" according to any cut grading system. The only difference in the subject diamonds is that of the girdle cutting, which unfortunately are not provided in standard Sarin analysis provided by most machines.
Back in June of 2005 when AGS released it's new cut grading system for round brilliant cuts, the cover story on the Rappaport Diamond Report (a trade journal many consult) was of the release of AGS' new system. However, hidden obscurely in the back pages of that same issue GIA had released a comprehensive article explaining the subject in detail which we wish to explain and expound upon showing how to identify these characteristics through the various scopes, scanners and technologies many consumers are consulting in their in-store and online purchases.
In brief, painting and digging involve certain shifted orientations in how the upper girdle facets and/or lower girdle facets are cut and how they are angled in relation to their neighboring main facet. Let's jump in with both feet and put this in layman's terms with graphics. The neat thing about this tutorial is that it demonstrates...
- A strength of the GIA Cut grading system and the newly released GIA Diamond Dock in being able to present an accurate depiction of how girdle cutting impacts diamond appearance.
- The science behind AGS ASET (Angular Spectrum Evaluation Tool) in being able to determine painting and digging. In this tutorial we will be referring to 3 different parts and measurements taken around the girdle.
In this tutorial we will be referring to 3 different parts and measurements taken around the girdle.
- One is the girdle thickness at the bezel depicted in blue. This is where the crown mains (or bezels) and pavilion main facets meet at the girdle.
- Second is the girdle thickness at the half facets (also called girdle bone) depicted in the red markers. This is where the half (both upper and lower) facets meet at the girdle.
- Lastly the girdle thickness in the valley's depicted by the green markers. This area is generally the thinnest part of the girdle and traditionally where girdle measurements and descriptions are given.