Assessing culet and girdle in standard round brilliant diamonds at the GIA Laboratory

ulet size and girdle thickness are important elements in the Gemological Institute of America’s (GIA) new Diamond Cut Grading System, as they can affect evaluations of the face-up appearance and design aspects of overall cut quality (see figure 1).This article reviews the criteria and methods used by the GIA Laboratory to assess culet and girdle, explains their role in the new cut grading system and presents specific examples of different culet sizes and girdle thicknesses. It is important to note that there will be no change in the GIA Laboratory’s methods for assessing culet size and girdle thickness due to the introduction of the new cut grading system. In GIA’s International Diamond Grading SystemTM,culet size (see figure 2) is described as none, very small, small, medium,slightly large, large,very large or extremely large. Girdle thickness is described as extremely thin, very thin, thin,medium,slightly thick,thick,very thick and extremely thick.Girdle thickness is assessed as a range from the thinnest BY BRUCE F. LANZL, PHILLIP M. YANTZER, RONALD H. GEURTS AND PETER A. DE JONG G E M O L O G Y