Polish Excellent (Pol Ex)
Polish Excellent (Pol Ex)
The top grade on GIA's polish scale, indicating no polish marks visible at 10×
Polish Excellent, abbreviated Pol Ex on a GIA diamond grading report, is the highest of the five polish grades GIA assigns. A stone graded Pol Ex shows no polish marks, scratches, or surface irregularities visible to a trained grader at 10× magnification. The grade is assessed independently of the symmetry grade and the proportions-based cut grade, although all three contribute to overall light performance.
What polish grading evaluates
Polish refers to the smoothness of each facet's surface. Even a mathematically perfect set of facet angles will return less light than expected if the surfaces themselves carry residual marks from the polishing wheel. The GIA polish grade describes the cumulative effect of these surface conditions across the whole stone, observed under standardised laboratory illumination at 10× magnification using a binocular microscope or loupe.
Common polish defects considered include polish lines, surface graining marks, abrasions on facet junctions, and burn marks left by overheating during the polishing process. A stone qualifying for Pol Ex is free of all such marks at the magnification used. The grade does not address proportions or symmetry; a stone can be Pol Ex but cut Fair, or cut Excellent but Pol VG.
Effect on appearance
The visible difference between Pol Ex and Pol VG is generally not detectable to the unaided eye, although collectors and dealers familiar with the comparison sometimes report a slight crispness to the reflections from a Pol Ex stone. Light return is theoretically optimised at Pol Ex because no surface scattering disrupts the geometry of total internal reflection, but the gain over Pol VG is small in practice and rarely reaches the threshold of casual observation.
In the trade
Triple Excellent — Cut Ex, Pol Ex, Sym Ex — is the standard combination sought for premium round-brilliant diamonds and commands a modest premium over Cut Ex stones with lesser polish or symmetry grades. The premium is real but limited: the market understands that the visible difference is small. For shapes other than round-brilliant, where GIA does not currently issue a cut grade, Pol Ex still functions as a meaningful quality marker on the report.