Polish and symmetry are the two execution grades assigned by GIA on every diamond grading report — for every shape, fancy or round. While the GIA cut grade exists only for round brilliants, polish and symmetry grades appear across the full spectrum of shapes: oval, emerald, cushion, pear, marquise, and all others. They are important, but they are also the most commonly misread line on a grading report.
The distinction matters: polish and symmetry are execution grades. They tell you how well the cutter executed the planned design — how clean the surfaces are, how well the facets align with each other. They do not evaluate whether the design itself is well-proportioned. A perfectly polished, perfectly symmetrical stone can still have terrible light performance if its depth, crown angle, or table percentage are outside ideal ranges. Excellent polish and symmetry is a necessary condition for a well-cut stone, not a sufficient one.
| Grade | Surface condition | Practical effect | Buyer action |
|---|---|---|---|
| Excellent | No polish features visible under 10× magnification | Negligible impact on light performance | No action needed |
| Very Good | Difficult to see under 10×; not visible face-up | Minimal impact; rarely noticeable | Acceptable; common on well-cut stones |
| Good | Easy to see under 10×; not visible face-up to naked eye | Small but measurable brightness reduction | Acceptable on stones where value matters more |
| Fair | May be visible face-up under magnification | Visible brightness reduction; slight haze possible | Avoid for center stones |
| Poor | Visible to naked eye face-up | Obvious haziness and brightness loss | Avoid |
| Defect | What it is | Visible effect |
|---|---|---|
| Off-center table | Table facet shifted from the stone's optical center | Pattern asymmetry; one side brighter than the other |
| Misshapen table | Table facet not a regular octagon | Irregular scintillation pattern face-up |
| Off-center culet | Culet displaced from the point directly below the table | Reflection distortion; affects pattern symmetry |
| Wavy girdle | Girdle undulates in thickness around the outline | Irregular profile; affects how light returns at the edge |
| Misaligned facets | Upper and lower half-facets don't align at the girdle | Visible break in pattern at the girdle plane |
| Out-of-round | Girdle outline not circular (for rounds) | Visible oval or irregular outline face-up |
| Extra facets | Additional facets not part of the standard design | Disruption in expected pattern symmetry |
| Natural on girdle | Remnant of rough diamond skin left on the girdle | Flat, rough patch on girdle edge |
Polish and symmetry are graded separately, but GIA's cut grade for round brilliants incorporates both as components of its overall assessment. For fancy shapes, polish and symmetry are the closest thing to a cut evaluation you will find on a GIA report — the cut grade field simply does not appear. This is why understanding what these grades measure — and what they don't — is especially important for fancy shape buyers.
The standard recommendation is to target Excellent or Very Good in both polish and symmetry. The difference between Excellent and Very Good is generally not visible to the naked eye and often not visible under 10× magnification. Good polish or symmetry introduces minor optical compromise that is measurable but rarely meaningful for a center stone in normal lighting conditions. Fair or Poor grades in either category should be avoided — they represent genuine optical deficiencies that a sharp eye can detect.
Polish and symmetry tell you how well a stone was executed — not how well it was designed. Excellent polish and symmetry are the baseline, not the goal. A stone with Excellent/Excellent polish and symmetry and a 68% depth is still a poorly proportioned stone. Target EX or VG in both grades, then evaluate proportions and cut grade (for rounds) separately. Never let polish and symmetry Excellent serve as a stand-in for overall cut quality.