Diamond Polish and Symmetry Explained
In short: Polish and symmetry are the 'finish' grades on a diamond report. Polish is how smooth the facets are; symmetry is how precisely they line up. Aim for Excellent or Very Good in both — anything lower can dull the sparkle, especially on a round brilliant.
What is diamond polish?
Polish grades the smoothness of a diamond's facet surfaces after cutting. Under magnification, a poorly polished facet can show faint marks, lines or a slightly hazy surface left by the polishing wheel. These scatter light instead of reflecting it cleanly, which can take a little life out of the stone.
What is diamond symmetry?
Symmetry grades how precisely the facets are shaped, sized and aligned. In a well-cut diamond the facets meet at exact points and mirror each other around the stone. Poor symmetry — misaligned facets, an off-center culet, a wonky table — sends light in the wrong directions, so the diamond doesn't sparkle as evenly as it should.
How they're graded
Both are graded on the same five-point scale as cut: Excellent, Very Good, Good, Fair and Poor. On a GIA report you'll find them listed separately from the overall cut grade, and together they're sometimes called the 'finish' of the diamond.
What grades to look for
Excellent or Very Good in both polish and symmetry is the safe target, and it doesn't cost much to insist on. Good is usually fine when viewed face-up and can be a sensible saving. Fair and Poor are best avoided, particularly in a round brilliant where precision has the biggest effect on sparkle.
How much they affect beauty and price
Polish and symmetry have a smaller effect than the main 4Cs, but they aren't nothing. A poor finish can visibly reduce brilliance and, at the lower grades, slightly lower the price. The sweet spot is Very Good to Excellent: you get the full sparkle without paying the top premium reserved for flawless finishing.
Do they matter for fancy shapes?
GIA only gives round brilliants an overall cut grade, so for fancy shapes like ovals, emeralds and pears, polish and symmetry become even more useful. With no cut grade to lean on, they're two of the clearest signals of how carefully the stone was finished — read them alongside the diamond's proportions and a 360-degree video.
How to check them
Both grades are printed on the diamond's grading report. Read them together with the cut grade and proportions, and back that up by viewing the stone itself, ideally on video. Numbers on paper tell you a lot, but seeing the sparkle in person confirms it.
Diamond polish and symmetry: frequently asked questions
What are polish and symmetry on a diamond report?
Polish is the smoothness of the facets; symmetry is how precisely those facets are shaped and aligned.
What polish and symmetry should I choose?
Excellent or Very Good in both gives the cleanest sparkle without paying the top premium.
Do polish and symmetry affect sparkle?
Yes. A poor finish scatters or misdirects light and can noticeably dull a diamond.
Are they as important as cut?
No. Cut matters most, but polish and symmetry fine-tune the finish, and they matter more on fancy shapes that have no overall cut grade.
Where do I find the polish and symmetry grades?
They're listed on the diamond's grading report, on the same Excellent-to-Poor scale as cut.
