Polish and symmetry

A diamond's beauty depends on its cut, and GIA assesses cut in terms of face-up appearance, design and craftsmanship. Design is mostly the proportions: the angles and sizes of the facets. Craftsmanship is polish and symmetry, meaning how well the cutter carried the design out.

GIA defines polish as the overall condition of the finished facet surfaces. It defines symmetry as the exactness of the shape and the placement of the facets.

Both are judged under magnification. At GIA, several graders view each diamond at 10x under standard conditions, evaluating it independently and recording clarity, polish and symmetry together. These are fine details, which is why the report states them as grades.

Both sit on the diamond grading report with the other quality results, including clarity and fluorescence. They are reported as their own grades, separate from the cut grade, and they are words rather than numbers. For a round brilliant, a polish or symmetry grade one step below the top does not rule out an Excellent cut grade, provided the stone's light performance and proportions are exceptional.

That matters for fancy shapes. As of 2026, GIA gives an official cut grade only to the round brilliant, which it describes as the only cut with standardized facets. An oval, pear, cushion or emerald cut diamond still has its polish and symmetry evaluated. For those shapes the two finish grades, together with the proportions, are the main craftsmanship information on the report.

GIA counts them as part of cut, and says a diamond with good polish makes better use of the light that enters it. GIA's buying advice is framed around the overall cut grade rather than polish or symmetry alone: aim for Excellent or Very Good to get a diamond that looks bright and balanced, with Very Good offering similar appeal at a lower cost. Stones graded Good, Fair or Poor typically show noticeable reductions in brightness or symmetry.

Because polish and symmetry feed into that overall picture, a one-step difference between two stones is a reason to compare them side by side, not a reason to rule one out. GIA's own reminder is that two diamonds with identical reports will still look different. The report narrows the field and your eyes make the final choice.

Treat them as a check on a stone you already like rather than as the starting point:

1. For a round diamond, read the cut grade first, then the polish and symmetry lines to see how they compare with it.
2. For a fancy shape, read polish and symmetry together with the proportions, then judge the face-up pattern yourself.
3. Compare two or three reports side by side, looking at the finish lines along with colour and clarity.
4. Look at the stones in person or on a clear video, in more than one light.

If the stone is going into a custom engagement ring, a showroom visit is the place to talk through the stone and the setting together.