Polish and symmetry are the two finish grades on a diamond report. Polish describes how smooth the facet surfaces are. Symmetry describes how evenly those facets are shaped and aligned, and how even the outline is. The Gemological Institute of America records both on a standard report, on a scale from Excellent through Very Good, Good and Fair to Poor. They are easy to skim past, but they tell you something useful about how carefully the stone was finished.
What polish means
Polish is about the surface of each facet. Fine scratches, marks or a slightly cloudy patch from the polishing wheel can all be polish features. GIA assesses them under magnification, looking at the diamond face up. An Excellent polish grade, in GIA's finish guidance, ranges from no visible polish features to a few minute ones that are hard to see even at 10 times magnification. A lower grade means those features are easier to find. Polish is not the same as clarity: a stone can have excellent surfaces and still have inclusions inside it, or the other way around.
What symmetry means
Symmetry is about whether the facets meet as they should, whether the outline is even, and whether one side of the stone mirrors the other. On a fancy shape this includes the shoulders of an oval or the alignment of the points on a marquise. GIA again works under magnification. Minute symmetry features can still sit within an Excellent grade if they are very hard to see face up. Larger misalignments or a noticeably uneven outline would be reflected in a lower grade.
For a standard round brilliant, polish and symmetry are part of the cut grade. GIA's finish guidance is that both must be Very Good or Excellent for the cut grade itself to be Excellent, and that they can be one grade lower than the cut grade without bringing that cut grade down. Our guide to why cut matters explains how those pieces fit together.
How we use the grades
Most fancy shapes do not receive a GIA cut grade, so polish and symmetry become even more useful to read, alongside the measurements and a view of the stone. We would not choose or reject a diamond from these two words alone. A Very Good finish can look beautiful in the hand. An Excellent grade is a good sign that the surfaces and outline have been carefully finished, but we still look at the diamond with you on a video consultation.
Nothing is made until you approve the design and the stone in writing. A 70 percent deposit is paid then, making time is 5 to 6 weeks, and the ring is UK hallmarked before insured, tracked FedEx delivery. If you would like to go through a report with us, get in touch, browse the diamonds we can source, or see our guide to how to read a GIA certificate.
Frequently asked questions
What are polish and symmetry on a diamond report?
Polish describes how smooth the facet surfaces are. Symmetry describes how evenly those facets are shaped and aligned, and how even the outline is. GIA records both as grades on a standard report, using a scale from Excellent through to Poor.
Do polish and symmetry affect the cut grade?
For a standard round brilliant, yes, they form part of the finish that GIA factors into the cut grade. To qualify for an Excellent cut grade, GIA requires polish and symmetry to be Very Good or Excellent. The two grades can be one step below the cut grade without bringing that cut grade down.
Can you see polish and symmetry without a loupe?
Often only the more obvious issues show in ordinary light. GIA assesses these grades under magnification. We still look at the stone with you on a video consultation, because a report grade and the impression in the hand should be considered together.
Do fancy shapes receive polish and symmetry grades?
Yes. Even when a fancy shape does not receive a GIA cut grade, the report still records polish and symmetry, along with the measurements. We review those grades with you when we shortlist stones.