BEYOND THE 4CS
Two small lines on the report that describe how carefully a diamond was finished. What they measure, and how much they should matter to you.
Cut is about a diamond’s proportions: the angles and depths that decide how light travels through it. Polish and symmetry are about finish: how smooth the facets are, and how precisely they line up. Together they describe the quality of the cutter’s work.
Both are graded on the same scale: Excellent, Very Good, Good, Fair and Poor.
Polish describes the condition of the diamond’s surface after cutting. Tiny polish lines left by the wheel, faint burn marks from too much heat, or small scratches all lower the grade. A well-polished diamond has crisp, glassy facets that reflect light cleanly.
At Excellent and Very Good, polish marks are invisible without magnification. Below Good, a very poor polish can slightly dull a stone, though this is rare in diamonds sold for engagement rings.
Symmetry describes how exactly the facets are shaped, placed and aligned: whether the table is centred, whether facets meet at neat points, whether the outline is even, and whether the culet sits in the middle. Good symmetry keeps the pattern of light balanced across the stone.
In fancy shapes such as ovals, pears and marquises, symmetry also affects the outline you see from above. A lopsided pear or a marquise with uneven halves is a symmetry problem you can see without any equipment.
For round brilliants, you will often hear the phrase triple excellent, or 3EX. It means the cut, polish and symmetry grades are all Excellent. It is the mark of a round diamond cut with real precision, and a sensible target if you are choosing a round.
For a round, aim for Excellent across the board. For fancy shapes, which do not receive an overall cut grade from GIA, Very Good or Excellent polish and symmetry are a good sign, but your eyes matter more than the report: look at the outline, the bow-tie and the overall brightness.
Beyond Very Good, differences in polish and symmetry are rarely visible on the hand. Do not pay a large premium for a grade you cannot see, but do not accept Good or below on a stone you will wear every day.
Cut grades a diamond’s proportions and how it handles light. Polish grades the smoothness of its surface. Symmetry grades how precisely its facets are shaped and aligned.
A round brilliant diamond graded Excellent for cut, polish and symmetry. It indicates precise, high-quality cutting.
Yes. Differences between Very Good and Excellent are not visible without magnification. Avoid Good or below for an engagement ring.
GIA gives an overall cut grade only to round brilliants. For fancy shapes, polish, symmetry and your own eyes are the best guide.
STILL HAVE QUESTIONS?
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