Diamond Polish and Symmetry Grades: Do They Really Matter?

Diamond polish and symmetry at a glance

Diamond polish and symmetry are two finish grades on a grading report. Polish describes how smooth and flawless the facet surfaces are, while symmetry describes how precisely the facets are shaped, aligned and positioned. Both are usually graded Excellent, Very Good, Good, Fair or Poor. Excellent or Very Good is ideal for most buyers, and the difference between them is rarely visible.

These grades sit quietly beneath the headline 4Cs, which is why many buyers overlook them. Yet they are part of what makes a diamond's cut quality, and for fancy shapes that receive no overall cut grade, they are among the few objective indicators of craftsmanship you can read on paper.

Understanding what each grade actually reflects helps you avoid two mistakes: paying a premium for perfect finish grades you will never see, and accepting poor finish grades that genuinely dull a stone.

What polish measures

After a diamond is cut, its facets are polished on a spinning wheel coated with diamond powder. The polish grade reflects how well this was done. Graders look under magnification for polish lines, which are fine parallel grooves, burn marks from excessive heat, scratches, nicks, and rough or bearded girdles.

Excellent polish means such features are extremely difficult to find at 10x magnification. Very Good means they are difficult to find. Good means they are noticeable under magnification but not to the naked eye. Fair and Poor grades indicate features that may begin to affect how cleanly light passes through and reflects from the surface.

In everyday wear, the difference between Excellent and Very Good polish is essentially invisible. Good polish is also usually fine for small stones. Only at Fair and Poor levels does polish start to matter visually.

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What symmetry measures

Symmetry looks at the geometry of the facets: whether they are the right shape, whether they meet neatly at points, whether the table is centred, whether the culet is centred, and whether the outline is even. Misalignments such as an off-centre table, a wavy girdle, extra facets or facets that do not meet precisely all lower the symmetry grade.

Symmetry affects how evenly light travels through the diamond. A stone with excellent symmetry tends to show an even, balanced pattern of light and dark when viewed face-up. A stone with poor symmetry may show uneven brightness, a slightly lopsided outline or a pattern that looks irregular.

For round brilliants, symmetry contributes to visual effects like a crisp "hearts and arrows" pattern seen with special viewers in very precisely cut stones. This pattern is a sign of extreme precision, not a requirement for beauty.

How polish and symmetry relate to cut grade

For round brilliant diamonds, many laboratories factor polish and symmetry into the overall cut grade. A stone generally cannot achieve the top cut grade with poor polish or symmetry. This is why you often see round stones described as "triple Excellent" or 3EX: Excellent cut, polish and symmetry.

For fancy shapes such as oval, pear, emerald, cushion, princess and marquise, labs often give no overall cut grade. Here, polish and symmetry grades become more important as indicators of craftsmanship, alongside proportions like depth percentage and length-to-width ratio, and a careful look at the stone itself.

Even so, a fancy shape with Excellent polish and symmetry can still have a strong bow-tie or a dull look if its proportions are off. These grades are necessary for quality, not sufficient on their own. Think of them as evidence of careful workmanship: they tell you the cutter took time over the finish, which often, though not always, goes hand in hand with well-judged proportions. Use them to shortlist fancy shapes, then let the video decide between the finalists.

Do polish and symmetry affect price?

Yes, but modestly compared with colour, clarity and carat. Stones with Excellent polish and symmetry typically sell at a small premium over those with Very Good grades, and Good grades often carry a further discount. Fair and Poor finish grades usually signal a stone that was cut with weight retention in mind rather than beauty.

For many buyers, a stone with Very Good polish or symmetry represents good value, especially if it looks lively on video. The saving may be small, but combined with smart choices elsewhere, such as an eye-clean clarity grade, it helps the budget stretch further.

For lab-grown diamonds, finish grades are frequently Excellent across the board, as growers often cut for beauty. Still, read the report rather than assuming.

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When a lower grade is perfectly fine

For small diamonds in earrings, pendants and multi-stone pieces, polish and symmetry grades are rarely provided, and differences would be invisible anyway. For solitaires, Very Good polish or symmetry is generally fine if the overall cut is strong and the stone looks bright on video.

Good symmetry can be acceptable in a fancy shape if the outline looks pleasing to you and the stone sparkles well. Some people prefer the character of slightly imperfect stones, especially in vintage-inspired designs or older cuts, where modern precision standards were not applied.

Where you should be cautious is with Fair or Poor grades on an important stone. These often accompany other compromises, like unusual depth or a thick girdle, and the stone may look noticeably less lively than its colour and clarity suggest.

Diamond polish and symmetry in older jewellery

Inherited and vintage diamonds, such as old mine or old European cuts found in family jewellery, were cut by hand with different goals and tools. Their polish and symmetry may not meet modern Excellent standards, yet they often have a soft, romantic glow that many people love.

If you are re-setting a family stone into a new ring or pendant, do not judge it harshly by modern grades. Ask a jeweller to check its condition, especially for chips around the girdle, and consider whether a light repolish is appropriate. Repolishing can improve surface finish but removes a tiny amount of weight, so discuss it carefully.

For insurance or valuation of older pieces, a fresh grading report can document the current polish and symmetry along with other characteristics.

How to see polish and symmetry in a video

You cannot see polish lines on a phone screen, but you can see some effects of symmetry. In a round brilliant viewed face-up, look for a balanced pattern where the arrow-shaped reflections and bright facets repeat evenly around the stone. If one side looks noticeably brighter or the pattern seems twisted, symmetry may be weaker. Check the outline too: a round stone should look truly round, and an oval should have smoothly matching sides.

For fancy shapes, check whether the two halves mirror each other. In a pear, the shoulders should be evenly curved and the point centred. In a marquise, both tips should line up with the centre. In an emerald cut, the step facets should form neat, parallel rows. Small asymmetries are common and often invisible once set, but obvious ones can make a stone look lopsided in a ring.

Ask the seller for a top view and a side view, in steady light, with the stone rotated slowly. Comparing two candidate stones in the same kind of video is the most reliable way to see whether an Excellent symmetry grade translates into a visibly neater stone for you.

Reading finish grades when you shop

On the certificate, find the polish and symmetry lines, usually below the 4Cs or in a section called "additional grading information". Check that the listing quotes the same grades. Then watch the video: look for an even, balanced sparkle pattern and a neat, symmetrical outline.

If you are choosing between two stones, one 3EX and one Excellent cut with Very Good symmetry, put them side by side on video. If you cannot see a difference, choose based on price, size and other grades. Diamond polish and symmetry matter most when they are poor; at the top end, your eye is the best judge.

As always, keep the certificate and GST invoice together, with the certificate number printed on the bill, so these details travel with the jewellery for future exchange, resale or insurance.

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