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Diamond Symmetry and Polish Grades Explained

Symmetry and polish are two of the three grades that make up a diamond's overall cut score, alongside proportions — and together they decide whether light bounces cleanly back to your eye or leaks out the sides. A diamond graded Excellent in both is judged to have facets that align almost perfectly and a surface free of visible blemishes under 10x magnification, which is why labs cap the overall cut grade at only one level above either one. In short: you can't have an Excellent-cut diamond with mediocre symmetry or polish, no matter how good the proportions look on paper.

Key takeaways

• Symmetry measures how precisely a diamond's facets are shaped, sized, and aligned; polish measures how smooth its surface is.
• Both are graded Excellent to Poor by GIA and IGI, under 10x magnification, by trained graders.
• Neither grade stands alone on a certificate — cut grade is effectively capped by the lower of the two, so a diamond can't be "Excellent cut" with "Good" symmetry.
• The visual and price difference between Excellent and Very Good is usually small; the difference between Good/Fair and Excellent is where light leakage becomes noticeable.
• Montare's Triple Excellent standard requires Excellent cut, polish, and symmetry on every stone — it's the only combination that guarantees nothing is quietly dragging your diamond's brilliance down.

What is diamond symmetry?

Symmetry describes how precisely a diamond's facets are shaped, sized, and positioned relative to one another, and how well the crown (the top half) lines up with the pavilion (the bottom half) at the girdle. A grader checks this under 10x magnification, looking for two categories of issue:

• Proportioning flaws — an out-of-round girdle outline, an off-centre table, an off-centre culet, or misalignment between the table and culet.
• Facet-pattern flaws — facets that should match (all eight pavilion mains, for example, or all eight bezel facets) but don't, in size, shape, or angle.

An Excellent symmetry grade means the facets align with no visible misalignment at 10x. Anything less introduces small distortions in how light travels through the stone.

What is diamond polish?

Polish grades the smoothness of the diamond's outer surface — the finishing work done after cutting. A grader looks for leftover polishing lines, tiny nicks, pits, or burn marks left by the polishing wheel, and rates their number, size, and visibility on the same Excellent-to-Poor scale. Poor polish doesn't just look hazy under magnification; enough surface texture will genuinely soften a diamond's brilliance, because light scatters slightly instead of reflecting cleanly.

How GIA and IGI grade polish and symmetry

Both labs use a five-tier scale, assessed independently by trained graders under 10x magnification. IGI adds an "Ideal" tier above Excellent on overall cut for round brilliants, but polish and symmetry themselves follow the same five grades industry-wide:

Grade	What it means	Visible to the naked eye?
Excellent	Facets align with no visible misalignment; surface essentially blemish-free at 10x	No
Very Good	Minor misalignment or surface marks with negligible effect on appearance	Almost never
Good	Noticeable facet misalignment or surface marks that can slightly reduce brilliance	Occasionally, on close inspection
Fair	Clearly visible misalignment or polish lines affecting light return	Sometimes
Poor	Significant flaws that visibly dull brilliance and sparkle	Often

What causes poor symmetry or polish in the first place

Symmetry and polish aren't manufacturing defects so much as trade-offs made during cutting. A rough diamond crystal rarely has a perfect shape, and a cutter has to decide how much weight to sacrifice chasing flawless facet alignment versus how much rough to keep for a larger finished carat weight. Cutting for maximum carat retention — squeezing the largest possible stone out of the rough — is one of the more common reasons symmetry suffers, because it can mean an off-centre culet, a slightly out-of-round girdle, or facets that don't quite match in exchange for a few extra points of weight.

Polish issues have a more mundane cause: the polishing wheel itself. Faster, less careful polishing leaves fine parallel lines, tiny pits, or small burn marks (a slight discolouration from friction heat) on the surface. None of this is visible without magnification in a well-polished stone, but it accumulates in diamonds cut for speed and yield rather than precision — which is exactly the category of stone a Triple Excellent standard is designed to filter out before it ever reaches a customer.

Practical buying tips: when Very Good is fine, and when it isn't

If you're shopping outside a house standard like Montare's and comparing individual certificates, a few rules of thumb help:

• Round brilliants: stick to Excellent or Very Good on both. Below that, light leakage becomes more likely to be visible even to an untrained eye, and the discount rarely compensates for the loss in sparkle.
• Fancy shapes (cushion, emerald, radiant, pear): pay closer attention here, since labs don't issue an overall numeric cut grade for most fancy shapes — polish and symmetry are two of the few objective cut indicators you have, alongside table and depth percentages.
• Larger stones (3ct+): flaws that are invisible at 10x on a 1ct diamond can become marginally easier to spot at larger sizes, simply because facets are larger and easier for the eye to resolve — another reason precision cutting matters more, not less, as carat weight goes up.
• Budgeting: if you need to make a trade-off somewhere, Very Good symmetry and polish is a far safer place to save than compromising on colour, clarity, or cutting for carat weight at the expense of proportions.

Why polish and symmetry matter more than shoppers realise

It's tempting to treat polish and symmetry as fine print beneath the headline cut grade. They're not. Poor symmetry doesn't just look uneven on a report — it can cause light to leak out of the side or bottom of the diamond instead of bouncing back toward your eye, dulling sparkle even when the proportions are technically ideal. Polish and symmetry feed directly into the overall cut grade, and cut has the single biggest effect on how a diamond looks, more than colour or clarity in most cases.

Because labs cap the overall cut grade at roughly one tier above the lower of the two, a diamond can't earn a Triple Excellent cut grade while carrying Good symmetry — the certificate simply won't allow it. That's a useful shortcut when you're comparing stones: if the cut grade is Excellent, polish and symmetry are already doing their job.

Does the grade actually change the price?

Yes, though less than colour, clarity, or carat weight. Industry pricing data suggests the gap between Excellent and Very Good polish and symmetry typically runs 5–12% on comparable stones, while a diamond with Excellent symmetry and polish can sit noticeably higher than one graded Good on both. Much of that premium reflects buyer preference for a clean certificate rather than a difference the naked eye can detect — Very Good and Good grades are frequently invisible without magnification, which is exactly why some buyers choose them deliberately to save on the parts of a diamond that don't affect how it looks.

Montare doesn't offer that trade-off, because we don't think it belongs in an engagement ring. Every diamond we set is Excellent across cut, polish, and symmetry — full stop.

How to check polish and symmetry on your certificate

Both grades sit in the same summary block as colour, clarity, and cut on an IGI or GIA report, usually labelled "Polish" and "Symmetry" directly beneath the overall "Cut" grade. If you're comparing two stones with the same colour, clarity, and carat weight, this is the section to check next — it's often the difference between a diamond that reads as merely good and one that reads as genuinely brilliant in person.

The Montare standard: why we only work with Triple Excellent

Montare's house standard requires D–E colour, VVS1–VVS2 clarity, Triple Excellent cut (cut, polish, and symmetry all graded Excellent), IDEAL table and depth percentages, a 3 carat minimum, and IGI certification on every stone. Triple Excellent is the part of that standard that speaks directly to symmetry and polish — it's our way of guaranteeing that nothing about the finishing work is quietly capping how much light your diamond returns. You'll never find a Montare stone with Very Good or Good symmetry hiding behind a headline cut grade, because we don't buy them in the first place.

Every ring is held to this standard, made to order in Toronto, and paired with our lifetime promise and a fully insured, free shipping across Canada.

Frequently asked questions

Is symmetry or polish more important?

Neither outweighs the other in isolation — both feed into the overall cut grade, and a weakness in either one can cap it. For light performance, symmetry has a slightly larger practical effect because misaligned facets change how light paths intersect inside the stone, while poor polish mainly affects surface clarity.

Can a diamond have Excellent cut but Good symmetry?

No. Labs cap the overall cut grade at roughly one tier above the lower of polish or symmetry, so an Excellent overall cut grade requires at least Very Good in both, and typically Excellent in both for a round brilliant to earn GIA's or IGI's top tier.

Is Very Good symmetry noticeably worse than Excellent?

Usually not to the naked eye. Very Good grades reflect minor misalignment with negligible visual effect — most people, including experienced jewellers, can't reliably tell a Very Good stone from an Excellent one without a loupe.

Do fancy shapes like cushion or emerald cut grade symmetry differently than round diamonds?

The grading criteria are broadly the same, but fancy shapes have more facet-pattern variation to assess, and neither GIA nor IGI issues an overall numeric cut grade for most fancy shapes the way they do for round brilliants — so polish and symmetry become more important as standalone indicators of quality on a cushion, emerald, or radiant cut.

Does Montare ever sell diamonds below Excellent symmetry or polish?

No. Triple Excellent — Excellent cut, polish, and symmetry — is a fixed part of our house standard alongside D–E colour, VVS1–VVS2 clarity, and IGI certification. It isn't an upgrade option; it's the floor.

Where do I find the symmetry and polish grades on my diamond's report?

They're listed in the grading summary of your IGI certificate, directly below the overall cut grade, alongside colour and clarity.