Introduction
Polish describes the surface condition of each facet on a finished diamond. After a cutter shapes the stone and grinds its facets on a rotating wheel, each facet surface should ideally be perfectly smooth and flat — a clean optical window that allows light to enter and exit without interference. The polish grade on a grading report tells you how closely the cutter achieved that ideal.
Polish is one half of what gemologists call finish — the other half being symmetry, which measures how precisely facets are aligned relative to each other. Together, polish and symmetry describe the quality of the craftsman's execution, separate from the diamond's proportions. For the broader relationship between these assessments, see Finish Overview.
Understanding polish matters for two practical reasons. First, it contributes to the overall cut grade for round brilliants — poor polish can lower an otherwise well-proportioned diamond's grade. Second, in severe cases, polish defects reduce the amount of light a diamond returns, affecting its visual brightness. Knowing what the grades mean and where the visible threshold lies helps you make a smarter purchase.
How Polish Is Graded
GIA assesses polish under standard 10x magnification — the same magnification used for clarity grading. A trained gemologist examines each facet surface for manufacturing marks left by the cutting process. The result is a grade on GIA's five-point scale:
Excellent
No polish features are visible under 10x magnification, or any features present are so insignificant that they have no effect on the facet's transparency. The surface acts as a clean window. This is the highest achievable polish grade.
Very Good
Minor polish features are visible under 10x magnification but are so faint that they have no impact on the diamond's face-up appearance. In practice, the difference between Excellent and Very Good polish is undetectable without magnification. Most gemologists and independent studies confirm that consumers cannot tell the two apart under normal viewing conditions.
Good
Polish features are clearly visible under 10x magnification and may occasionally be noticed by a skilled observer under the unaided eye in certain lighting conditions. At this level, the features do not dramatically reduce light return, but they are no longer negligible. A Good polish grade warrants visual inspection of the actual stone before purchase.
Fair
Features are noticeable under magnification and may be visible to the unaided eye. They can begin to affect how light passes through the affected facets, reducing the diamond's overall transparency and brightness. Fair polish is uncommon in reputable Czech retail channels.
Poor
Significant surface defects are visible without magnification and clearly affect the diamond's ability to transmit and return light. The stone may appear hazy or dull in the areas where polish is compromised. See Poor Polish Haze for more on how manufacturing defects scatter light. Poor polish is rare in the Czech market — most suppliers screen out stones at this level.
Common Polish Defects
The cutting process uses a polishing wheel impregnated with diamond powder to grind and smooth each facet. This process can produce several types of surface features, each with a distinct appearance under the loupe:
Burn marks
Whitish, hazy patches on a facet surface caused by excessive heat during polishing. When the diamond generates too much friction against the wheel, the surface can develop a clouded, frostbitten appearance. Burn marks are among the more noticeable polish defects and are a common reason for a downgrade below Very Good.
Scratches
Fine lines on the facet surface — not fractures within the stone, but surface-level marks from the polishing process. A single faint scratch on one facet rarely affects the grade, but multiple or prominent scratches across several facets will. Scratches are distinct from the naturals and surface graining that appear as clarity features.
Rough girdle
A granular, pitted, or uneven texture along the girdle — the narrow band around the diamond's widest point. While some girdle texture is normal (particularly on unpolished or "bruted" girdles), excessive roughness is graded as a polish feature. A rough girdle can affect how the diamond sits in its setting and may cause minor light scattering along the stone's edge.
Lizard skin
A textured, bumpy surface that resembles reptile skin, caused by the diamond's crystal structure resisting the polishing direction. Certain grain orientations are harder to polish smoothly, and when a cutter works against the grain, the surface may develop this characteristic uneven texture. Lizard skin typically appears on specific facets rather than across the entire stone.
Other features
Additional polish features include abrasion (tiny nicks or roughness along facet junctions), nicks (small chips at facet edges), and pits (tiny surface cavities). These are less common but are assessed the same way — under 10x magnification, judged by their visibility and effect on light transmission. For a comprehensive catalogue of individual polish features and how they appear on grading reports, see Polish Characteristics.
How Polish Affects the Cut Grade
For standard round brilliant diamonds, GIA incorporates the polish grade into the overall cut grade alongside proportions and symmetry. However, the three components are not weighted equally. Proportions — the angles and measurements that govern light performance — carry the most weight. Symmetry has a somewhat greater influence than polish, because a misaligned facet redirects more light than a surface scratch.
That said, polish can act as a limiting factor. A round brilliant with optimal proportions and Excellent symmetry but only Good polish will typically receive a Very Good overall cut grade rather than Excellent. The relationship is explained in detail in Cut Grade Scale.
For fancy-shape diamonds — ovals, cushions, emeralds, and others — GIA does not assign an overall cut grade. Polish and symmetry are graded individually, and they become the buyer's primary indicators of cutting quality. In that context, the polish grade carries proportionally more weight in your purchase decision.
When Polish Grade Matters — and When It Doesn't
The practical question for buyers is: where is the visible threshold?
Excellent vs Very Good: no visible difference. The features that separate these grades exist only under 10x magnification. For engagement rings, pendants, and everyday jewellery, a VG polish grade delivers the same visual result as EX at a lower price. In the Czech market, the price gap between otherwise identical stones with EX versus VG polish is typically 1–3%.
Good: worth inspecting. At the Good level, polish features are more than cosmetic under magnification — they may begin to affect how light moves through specific facets. This does not make the diamond unattractive, but it does mean you should view the stone (or high-resolution imagery) before committing. The savings over VG can be meaningful, especially in larger carat weights, so Good polish is not automatically a deal-breaker — just a reason for due diligence.
Fair and Poor: proceed with caution. These grades indicate features that may visibly reduce transparency and brightness. Unless the price reflects a significant discount and you have inspected the stone, these grades are best avoided. Polish defects at this level can contribute to the haze effect described in Transparency Problems.
Practical Tips for Czech Buyers
- Check polish and symmetry independently on the grading report. They are separate assessments — a diamond can have Excellent polish and only Good symmetry, or the reverse.
- For budget optimisation, Very Good polish is the strongest value position. Redirect the savings toward a better cut grade or higher carat weight, where the difference is actually visible.
- If comparing two stones with identical colour, clarity, and proportions, treat polish as a tiebreaker — but only when deciding between Good and Very Good or better. The gap between two Excellent stones is negligible.
- For fancy-shape diamonds without an overall cut grade, pay closer attention to both polish and symmetry, as they are your only standardised indicators of cutting quality.
- Czech consumer protection law requires that grading report grades accurately represent the stone. If a seller quotes "Excellent polish," that claim must be verifiable against the accompanying laboratory report.
Summary
Polish measures the surface smoothness of a diamond's facets — how cleanly the cutter finished each optical window. GIA grades it on five levels under 10x magnification, from Excellent (no visible features) to Poor (defects visible to the unaided eye that reduce light return). Common defects include burn marks, scratches, rough girdle texture, and lizard skin, all left by the cutting and polishing process. For most buyers, Very Good polish is indistinguishable from Excellent without a loupe and offers a better price-to-quality ratio. Reserve your scrutiny for diamonds graded Good or below, where polish features may begin to affect transparency — and always check the polish grade independently from symmetry on the report.