Introduction
A diamond's polish grade tells you how smoothly its facets were finished — but it does not tell you what specific surface features the grader found. For that, you need to look at the Comments section of the grading report, where individual polish characteristics are listed by name.
Polish characteristics are surface defects introduced during the cutting and polishing process. When a cutter shapes a rough diamond into a finished stone, each facet is ground and polished against a rotating wheel coated with diamond powder. This process transforms rough crystal surfaces into the flat, smooth optical windows that allow light to enter and exit the stone. But friction, heat, crystal grain orientation, and human handling can leave marks on those surfaces — marks that gemologists classify, assess under standard 10x magnification, and factor into the polish grade.
Understanding individual polish characteristics helps you move beyond the single-letter grade. Two diamonds both graded Very Good for polish may carry different types and quantities of surface features. Knowing what each defect looks like, why it occurs, and how it affects the stone gives you a more informed reading of the report — and a better sense of whether a particular polish grade matters for the stone you are considering.
Key Points
Burn Marks
Burn marks are whitish, hazy patches on a facet surface caused by excessive heat during polishing. Diamond is an exceptional thermal conductor, but when a facet is held against the polishing wheel at the wrong angle, speed, or pressure for too long, localised friction generates enough heat to alter the surface structure. The result is a clouded, frostbitten area that disrupts the facet's transparency.
Burn marks are among the more visually significant polish characteristics. They tend to cover a broader area than a scratch or pit, and because they affect the facet's ability to transmit light cleanly, they are a common reason for a polish downgrade below Very Good. On a grading report, burn marks listed in the Comments section warrant close attention — particularly if they appear on the table or crown facets, where their effect on light return is most pronounced.
Scratches
A scratch is a fine line on the facet surface — a surface-level mark, not an internal fracture. Scratches occur when the diamond contacts abrasive material during polishing or subsequent handling. Under 10x magnification, they appear as thin, slightly raised or indented lines running across a facet.
A single faint scratch on one facet rarely affects the polish grade. Multiple scratches across several facets, or a prominent scratch on the table, will. It is worth noting the distinction between a polish scratch (a surface blemish) and surface graining or a feather reaching the surface — these are different characteristics with different grading implications. Scratches are also listed as blemishes in clarity grading contexts; see Inclusions vs Blemishes for how the categories overlap.
Rough Girdle
The girdle is the narrow band around the diamond's widest point — the boundary between the crown and pavilion. Some diamonds have a polished or faceted girdle, but many retain a "bruted" girdle with a matte, granular texture left by the initial shaping process. A rough girdle goes beyond normal bruted texture: the surface is pitted, uneven, or excessively grainy, indicating that the shaping process left the girdle in a condition the polisher did not adequately refine.
Rough girdle texture is graded as a polish characteristic when it exceeds what is expected for the girdle's finish type. It can affect how the diamond sits in a setting — an uneven girdle may not seat uniformly in a bezel or channel mount — and may cause minor light scattering along the stone's edge. For engagement rings where the girdle is partially visible between prongs, a rough girdle is worth noting, though it is rarely the sole reason for a significant polish downgrade.
Lizard Skin
Lizard skin is a textured, bumpy surface that resembles reptile scales. It results from the diamond's crystal structure resisting the polishing direction. Diamond hardness varies with crystal orientation — certain grain directions are significantly harder to polish than others. When a cutter works against a difficult grain direction, the polishing wheel cannot achieve a uniformly smooth surface, leaving a characteristic undulating texture.
Lizard skin typically appears on specific facets rather than across the entire stone, because each facet encounters the crystal grain at a different angle. It is most common on facets where the grain runs nearly parallel to the polished surface, making smooth finishing mechanically difficult. Lizard skin is a moderate polish characteristic — it indicates a craftsmanship challenge that the cutter could not fully overcome, and when prominent, it reduces the facet's optical clarity.
Polishing Lines
Polishing lines are fine, transparent lines or drag marks left on a facet by the polishing wheel. They follow the direction of polishing — typically running parallel across the facet surface. Under 10x magnification, they appear as faint, regular striations that catch light at certain angles.
Most polishing lines are extremely subtle and are among the least significant polish characteristics. A few faint polishing lines on pavilion facets are unlikely to affect the polish grade or the diamond's visual performance. They become relevant only when they are numerous, prominent, or concentrated on the table facet, where they may be visible as a faint sheen or directional haze under specific lighting. Polishing lines are distinct from surface graining, which follows the diamond's internal crystal structure rather than the polishing direction.
Abrasion
Abrasion is a series of minute scratches or roughening along facet edges — the junctions where two polished surfaces meet. Under magnification, abraded edges appear fuzzy, white, or slightly rounded rather than crisp and sharp. Abrasion can occur during the polishing process itself, during handling and transport of the finished stone, or from contact with other diamonds (a common scenario in mixed diamond parcels).
Abrasion is one of the more common polish features, particularly on older stones or diamonds that have been through multiple handling stages. It is typically a minor characteristic — graders note it but it rarely drives the polish grade unless it is widespread across many facet junctions. In practical terms, light abrasion along a few girdle facet edges has no visible impact on the diamond's face-up appearance.
Pit
A pit is a tiny opening or cavity on the polished facet surface. Pits most commonly form when a near-surface pinpoint inclusion is dislodged during polishing, leaving a small void. They can also result from localised chipping of the facet surface during the cutting process.
Under 10x magnification, a pit appears as a small, dark dot — superficially similar to a pinpoint inclusion but located on the surface rather than within the stone. A single pit is a minor feature. Multiple pits or a pit on the table facet carry more weight in the polish assessment. Pits are also classified as blemishes in clarity grading, where they follow the same general principle: surface features carry less grading weight than internal inclusions.
Nick
A nick is a small chip or notch at a facet edge or junction. It is typically caused by mechanical impact — contact with another diamond, a setting tool, or a hard surface during handling. Nicks most commonly appear along the girdle or at the point where crown facets meet, where the diamond's edge is thinnest and most vulnerable.
A nick differs from abrasion in scale: abrasion is microscopic roughening spread along an edge, while a nick is a discrete, localised chip. Minor nicks are common and do not significantly affect polish grade or appearance. A larger nick on a prominent facet junction may warrant attention, particularly if the diamond will be set in a style that leaves that area exposed. In severe cases, a nick can develop into a small feather if the diamond experiences further impact — a consideration for durability risk.
Summary
Polish characteristics are the specific surface marks that determine a diamond's polish grade. Each has a distinct cause rooted in the cutting process: burn marks from excess heat, scratches from abrasive contact, rough girdle from incomplete shaping, lizard skin from resistant crystal grain, polishing lines from wheel drag, abrasion from edge wear, pits from dislodged pinpoints, and nicks from mechanical impact. Most are visible only under 10x magnification and have no practical effect on how the diamond looks to the unaided eye. They become a concern when they are numerous, prominent, or concentrated on optically important facets like the table — which is when the polish grade drops to Good or below. When comparing diamonds, read the Comments section of the grading report to see which characteristics are present, and weigh them accordingly: burn marks and lizard skin tend to affect larger areas than a single scratch or pit.