Diamond Blemishes: Full Guide

A diamond blemish is a surface-level characteristic — a scratch, nick, extra facet, polish line, or similar feature confined to the outside of the stone — as opposed to an inclusion, which is an internal characteristic. Blemishes are one of the two categories a grading lab evaluates when assigning a clarity grade, and while most are minor and many result from the cutting and polishing process rather than the stone's natural formation, they still factor directly into where a diamond lands on the clarity scale.

Understanding blemishes matters most at the top of the clarity scale, where the distinction between Flawless and Internally Flawless comes down entirely to whether any blemish is present, and it matters again anywhere a buyer is trying to judge whether a specific clarity grade will actually show up to the naked eye. This guide covers what defines a blemish, the main types a grading report can list, how blemishes differ from inclusions in both cause and consequence, how they interact with clarity and polish grades specifically, whether they can be removed, how to read a blemish on a certificate's clarity plot, and what to check when evaluating stones with blemishes noted on their reports.

What Is a Diamond Blemish?

A blemish is any clarity characteristic confined to the diamond's exterior surface — it does not extend into the stone's interior the way an inclusion does. Most blemishes are the direct result of the cutting and polishing process itself: a polishing wheel leaves fine surface lines, a cutter's tool nicks the girdle, or a facet is added slightly off the intended symmetrical pattern. Others, like naturals, are remnants of the rough diamond's original outer surface deliberately left unpolished at the girdle to preserve carat weight. A smaller number of blemish types can occur from wear after a diamond is set and worn over time, such as an abrasion along a facet junction.

Because blemishes sit on the surface, they are generally easier for a grader to identify and characterize precisely than an internal inclusion, and — outside of a few specific exceptions covered below — they are also generally less consequential to a stone's durability than an inclusion of comparable visibility, since a blemish does not represent a structural weak point running into the stone's interior the way certain inclusion types can.

Why Blemish Type Still Matters, Not Just the Clarity Grade Alone

Two diamonds carrying the identical clarity grade can present very different blemish profiles. A VS1 diamond with a single small extra facet at the pavilion behaves completely differently — cosmetically and in terms of any resale or appraisal conversation — than a VS1 diamond with several visible polish lines across the table. The clarity grade summarizes overall visibility and severity; the specific blemish type tells a buyer or grader what they're actually looking at, whether it's cosmetic only, and whether it's the kind of characteristic that could theoretically be improved with a repolish.

The Main Types of Diamond Blemishes

Extra Facet

An extra facet is an additional facet cut onto the diamond that doesn't conform to the intended overall facet pattern and symmetry — often added to remove a small surface inclusion or another blemish near the girdle, or simply the result of a minor cutting adjustment. Extra facets are extremely common and are usually cosmetically insignificant unless positioned somewhere highly visible, such as directly under the table.

Naturals

A natural is a small remnant of the original rough diamond's outer surface, deliberately left unpolished, almost always at the girdle. Cutters leave naturals intentionally to preserve carat weight rather than polishing away every trace of the rough's original surface. A natural is typically only a cosmetic concern if it's large enough or positioned somewhere that breaks the visual continuity of the girdle's finish.

Nicks and Pits

A nick is a small notch, usually along the girdle or at a facet junction, most often caused during the cutting, polishing, or setting process. A pit is a tiny opening on the surface, often located at the intersection of facet junctions, that can look like a tiny white dot under magnification. Both are typically minor and confined strictly to the surface.

Polish Lines

Polish lines are fine parallel lines left on a facet's surface from the polishing wheel during the cutting process. They're one of the most common blemish types found on nearly every diamond to some degree, and at a minor level they're specifically what separates Internally Flawless from true Flawless — IF permits minor surface polish marks that FL does not.

Scratches

A scratch is a thin surface line, similar in appearance to a polish line but generally isolated rather than part of a repeated parallel pattern, and can occur during cutting, polishing, setting, or later wear. Light scratches are common and usually cosmetically insignificant; deeper or more numerous scratches can be more visible and, in rare cases, may be addressed with a light repolish.

Surface Graining

Surface graining appears as faint lines, growth marks, or a slightly hazy or reflective effect on a facet's surface, related to irregularities in the crystal growth structure reaching the exterior of the stone. Unlike polish lines, surface graining is a natural growth feature rather than a cutting artifact, and it can't be removed by repolishing since it originates from the crystal structure itself, not the surface finish.

Abrasion

Abrasion refers to minor wear along facet junctions, typically the girdle, that develops from ordinary wear over time as a set diamond knocks against other surfaces. It's the one blemish type most commonly associated with age and use after a diamond leaves the cutting factory rather than with the original cutting and polishing process.

Blemishes vs. Inclusions: Comparison Table

How Blemishes Affect the Overall Clarity Grade

A grading lab assigns a diamond's final clarity grade based on the more significant of its blemishes and inclusions combined — a stone with pristine internal clarity but a visible surface scratch is capped by that blemish, exactly as a stone with a serious inclusion is capped by that inclusion regardless of how clean its surface is. In practice, blemishes rarely drive a diamond's grade downward as far as a serious inclusion would, since most blemish types by nature are minor, but they are never simply ignored in favor of internal characteristics — the final grade always reflects whichever category presents the more visible or more numerous characteristics.

This is also exactly why FL (Flawless) is so much rarer than IF (Internally Flawless) in practice. Achieving zero inclusions under 10x magnification is difficult but achievable; achieving zero blemishes as well — including the fine polish lines that appear on nearly every diamond to some degree from the cutting process — is dramatically harder, which is why true Flawless stones are so scarce relative to Internally Flawless ones.

Blemishes and the Polish Grade: A Separate but Related Assessment

Several blemish types — polish lines, scratches, nicks, pits, and abrasion in particular — also feed into a diamond's separately assigned polish grade, one of the components alongside symmetry that makes up the overall cut grade on a GIA report. A diamond can carry a strong clarity grade overall while still receiving a lower polish grade if its surface shows more of these polish-related blemishes than the clarity grade alone might suggest, since polish is evaluated as its own distinct scale (Excellent through Poor) specifically focused on surface finish quality. A buyer comparing two similarly clarity-graded stones should check the polish grade separately, since it's the more direct indicator of how clean and well-finished the actual facet surfaces are.

Can Diamond Blemishes Be Polished Out?

Some blemish types can theoretically be removed or reduced through a light repolish — polish lines, light scratches, minor nicks, and small pits are all surface-level and can, in principle, be polished away. In practice, this is rarely worth doing on an already-cut and certified stone, for a simple reason: repolishing removes material, which means losing carat weight, and the value lost from a smaller final weight typically outweighs any clarity or polish grade improvement gained. Some blemish types can't be removed at all regardless of the tradeoff — surface graining originates from the crystal structure itself and isn't a surface-finish artifact, so no amount of repolishing addresses it. In practice, blemishes are almost always left as-is once a stone is cut and certified, with repolishing reserved for specific cases like preparing a stone for resetting or addressing wear-related abrasion on an older piece.

Reading Blemishes on a Certificate's Clarity Plot

Beyond the letter grade, most grading certificates include a clarity plot — a diagram of the diamond from the table and pavilion views, with symbols marking the type, size, and position of every inclusion and blemish the grader identified. Blemish symbols are typically shown in a different color from inclusion symbols (commonly green or black for blemishes, versus red or green for inclusions, depending on the specific lab's convention), and each symbol type corresponds to a specific blemish category — a distinct symbol for an extra facet, a different one for a natural, and so on. Reviewing the plot directly, rather than relying on the clarity grade letter alone, tells a buyer exactly what's actually present on a given stone and where, which matters most for stones in grades where individual characteristics vary widely between examples of the same letter grade.

Do CVD Lab-Grown Diamonds Show the Same Blemish Types?

Blemishes that arise from the cutting and polishing process — extra facets, polish lines, nicks, pits, scratches — occur identically on CVD lab-grown diamonds and natural diamonds, since both are cut and polished using the same techniques and tools regardless of how the rough material formed. Naturals, however, are specific to how a stone's rough outer surface is handled during cutting, and while the concept applies to both, the underlying rough shape a cutter is working from can differ somewhat between lab-grown and natural material, affecting exactly how naturals show up in practice. Surface graining, being tied to the crystal's growth structure, can appear in both natural and lab-grown stones, since both are real crystalline diamond material subject to growth-related structural characteristics, just formed under different conditions. Overall, a lab-grown diamond's blemish profile is graded on the identical scale and using the identical terminology as a natural diamond's, with no separate blemish standard applied to either.

How Blemish Position Affects Visibility

Where a blemish sits on the stone matters as much as what type it is. A characteristic located directly under the table — the largest, flattest facet, and the one a viewer looks straight through first — is far more likely to be noticed than the identical characteristic tucked near the girdle, where it's partially obscured by the setting and viewed at a steeper angle. This is one reason two stones can carry the same clarity grade and the same blemish type, yet look meaningfully different in how "clean" they appear face-up once mounted: the grade accounts for severity and visibility under 10x magnification in the lab, but a buyer evaluating a specific stone for a specific setting should also think about how the setting itself will frame or hide a given blemish's position.

Grading labs account for this to some degree already — position is one of the five factors (alongside size, number, nature, and relief) that determines where a characteristic lands a stone within its grade range — but a buyer with the clarity plot in hand can go a step further and think specifically about how a chosen setting style will interact with a noted blemish's exact location, something the grade letter alone can't communicate.

Blemishes in Fancy Shapes vs. Round Brilliants

Blemish visibility isn't uniform across diamond shapes. Step-cut shapes like emerald and asscher have large, open facets and minimal light scattering compared with a round brilliant's dense facet pattern, which means any surface blemish — a polish line, a scratch, a natural at the girdle — is generally easier to spot on a step cut than the identical blemish would be on a round brilliant, where the brilliant facet pattern's constant light-and-dark interplay does more to visually camouflage minor surface characteristics. This is a well-known reason buyers are often advised to accept a higher clarity grade on a step-cut stone than they would insist on for a round brilliant of similar size and budget — the shape itself is less forgiving of blemishes that a round brilliant would largely hide from casual view.

QC Checklist: Evaluating Blemishes Before Purchase

A few practical checks help a buyer evaluate blemish-related clarity characteristics before committing to a purchase:

• Review the clarity plot, not just the letter grade. Two stones at the same clarity grade can carry very different blemish profiles — check what specific blemish types are present and where.
• Check the polish grade separately from clarity. A strong clarity grade doesn't guarantee a strong polish grade, and polish-related blemishes are exactly what that separate grade is measuring.
• Ask whether any noted blemish sits in a highly visible position. A blemish located under the table is far more likely to be noticeable than the same blemish tucked near the girdle.
• Don't assume a blemish is a durability concern by default. Most blemish types are cosmetic only — confirm with the certificate or a grader whether a specific noted characteristic (such as a deep abrasion or a large nick) carries any structural implication, rather than treating every blemish as equally serious.
• Confirm certification lab and consistency. GIA, IGI, and GCAL all use comparable blemish terminology and clarity-plot conventions, but confirming the specific lab and reviewing the plot directly gives a more precise picture than the grade letter alone.

Blemishes and Long-Term Wear

A diamond's blemish profile isn't necessarily fixed forever at the moment it's graded. Abrasion, in particular, can develop or worsen over years of daily wear as a set stone's girdle and facet junctions knock against other jewelry, countertops, and general daily contact — which is one reason a diamond's clarity characteristics, when re-examined by an appraiser years after its original certification, can occasionally show minor wear-related changes not present on the original report. This is generally cosmetic rather than a durability concern, but it's a useful thing for a jeweler to mention to a client: a grading report reflects the stone's condition at the time it was graded, not a permanent, unchanging snapshot for the life of the piece, and periodic professional cleaning and inspection helps catch developing wear before it becomes cosmetically noticeable.

Sourcing Consistently Graded Stock

Guru Diam sources both CVD lab-grown and natural diamonds with full IGI, GIA, or GCAL certification, giving trade buyers direct access to each stone's clarity plot and polish grade rather than a clarity letter alone — useful for a jeweler who wants to confirm exactly what blemish characteristics, if any, are present and where before quoting a client. Because Guru Diam's lab-grown catalog is CVD-only, buyers comparing blemish and polish characteristics across lab-grown parcels are working with a single, consistent growth method rather than a mixed CVD/HPHT supply chain. Trade buyers can browse certified loose stones through the certified diamonds category, source matched pairs with consistent finish quality through matching pairs, and apply for a wholesale account through trade partner. Current terms and full catalog access are available at the wholesale hub, and buyers building a custom piece around a specific stone can start at custom jewelry, completed in 4 to 6 days once the design and stone are confirmed.

Frequently Asked Questions

What is the difference between a diamond blemish and an inclusion?

A blemish is a surface-level characteristic — like a scratch, nick, or polish line — confined to the outside of the stone. An inclusion is an internal characteristic, such as a crystal, feather, or cloud, that forms within the diamond during crystal growth. Both factor into the overall clarity grade, but they're evaluated as distinct categories.

What are the most common types of diamond blemishes?

Extra facets, naturals, polish lines, nicks, pits, scratches, surface graining, and abrasion are the main blemish types a grading report can note. Polish lines are among the most universally present, appearing to some degree on nearly every cut and polished diamond.

Can diamond blemishes be polished out?

Some can — polish lines, light scratches, minor nicks, and small pits are surface-level and can theoretically be reduced through a light repolish. In practice this is rarely done on an already-certified stone, since repolishing removes material and the resulting carat weight loss typically isn't worth the grade improvement. Surface graining can't be removed at all, since it comes from the crystal structure rather than the surface finish.

Do blemishes affect a diamond's durability?

Generally minimally. Most blemish types are cosmetic surface characteristics rather than structural weak points, unlike certain inclusion types that can extend into the stone's interior. Deep abrasion or a significant nick are the exceptions worth flagging specifically with a grader.

What is the difference between Flawless and Internally Flawless diamonds?

Flawless (FL) means no inclusions and no blemishes are visible under 10x magnification — including fine surface polish marks. Internally Flawless (IF) means no inclusions are visible, but minor surface blemishes, typically from polishing, are permitted. That blemish allowance is the entire distinction between the two grades.

Are blemishes graded the same way on lab-grown and natural diamonds?

Yes. Cutting and polishing-related blemishes — extra facets, polish lines, nicks, scratches — are graded identically on CVD lab-grown and natural diamonds, since both are cut and finished using the same techniques and evaluated on the same clarity scale by the same major labs.