Blemish
A surface feature on a polished diamond — scratches, nicks, polish lines and naturals. Unlike inclusions, blemishes do not extend inside the stone.
When a GIA grader assesses clarity, they look at both internal features (inclusions) and external features (blemishes). Blemishes are confined to the surface: they exist on one or more polished facets but do not penetrate into the crystal.
Most blemishes are minor. A fine polish line or a microscopic scratch on a pavilion facet will rarely affect anything visible to the naked eye — it shows up in the grade but not in how the stone looks. A chip or significant nick is more consequential, as it can affect both the light pattern and the stone's durability.
Because blemishes are surface features, many can be corrected by re-polishing the affected facet, at the cost of a small weight reduction. This distinguishes them from inclusions, which are typically permanent.
- LOCATION
- Surface only
- VS INCLUSION
- External
- REPAIRABLE
- Often yes
Scratch
A fine white line on the surface, usually from contact with another diamond or abrasive material during handling. Most scratches are very shallow and can be polished out.
Appears as a thin line on a facet surface, often only visible under directed light.
Nick
A tiny notch on a facet edge or the girdle, usually caused by knocking against a hard surface. Very small nicks are typically graded as surface-reaching chips.
Found most often at the girdle or on facet junctions. Can usually be re-polished away.
Polish line
Parallel lines left on a facet surface by imperfections in the polishing wheel or grain direction misalignment during finishing. Extremely fine; rarely affects appearance.
Visible only under magnification. Does not penetrate the surface — purely cosmetic at the microscopic level.
Burn mark
A cloudy or hazy patch caused by overheating during polishing. The surface has been microscopically damaged rather than scratched. Usually polishable.
Looks like a dull patch under reflected light. Affects one facet only.
Natural
A portion of the original rough diamond surface left intentionally by the cutter, usually at the girdle to preserve carat weight. Not damage — a deliberate decision.
Sometimes shows the original crystal texture or skin of the rough. Harmless and often invisible face-up.
Extra facet
An additional polished flat surface added outside the standard facet arrangement, often to remove an inclusion or correct a chip. Visible face-up if near the table.
Can disrupt symmetry if placed prominently. Less concerning when on the pavilion.
Blemish vs Inclusion
Both affect clarity grading, but they differ in location, repairability and typical severity.
Surface feature
- Located on a polished facet surface
- Does not penetrate the crystal
- Often repairable by re-polishing
- Usually minor in clarity impact
- Examples: scratch, nick, polish line, natural
- Caused by handling, polishing or deliberate cutter decisions
Internal feature
- Located inside the crystal or reaching inward
- Permanent — cannot be polished away
- Range from minor to grade-defining
- Examples: crystal, cloud, feather, needle, pinpoint
- Caused during crystal growth in the earth
- Some inclusions (feathers) affect durability
All blemish types
GIA recognised surface characteristics
How blemishes affect clarity grading
GIA grades blemishes using the same five factors used for inclusions: size, number, position, nature and relief. A blemish large enough to be seen at 10× under diffused lighting will affect the grade; one that requires directed lighting or specific angles to see will have less impact.
The position matters: a scratch across the table is more penalising than one on the pavilion. A nick on the girdle is less concerning than a chip near the culet. Extra facets near the table can affect the visual symmetry of the facet pattern and therefore the grade.
In practice, blemishes are more commonly the grade-determining feature in the VS and VVS range. A stone might be internally Flawless but have a single polish line that prevents it from reaching FL — grading it IF instead.
Flawless
No blemishes visible at 10× under skilled grading
Internally Flawless
No inclusions; minor surface blemishes only (polish lines, naturals)
VVS1 / VVS2
Minute blemishes extremely difficult to see at 10×
VS1 / VS2
Minor blemishes difficult to see; a scratch can put a stone here
SI1 / SI2
Blemishes noticeable at 10×; still usually eye-clean
I1–I3
Blemishes (chips, significant scratches) visible to the naked eye
Questions about blemishes
What is the difference between a blemish and an inclusion?
An inclusion is a feature inside or reaching into the diamond — crystals, clouds, feathers, needles. A blemish is a surface-only feature — scratches, nicks, polish lines, naturals. Both affect clarity grading, but blemishes are generally less significant because they are confined to the surface, often repairable by re-polishing, and less likely to affect the stone's structural integrity.
Do blemishes affect a diamond's appearance to the naked eye?
Rarely. Most blemishes are microscopic and visible only under 10× magnification. The exception would be a significant scratch across a prominent table facet, a large nick on the girdle, or a badly placed extra facet that disrupts the light pattern. For stones graded VS2 or better, blemishes are essentially invisible in normal viewing conditions — which is why the grading report matters more than worrying about individual surface features.
Can blemishes be removed?
Many can. Scratches and polish lines can typically be removed by re-polishing the affected facet. Nicks on the girdle can sometimes be re-cut. The downside is a small loss of carat weight (and therefore value) and the cost of the recutting service. For minor blemishes on a VS or SI stone, re-polishing is rarely worth the trade-off. For a significant blemish on an otherwise high-grade stone, it can make sense.
Which blemishes matter most in a clarity grade?
GIA weights blemishes by their impact on beauty and durability. A scratch or polish line on an otherwise clean stone will typically result in a VVS2 or VS1 rather than a higher grade. A significant nick on the girdle or a chip can pull a stone down to VS2 or even SI1 depending on size and visibility. Extra facets near the table are more penalising than those on the pavilion. Naturals at the girdle are usually considered minor.
Should I avoid diamonds with blemishes?
Not necessarily. A stone graded VS1 with a minor polish line is visually identical to a VVS2 with no blemishes — the grade difference is real but the appearance difference is not. The relevant question is whether the blemish is eye-clean, not whether it exists at all. Focusing on the clarity grade range (VS2–SI1 for most buyers) and confirming eye-cleanliness is more useful than avoiding blemishes as a category.
Does DiamondTheGuide filter out diamonds with blemishes?
DiamondTheGuide filters by GIA/IGI clarity grade, which already encodes blemish severity. The price benchmarks for each grade bucket include all stones at that grade — whether the grade was driven by an inclusion or a blemish. If you select VS1 in DiamondTheGuide, you get the median price for all VS1 stones, including those where a minor blemish is the primary grade determinant.