Graining in Diamonds: What It Is, How It Forms and Whether It Matters

What is graining in diamonds?

Graining is the gemmologist's word for irregularities in a diamond's crystal structure. A diamond is carbon atoms locked in a repeating cubic lattice. Where that lattice grew unevenly, or was bent and squeezed after it formed, the change shows up as faint lines, bands, a soft haze or a colourless reflection that flashes as the stone moves. Nothing foreign is trapped inside. Graining is the diamond itself, slightly out of step with the crystal around it.

Grading labs treat graining as a clarity characteristic, one of the features they weigh when they assign a clarity grade. Clarity is the C that our guide to colour, cut, clarity and carat explains in full. Internal graining sits inside the stone and counts as an inclusion. Surface graining reaches the polished facets and counts as a blemish (a feature confined to the surface).

Graining is common. Under a 10× loupe, the standard grading magnification, many natural diamonds show at least a trace of it, and it is one of the least worrying things you can find in a stone. Our wider diamond education hub covers the other inclusion types, and any unfamiliar word on this page is defined in the GemTrove jewellery glossary.

How does graining form in natural and lab-grown diamonds?

Natural diamonds crystallise roughly 150–200 km below the surface, under enormous pressure and at temperatures of around 900–1,300 °C. They can spend a very long time down there before an eruption carries them up. That long, violent history is where most graining comes from. There are three main causes:

• Irregular growth: different zones of the crystal grow at different speeds or take in different amounts of nitrogen. The boundaries between those zones can show as straight lines or faint colour bands.
• Plastic deformation: after growth, pressure and movement in the mantle bend the lattice along its octahedral planes, much as a deck of cards slides when you push it. This leaves sets of parallel lines, often called deformation lines or glide planes.
• Twinning: part of the crystal changes direction along a twin plane. Graining often runs along that plane, and it is closely related to the twinning wisps that form where twin planes trap tiny crystals.

Plastic deformation also explains most natural brown and pink diamonds. The colour sits in thin parallel bands that follow the deformation, which gemmologists call coloured graining. Pink diamonds from Western Australia's Argyle mine, which closed in 2020, are well known for their pink grain lines. When brown type IIa diamonds (a rare, nitrogen-poor type) are treated with high pressure and high temperature (HPHT) to lighten their colour, the brown can fade but the graining and strain usually remain. Any such treatment must be disclosed on the report.

Lab-grown diamonds are real diamond, grown in a laboratory rather than mined. They can show growth features too. HPHT lab-grown diamonds grow in distinct sectors that sometimes show as faint banding, while CVD (chemical vapour deposition) diamonds grow layer by layer on a seed plate and can show fine striations or strain running in the growth direction. In most well-grown laboratory-grown stones these features are hard to see at 10×, but labs use them, with fluorescence imaging and a polariscope (a viewer with crossed polarising filters that reveals strain), to help confirm whether a diamond is natural or lab-grown.

What types of graining do grading labs describe?

Graders describe graining by how it looks, not just by what caused it. Four internal types and one surface type cover almost everything you will see:

Surface graining appears where a grain boundary meets a facet. The two sides of the boundary have slightly different crystal orientations, so they polish at different rates and the polishing wheel leaves a fine step or line. It is part of the diamond, so polishing cannot remove it. Our page on how polish grades from Excellent to Poor are set covers how graders weigh it.

A related polishing feature is lizard skin, a wavy, textured patch left when a facet is polished too close to the diamond's natural grain direction. See our guide to burn marks, lizard skin and other polishing marks for how these differ.

Where does graining show on a diamond grading report?

A full grading report includes a plot diagram, a map of the diamond's crown (top) and pavilion (bottom) with symbols showing each clarity characteristic. Inclusions are drawn in red and blemishes in green. Graining is the odd one out, because it is often spread through the stone and hard to draw as a single symbol.

Here is what to look for:

• Key to symbols: if internal graining appears here, it was significant enough to draw on the plot, often as a series of red lines.
• Comments: "Internal graining is not shown": graining is present but was left off the plot. It may or may not influence the grade.
• Comments: "Surface graining is not shown": grain lines reach the facets but were judged minor.
• Comments: "Clarity grade is based on internal graining that is not shown": the most important wording. Graining is the main reason for the grade, so look at the stone itself before you decide.

Smaller-format reports for diamonds under about 2 carats sometimes have no plot at all, so the comments are your only clue. GIA and IGI both note graining on natural and laboratory-grown diamond reports, and the report will always state whether the stone is natural or lab-grown.

Does graining in diamonds affect the clarity grade?

It can. Graders consider five things for every characteristic: size, number, position, nature and relief (how much it stands out from the surrounding diamond). Graining usually has low relief, because it is the same material as the rest of the stone, so a fair amount of it can be present before the grade drops. The table shows the typical pattern:

Position matters. Graining under the table (the large top facet) is easier to see than graining near the girdle (the thin outer edge). Graining is also directional: it can be obvious with the stone tilted one way and disappear when you turn it a few degrees, which is why two graders can see the same stone slightly differently.

Is a diamond with graining eye-clean?

In most cases, yes. An eye-clean diamond is one with no clarity characteristics you can see without magnification, face-up, at a normal viewing distance of about 25–30 cm. Colourless graining almost never shows at that distance, and reflective graining rarely does, even in SI grades, so a VS or SI stone graded down for graining often looks as clean as a VVS. Our guide to finding eye-clean diamonds explains how to judge this grade by grade.

The exception is whitish graining. In strong amounts it scatters light and gives the diamond a soft, slightly milky look, with less contrast between bright and dark facets. It can resemble the oily look a small minority of stones with very strong blue fluorescence under ultraviolet light show in sunlight. A hazy diamond can still have an Excellent cut grade, so if the report says the clarity grade is based on graining that is not shown, see the stone or a sharp video in daylight before you commit.

For brightness, cut matters far more than a trace of graining. A well-proportioned stone returns enough light to overwhelm faint internal lines; our comparison of Excellent, Very Good and Good cut grades shows the difference that makes.

Is graining in diamonds a durability risk?

For everyday wear, the risk is low. Graining is not a crack and is not open to the surface. Diamond is 10 on the Mohs hardness scale, with a refractive index of about 2.42, and a grained diamond keeps both. That puts graining in a different category from a feather (an internal fracture), from bearding, the fine hair-like fractures along the girdle, or from etch channels, natural tunnels that reach the surface, all of which can matter for durability.

Where graining does matter is at the bench. Heavily grained or strained areas, which cutters call knots or hard spots, resist the polishing wheel, so recutting a chipped stone or repolishing a scratched facet can take longer and may not finish perfectly. Some jewellers also check strongly strained stones under a polariscope before heavy setting work or a repair involving heat, as a precaution.

• Everyday wear: no special care beyond normal diamond care.
• Cleaning: ultrasonic cleaning is generally fine for diamonds with graining alone; avoid it if the stone also has surface-reaching feathers.
• Setting and repairs: tell your jeweller the report mentions graining, so they can plan claw work and any repolishing.

How is graining different from twinning wisps, feathers and polish lines?

Graining is often confused with other features at 10×. This table sets out the differences:

The quickest test is the facet edge. Polish lines stay within one facet; surface grain lines run straight across facet junctions because they follow the crystal, not the wheel. Inside the stone, a feather has visible depth and catches light at its edges, while reflective graining is flat and featureless. Laser channels look like fine white tubes leading to the surface; see how laser drilling works and how it is disclosed. Small surface cavities and stray facets are covered in our page on pits and extra facets that affect polish and symmetry.

Should you buy a diamond with graining?

Often it is a sensible choice. A VS2 or SI1 diamond graded down for colourless graining usually looks no different face-up from a stone two grades higher, and the lower clarity grade costs less. That saving can go towards carat weight, colour or a better cut, which is exactly the trade-off weighed in choosing between a bigger diamond and a better grade.

Be more careful with whitish graining that causes haze, with coloured graining in a stone sold as near-colourless, and with any stone whose grade is based on graining you cannot inspect. If face-up size is the goal, the cut and setting tricks in ways to make a diamond look bigger do more than chasing a higher clarity grade.

Both natural and lab-grown diamonds can carry graining comments, and lab-grown diamonds cost much less than natural diamonds of the same grades. If you are comparing a solitaire with a cluster or multi-stone ring, check the weight terms too; our explainer on ct, ctw and tcw carat weight terms shows how to read them.

How to check a diamond for graining: step by step

1. Read the report comments. Look for "Internal graining is not shown", "Surface graining is not shown" or "Clarity grade is based on internal graining".
2. Check the key to symbols. If graining is drawn on the plot, note where it sits, especially under the table.
3. View the stone at 10× and rotate it. Tilt it slowly through several angles; graining appears and disappears with direction.
4. Check face-up at 25–30 cm in daylight. Judge whether it is eye-clean and whether the stone looks crisp or slightly hazy, using the checks in our eye-clean checklist by clarity grade.
5. Look along the facet edges. Lines that cross from one facet to the next are surface graining, not polish lines.
6. Ask about strain for strongly grained stones. A polariscope view shows how much strain is present before setting or repair work.