Diamond Inclusions Explained: A UK Buyer's Guide to What's Really Inside Your Diamond

Almost every natural diamond contains inclusions — tiny internal features formed when the diamond crystallised under the earth. Some are microscopic and completely invisible. Others affect how the diamond looks, how bright it is, and in rare cases how durable it is. Understanding which is which is one of the most useful things a buyer can do before choosing a stone.

If you're comparing diamonds for an engagement ring, this guide covers what inclusions actually are, the main types you'll see on a GIA or IGI certificate, and which ones matter enough to influence your decision.

For a broader introduction to how inclusions translate into a clarity grade, see our diamond clarity grades guide.

What is a diamond inclusion?

A diamond inclusion is a natural internal characteristic inside a diamond — a small crystal, cavity, fracture, or feather that formed during the diamond's growth deep in the earth. Inclusions are graded under 10x magnification by laboratories such as the GIA and IGI, and their number, size, position, and type together determine the diamond's clarity grade.

A few things to hold in mind:

• Almost all natural diamonds have inclusions. Flawless (FL) and Internally Flawless (IF) stones are genuinely rare and priced accordingly.
• Most inclusions are invisible to the naked eye. From VS2 upwards, and often into SI1, a well-chosen diamond is "eye-clean" — meaning you can't see any inclusions without magnification.
• Not all inclusions are equal. A small white crystal on the edge of a stone is very different from a long feather running through the centre.

The word "inclusion" sounds like a flaw. In practice, it's closer to a fingerprint — proof the diamond is natural, and something to understand rather than fear.

How inclusions appear on a diamond certificate

Every GIA or IGI grading report includes a clarity plot: a diagram of the diamond with symbols showing where each inclusion sits and what type it is. Red symbols indicate internal inclusions; green indicates surface features (blemishes). The report also lists the clarity characteristics in order of grading significance.

Learning to read the plot is the single most useful skill when comparing stones online. Two diamonds with the same clarity grade can look very different depending on where their inclusions sit — one might be perfectly clean face-up, another might have an obvious mark under the table.

Our guide on how to read a diamond certificate walks through the full report in detail.

The main types of diamond inclusions

Below are the inclusion types you're most likely to see on a UK diamond certificate, what they actually are, and how much they matter.

Crystal

A small mineral crystal — often another diamond, or a mineral like garnet — trapped inside the stone during formation. Crystals can be white, black, or coloured. White crystals are usually harmless if small and away from the table. Black crystals are more visible against the diamond and can be a reason to keep looking, especially near the centre.

Feather

A small internal fracture that resembles a feather when magnified. Feathers are the inclusion type buyers ask about most, because the name sounds alarming. In most cases they're not a durability concern — feathers are common and stable. The exceptions are large feathers that break the surface, or feathers running through a corner or edge of a fancy-shaped stone (pear, marquise, princess), which can occasionally raise a durability question. A reputable jeweller will flag these.

Cloud

A cluster of very small pinpoint inclusions grouped closely together. Small clouds are invisible; large or dense clouds can give a diamond a slightly hazy or "milky" appearance that reduces brightness. This is one of the inclusions worth actively watching for on SI-grade stones — a heavy cloud can dull an otherwise good diamond.

Pinpoint

A single, tiny crystal appearing as a dot under magnification. Pinpoints are so small they're almost always invisible to the naked eye and rarely affect the look of the diamond. Most VS-grade stones contain a few pinpoints without any visible impact.

Needle

A long, thin crystal inclusion. Needles are usually thin enough to be invisible face-up, and unless they're clustered or oriented across the table, they rarely affect appearance.

Twinning wisp

A ribbon-like inclusion formed where the diamond's growth was distorted during crystallisation. Twinning wisps are common and usually invisible in higher clarity grades. In lower grades they can appear as a faint white or silvery streak.

Cavity

An open opening on the surface where a crystal has fallen out or been polished around. Cavities are worth avoiding if they're on the crown of the stone, because they can trap dirt and be visible after wear.

Chip

A small piece of the diamond missing, usually at the girdle or a corner. Chips are uncommon in graded diamonds but do occur, especially in shapes with pointed corners. Any chip is worth understanding — sometimes it can be hidden by the setting, sometimes not.

Indented natural

A remnant of the diamond's original rough surface left after polishing, usually along the girdle. Indented naturals are almost always benign and often invisible once the stone is set.

Bruise

A tiny impact mark, usually near the girdle. Small bruises are cosmetic; larger ones are rare and would show on the plot.

Which inclusions matter, and which don't

Not every inclusion deserves the same weight. As a working guide for UK buyers looking at VS2–SI2 stones:

Usually fine: - Small white crystals away from the table - Pinpoints and needles - Small feathers that don't break the surface - Indented naturals along the girdle - Small twinning wisps

Worth a closer look: - Black crystals under or near the table - Large or dense clouds affecting brightness - Feathers that break the surface or run through a corner - Cavities on the crown - Any inclusion the certificate flags as the primary grade-setting feature and that sits centrally

The location and visibility of inclusions matter more than the raw count. A stone with three small inclusions tucked under the crown facets can look cleaner than one with a single well-placed inclusion under the table.

Eye-clean vs. clarity grade

"Eye-clean" is not an official grading term, but it's the one that matters most for how the diamond looks on the hand. An eye-clean diamond has no inclusions visible to a normal viewer at a normal distance (roughly 20–30cm) with the naked eye.

• VVS1–VVS2: Always eye-clean.
• VS1–VS2: Almost always eye-clean.
• SI1: Often eye-clean, depending on inclusion type and location. Worth checking individually.
• SI2: Sometimes eye-clean. Highly dependent on the specific stone.
• I1 and below: Rarely eye-clean.

For most engagement rings, a well-chosen VS2 or eye-clean SI1 gives you a diamond that looks flawless in daily wear without paying for grades you can't see. This is where a jeweller who actually looks at the stone under magnification adds real value.

How inclusions differ by diamond shape

Certain diamond shapes hide inclusions better than others.

• Round brilliant, cushion, oval, radiant — brilliant cuts with lots of facets scatter light and disguise minor inclusions well. You can often go down a clarity grade without visible impact.
• Emerald, Asscher, baguette — step cuts have large open facets that show inclusions clearly. VS2 or better is usually the sensible floor, and eye-clean SI1s are rare.
• Marquise, pear — the pointed corners are the most fragile part of the stone. Feathers or chips near a point deserve extra attention.
• Princess — hides inclusions well overall, but corners are exposed and best avoided as inclusion sites.

If you're comparing shapes, our guide on how to choose a diamond shape covers how each shape wears in daily life.

How Diamond Hub approaches inclusions in bespoke work

When we source diamonds for a bespoke engagement ring, we work through inclusions in a specific order:

1. Read the plot first, not just the grade. The clarity grade is a summary. The plot shows what you're actually buying.
2. Look at the stone under 10x magnification. Certificates describe inclusions; only inspection tells you how they read in the actual stone.
3. Check face-up eye-cleanliness at a normal viewing distance. For everyday wear on the hand, this matters more than the paper grade.
4. Consider the setting. A four-prong solitaire hides less than a halo or a bezel. If a stone has one meaningful inclusion at the edge, a setting can often place it under a prong.
5. Discuss the trade-off honestly. For most clients, dropping from VS1 to VS2 or a good SI1 frees up budget for a bigger stone or a better cut — often the better outcome.

You can see how the full bespoke process works on our bespoke engagement rings page, or book a consultation if you'd like us to review specific certificates with you.

What to think about before choosing a diamond by inclusions alone

• Don't over-pay for grades you'll never see. For most engagement rings, VVS-grade stones are more about a specification than a visible difference.
• Don't buy on grade alone either. Two SI1s can look completely different. Always check the specific stone.
• Balance clarity against cut. Cut is the single biggest driver of how a diamond actually looks. A poorly cut VVS1 will look duller than a well-cut VS2. Our diamond cut grades guide covers this in detail.
• Match the clarity to the shape. Step cuts need higher clarity; brilliants are more forgiving.
• Prioritise eye-clean over paper-perfect. In real-world wear, no one is looking at your ring under a loupe.

FAQ

What are diamond inclusions?

Diamond inclusions are natural internal features — small crystals, feathers, clouds, or other characteristics — that form inside a diamond as it crystallises. Almost every natural diamond has them, and their number, size, and position determine the diamond's clarity grade.

Which diamond inclusions should I avoid?

The inclusions worth avoiding are those visible to the naked eye or those that affect the stone's brightness or durability: black crystals near the table, dense clouds that make the diamond look hazy, large feathers that break the surface, cavities on the crown, and any inclusions near the pointed corners of shapes like marquise or pear.

Are diamond inclusions bad?

No, in most cases. Small inclusions that aren't visible to the naked eye have no impact on how the diamond looks or wears. They're a normal feature of natural diamonds. Only certain types, in certain positions, are worth avoiding.

What does "eye-clean" mean?

Eye-clean means no inclusions are visible to the naked eye at a normal viewing distance of around 20–30cm. It's not an official grading term but is the most practical way to think about clarity for an engagement ring. VS2 diamonds are almost always eye-clean; SI1s often are, depending on the individual stone.

What is a feather in a diamond?

A feather is a small internal fracture inside the diamond that looks feather-like under magnification. Most feathers are stable and invisible to the naked eye. Larger feathers that break the surface or sit near a corner or edge can occasionally raise a durability concern and are worth checking with a jeweller.

Do lab-grown diamonds have inclusions?

Yes. Lab-grown diamonds are graded on the same clarity scale as natural diamonds and can contain inclusions — though the inclusion types are slightly different (metallic inclusions from HPHT growth, for example, instead of mineral crystals). Our lab-grown vs natural diamonds guide explains the differences in more detail.

Can inclusions be removed or hidden?

Some surface-reaching inclusions can be laser-drilled or filled, but the treatment must be disclosed on the certificate and generally reduces the diamond's value. In practice, the better approach is to choose a stone whose inclusions sit where the setting will naturally conceal them.

In summary

Every natural diamond has a story written inside it in the form of inclusions. Understanding what to look for turns a confusing grading letter into a real decision — one that lets you choose a diamond that looks beautiful in daily wear without paying for perfection you'd never see.

If you'd like help reviewing specific diamonds or choosing the right clarity for your ring, our team is happy to talk through certificates with you. Start with our bespoke engagement rings page, or book a consultation.