Diamond Knowledge

The Brilliani Labs Diamond Guide

A plain-English guide to how diamonds are described and judged. The terms below make up the shared language the trade uses to talk about a stone — the same language whether a diamond is mined or grown in a lab. Where there's a fact worth knowing, you'll find it here, without the jargon for its own sake.

The Four Cs

What are the Four Cs, and why do they matter?

The Four Cs — Cut, Colour, Clarity and Carat Weight (often written as the 4Cs) — are the four characteristics used to describe the quality of a diamond. Before they became standard, there was no agreed way to judge a stone: terms varied from jeweller to jeweller, and a buyer had little way of knowing exactly what they were paying for.

The Four Cs changed that in two ways. Diamond quality could finally be described in one universal language, and a buyer could know precisely what they were about to purchase. That standard, settled in the middle of the 20th century, is still the method used to assess a diamond's quality anywhere in the world.

Where did the Four Cs come from?

For most of history there were no standard terms for diamond quality, which made it hard for sellers to explain value and harder still for buyers to understand it. In the early-to-mid 20th century the trade settled on four clear factors — Cut, Colour, Clarity and Carat Weight — as a simple, memorable way to learn, remember and explain what determines a diamond's worth. The shorthand stuck, and the Four Cs became the industry's common reference point.

Colour

How is a diamond's colour graded?

Most diamonds used in jewellery appear colourless or near-colourless, but very few are perfectly so. Colour is graded on a scale that runs from D (completely colourless) to Z (light yellow or brown), with each letter marking a small, defined step away from colourless. The less colour a diamond shows across this range, the rarer it is.

Why does the colour scale start at D, not A?

Earlier grading methods used all sorts of overlapping terms — A, B and C without clear definitions, numbers, and loose descriptions like "blue white" that were wide open to interpretation. When the modern scale was designed, its creators wanted a clean break with those older systems, so they started fresh at the letter D. That scale has since become the universal standard, and the looser systems have all but disappeared.

How is colour actually evaluated?

Light and background strongly affect how a diamond looks, so colour is judged in a controlled viewing environment and compared against a set of master stones of known colour. At a reputable laboratory, at least two graders assess each diamond independently, and depending on how closely their grades agree — and on the size and quality of the stone — more graders may be brought in. A final grade is only assigned once there is clear consensus.

When does a diamond become a "fancy" coloured diamond?

The D-to-Z scale covers diamonds in the colourless-to-light-yellow/brown range. Once a yellow or brown diamond shows more colour than the Z reference point, it is no longer graded on that scale — it is treated as a coloured diamond. When its hue, tone and saturation are strong enough, it earns a "fancy" colour grade. Diamonds also occur in other hues, including red, pink, blue and green.

Clarity

What is clarity, and what do the grades mean?

Clarity describes the presence or absence of internal features (inclusions) and surface features (blemishes) in a diamond. The standard clarity scale has six categories, several of them subdivided, for eleven grades in total:

• Flawless (FL): No inclusions or blemishes visible under 10x magnification.
• Internally Flawless (IF): No inclusions, and only blemishes visible under 10x.
• Very, Very Slightly Included (VVS1, VVS2): Minute inclusions, ranging from extremely to very difficult to see under 10x.
• Very Slightly Included (VS1, VS2): Minor inclusions, ranging from difficult to somewhat easy to see under 10x.
• Slightly Included (SI1, SI2): Noticeable inclusions, ranging from easy to very easy to see under 10x.
• Included (I1, I2, I3): Obvious inclusions, visible under 10x, which may affect transparency and brilliance.

What causes inclusions?

Inclusions usually form while the diamond itself is forming. Small crystals can become trapped inside the stone, and as the diamond grows its atomic structure can develop small irregularities. These features are part of how each stone is made — and part of what makes it unique.

How is clarity evaluated?

Clarity is graded under standard conditions at 10x magnification. A grader first examines the stone closely to identify its clarity and finish characteristics, along with any signs of treatment such as fracture filling or laser drilling. At least two graders then assess the diamond independently and agree a grade, plotting the characteristics on a diagram that matches the stone's shape and faceting.

Cut

What is cut grade?

Cut grade describes how well a diamond's proportions, symmetry and polish have been executed — in other words, how well it was designed and crafted to return light. It is the C with the most direct effect on how a diamond looks. For round brilliant diamonds, cut is rated on a five-point scale from Excellent to Poor. All else being equal, a better cut grade means a more beautiful and more valuable stone, which makes cut central to choosing a diamond that is both lovely and good value.

The modern cut scale was not guesswork: it was built on extensive computer modelling of many thousands of proportion combinations, then validated against what real people, looking at real diamonds, actually found attractive.

Isn't cut the same as a diamond's shape?

It is a common mix-up, but no. Shape is the outline — round, oval, pear, marquise, cushion, and so on. Cut grade is about the quality of the craftsmanship for a given shape. The round brilliant is by far the most common shape in jewellery; every other outline is known as a fancy shape.

How does pavilion depth affect the cut?

The pavilion is the lower portion of the diamond, running from the girdle (its widest edge) down to the culet (the point at the bottom). If the pavilion is cut too shallow or too deep, light escapes through the side or leaks out of the bottom instead of returning to your eye. A well-cut pavilion sends more light back up through the top of the stone — which is what makes it look bright and lively.

Do more facets make a diamond brighter?

Not really. The number of facets changes the pattern of reflections rather than the overall brightness — more facets simply means more, smaller reflections instead of fewer, larger ones. Brightness comes down to proportions, polish and symmetry, not facet count.

How is cut evaluated for round brilliant diamonds?

Optical measuring instruments capture the proportions of the facets that shape a diamond's face-up appearance. Those measurements are compared against large reference databases of stones with known grades, alongside an expert's visual assessment of polish and symmetry, to arrive at the cut grade.

Why isn't there a standard cut grade for fancy shapes?

Setting reliable cut-quality standards for fancy shapes is far harder than for round diamonds, simply because there is so much more variation in outline — and the measuring technology has to capture the features that matter for each shape. Work continues across the industry towards systems that are accurate, comprehensive and practical, but for now a like-for-like cut grade is generally offered only for round brilliants.

Carat weight

How is carat weight measured?

Carat is a measure of weight, not size. A diamond is weighed on a highly accurate electronic balance, precise to the fifth decimal place (a hundred-thousandth of a carat), and that figure is then rounded to two decimal places — a hundredth of a carat — for the grading report.

Fluorescence

What is fluorescence?

Fluorescence is the visible light some diamonds give off when exposed to ultraviolet (UV) rays — an everyday component of daylight. On a grading report, fluorescence describes the strength of that reaction under long-wave UV. The glow lasts only as long as the stone is under the UV source. Roughly a quarter to a third of diamonds show some fluorescence; in more than 95% of those, the colour seen is blue, and only occasionally yellow, white or another colour.

Does fluorescence change how a diamond looks?

For the great majority of diamonds, fluorescence has no noticeable effect on appearance — and some people actually prefer the look of stones with medium to strong blue fluorescence. In rare cases, very strong fluorescence can make a diamond appear slightly hazy or oily, but this affects only a tiny fraction of fluorescent stones.

Does fluorescence weaken a diamond?

No. A diamond that fluoresces is just as sound as one that does not. The same subtle features in the diamond's structure that cause fluorescence can also prevent it; neither makes the stone any weaker.

Treatments & disclosure

What are treatments, and why are diamonds treated?

Beyond ordinary cutting and polishing, a stone can be treated to alter its colour or clarity, and sometimes to change its durability. Because these treatments are not always visible to the untrained eye — and can be hard even for experts to spot — anyone selling a treated gem is legally required to disclose what has been done to it. Honest disclosure is the whole point: you should always know exactly what you are buying. That is what Born Clear means in practice — clear origin, and nothing hidden about how a stone came to look the way it does.

How do I know whether a diamond has been colour-treated or clarity-enhanced?

A proper grading report makes it plain. Stones with treated colour are identified as such on the report and are typically laser-inscribed to say so. Clarity treatments such as laser drilling are noted in the report's symbols and comments. Stable, permanent treatments are recorded on a standard grading report; less stable treatments, such as coatings or fracture filling, are usually documented on a separate identification report instead. If a stone has a report from a recognised laboratory, the relevant facts will be there.

Lab-grown diamonds

What are lab-grown diamonds?

Lab-grown diamonds are grown in controlled conditions over a short period — often a couple of weeks or less — rather than over the vast timescales of natural formation. A longer growth period yields larger crystals, and steady conditions are needed throughout to produce high-quality material. That very different growth history also leaves features that allow lab-grown stones to be distinguished from mined ones.

Are lab-grown and natural diamonds both "real" diamonds?

Yes. A lab-grown diamond is chemically, physically and optically a diamond — the same material as a mined one, with the same brilliance. The meaningful difference is origin, not quality: one grew in the earth, the other in a lab. Being lab-grown is a feature, not a compromise — clear origin, every time.

How are lab-grown diamonds made?

Two methods are used:

• High-Pressure, High-Temperature (HPHT): Uses high pressure, high heat, a molten-metal flux and a diamond seed to start crystal growth. It most closely mirrors the conditions under which natural diamonds form, and produces a distinctive crystal shape.
• Chemical Vapour Deposition (CVD): Uses lower pressure and high heat in a vacuum chamber. A carbon-rich gas such as methane is introduced and broken down into its atoms, which settle onto a flat diamond seed plate — building up a tabular crystal layer by layer.

The first commercially viable lab-grown diamonds were produced by the HPHT method in the 1950s; CVD was largely developed more recently. Production now takes place all over the world.

What treatments are common in lab-grown diamonds?

The same treatments seen in natural diamonds can be applied to lab-grown ones:

• Irradiation can introduce green, blue, brown, yellow, black and other colours, and is sometimes followed by annealing. Irradiated stones are heat-sensitive, so repairs, re-cutting or re-polishing can change their colour.
• Annealing is controlled heating and cooling, often used after irradiation to shift colour towards brown, orange or yellow (and sometimes pink, red or purple). Later heat — during routine repairs, for instance — can alter the colour again.
• HPHT treatment heats a stone under high pressure to remove or change its colour.

As with natural stones, any such treatment should be disclosed.

Can a lab-grown diamond be identified outside a laboratory?

Sometimes, but not always reliably. Because they form under such different conditions, lab-grown diamonds can show tell-tale signs — colour zoning, dark metallic inclusions, weak strain patterns, and distinctive UV-fluorescence patterns — some visible under a microscope. But not every characteristic can be confirmed by eye, so confident separation often calls for specialist instruments, such as those using ultraviolet spectroscopy to tell natural, lab-grown and simulant stones apart.

Do lab-grown diamonds get grading reports?

Yes. Lab-grown diamonds are graded on dedicated reports that look distinctly different from those for natural stones, and they are typically laser-inscribed as laboratory-grown. They are assessed on the same colour and clarity scales as natural diamonds — the D-to-Z range for near-colourless stones, and the same eleven clarity grades — with the report also noting how the diamond was grown and whether it was treated afterwards. Reputable laboratories have issued dedicated lab-grown reports since the mid-2000s.

Simulants

What is a simulant?

A simulant is a material that merely looks like a diamond without being one — it imitates the appearance but is not the same substance. Simulants can be natural or man-made. ("Imitation" and "substitute" mean the same thing.) This is different from a lab-grown diamond, which genuinely is a diamond. Common simulants include moissanite and cubic zirconia.

How do I know my stone is a diamond and not a simulant?

A grading report is your assurance. Reputable laboratories test every stone to confirm it really is a diamond before issuing a diamond grading report, and they do not issue diamond reports for simulants. So if your stone comes with a report from a recognised lab, it has been verified as a diamond.

Reports, rarity & ethics

What does a grading report actually tell me?

A grading report is an independent, expert assessment of a stone — recording its Four Cs and confirming whether it is natural or lab-grown, and whether it has been treated. It is proof rather than opinion, which is exactly why it matters: it lets you see what you are buying instead of taking it on trust.

Are diamonds conflict-free?

The Kimberley Process, established in 2002 by a coalition of governments, industry and non-governmental organisations, controls the import and export of rough diamonds to keep conflict diamonds out of the market. Today the overwhelming majority of diamonds in the trade are conflict-free.

Are diamonds rare?

All gem-quality diamonds are rare in nature. Lab-grown diamonds, by contrast, can be produced to order — part of why they offer the look of a fine diamond at a different price.