The Complete Reference Diamond Guide

Twelve shapes, four grading scales, and the working knowledge our gemologists use every day — written so you can walk into any showroom, including ours, and know exactly what you are looking at.

12 SHAPESTHE 4 C’SGRADING SCALES SETTINGS & CAREGLOSSARY

Loose natural diamonds Loose lab-grown diamonds

Anatomy of a Diamond

Every grading term on a report refers to one of five regions. Once you can name them, a certificate reads like a plan rather than a code.

TABLE

The large flat facet on top, and the main doorway for light entering and leaving. Expressed as a percentage of the stone’s diameter, it usually sits between 53 and 58 per cent in a well-cut round.

CROWN

The angled upper section between table and girdle. Its angle, close to 34 degrees in an ideal round, decides how much white light is split into colour.

GIRDLE

The narrow band at the widest point, where the setting takes hold. Graded from extremely thin to extremely thick; the extremes either chip easily or hide weight where no one can see it.

PAVILION

The lower cone that acts as the mirror. Its angle, near 41 degrees, determines whether light bounces back to your eye or escapes out of the bottom.

CULET

The tip at the very base. On a modern diamond it should be graded none or very small; a large culet reads as a grey window in the centre of the stone.

Three things happen when light meets a diamond. Brilliance is the white light returned to your eye. Fire is that light split into spectral colour. Scintillation is the flash pattern that appears as the stone, the light, or you move. A good cut produces all three at once.

The Twelve Shapes

Shape describes the outline of a diamond; cut describes how well it was proportioned. Round is the only shape with an industry-standard cut grade, which is why the notes below matter more for every other shape on this page.

Round Brilliant

The benchmark for light return

The round brilliant is the most studied shape in the diamond world. Its 57 or 58 facets are placed by mathematics rather than by eye, and because those proportions are standardized it is the only shape GIA assigns an overall cut grade to. That makes it the easiest diamond to compare on paper. It also returns more white light than any other cut, which means a round will forgive a slightly lower colour or clarity grade that a step cut would put on display.

Facets: 57–58
Cutting style: Brilliant
Ideal length to width: 1.00 – 1.03
Size at 1 carat: 6.4 × 6.4 mm

Face-up spread Medium

Watch forRounds waste the most rough in cutting, so they carry the highest cost per carat of any shape.

Oval

Round brilliance, drawn out

An oval is a round brilliant stretched along one axis, so it keeps the same facet logic and nearly the same fire while covering noticeably more of the finger. At equal weight an oval reads larger than a round and visually lengthens the hand. Every oval carries some bow-tie, a dark band across the centre where the pavilion shadows itself. A faint one adds contrast; a heavy one reads as a dead zone, and it never appears on the grading report.

Facets: 57–58
Cutting style: Brilliant
Ideal length to width: 1.35 – 1.50
Size at 1 carat: 7.7 × 5.7 mm

Face-up spread High

Watch forBow-tie severity, and warmth pooling at the two ends.

Cushion

Soft corners, candlelit fire

Named for its pillow outline, the cushion descends from the old mine cuts of the 1800s and still behaves like them. Larger facets throw broad coloured flashes rather than the fine white sparkle of a round, which is why cushions look so alive under warm light. Two temperaments exist: chunky cushions with big, distinct facets, and crushed-ice cushions with many small facets that glitter. Rounded corners leave no vulnerable point, making this one of the most durable shapes to wear daily.

Facets: 58–64
Cutting style: Brilliant / mixed
Ideal length to width: 1.00 – 1.09 square · 1.15 – 1.30 elongated
Size at 1 carat: 5.8 × 5.8 mm

Face-up spread Low

Watch forCushions hold weight in the pavilion, so they face up smaller than a round of equal carat.

Princess

Square outline, brilliant heart

The princess is a brilliant cut wearing a square outline, introduced in the 1980s and the most popular square shape ever since. It keeps far more of the original rough than a round does, so the same weight costs less and gives more stone. The trade-off sits at the four sharp ninety-degree corners, which are the most chip-prone points in any common cut. V-prongs or a bezel solve this completely. Colour also gathers in those corners, so a princess wants one grade whiter than a round.

Facets: 57–76
Cutting style: Brilliant
Ideal length to width: 1.00 – 1.05
Size at 1 carat: 5.5 × 5.5 mm

Face-up spread Medium

Watch forThe corners are the most vulnerable point of the shape.

Radiant

Emerald outline, brilliant sparkle

The radiant is the bridge between the emerald and the princess: a cut-cornered rectangle or square carrying a full brilliant facet pattern underneath. Those cropped corners are structurally strong, and the brilliant faceting scatters light so effectively that a radiant hides inclusions and warmth better than any step cut of the same grades. If you love the elongated emerald silhouette but want real sparkle, this is the answer.

Facets: 70
Cutting style: Brilliant
Ideal length to width: 1.00 – 1.05 square · 1.25 – 1.50 elongated
Size at 1 carat: 6.2 × 5.3 mm

Face-up spread Medium

Watch forElongated radiants can carry a light bow-tie.

Asscher

Art Deco, the hall of mirrors

Developed by the Asscher brothers in 1902 and revived with the Deco period, the Asscher is essentially a square emerald cut with a taller crown and deeply cut corners. Its step facets form concentric squares that pull the eye straight down into the stone, an effect cutters call the hall of mirrors. That open architecture is also its demand: there is nowhere for an inclusion or a warm tint to hide, so clarity and colour carry more weight here than in any brilliant cut.

Facets: 58
Cutting style: Step
Ideal length to width: 1.00 – 1.05
Size at 1 carat: 5.5 × 5.5 mm

Face-up spread Low

Watch forThe open table means inclusions and colour show readily.

Heart

The most personal shape

A heart is structurally a pear with a cleft cut into the round end, and it is judged almost entirely on symmetry. The two lobes must mirror each other, the cleft must be sharp and clearly defined, and the point must line up with the centre of the cleft. Below roughly half a carat the outline becomes hard to read once prongs are added, so stones below 0.50 ct are uncommon in this shape. Three or five prongs is standard, with one always guarding the point.

Facets: 56–59
Cutting style: Brilliant
Ideal length to width: 0.95 – 1.05
Size at 1 carat: 6.5 × 6.5 mm

Face-up spread Medium

Watch forLopsided lobes and a shallow, undefined cleft. Symmetry is the whole game.

Emerald

Clarity on display

The emerald cut is a step cut: long parallel facets running like stairs down to the culet, with the corners cropped for strength. It does not sparkle so much as flash, producing broad alternating planes of light and shadow that cutters describe as a hall of mirrors. The wide open table works as a window into the stone, so inclusions and warmth read plainly. In exchange, an emerald faces up larger than a round of the same weight and carries a restrained, architectural presence that nothing else matches.

Facets: 57–58
Cutting style: Step
Ideal length to width: 1.30 – 1.50
Size at 1 carat: 7.0 × 5.0 mm

Face-up spread High

Watch forInclusions under the table are unmissable.

Pear

Round at one end, pointed at the other

Also called a teardrop, the pear is a hybrid of the round brilliant and the marquise, and it delivers one of the highest face-up spreads of any shape. Worn with the point toward the fingernail it elongates the hand considerably. Two things decide a good pear: symmetry, where the shoulders must mirror each other and the point must sit on the centreline of the rounded end, and the bow-tie, which behaves exactly as it does in an oval. The point itself needs a V-prong, without exception.

Facets: 56–58
Cutting style: Brilliant
Ideal length to width: 1.45 – 1.75
Size at 1 carat: 8.7 × 5.7 mm

Face-up spread High

Watch forBow-tie, uneven shoulders, and an unguarded point.

Marquise

The largest face-up size per carat

Boat-shaped and pointed at both ends, the marquise is said to have been commissioned by Louis XV and it remains the most efficient shape on the finger: at equal weight it presents roughly a third more surface than a round. That spread comes from a shallow, elongated pavilion, which is also why the shape shows any bow-tie readily and why cut quality matters more here than the certificate suggests. Both points must be protected, and the two halves must match precisely or the stone will look bent.

Facets: 56–58
Cutting style: Brilliant
Ideal length to width: 1.85 – 2.10
Size at 1 carat: 10.5 × 5.2 mm

Face-up spread Highest

Watch forTwo vulnerable points, bow-tie, and any asymmetry between the halves.

Trillion

Triangular, usually a side stone

The trillion, sometimes written trilliant, is a shallow triangular cut that reads far larger than its weight. Sides may be straight or gently convex. It is most often supplied as a matched pair flanking a centre stone, where the two must agree in colour, outline and depth, though it is occasionally set alone for an unmistakably modern ring. Because it is cut shallow, warmth travels across the whole stone rather than pooling, so colour shows earlier than in a deeper shape.

Facets: 31–50
Cutting style: Brilliant / mixed
Ideal length to width: 1.00
Size at 1 carat: 7.0 × 7.0 mm

Face-up spread High

Watch forThree sharp points, and colour showing sooner than expected.

Baguette

The architectural accent

A baguette is a step-cut rectangle with just fourteen facets, the fewest of any cut in this guide. Straight baguettes sit shoulder to shoulder in a row; tapered baguettes narrow at one end so they can wrap a centre stone. With so few facets there is no brilliance to hide behind, so baguettes are cut from clean, white material and a set is judged on how precisely the stones match one another in length, colour and clarity. They are accents by design, and they give a ring its line.

Facets: 14
Cutting style: Step
Ideal length to width: 1.50 – 2.50
Size at 1 carat: Typically 0.03 – 0.25 ct each

Face-up spread High

Watch forMismatched lengths or colour across a set will read immediately.

Spread is why two one-carat diamonds can look nothing alike. A marquise carries its weight across the surface; a cushion carries it in the depth. Same carat, very different stone on the hand.

Cut

Cut is not the shape of a diamond. It is the quality of its proportions, symmetry and polish — the workmanship that decides how much light comes back out. It is the only one of the four Cs created entirely by human hands, and the one that most affects how a diamond looks.

TOO SHALLOW

A pavilion cut too flat lets light pass straight through the bottom instead of reflecting it back. The stone looks wide but washed out, often with a dark ring at the centre.

WELL PROPORTIONED

Light entering the crown strikes one pavilion facet, reflects to the opposite facet, and leaves through the top. This double bounce is what produces brilliance, fire and scintillation together.

TOO DEEP

An over-deep pavilion sends light out through the side. The diamond looks dark in the middle and, because the weight is buried below the girdle, smaller than its carat suggests.

THE GIA CUT SCALE

Excellent

Nearly all light entering the crown returns through the table. Crisp white brilliance, strong fire, and even scintillation across the whole stone.

Very Good

Returns most of the light an Excellent does, and to the unaided eye the difference is usually invisible.

Good

Reflects a good deal of light and still looks lively, though the pattern is less even and the stone can look slightly duller beside a better cut.

Fair

Noticeable light leakage. The stone appears flat or glassy, and a well-cut smaller diamond will often outshine it.

Poor

Most light escapes through the sides or the bottom. The diamond looks dull or dark regardless of its colour and clarity grades.

What the grade covers

An overall cut grade weighs seven factors: brightness, fire, scintillation, weight ratio, durability, polish and symmetry. Polish and symmetry are also reported separately.

For a round brilliant, the numbers behind an Excellent grade generally fall in these ranges: table 53 to 58 per cent, total depth 59 to 62.5 per cent, crown angle 34 to 35 degrees, pavilion angle 40.6 to 41 degrees, with a thin to slightly thick girdle and no culet.

The fancy-shape exception

GIA does not issue an overall cut grade for any shape other than round brilliant. An oval, pear or emerald report will show polish and symmetry, but nothing that summarises light performance.

This is the single most useful thing to know when shopping fancy shapes. There is no grade to hide behind, so proportions, bow-tie and face-up appearance have to be judged by eye. Bring the stone into daylight, tilt it, and watch what the centre does.

Colour

Colour grading measures the absence of colour. Stones are graded face-down against a set of masterstones under controlled lighting, which is a far more demanding test than the way anyone actually wears a ring. The scale runs from D, entirely colourless, through Z, distinctly yellow.

K – M

N – R

S – Z

COLOURLESSNEAR COLOURLESSFAINTVERY LIGHTLIGHT

Exceptional white +

Absolutely colourless, the rarest grade on the scale.

Exceptional white

Traces of colour only a gemologist could detect.

Rare white +

Nearly imperceptible colour. Face-up, indistinguishable from D.

Rare white

Reads white in every setting. The value grade for platinum and white gold.

White

Still reads white face-up, especially in brilliant cuts.

Slightly tinted white

A faint warmth appears when compared side by side with a G. Alone, it looks white.

Slightly tinted white

Warmth is detectable in larger stones and step cuts. Excellent in yellow or rose gold.

K – M

Faint yellow

A visible warm cast, which many buyers actively prefer in yellow gold and vintage settings.

N – R

Very light yellow

Clearly tinted face-up in any metal.

S – Z

Light yellow

Distinctly yellow. Below Z, a diamond is graded on the fancy colour scale instead.

Fluorescence

Roughly a quarter to a third of diamonds glow, usually blue, under ultraviolet light. It is reported as none, faint, medium, strong or very strong.

In daylight most fluorescence is invisible, and in a near-colourless stone graded I or J a faint blue can actually make the diamond look whiter. Only in a small number of strong and very strong stones does it produce a milky or oily cast, which is why we look at any strongly fluorescent diamond in natural light before it goes on the floor.

Diamonds falling below Z, or showing colour outside the normal range, are graded on an entirely separate fancy colour scale that runs from Faint to Fancy Vivid.

Clarity

Diamonds form under enormous heat and pressure, and nearly all of them carry evidence of it. Internal features are called inclusions, surface ones blemishes. Clarity grading records what a trained grader can find at ten times magnification — not what you can see across a dinner table.

VVS1

VVS2

VS1

VS2

SI1

SI2

I2 – I3

FEWEST INCLUSIONSMOST INCLUSIONS

Flawless

No inclusions and no blemishes visible to a skilled grader at 10× magnification. Fewer than one diamond in five thousand reaches this grade.

Eye-cleanAlways

Internally Flawless

No inclusions inside the stone. Only minor surface characteristics remain, and a polisher could often remove them at the cost of a little weight.

Eye-cleanAlways

VVS1

Very, Very Slightly Included 1

Inclusions are extremely difficult to see at 10×, and typically sit near the girdle rather than under the table.

Eye-cleanAlways

VVS2

Very, Very Slightly Included 2

Still very difficult to locate at 10×. A pinpoint or two, usually off to one side.

Eye-cleanAlways

VS1

Very Slightly Included 1

Minor inclusions, difficult to see at 10×. Invisible to the unaided eye in every practical sense.

Eye-cleanAlways

VS2

Very Slightly Included 2

Minor inclusions, somewhat easier to find at 10× but essentially never visible without it.

Eye-cleanAlways

SI1

Slightly Included 1

Inclusions are noticeable at 10×. Many SI1 stones are still eye-clean, particularly in brilliant cuts where faceting breaks up the view. Position matters more than the grade.

Eye-cleanUsually

SI2

Slightly Included 2

Easily seen at 10×, and sometimes visible to the unaided eye depending on where the inclusion sits and whether it is white or dark.

Eye-cleanSometimes

Included 1

Obvious at 10× and generally visible to the unaided eye. May begin to affect how much light the stone returns.

Eye-cleanRarely

I2 – I3

Included 2 and 3

Inclusions are prominent, affect brilliance, and in the lowest grades can compromise the durability of the stone. We do not stock these grades as centre stones.

Eye-cleanNo

Grade is not the whole story

Two SI1 diamonds can look completely different. Four things decide whether an inclusion matters:

Position. Directly beneath the table is the worst place. Near the girdle, where prongs sit, is the best.
Nature. A feather reaching the surface is a durability question, not just a cosmetic one. A crystal or cloud is purely cosmetic.
Contrast. A dark crystal draws the eye at a grade where a white cloud would disappear.
Shape. A brilliant cut breaks up the view and forgives a great deal. An emerald or Asscher shows everything.

Reading the plot

A full grading report includes a plotting diagram: red symbols for internal inclusions, green for surface blemishes, mapped onto an outline of the stone. Use it to locate what the grader saw, then find it under a loupe yourself.

Common terms you will meet there include crystal, a mineral inclusion; feather, a small internal fracture; cloud, a hazy group of pinpoints; needle, a thin rod; twinning wisp, a ribbon formed during growth; and natural, a piece of the original rough surface left on the girdle.

For most buyers, VS2 to SI1 is where clarity stops being visible and starts being paperwork.

Carat Weight

A carat is a unit of weight, not size: one carat equals 200 milligrams, divided into a hundred points. Two diamonds of identical weight can differ noticeably in how large they look, because weight can be spread across the surface or buried in the depth.

ROUND BRILLIANT DIAMETERS, DRAWN TO SCALE

0.25 ct4.1 mm

0.50 ct5.2 mm

0.75 ct5.9 mm

1.00 ct6.5 mm

1.50 ct7.4 mm

2.00 ct8.2 mm

3.00 ct9.4 mm

PRINTED AT 100% ON LETTER OR A4, THESE CIRCLES ARE ACTUAL SIZE. ON SCREEN THEY ARE APPROXIMATE.

Pricing at the carat marks

Diamond prices step up sharply at the half and full carat — 0.50, 0.75, 1.00, 1.50 and 2.00 — because those are the numbers people ask for.

A 0.92 carat round measures about 6.3 millimetres across; a 1.00 carat measures about 6.5. The difference is two tenths of a millimetre, invisible on the hand, and it can move the price considerably. If the number on the report matters less to you than the stone, this is the easiest place to gain.

Size is relative

The same diamond looks larger on a slender finger and on a narrower band. A thin, low-profile setting gives a stone more presence than a wide, heavy one.

Shape matters just as much. At one carat, a marquise measures roughly 10.5 millimetres long against a round’s 6.5, and a halo of small accent stones can add three to four millimetres of apparent diameter to a centre stone of any weight.

Grading Reports

A grading report is an independent laboratory’s scientific description of a diamond. It is not an appraisal and it carries no valuation. Every significant diamond we sell arrives with one.

The laboratories

GIA, the Gemological Institute of America, created the modern four Cs and remains the strictest and most widely accepted authority. AGS is known for its light-performance approach and its zero-to-ten cut scale, where zero is Ideal.

IGI, HRD and GCAL also issue reports and are common on laboratory-grown stones.

Grading standards are consistent within a laboratory, not between them. The same diamond can receive different grades from different labs, so compare like with like.

What to check

The report number is usually laser-inscribed on the girdle. Under magnification you can match the stone in front of you to the paper in your hand.
Verify the number on the laboratory’s own website before purchase.
Confirm the origin line: natural or laboratory-grown.
Check the comments section, where treatments and clarity characteristics not shown on the plot are disclosed.

Natural and laboratory-grown

A laboratory-grown diamond is chemically, physically and optically the same material as a natural one, and it is graded on the same four Cs. The difference is origin and rarity, and the two markets behave very differently.

Laboratory-grown stones are identified as such on the report and are typically laser-inscribed on the girdle. Any diamond we describe as natural is exactly that.

Treatments

Several processes can improve a diamond’s apparent grade, and all of them must be disclosed: fracture filling to mask feathers, laser drilling to reach and lighten dark inclusions, and HPHT or irradiation to alter colour.

Fracture-filled stones in particular must never be steam cleaned or exposed to a jeweller’s torch, and they should be identified before any repair work begins.

Settings and Metal

The setting decides how much light reaches the stone, how large it appears, and how well it survives daily wear. It is not a finishing touch; for pointed and sharp-cornered shapes it is a structural requirement.

Common settings

Prong. Four prongs show more of the stone; six hold more securely and make a round look slightly smaller. The standard for solitaires.
V-prong. A prong shaped to wrap a point or corner. Essential on pear, marquise, heart and princess.
Bezel. A metal rim around the whole girdle. The most protective of the settings, fully enclosing the girdle.
Halo. A ring of small diamonds around the centre stone, adding three to four millimetres of apparent size.
Three-stone. A centre stone flanked by two matched sides, often trillions, tapered baguettes or pears.
Pavé and channel. Small diamonds set flush along the band, either bead-set or held between two walls of metal.

Choosing the metal

Platinum is dense, naturally white and hypoallergenic. It does not fade to yellow, and over time it develops a soft patina rather than wearing thin. The most secure choice for holding a diamond.

White gold is lighter and more affordable, finished with rhodium plating that should be renewed every one to three years to keep its brightness.

Yellow and rose gold warm the stone they hold. This is a genuine advantage: a J or K colour diamond that would read faintly warm in platinum looks crisp and white against gold, and the saving can go into size or cut instead.

Care and Longevity

Diamond is the hardest natural substance on earth, a ten on the Mohs scale. Hard is not the same as unbreakable: a diamond has cleavage planes, and a sharp knock on a point or corner can chip it. Everything below follows from that one fact.

Cleaning at home

Diamonds attract grease, and a film of lotion or soap dulls a stone faster than any amount of wear. Clean weekly.

Soak for twenty minutes in warm water with a drop of mild dish soap.
Brush gently with a soft toothbrush, paying attention to the underside of the pavilion where film collects and light enters.
Rinse in a bowl rather than an open drain, and dry with a lint-free cloth.
Chlorine bleach and abrasive cleaners attack the alloys in gold rather than the diamond itself.

An ultrasonic cleaner is safe for most untreated diamonds in sound settings, but never for fracture-filled stones, heavily included stones with feathers reaching the surface, or any setting with a loose stone.

Wearing and storing

Take the ring off for the gym, gardening, heavy lifting and swimming. Cold water also shrinks fingers, which is how rings are lost in pools and the ocean.
Apply lotion, sunscreen and hairspray before putting jewellery on.
Store each piece separately in a soft pouch or a lined box. A diamond will scratch every other gemstone it touches, and another diamond as well.
Have prongs and settings checked every six to twelve months. Prongs wear thin with use, and re-tipping costs a fraction of replacing a lost stone.

Bring your jewellery to us for professional cleaning and inspection at any time. It takes a few minutes.

Glossary

The vocabulary you will meet on a grading report and across a showroom counter.

Bow-tie: A dark band shaped like a bow tie across the centre of an elongated cut, caused by the pavilion shadowing itself. It is never noted on a grading report.
Brilliance: The white light a diamond returns to the eye.
Brilliant cut: A faceting style built from triangular and kite-shaped facets radiating from the centre, engineered to maximise light return.
Culet: The point or tiny facet at the very bottom of the pavilion. Ideally graded none or very small.
Depth percentage: Total depth divided by average girdle diameter. Governs whether light returns to the eye or leaks away.
Dispersion: The splitting of white light into spectral colours, seen as fire.
Eye-clean: No inclusions visible to the unaided eye at normal viewing distance. A description, not a graded term.
Fluorescence: A glow, usually blue, under ultraviolet light. Present in roughly a quarter to a third of diamonds and generally neutral in daylight.
Girdle: The narrow band around the widest part of the stone where crown meets pavilion. Graded from extremely thin to extremely thick.
Inclusion: An internal characteristic formed as the diamond crystallised. A blemish, by contrast, is on the surface.
Loupe: A 10× magnifier. The standard instrument for clarity grading worldwide.
Pavilion: The lower portion of the diamond, below the girdle.
Point: One hundredth of a carat. A 0.75 ct diamond is a seventy-five pointer.
Scintillation: The flashing sparkle produced as the diamond, the light source, or the observer moves.
Spread: How large a diamond appears face-up relative to its actual weight.
Step cut: A faceting style of long parallel facets arranged like stairs. Emerald, Asscher and baguette are step cuts.
Table: The large flat facet on the top of the diamond.
Table percentage: Table width divided by average girdle diameter.

Now look at some stones

Everything above is easier to judge with a diamond in front of you. Search current availability by shape, carat, colour and clarity.

Loose natural diamonds Loose lab-grown diamonds

Diamond illustrations are schematic and are drawn to show facet arrangement, not to represent any individual stone. Millimetre figures are typical for a well-proportioned diamond at the stated weight and will vary between stones. Grading terminology follows the Gemological Institute of America. This guide is educational and is not an appraisal or a valuation.