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The 4Cs — Cut
Diamond Cut Guide
Of the four Cs, Cut is the most important — and the only one entirely determined by the craftsperson, not by nature. A diamond's cut grade determines how brilliantly it reflects light, how alive it appears on the hand, and how much presence it has in any lighting condition.
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The Most Important C
Why Cut Matters Most
Cut is the single largest determinant of a diamond's beauty. It is the only one of the 4Cs you should never compromise on — and it is the one that most buyers underestimate.
Every diamond begins as a rough crystal. A cutter must decide how to divide, shape, and facet that rough into a polished stone — balancing maximum beauty against maximum carat weight retention. The proportions they choose determine everything: how much light enters the diamond, how much is reflected back to the eye, and how much leaks out through the bottom and sides.
A well-cut diamond with an Excellent or Ideal grade returns 90–95% of the light that enters it. The result is a stone that blazes with brilliance and fire in any lighting condition — natural or artificial, bright or dim. A poorly cut diamond returns a fraction of that light, appearing dull, flat, or glassy regardless of its colour or clarity grade.
This is the critical insight: a 0.80ct Excellent-cut diamond will outperform a 1.20ct Good-cut diamond in every lighting condition, every time. Colour and clarity can be masked by a setting, lighting, or distance. Cut cannot be hidden. It is what the diamond does when it moves — and what people notice across a room.
At LuxeBrilliance, we recommend Excellent cut as a minimum for all centre stones. We offer Excellent and Very Good grades only — Fair and Poor grades are not carried in our collection.
90–95%
Light Returned — Excellent Cut
An Excellent-grade diamond returns nearly all the light that enters it, producing maximum brilliance and fire.
#1
Most Important of the 4Cs
Cut is the only C that is entirely determined by skill — not by nature. It is the one you should protect above all others when making budget trade-offs.
15–25%
Price Premium — Excellent vs Very Good
The price difference between Excellent and Very Good is real — but the visual difference between Excellent and Good is far more significant than the price jump suggests.
The Three Pillars of Cut
Brilliance, Fire & Scintillation
When gemologists assess cut quality, they are measuring three distinct visual properties. Understanding each one helps you see exactly what a high-grade cut delivers — and what a poor cut destroys.
Brilliance — Image Coming Soon
Property 01
Brilliance
White Light Return · Internal & External Reflection
Brilliance is the white light reflected from within and from the surface of a diamond. It is the overall brightness you perceive when looking at a diamond — the sense that the stone is glowing from within. Brilliance is maximised when the proportions allow light to enter through the table, reflect off the pavilion facets, and return directly upward through the table to the viewer's eye. A poorly proportioned diamond allows light to escape through the sides or base, dramatically reducing brilliance.
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Property 02
Fire
Spectral Dispersion · Rainbow Flashes
Fire is the dispersion of white light into spectral colours — the rainbow flashes of red, orange, yellow, green, and blue visible when a diamond moves. It is caused by the prism-like refraction of light through the diamond's angled facets. Fire is most visible in warm, directional lighting (candlelight, dimmer rooms) and is what gives a diamond its dramatic, colourful sparkle in lower-light environments. The crown angle and bezel facets are the primary determinants of a diamond's fire.
Scintillation — Image Coming Soon
Property 03
Scintillation
Sparkle & Pattern · Motion-Dependent
Scintillation is the pattern of light and dark areas visible in the diamond — and the flashing sparkle that appears as the stone, the viewer, or the light source moves. It is what people see when a diamond "dances" on the hand while walking or gesturing. A well-cut diamond produces a balanced, symmetrical scintillation pattern — alternating bright and dark areas in pleasing contrast. An asymmetric or overly dark pattern indicates proportional issues. High scintillation is what makes a diamond appear alive.
Diamond Anatomy
The Parts of a Diamond
Understanding the anatomy of a diamond — the names and roles of each part — is the foundation for understanding how cut quality is measured and why specific proportions matter.
Table
The large flat facet on top of the diamond — the primary entry point for light. Expressed as a percentage of the girdle diameter. Ideal table percentage for a round brilliant: 54–58%. A table too wide or too narrow reduces brilliance.
Crown
The upper portion of the diamond above the girdle, comprising the table facet and the surrounding facets. The crown angle — the angle between the bezel facets and the girdle plane — is one of the two most critical proportion measurements. Ideal crown angle: 34–35°.
Girdle
The narrow band at the widest point of the diamond — where the crown meets the pavilion. The girdle is used to set the diamond in a ring, and its thickness affects both the setting security and the diamond's proportion performance. Ranges from extremely thin to extremely thick; "thin to slightly thick" is ideal.
Pavilion
The lower cone-shaped portion of the diamond below the girdle. The pavilion angle — typically 40.6–41.0° for an ideal round brilliant — determines how light is reflected back upward through the table. If the pavilion is too deep, light leaks out the sides. Too shallow, and it leaks through the base.
Culet
The point at the very bottom of the pavilion. In modern diamonds, the culet is typically absent (a pointed tip) or "none to very small." A large culet was common in older cuts and allows light to escape directly through the base, appearing as a dark circle visible through the table.
Total Depth
The total height of the diamond from the table to the culet, expressed as a percentage of the girdle diameter. Ideal depth percentage for a round brilliant: 59–62.5%. Depth percentage affects how the carat weight is distributed — a diamond cut too deep "hides" weight below the girdle where it cannot be seen.
GIA Cut Grade Scale
The Five Cut Grades
The GIA grades round brilliant diamonds on a five-point scale from Excellent to Poor. IGI uses the same scale with the addition of an "Ideal" grade above Excellent. These are the grades you will see on all certified diamond reports.
Grade 01 · GIA Top Grade
Excellent
90–95% Light Return
The highest GIA cut grade. Excellent-cut diamonds are proportioned to maximise brilliance, fire, and scintillation simultaneously. Every facet is angled and sized to return the maximum amount of light directly to the eye. An Excellent-cut diamond in any lighting condition — indoor, outdoor, direct or diffused — performs at its absolute peak. LuxeBrilliance recommends Excellent cut for all centre stones.
Our RecommendationGrade 01A · IGI Top Grade
Ideal
90–98% Light Return
IGI's top grade, sitting above Excellent. Ideal is equivalent to GIA Excellent but may be applied to a slightly narrower proportion range. For lab-grown diamonds certified by IGI, Ideal is the target grade. The terms Excellent (GIA) and Ideal (IGI) describe comparable performance. Some retailers distinguish a "super ideal" category — stricter proportions within the Ideal range that produce Hearts & Arrows patterns.
Recommended for Lab-GrownGrade 02
Very Good
85–90% Light Return
Very Good cut diamonds reflect nearly as much light as Excellent, but allow slightly more to escape through non-optimal proportions. To most observers under normal viewing conditions, the visual difference between Excellent and Very Good is minimal. Very Good can offer meaningful savings — typically 10–15% below Excellent — while delivering outstanding performance. Always view the specific stone before deciding.
Good Value ChoiceGrade 03
Good
75–85% Light Return
Good-grade diamonds reflect a decent amount of light but allow a noticeable proportion to escape. At this grade, the difference in brilliance compared to Excellent is visible to most observers, particularly in lower-light conditions. Buyers sometimes choose Good to prioritise carat weight within a fixed budget — but we advise against compromising cut below Very Good for any centre stone intended to be the focal point of a ring.
Not RecommendedGrade 04–05
Fair & Poor
Under 75% Light Return
Fair and Poor cut diamonds lose significant amounts of light through the base and sides, appearing dull or glassy. Poor-cut stones may show a dark centre where light has leaked entirely. High colour and clarity grades cannot compensate for a Poor cut — the stone will still appear lifeless. LuxeBrilliance does not carry Fair or Poor grades in any category. No high-quality fine jewellery retailer should offer them as centre stones.
Not Available at LuxeBrillianceHow Light Travels
Cut & Light Performance
The same diamond shape — three completely different cutting decisions — three completely different light performances. This is what cut grade means in practice.
Excellent Cut
90–95% Light Returned Upward
Light enters through the table, strikes the pavilion facets at the precise angle for total internal reflection, and exits back through the crown directly toward the viewer. Almost no light is lost. Maximum brilliance and fire.
Cut Too Deep
Light Leaks Through the Sides
When the pavilion angle is too steep, light strikes the pavilion facets at the wrong angle and refracts out through the sides of the stone rather than reflecting upward. The diamond appears dark in the centre — a "nailhead" effect.
Cut Too Shallow
Light Leaks Through the Base
When the pavilion angle is too flat, light passes straight through the bottom of the diamond rather than reflecting upward. The diamond looks glassy or like a window — appearing transparent rather than brilliant. Known as the "fish-eye" effect.
Proportion Guide
Ideal Proportions for a Round Brilliant
The GIA Cut Grade system evaluates round brilliant diamonds against a specific set of proportion ranges. These are the target measurements that define each grade — and the sweet spot within Excellent that most buyers should aim for.
| Cut Grade | Table % | Depth % | Crown Angle | Pavilion Angle | Girdle Thickness | Culet | Recommended |
|---|---|---|---|---|---|---|---|
| Excellent (Sweet Spot) | 54–58% | 59–62.5% | 34–35° | 40.6–41.0° | Thin–Slightly Thick | None to Very Small | ✓ Best Choice Our Pick |
| Excellent (Full Range) | 53–62% | 58–63% | 32–36° | 40.0–41.5° | Very Thin–Thick | None to Very Small | ✓ Recommended |
| Very Good | 52–64% | 57.5–64% | 31.5–36.5° | 39.8–42.2° | Very Thin–Thick | None to Small | ✓ Good Value |
| Good | 50–66% | 56.5–65% | 31–37° | 39.3–43.0° | Very Thin–Very Thick | None to Medium | Not Recommended |
| Fair | 47–69% | 53–66% | 22–40° | 35–46° | Extremely Thin–Very Thick | None to Large | Avoid |
| Poor | Under 47% or over 69% | Under 53% or over 66% | Under 22° or over 40° | Under 35° or over 46° | Extremely Thin–Very Thick | Any | Avoid |
Fancy Shapes
Cut Grades for Non-Round Diamonds
GIA does not assign an overall cut grade to fancy-shaped diamonds — only to round brilliants. For ovals, pears, emerald cuts, and other shapes, you must evaluate cut quality differently.
The GIA Cut Grade system was developed specifically for round brilliant diamonds, whose symmetrical geometry allows precise proportion analysis. Fancy shapes — ovals, pears, marquises, emerald cuts, cushions, princesses, and others — have more variable outlines and proportions, making a single overall grade much harder to define.
IGI does provide cut grades for certain fancy shapes (including Ideal and Excellent designations for ovals and pears), but GIA does not. For GIA-certified fancy shapes, the certificate will show Polish and Symmetry grades — both important indicators of craftsmanship — but no overall Cut grade.
For fancy shapes, light performance must be assessed visually or through specialised imaging tools rather than from the certificate alone. This is why high-quality photographs, video, and ideally in-person viewing are important when purchasing non-round diamonds. Look for a pleasing outline, even facet distribution, no "bow-tie" effect where possible, and a strong Polish and Symmetry grade from the certifying laboratory.
Oval
No GIA Cut Grade · IGI Graded
The most popular fancy shape in 2026. Prone to a "bow-tie" effect — a dark shadow across the centre — in poorly cut stones. Look for balanced outline, even sparkle distribution, and no visible bow-tie in video or direct viewing. Length-to-width ratio between 1.30 and 1.50 is considered most pleasing.
Emerald Cut
No GIA Cut Grade · Step Cut
A step-cut shape assessed for its open, reflective flashes rather than brilliance. Polish and symmetry are especially critical — any misalignment is clearly visible through the large table. Ideal length-to-width ratio: 1.30–1.50. Clarity is more visible in emerald cuts, so prioritise a higher clarity grade.
Pear
No GIA Cut Grade · IGI Graded
A pear should have a symmetrical outline, a well-defined point, and even rounded shoulders. Bow-tie effects are common in poorly cut pears. Ideal length-to-width ratio: 1.50–1.75. The pointed tip is vulnerable to chipping — V-prong settings are essential for pear-shaped centre stones.
Cushion
No GIA Cut Grade · Visual Assessment
Cushion cuts vary significantly in facet arrangement — "chunky" vs "crushed ice" patterns. Chunky cushions have larger, more defined facets and stronger brilliance; crushed ice produces a more glittery, diffuse effect. Neither is objectively superior — choose based on the look you prefer. Ideal ratio for square cushion: 1.00–1.05.
Expert Guidance
What Our Gemologists Always Advise
Four principles about cut that every buyer should understand before making a final decision.
01
Never Compromise on Cut
If budget forces trade-offs across the 4Cs, reduce Colour from D to G, or reduce Clarity from VVS to VS2 — but always protect Cut. A slight warmth in colour grade and an eye-clean SI1 clarity grade are invisible in a mounted ring. A mediocre cut is immediately visible in any lighting condition. Cut is what makes a diamond look alive.
02
Excellent vs Very Good
The visual difference between GIA Excellent and Very Good is real but subtle in most everyday lighting conditions. If budget is genuinely tight, a carefully chosen Very Good cut stone — where the specific proportions fall within the Excellent range on key measurements like table and depth — can be outstanding value. Ask to see the actual proportion report, not just the grade.
03
Cut Affects Apparent Size
A well-cut diamond appears larger per carat than a poorly cut one. This is because an ideal-proportioned diamond distributes its weight across the face rather than hiding it in depth. Two 1.00ct diamonds can have face-up diameters of 6.2mm vs 6.6mm depending on their proportions — a visible difference. Well-cut stones also appear larger because their brilliance makes them stand out more in any environment.
04
Polish and Symmetry Matter
The diamond grading report shows two additional grades alongside Cut: Polish (how smooth the facet surfaces are) and Symmetry (how precisely the facets align with each other). Both should be Excellent or Very Good. Poor polish leaves micro-surface scratches that reduce light transmission. Poor symmetry misaligns facets and disrupts the light performance achieved by the cutting proportions. Never overlook these two sub-grades.
Common Questions
Frequently Asked
The cut questions our team receives most often — answered clearly.
GIA Excellent and IGI Ideal are the top cut grades of their respective laboratories, and they describe comparable levels of light performance. GIA does not offer a grade above Excellent for round brilliants. IGI introduced the "Ideal" grade to describe the very best-performing stones — essentially the top tier within what GIA would also call Excellent. For practical purposes, both grades indicate a superbly cut diamond. GIA Excellent is the standard for natural diamonds; IGI Ideal is the target for lab-grown diamonds.
GIA's cut grading system was developed specifically for round brilliant diamonds, whose perfect symmetry allows precise mathematical analysis of proportions. Fancy shapes — ovals, pears, marquises, emeralds, cushions — have more variable outlines and acceptable proportion ranges that cannot be reduced to a single number. GIA provides Polish and Symmetry grades for all shapes, but the overall Cut grade remains round-brilliant-only. IGI has extended cut grading to certain fancy shapes including ovals and pears, but GIA remains the industry benchmark.
Hearts and Arrows is a visual phenomenon observed in super-ideal round brilliant diamonds — diamonds cut to the very highest precision within the Excellent/Ideal range. When viewed through a special scope from above, a Hearts and Arrows diamond shows eight symmetrical arrows; from below, eight perfectly formed hearts. These patterns are only visible in diamonds cut to extremely precise symmetry tolerances. Less than 1% of all diamonds exhibit true Hearts and Arrows. They represent the pinnacle of round brilliant cutting craftsmanship, typically priced 10–20% above standard Excellent-grade stones.
Yes — cut grade is one of the factors considered in secondary market valuation. An Excellent-cut diamond will generally hold its value better than a comparable stone with a Very Good or Good cut grade, all else being equal. This is because a well-cut stone is more desirable to buyers and will always be easier to sell. When purchasing a diamond as a long-term investment or heirloom, Excellent or Ideal cut is the appropriate choice for this reason as well as for its immediate visual superiority.
Yes — for almost all buyers in almost all circumstances. Colour differences between D and G are virtually invisible in a mounted ring; clarity differences between VVS and VS2 are invisible to the naked eye entirely. But the difference in brilliance between an Excellent and a Good cut is readily apparent in any lighting condition. Cut is what makes a diamond look alive — and what strangers notice across a room. Colour and clarity affect value on paper; cut affects beauty in person. Always protect cut above the other Cs when making budget decisions.
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