Diamond Cut
The most important factor in a diamond's beauty — how light performs within the stone.
Understanding Diamond Cut
Cut is widely considered the most important of the 4 C's because it has the greatest influence on a diamond's sparkle and visual appeal.
It's important to note that cut does not refer to a diamond's shape — round, oval, princess and so on describe the outline. Cut refers to how well a diamond's proportions, symmetry and polish work together to interact with light. A well-cut diamond reflects light internally from one facet to another, then disperses it back through the top of the stone — creating that mesmerising brilliance.
Key insight: Prices jump significantly at "magic numbers" — 0.50ct, 1.00ct, 1.50ct and 2.00ct. A 0.95ct diamond looks virtually identical to a 1.00ct diamond but can cost 15–20% less. Savvy buyers take advantage of this pricing quirk.
The Three Components of Cut
A diamond's cut quality is expressed through three visible effects:
Brilliance
The total white light reflected from a diamond, both internally and externally. A well-cut diamond acts like a series of tiny mirrors, bouncing light back to your eye through the top of the stone (the table). A poorly cut diamond leaks light through the bottom or sides, appearing dark and dull.
Fire
The dispersion of white light into the colours of the spectrum — those rainbow flashes you see when a diamond catches the light. Fire is created by light bending as it passes through angled facets, separating into its component colours. A well-proportioned crown angle maximises fire.
Scintillation
The pattern of light and dark areas, and the flashes of sparkle when a diamond or the light source moves. Scintillation is what makes a diamond feel "alive" — that dynamic play of contrast and brightness. Good symmetry and precise facet alignment are essential for even scintillation.
Anatomy of a Diamond
To understand how cut affects light performance, it helps to know the key parts of a polished diamond:
Table
The large flat facet on top — the main window through which light enters and exits. Table percentage (table width relative to total diameter) is a key proportion.
Crown
The upper portion between the table and girdle. Crown angle affects the balance between brilliance and fire — too steep or too shallow disrupts light return.
Girdle
The widest edge where crown meets pavilion. An extremely thin girdle risks chipping; an extremely thick girdle hides carat weight without adding visual size.
Pavilion
The lower portion from girdle to culet. Pavilion depth is critical — too deep and light escapes the sides; too shallow and it leaks through the bottom.
A round brilliant diamond has 57 or 58 facets (the 58th being a small culet at the very bottom). Each must be cut at precise angles for optimal light performance. This is what separates an Excellent cut from a Poor one — not the number of facets, but the precision of every angle and proportion.
Cut Grade Scale
The GIA grades round brilliant diamonds on a scale from Excellent to Poor. Each grade represents a range of proportions and face-up appearances:
| Grade | Description | Light Performance | Rarity |
|---|---|---|---|
Excellent |
Maximum fire and brilliance. Reflects nearly all light that enters the diamond. | Performance: Outstanding | Rarity: Top ~3% |
Very Good |
Reflects most light. Minor deviations from excellent proportions. | Performance: Very High | Rarity: Top ~15% |
Good |
Reflects a majority of light. Noticeable but not significant brilliance loss. | Performance: High | Rarity: Top ~25% |
Fair |
Some light escapes through sides or bottom. Still a quality diamond but visibly less brilliant. | Performance: Moderate | Rarity: Top ~35% |
Poor |
Significant light loss. Diamond appears dull and lifeless to the naked eye. | Performance: Low | Rarity: — |
Cut Grading: GIA vs HRD Antwerp vs IGI
At Diamantwerp, every diamond comes with certification from GIA, HRD Antwerp or IGI. Each laboratory uses its own system for grading cut quality. Understanding the differences helps you compare diamonds across certificates:
| GIA | HRD Antwerp | IGI | |
|---|---|---|---|
| Highest grade | GIA: Excellent | HRD: Excellent | IGI: Ideal (above Excellent) |
| Grade scale | GIA: Excellent → Poor(5 grades) | HRD: Excellent → Fair(4 grades, no "Poor") | IGI: Ideal → Fair(5 grades incl. Ideal) |
| Sub-grades | GIA: Overall cut grade only | HRD: Proportions, Polish, Symmetry(each graded separately) | IGI: Overall cut + Polish & Symmetry |
| Round brilliants | GIA: Full cut grade ✓ | HRD: Full cut grade ✓ | IGI: Full cut grade ✓ |
| Fancy shapes | GIA: No cut grade ✗ | HRD: No cut grade ✗ | IGI: Cut grade available ✓ |
| Polish & Symmetry | GIA: Excellent → Poor | HRD: Excellent → Fair | IGI: Excellent → Fair |
| Headquarters | GIA: Carlsbad, USA | HRD: Antwerp, Belgium | IGI: Antwerp, Belgium |
Diamantwerp note
HRD Antwerp is based right here in Antwerp's diamond district — just minutes from our office at Pelikaanstraat 62. Since January 2009, HRD has refined its cut grading to separately assess proportions, polish and symmetry, giving you a more detailed picture than a single overall grade. Their system uses 4 categories (Excellent, Very Good, Good, Fair) for each sub-grade. The overall cut impression is determined by the lowest of the three sub-grades.
Key difference: IGI grades fancy shapes
IGI is currently the only major laboratory that assigns formal cut grades to fancy shaped diamonds (oval, princess, emerald, cushion, etc.). GIA and HRD only grade the cut of round brilliants. If you're buying a fancy shape, an IGI certificate with a cut grade can provide additional confidence in the stone's craftsmanship.
Key Proportions for Round Brilliants
Two numbers on any diamond certificate tell you a great deal about cut quality. Here are the ranges typically associated with each grade:
| Parameter | Excellent Range | Very Good | Good |
|---|---|---|---|
| Table % | Excellent: 52 – 62% | Very Good: 53 – 66% | Good: 53 – 69% |
| Depth % | Excellent: 57.5 – 63% | Very Good: 56 – 66.5% | Good: 53.5 – 70% |
| Crown Angle | Excellent: 31.5° – 36.5° | Very Good: 26.5° – 38.5° | Good: 22° – 40° |
| Pavilion Angle | Excellent: 40.6° – 41.8° | Very Good: 39.8° – 42.4° | Good: 38.8° – 43° |
| Girdle | Excellent: Thin – Slightly Thick | Very Good: Very Thin – Thick | Good: Very Thin – Very Thick |
| Culet | Excellent: None – Very Small | Very Good: None – Small | Good: None – Medium |
Based on GIA Estimating Cut Grade charts. Actual grades depend on the interplay of all proportions — no single parameter determines the grade in isolation. Star length (55%), lower half length (80%) and polish/symmetry also factor in.
Polish & Symmetry
Beyond proportions, two finishing qualities affect a diamond's final appearance:
Polish refers to the smoothness of each facet surface. During cutting, tiny imperfections such as scratches or burn marks can occur. High-quality polish ensures each facet acts as a clean mirror.
Symmetry measures how precisely the facets are aligned — whether the table is centred, whether opposite facets mirror each other, and whether the culet sits at the exact bottom. Even slight misalignment can redirect light away from the viewer.
Both are graded from Excellent to Poor (GIA) or Excellent to Fair (HRD/IGI). For maximum brilliance, look for at least Very Good in both. A "triple excellent" diamond — Excellent cut, Excellent polish, Excellent symmetry — represents the highest level of craftsmanship available.
Why Cut Affects Price
Cutting a diamond is always a trade-off between beauty and carat weight. A rough diamond can be cut to preserve maximum weight — resulting in a larger but poorly proportioned stone — or cut to ideal proportions, sacrificing some weight for superior light performance.
An Excellent cut costs more per carat because the cutter deliberately sacrificed rough material to achieve optimal proportions. A poorly cut diamond may weigh more, but it will look dull — a poor investment regardless of its size.
This is precisely why cut grade matters more than carat weight alone. A 0.90ct Excellent cut diamond will typically look brighter, larger and more impressive than a 1.00ct Fair cut diamond — and often costs less.
Interactive Cut Grade Estimator
Adjust the sliders to see how proportions affect a round brilliant diamond's estimated cut grade. This tool is based on GIA's proportion-based grading guidelines.
Diamond Cut Estimator
For round brilliant diamonds — adjust table %, depth %, crown angle and pavilion angle.
This diamond has ideal proportions. Nearly all light is reflected back through the table, producing outstanding brilliance, fire and scintillation.
This is a simplified estimator based on GIA proportion guidelines. Actual cut grades also depend on star length, lower half length, girdle variation, polish, symmetry and other factors. Always refer to the laboratory certificate for the official grade.
Our Recommendation
At Diamantwerp, we strongly recommend choosing Excellent or Very Good cut grades — never compromise on cut. The difference in beauty is dramatic: a well-cut diamond will appear brighter, larger and more lively than a higher-carat stone with a poor cut.
If your budget requires trade-offs, reduce colour or clarity before cut — the visual impact of a superior cut far outweighs a grade or two in colour. A G-colour Excellent cut diamond will look whiter and more brilliant than a D-colour Fair cut diamond.
With our prices up to 75% below retail, you can invest in the best cut without stretching your budget. Browse our collection or contact us for personal advice.
For the highest possible standard, look for a Triple Excellent diamond — achieving Excellent grades for cut, polish and symmetry simultaneously.
COMMON Questions
