Diamond Cut Guide
Cut is how well a diamond's facets work with light. Of the four Cs it does most for brilliance and sparkle, and it is not the same thing as shape.
Cut vs. shape
Shape is the outline seen from above: round, oval, princess. Cut is the quality of the work inside that outline — the proportions, symmetry and polish that decide how light behaves once it enters the stone.
Any shape can be cut well or badly. A round is simply the only one measured against a published standard.
Rounds are graded; fancy shapes are judged
GIA issues an overall cut grade for round brilliants only, and so does IGI, whose top round grade is Ideal. Every other shape is graded for polish and symmetry, and its light performance is judged on the stone — which makes proportions, length-to-width ratio and seeing the diamond matter more.
The twelve shapes we carry
The cut grade scale
GIA grades round brilliants on five steps, from Excellent to Poor. The difference between them is how much of the light entering the top finds its way back out of it. Real round brilliants from current stock are listed under their grade.
Excellent
Maximum brilliance, fire and scintillation. Proportions return nearly all the light that enters.
- Round 1.50 ct · lab-grown, IGI
Round in stock: 130 lab-grown
Very Good
Returns most of the light that enters. Close to Excellent face up, usually at a better price.
- Round 1.50 ct · lab-grown, IGI
Round in stock: 23 lab-grown
Good
Returns a good share of light, with some escaping. A solid option where budget leads.
- Round Brilliant 0.81 ct · lab-grown, IGI
Round in stock: 2 lab-grown
Fair
Noticeably less brilliance. Proportions let light escape through the sides or the bottom.
None in stock
Poor
Significant light loss. The stone looks dull or dark in areas, even in good light.
Not stocked
| Grade | What it means |
|---|---|
| Ideal | IGI only, for round brilliants: its top grade, above Excellent. GIA's scale has no equivalent above Excellent. |
| Excellent | Maximum brilliance, fire and scintillation. Proportions return nearly all the light that enters. |
| Very Good | Returns most of the light that enters. Close to Excellent face up, usually at a better price. |
| Good | Returns a good share of light, with some escaping. A solid option where budget leads. |
| Fair | Noticeably less brilliance. Proportions let light escape through the sides or the bottom. |
| Poor | Significant light loss. The stone looks dull or dark in areas, even in good light. |
Fancy shapes in current stock
This week's featured fancy shapes, with the finish grades that apply to them. Judge their light performance on the stone, or ask for images.
- Radiant 1.00 ctPolish Excellent · Symmetry Very GoodNatural · GIA · SKU OM-1279
- Oval 1.00 ctPolish Excellent · Symmetry FairNatural · GIA · SKU OM-1058
- Emerald Cut 2.77 ctPolish Excellent · Symmetry ExcellentLab-grown · IGI · SKU TP-250325-1119
- Pear Brilliant 2.00 ctPolish Excellent · Symmetry ExcellentLab-grown · IGI · SKU TP-030926-3383
- Asscher 1.03 ctPolish Good · Symmetry GoodNatural · GIA · SKU OM-1026
What makes up a cut grade
Three things, and our listings show each of them by name.
- ProportionsOn a listing: Cut (round brilliants)
- Table %, depth %, and the crown and pavilion angles — how the shape is built to return light.
- SymmetryOn a listing: Symmetry
- How precisely the facets are aligned, placed and matched to each other and to the outline.
- PolishOn a listing: Polish
- The smoothness of every facet surface: no drag lines, burn marks or nicks.
How cut affects appearance
Cut controls three separate effects. A stone can be strong in one and weaker in another, which is why two diamonds with the same grades can look different.
- Brilliance
- White light returned to the eye. The overall brightness of the stone.
- Fire
- Light split into flashes of colour as it leaves through the crown.
- Scintillation
- The sparkle and pattern of light and dark as the stone, the light or the viewer moves.
Cut grade and price
At the same carat, colour and clarity, cut moves the price substantially. An Excellent cut commands a premium because it shows the stone's other qualities at their best: the colour you paid for looks whiter and the size you paid for faces up in full.
Very Good often gives the best balance of performance and price. Below Good, the saving rarely makes up for the light lost.
- ExcellentPremiumThe most light, and the price that goes with it.
- Very GoodBest valueVery close face up, at a meaningful saving.
- GoodBudgetVisibly less lively beside the grades above.
- Fair · PoorAvoidLight loss outweighs the lower price.
Choosing the right cut grade
Put cut first
If the budget is limited, protect cut before colour, clarity or carat. It has the largest effect on how the stone looks.
Round brilliants
Choose Excellent or Very Good — or Ideal on an IGI report. Avoid Fair and Poor.
Fancy shapes
With no overall grade to lean on, look at the length-to-width ratio, the depth and table figures, and how even the facet pattern is.
Ask for light images
An ASET or Idealscope image shows where a stone returns light and where it leaks. Ask for one where it is available.
Read the three together
Compare Cut, Polish and Symmetry side by side, as our listings show them, rather than the cut grade alone.
Frequently Asked Questions
What buyers ask most often about cut before choosing a stone.
What's the difference between cut and shape?
Shape is the outline seen from above: round, oval, emerald and so on. Cut is how well that shape has been executed — its proportions, symmetry and polish — and it decides how the stone handles light. Any shape can be cut well or badly.
Is Excellent cut always worth the extra cost?
Not always. Excellent returns the most light, and on a round brilliant it is worth favouring. But a well-chosen Very Good stone can be very hard to tell apart face up, and the saving can go into a better colour or a little more weight. Judge the stone, not only the grade.
Do fancy-shaped diamonds have official cut grades?
No. GIA and IGI issue an overall cut grade for round brilliants only. Fancy shapes are graded for polish and symmetry, and their reports give the measurements and proportions; how well they return light is judged on the stone itself.
What is a 'Hearts and Arrows' diamond?
A round brilliant cut to such precise symmetry that a special viewer shows eight arrows looking down through the top and eight hearts looking up through the bottom. It indicates exceptional optical symmetry. It is a pattern, not a laboratory grade, so ask to see the viewer image rather than relying on the name.
Why don't all lab-grown listings show a Cut grade?
Because the report does not carry one. IGI, which grades most of our lab-grown stock, issues an overall cut grade only for round brilliants — sometimes as Ideal, its top grade. For emerald, pear and every other fancy shape the report gives polish and symmetry instead, and so does our listing.
Shop Diamonds by Cut
Choose a round brilliant's cut grade, or another shape, to open the catalogue already filtered. If nothing in stock fits, enquire and we will source to the specification.