Cut
How well the diamond is proportioned and finished. The biggest influence on sparkle.
Diamond education
The 4Cs of Diamonds, Explained
Cut, colour, clarity and carat describe every diamond, natural or lab-grown. Understanding them helps you see what you’re paying for — and where you can save without seeing any difference.
The 4Cs
A common language for every diamond
The 4Cs were developed by the Gemological Institute of America (GIA) so that any diamond can be described in the same way, anywhere in the world. No single “C” makes a diamond beautiful — it’s the balance between them that matters, and that balance depends on your budget and the look you love.
01 · Cut
Cut: the source of sparkle
Cut is about how a diamond’s facets are angled and proportioned — not its shape. A well-cut diamond returns light to your eye as brilliance (white light), fire (flashes of colour) and scintillation (sparkle as it moves). A poorly cut diamond leaks light and can look dull or dark, even with excellent colour and clarity.
Round brilliant diamonds receive an official cut grade, from Excellent down to Poor on GIA reports (IGI also uses “Ideal” at the top). Fancy shapes such as ovals and emeralds don’t receive an overall cut grade, so we look at proportions, symmetry and how the stone actually performs.
TipIf you prioritise one C, make it cut. We recommend Excellent (or Ideal) for round diamonds.
Cut grades (round diamonds)
- Our sweet spotExcellent / IdealMaximum light return
- Very GoodStrong sparkle, slightly less light return
- GoodNoticeably less brilliant
- Fair & PoorDull, leaks light; we don’t recommend
02 · Colour
Colour: from icy white to warm
White diamonds are graded from D (completely colourless) to Z (light yellow or brown). The differences between neighbouring grades are very subtle and often only visible side by side under controlled lighting.
Your metal matters. In platinum or white gold, near-colourless G–H diamonds look bright and white. In yellow or rose gold, the warm metal reflects into the stone, so a slightly warmer grade can look just as beautiful for less.
The colour scale
- D–FColourless
- Our sweet spotG–JNear colourless
- K–MFaint colour
- N–RVery light colour
- S–ZLight colour
03 · Clarity
Clarity: what you can and can’t see
Almost all diamonds contain tiny characteristics — internal “inclusions” and surface “blemishes” — formed as they grew. Clarity grades describe how many there are, how large, and how visible under 10x magnification.
The goal for most couples is an “eye-clean” diamond: one with no inclusions visible to the naked eye. That’s often achievable at VS2 or SI1 for brilliant shapes like round and oval. Step cuts such as emerald and Asscher have open, mirror-like facets that show more, so we usually suggest VS1 or higher.
The clarity scale
- FL / IFFlawless / Internally flawless
- VVS1–VVS2Very, very slightly included
- Our sweet spotVS1–VS2Very slightly included
- Our sweet spotSI1–SI2Slightly includedOften eye-clean at SI1
- I1–I3IncludedVisible to the eye
04 · Carat
Carat: weight, not size
Carat is a measure of weight: one carat is 0.2 grams, divided into 100 “points” (so a 0.75ct diamond is 75 points). Larger diamonds are rarer, so price rises faster than weight.
Two diamonds of the same carat can look different in size depending on cut and shape. A well-cut diamond spreads its weight across its face, and elongated shapes like oval, pear and marquise look larger than a round of the same weight.
TipPrices step up at “magic” weights like 0.50ct, 1.00ct and 1.50ct. A diamond just below — say 0.90ct — can cost noticeably less and look almost identical on the hand.
Beyond the 4Cs
Other details worth knowing
Polish and symmetry
How precisely the facets are finished and aligned. Excellent or Very Good is ideal.
Fluorescence
Some diamonds glow under UV light. Usually invisible in daylight; very strong fluorescence can occasionally make a diamond look slightly hazy.
Shape
The outline of the diamond. It affects sparkle, apparent size and which settings suit it.
Proportions
For fancy shapes, the length-to-width ratio changes the look — a slimmer or rounder oval, for example.
Origin
Natural and lab-grown diamonds are graded on the same 4Cs. The difference is origin and price.
Certificate
An independent grading report confirms everything above. Never buy a significant diamond without one.
Certification
Read the certificate, not just the price
Every Primo centre diamond comes with an independent grading report from GIA or IGI. The report records the 4Cs, measurements, proportions, polish, symmetry and fluorescence, and many diamonds also carry a microscopic laser inscription of the report number on their girdle.
Balancing the 4Cs
Where to spend and where to save
| C | Spend here if… | Save here by… |
|---|---|---|
| Cut | Always — it drives sparkle | Not recommended |
| Colour | You want an icy look in platinum or white gold | Choosing G–J, or warmer grades in yellow or rose gold |
| Clarity | You choose a step cut like emerald or Asscher | Choosing an eye-clean VS2–SI1 for brilliant shapes |
| Carat | Size on the hand matters most to you | Going just under magic weights, or choosing an elongated shape |
Collection
Settings made to show off your diamond
Choose the diamond for how it will be worn, not only how it looks in a tray.
Francesco NicolaouFounder, Primo Diamonds
Questions
Frequently asked questions
Which of the 4Cs is most important?
Cut, because it has the biggest effect on sparkle. After that, the balance depends on your budget and whether size, whiteness or clarity matters most to you.
What is a good colour and clarity for an engagement ring?
For most rings, G–H colour and VS2–SI1 clarity give a white, eye-clean diamond with excellent value. Step cuts may need higher clarity.
Does carat mean size?
No, carat is weight. Cut and shape affect how large a diamond looks.
Are lab-grown diamonds graded the same way?
Yes. They are graded on the same 4Cs by independent laboratories such as IGI and GIA.
Is a flawless diamond worth it?
Flawless diamonds are very rare and priced accordingly, but an eye-clean diamond looks the same to the naked eye.
What does “eye-clean” mean?
No inclusions are visible to the naked eye at a normal viewing distance.
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Related guides
Compare diamonds side by side
The 4Cs make much more sense in person. Visit our Hatton Garden showroom and we’ll show you diamonds of different grades together, with no pressure to decide on the day.