The 4Cs - carat, cut, colour, and clarity, are the universal language of diamond grading. Every reputable diamond comes with a certificate from an independent gemological lab (GIA or IGI being the most recognised) that grades the stone across all four.
Understanding what each grade actually means and more importantly, how to prioritise them, is the difference between buying a diamond on paper and buying a diamond you'll love in real life.
Here's what you actually need to know.
Cut: The One That Matters Most
Cut is the most important of the 4Cs, and the most misunderstood. It doesn't refer to the shape of the diamond (round, oval, pear) but to the quality of the way it's been cut: the precision of its angles, the symmetry of its facets, the proportions that determine how light moves through the stone.
A well-cut diamond captures light and returns it to the eye as brilliance, fire, and scintillation, the brightness, the coloured flashes, the sparkle as it moves. A poorly cut diamond leaks light. It looks flat and lifeless, regardless of how it grades on the other Cs.
For round brilliant diamonds, the GIA grades cut from Excellent down to Poor. We recommend Excellent or Very Good at minimum, and for most buyers, Excellent cut is where the money is best spent, even if it means coming down on carat or colour to stay within budget.
For fancy shapes (oval, pear, cushion, emerald, and others), there's no standardised cut grade on a certificate which makes buying in person, or with an experienced guide, particularly important. We assess fancy shape cut quality ourselves when sourcing stones on your behalf, and we'll explain exactly what we're looking for and why.
Colour: Less Is More (Mostly)
Diamond colour is graded on a scale from D (completely colourless) to Z (noticeably yellow or brown tint). The difference between adjacent grades is almost impossible to see with the naked eye. It takes a trained gemologist with comparison stones under controlled lighting to reliably detect.
For round brilliants set in white gold or platinum, we typically recommend G or H colour. These grades face up white to the naked eye in virtually all lighting conditions, but cost significantly less than D-F stones without any visible difference in appearance.
For yellow gold settings, you can often go as low as J or K without any warmth being noticeable because the warm tone of the gold absorbs any slight body colour in the stone.
For fancy shapes, we tend to recommend going one or two grades higher (more colourless), because elongated shapes like ovals and pears can show colour more in the tips.
The bottom line: for most buyers, G-H colour in white metal is the sweet spot. Genuinely beautiful, with significant budget freed up for cut and carat.
Clarity: What You Can't See Doesn't Matter
Clarity measures the presence of inclusions (internal characteristics) and blemishes (surface characteristics) in a diamond. The scale runs from Flawless (FL) - no inclusions visible under 10x magnification, down to Included (I1-I3), where inclusions are visible to the naked eye.
The practical question isn't 'how clean is this diamond under a loupe?', it's 'can you see anything with the naked eye?' For most buyers, the answer at SI1 and many SI2 grades is no. An eye-clean SI1 is indistinguishable from a VVS2 to anyone looking at your ring in normal life.
We recommend VS2 or SI1 as the target range for most buyers. Eye-clean in the vast majority of cases, with meaningful budget savings over VS1 and above. We assess clarity in person when sourcing, because not all SI1 stones are eye-clean, that's a judgment call that a certificate grade alone can't make.
The exception is emerald and Asscher cuts, which have an open, mirror-like table that makes inclusions more visible. For these shapes, we recommend VS1 or VS2 at minimum.
Carat: Size, Weight, and What Actually Looks Big
Carat is a unit of weight. One carat equals 0.2 grams. It broadly correlates with size, but two diamonds of identical carat weight can look quite different depending on their cut and shape.
A round brilliant cut 1.0ct diamond has a diameter of roughly 6.4mm. An oval of the same weight, because it's elongated, will look significantly larger face-up, which is one of the reasons ovals have become so popular. A cushion cut of the same weight will look smaller, because more of its weight is in the depth of the stone.
Practically, carat is the easiest variable to flex when managing a budget. There are meaningful price jumps at round numbers (0.5ct, 1.0ct, 1.5ct, 2.0ct), because of demand. A 0.9ct stone of excellent cut and colour will look almost identical to a 1.0ct stone and cost considerably less. We source across these thresholds deliberately when it's in a client's interest.
How to Actually Use the 4Cs
In order of priority for most buyers: Cut first, always. Then colour and clarity together - choosing grades that are genuinely beautiful in real life, not just impressive on paper. Then carat, calibrated to what the budget allows after the other three are right.
But here's the thing: reading about the 4Cs is useful context. Seeing diamonds in person is how you actually make the decision. Two stones with identical certificates can look meaningfully different, and the one that speaks to you in natural light, in your hand, is the right choice, regardless of what the numbers say.
At Micheli, we source a selection of stones that meet your brief and present them to you in store before any commitment is made. You compare them side by side, ask every question you have, and make the decision with your own eyes. That's the only way to buy a diamond you'll love for life.
