Diamond Grading Explained: The 4Cs, the Clarity Chart and How to Read a Report

Every diamond report, whoever issues it, describes a stone with the same four measures: cut, colour, clarity and carat weight, the "4Cs" the Gemological Institute of America codified in the 1950s. Once you can read them, a report tells you more about a diamond than any photograph. This is what each grade means, and what the differences look like on a finished piece of jewellery.

Colour: the D to Z scale

Colour grading measures the absence of colour. The scale runs from D, entirely colourless, to Z, a visible light yellow or brown, and is read against master stones under controlled light. D, E and F are graded colourless; G, H, I and J near-colourless; K to M faint; N to Z light. The differences at the top of the scale are invisible outside a laboratory: a G and a D set side by side in yellow gold cannot be told apart by eye, which is why G–H is the sweet spot for jewellery that is meant to look white without paying for a letter no one will see. Below J the warmth begins to show, more so in white gold than yellow.

Clarity: the chart from FL to I3

Clarity grades the inclusions inside a stone and the blemishes on its surface, as seen under 10x magnification. The chart runs: FL (flawless) and IF (internally flawless); VVS1 and VVS2 (very, very slightly included, hard to see even at 10x); VS1 and VS2 (very slightly included, minor inclusions at 10x, invisible to the naked eye); SI1 and SI2 (slightly included, visible at 10x and sometimes to the eye); I1, I2 and I3 (included, visible to the eye and in I3 affecting durability). The line that matters to a buyer is "eye-clean": VS and above is eye-clean in every case, SI1 usually, SI2 sometimes, I never. Paying for VVS over VS buys a difference only a gemmologist will find.

Cut: the grade that controls sparkle

Cut is not the shape (round, oval, pear) but how well the facets are proportioned and polished to return light. GIA grades round brilliants from Excellent to Poor on proportions, symmetry and polish. A well-cut stone looks larger and brighter than a poorly cut stone of higher colour and clarity; a deep or shallow cut leaks light out of the sides or bottom and reads dull. Of the four Cs, cut is the one to compromise on last.

Carat: weight, not size

A carat is 0.2 grams. Two stones of the same carat weight can look different in size depending on cut depth, and price steps up sharply at the round numbers (0.50, 1.00, 2.00 ct), so a 0.90 ct stone can be noticeably cheaper than a 1.00 ct one that looks the same. In a piece with many small stones, a tennis bracelet or a pavé setting, the report gives total carat weight, and the quality of each stone matters more than the total.

Reading a grading report

A laboratory report (GIA, IGI, HRD and others) lists the 4Cs, the measurements in millimetres, fluorescence, a plotted diagram of inclusions and, for lab-grown stones, the origin and growth method. The laser inscription on the girdle matches the report number. A report grades the loose stone before setting; a jeweller's certificate of authenticity describes the finished piece, its gold, its stones and their total weights. The two documents do different jobs and a serious piece can come with either or both.

How Aquae Jewels grades

We set natural diamonds at G–H colour and VS clarity: near-colourless and eye-clean, the range that reads white against 18K gold without paying for grades that cannot be seen. Stones are selected from trusted suppliers and re-assessed on arrival in our own Dubai workshop against those standards, with provenance documentation kept for every stone. Every finished piece leaves with its certificate of authenticity stating the gold, the stones and their weights, and all of it is in solid 18K gold, hallmarked 750.

Frequently asked questions

What is the best clarity grade for a diamond?

For jewellery worn every day, VS1 or VS2: eye-clean at a sensible price. FL and VVS grades are for collectors and for very large stones where an inclusion would be easier to find.

Is G colour a good diamond?

Yes. G is the top of the near-colourless range and indistinguishable from D–F once set; it is the standard for fine jewellery that wants a white stone at a rational price.

Is SI clarity worth buying?

SI1 is often eye-clean and good value in a solitaire if you can see the stone or its plot before buying; in pavé or a tennis line, where stones are small and many, VS is the safer standard.

What is diamond fluorescence?

Some diamonds glow blue under ultraviolet light. Faint to medium fluorescence has no visible effect and can make a slightly warm stone look whiter; strong fluorescence can, rarely, make a stone look hazy, and reports note it so you can check.