Diamond Education: How Diamonds Are Graded, Explained

What is diamond education and why does it matter?

Diamond education is simply knowing what the words on a grading report mean, and which of them you can actually see. Two round diamonds of 1 carat can sit thousands of dollars apart, and almost all of that gap is explained by four grades plus a handful of extra details such as fluorescence, polish and symmetry. Once you can read them, you can compare stones on your own terms instead of taking anyone's word for it.

This page is the starting point for the GemTrove diamond education library. It gives you the short version of each grade, then points you to a detailed page for every colour band, clarity grade and cut grade. For how the four grades trade off against each other, see our full guide to the diamond 4Cs. If you are shopping for a ring, the engagement ring education hub picks up where this page finishes.

A note on who is explaining: GemTrove has been in Melbourne since 2008, and our family has been in the jewellery trade since 1984. Raj Sood is a Graduate Gemologist (GIA), holds the AJP (GIA) and is a master jeweller. The practical advice here comes from grading and setting stones at the bench, not from a spec sheet.

What are the 4Cs of diamonds, explained simply?

The 4Cs are the shared language of the diamond trade. The Gemological Institute of America (GIA) popularised them in the 1950s, and today every major grading laboratory uses the same four headings, even if their reports look slightly different. Here is the whole diamond grading scale in one table.

The grades do not carry equal weight. Cut decides how a diamond looks more than anything else, so a well-cut G VS2 will usually look livelier than a poorly cut D FL. Colour and clarity matter, but only up to the point where your eye stops seeing a difference. Carat drives price fastest of all. Good diamond education is really about knowing where each of those thresholds sits.

How are diamond cut grades decided?

Cut is about proportions and finish, not shape. A grader looks at the table (the flat top facet), the crown angle (the slope of the upper half), the pavilion angle (the slope of the lower half), girdle thickness and overall depth. When those angles are right, light entering the top bounces off the pavilion and comes back out through the crown. When the pavilion is too shallow or too deep, light leaks out the bottom and the stone looks glassy or dark in the centre.

For round brilliants GIA gives five cut grades: Excellent, Very Good, Good, Fair and Poor. IGI, which grades many lab-grown diamonds, also uses an Ideal grade at the top. In practice most buyers choose Excellent or Very Good, and the difference between them can be small in some stones and obvious in others. Our page on Excellent, Very Good and Good cut compared shows where the line usually falls.

Two finish grades sit alongside cut. Polish describes the smoothness of the facet surfaces and symmetry describes how precisely the facets line up. A stone graded Excellent in cut, polish and symmetry is often called triple Excellent or 3EX. Our guide to polish and symmetry grades explains when a Very Good in either one matters and when it does not.

Oval, pear, emerald, cushion and other fancy shapes do not receive an overall GIA cut grade, so you have to judge them differently: length-to-width ratio, table and depth percentages, bow-tie darkness and outline symmetry. We cover that method in judging cut in fancy shapes without a GIA cut grade.

How does the diamond colour chart work?

White diamonds are graded on how little colour they show, from D (none at all) down to Z (a clear light yellow or brown). Graders compare each stone face-down against master stones of known colour under controlled light, because colour is easiest to see through the side. Face-up, sparkle masks a lot of it, which is why grades a few letters apart can look identical on the hand.

Metal changes everything. Yellow and rose gold reflect warmth into the stone, so an I or J can look as white as a G set in platinum. Warmer grades also have their own fans: L and M faint yellow diamonds give a soft, antique tone at a much lower price than the colourless grades.

The letter grade only measures yellow-to-brown depth of colour. Some stones carry a slight nuance (an undertone) that the letter does not name. Our page on brown, grey or blue nuance explains why two H-colour stones can look a little different and how to spot it on video.

What is the diamond clarity chart, grade by grade?

Almost every diamond, natural or lab-grown, contains tiny features from its growth. Those inside the stone are inclusions (crystals, feathers, clouds, pinpoints); those on the surface are blemishes (polish lines, nicks). A trained grader examines the stone at 10× magnification and weighs five things: size, number, position, nature and relief (how much each feature contrasts with the diamond around it).

Each grade has its own detailed page with photographs of real inclusions:

• Flawless and Internally Flawless: the rarest grades, chosen for the certainty rather than any difference you can see.
• VVS1 clarity and VVS2 clarity: inclusions so small an experienced grader has to hunt for them.
• VS1 diamonds and VS2 diamonds: eye-clean in nearly every brilliant cut; see whether you can see the difference between VS1 and VS2.
• SI1: often eye-clean if the inclusion is light or near the edge; we explain when SI1 is a smart pick.
• SI2 clarity: can work in a brilliant cut with a well-placed inclusion, but inspect every stone.
• I1 to I3 included grades: visible inclusions, sometimes with durability concerns.

Position matters for durability as well as looks. Surface-reaching features such as cavities and chips are worth understanding before you buy, because a setting claw placed over them can either protect or stress the stone.

How does carat weight affect size and price?

Carat is weight, not size. One carat is 0.20 grams and is split into 100 points, so a 0.75 ct diamond is often called a 75-pointer. Price per carat rises as stones get bigger, because larger rough is rarer, which means a 2 ct diamond typically costs well over twice as much as a 1 ct of the same grades.

Prices also jump at so-called magic sizes: 0.50, 0.70, 0.90, 1.00, 1.50 and 2.00 ct. A 0.95 ct stone looks the same as a 1.00 ct on the hand (the diameter differs by roughly a tenth of a millimetre), yet usually sits noticeably lower in price.

Notice that doubling the weight from 1 ct to 2 ct adds only about 1.7 mm across. A stone cut too deep hides weight underneath and looks smaller face-up, while a well-proportioned one spreads its weight across the top. Always compare the millimetre measurements on the report, not just the carat figure.

What is diamond fluorescence, and does it matter?

Fluorescence is a glow some diamonds give off under ultraviolet light, such as a blacklight or strong sunlight. In natural diamonds it is usually blue, caused by traces of nitrogen. Reports grade its strength as None, Faint, Medium, Strong or Very Strong. Our introduction to how diamond fluorescence works covers the science, and we explain each fluorescence strength from None to Very Strong with photographs.

For most stones it makes no visible difference indoors. In I, J and K colours, medium to strong blue fluorescence can make a diamond look slightly whiter in daylight, and those stones are often priced a little lower than non-fluorescent equivalents. In a small number of high-colour stones, very strong fluorescence can make the diamond look faintly hazy or oily, which is why it is worth seeing a video in daylight. Lab-grown diamonds can fluoresce too, sometimes in other colours, and the report will say so.

Are lab-grown and natural diamonds graded the same way?

Largely, yes. A laboratory-grown diamond is real diamond: the same carbon crystal, the same hardness of 10 on the Mohs scale and the same refractive index of about 2.42. It is grown in a lab by HPHT (high pressure, high temperature) or CVD (chemical vapour deposition) instead of forming deep in the earth. It is graded for cut, colour, clarity and carat, and every reputable report states clearly that the stone is laboratory-grown, usually with a matching laser inscription on the girdle.

The two look identical to the eye; only specialist equipment can tell them apart. Lab-grown costs much less, which lets buyers choose a larger stone or higher grades for the same budget. Natural diamonds are rarer and some people value their geological origin. Neither choice is the wrong one; it depends on what matters to you.

Whichever you choose, read the report itself: the report number, measurements, proportions diagram, clarity plot (a map of the inclusions) and the comments line, where details such as clouds not shown or additional clarity characteristics appear.

How to use diamond education to choose a stone: step by step

1. Set your budget and shape. Decide on round or a fancy shape first, because it changes which grades matter.
2. Put cut first. For rounds, choose Excellent or a strong Very Good; for fancy shapes, check ratio, depth and bow-tie on video.
3. Choose colour by metal. G–H usually looks white in platinum or white gold; I–J often looks just as white in yellow or rose gold.
4. Aim for eye-clean, not flawless. VS2 or a carefully chosen SI1 is eye-clean in most brilliant cuts; step cuts such as emerald need VS1 or higher more often.
5. Shop just below magic sizes. Compare a 0.90–0.99 ct with a 1.00 ct and look at the millimetre difference.
6. Check fluorescence and the comments line. Faint or Medium is rarely a concern; Very Strong deserves a daylight video.
7. Verify the report. Match the report number to the girdle inscription and look up the report on the lab's website. Unfamiliar terms are defined in our jewellery glossary.

Diamond education does not need to end with a perfect score on every grade. The aim is to spend where your eye can see the difference and save where it cannot.