Every diamond you will ever look at is pure carbon, arranged under enormous heat and pressure into the hardest natural material on earth. That hardness is why a diamond takes a lifetime of daily wear and keeps its brightness. This guide explains how to judge a diamond and how to choose one: the 4Cs, how natural and lab grown diamonds differ, the shapes a diamond comes in, how diamonds are certified, and how to choose and care for one. Each section gives you the short answer first, then links to a fuller article if you want to go deeper.
A diamond's quality comes down to the 4Cs: cut, colour, clarity and carat. Cut has the greatest effect on how a diamond looks. Natural and lab grown diamonds are both real diamonds, graded the same way, and differ mainly in origin and price.
What is a diamond?
A diamond is a single crystal of pure carbon, and the hardest natural material there is. On the Mohs scale, which jewellers use to rank how hard a stone is from talc at 1 up to diamond at 10, a diamond sits right at the top. That is what lets it resist scratching and hold its polish through years of wear, and it is the main reason diamonds are set in pieces meant to be worn every day rather than saved for occasions.
Most diamonds run from colourless through to a faint yellow or brown, and the rarest are completely colourless. Diamonds also occur in vivid natural colours such as blue, pink and yellow, which are known as fancy colours and graded on a different scale, but the great majority of diamonds in jewellery sit in the colourless to near-colourless range.
What are the 4Cs of a diamond?
The 4Cs are cut, colour, clarity and carat, the four qualities used to grade every diamond, whether natural or lab grown. They were set out by the Gemological Institute of America, usually shortened to the GIA, in the 1940s, and are now the standard the whole trade uses worldwide. Read together, they describe both how a diamond looks and how rare it is.
| The C | What it measures |
|---|---|
| Cut | How well the diamond is faceted to return light, which is what creates its brightness and sparkle |
| Colour | How little colour the diamond shows, graded from D (colourless) down to Z (light yellow or brown) |
| Clarity | How few natural marks, called inclusions, the diamond carries inside |
| Carat | The diamond's weight, where one carat equals 0.2 grams |
Of the four, cut has the greatest effect on how a diamond actually looks. A well-cut diamond sends light back to your eye as brightness and fire, while a poorly cut one leaks light and looks flat, even if its colour and clarity grades are high. It is the C most worth understanding, and the one most worth spending on. You can read the 4Cs explained in full, including where each grade stops mattering to the eye.
Carat is the one people most often misread, because it measures weight rather than size. Two diamonds of the same carat weight can look quite different depending on how they are cut and shaped. We cover that, with a size chart, in diamond carat weight and size.
Are lab grown diamonds real diamonds?
Yes. A lab grown diamond is a real diamond, chemically, physically and optically identical to one formed in the earth. The only genuine difference is origin. A lab grown diamond is grown in a laboratory over a matter of weeks, using equipment that recreates the heat and pressure of the earth, while a natural diamond formed deep underground over hundreds of millions of years. Because they are the same material, they are graded by the same laboratories on the same 4Cs, and you cannot tell them apart by eye.
Left to right: a lab-grown CVD rough, a lab-grown HPHT rough, and a natural diamond rough, all shown before cutting and polishing.
Lab grown diamonds are sometimes called cultured diamonds, in the same way cultured pearls are grown with a helping hand rather than left entirely to nature. They should not be confused with diamond simulants such as cubic zirconia or moissanite, which only look similar and are made of entirely different materials.
The practical difference for a buyer is price. A lab grown diamond costs considerably less than a natural diamond of the same size and quality, which means the same budget can buy a larger or higher-grade stone. Neither is the better choice in the abstract, and which suits you comes down to what you value. We weigh it up properly, with New Zealand pricing, in lab grown vs natural diamonds.
What are the different diamond shapes?
Shape is the outline of a diamond seen from above, round, oval, pear, emerald and so on. It is worth separating from cut, which describes how well the diamond is faceted. Two diamonds can share the same shape and still sparkle very differently depending on how well each is cut.
The round brilliant is by far the most popular shape, and the most sparkling, because its facets are worked out to return the most light. Every other shape is known as a fancy shape. Some, like oval, pear and marquise, are elongated, which makes them look a little larger for their weight and lengthens the look of the hand. Others, like the emerald cut, use long straight facets for a calmer, glassier look rather than sparkle. There is no best shape, only the one you are drawn to. We go through each in diamond shapes explained.
How are diamonds certified?
A diamond is certified when an independent laboratory grades it against the 4Cs and issues a report, sometimes called a certificate. That report lets you compare one diamond with another on the same terms, rather than taking a seller's word for it. The two most recognised laboratories are the GIA and the International Gemological Institute, or IGI.
The two grade to slightly different standards. The GIA is generally regarded as the stricter of the two and its reports tend to hold value well, while the IGI grades a little more leniently, costs less, and has become the leading authority for lab grown diamonds. Neither is the wrong choice, but it helps to know which report you are reading. We explain how to read one, and the differences, in GIA and IGI certification explained.
How do you choose a diamond?
Start with cut, because it does the most for how a diamond looks, then balance colour, clarity and carat against your budget. A common and sensible approach is to choose the lowest colour and clarity grades that still look clean and white to your eye, which the trade calls eye-clean and near-colourless, and put the saving into a better cut or a little more size.
Choose cut first. A smaller, well-cut diamond outshines a larger, poorly cut one, so prioritise cut, then balance colour, clarity and carat against your budget.
The setting matters too. Whether a diamond is held in a smooth bezel or fine claws changes how much light reaches it and how protected it is, which is worth thinking about for a piece you will wear every day. For a fuller walkthrough aimed at the diamond pieces you are most likely to buy, see how to choose a diamond.
How do you care for a diamond?
A diamond is hard-wearing, but skin oils, hand cream and everyday grime build up behind the stone and dull its sparkle over time, so it needs an occasional clean. The safe method is simple: soak it for twenty minutes or so in warm water with a drop of mild dish soap, brush gently with a soft toothbrush to reach behind the stone, rinse, and dry with a soft lint-free cloth rather than paper towel, which can scratch. Avoid harsh chemicals and anything with chlorine or bleach, and take a moment to check the setting feels secure while you are there. The full routine is in how to care for diamonds.
Once you know what you are looking at, the rest is personal. If you would like to see diamonds set in pieces made to be worn every day, our diamond stud earrings, diamond tennis bracelets and diamond pendants are all set in solid gold and ethically sourced.
