Buying Diamonds

Advice section hero Buying Diamonds

Whenever you buy a diamond or a piece of diamond jewellery, ensuring that you get the best possible value for money is a prime concern. There are many factors to be taken into account and we offer some useful tips and information to help.

Diamonds are immensely old and were formed long before dinosaurs roamed the earth. The youngest natural diamond is 900 million years old and the oldest is 3.2 billion years old. Because they are ancient, natural objects, each and every diamond is unique with its own tiny flaws and imperfections. These are frequently invisible to the naked eye and can only be spotted by diamond experts using an eyepiece or microscope. Understanding, however, the global criteria on which diamonds are assessed is a useful starting point in your quest.


What do I call a Diamond?


Diamonds, synthetic diamonds and diamond simulants are different products catering to different markets with different value propositions.

A synthetic diamond is an artificial (man-made) product that has essentially the same chemical composition, crystal structure and physical (including optical) properties as a diamond.

A diamond simulant is a product (natural or artificial) that imitates the appearance of a diamond without having its chemical composition, physical properties or structure. Examples are cubic zirconia, moissanite, white sapphire and yttrium aluminium garnet.

Diamond simulants may also include items made from other products or gemstones that have then been coated in synthetic diamond.

The National Association of Jewellers (NAJ) together with eight of the leading diamond industry organisations (AWDC, CIBJO, GJEPC, IDI, IDMA, NDC, WDC and WFDB) endorses the present guideline to encourage full, fair and effective use of a clear and accessible terminology for diamonds, synthetics diamonds and imitations of diamonds by all sector bodies, organisations and traders.

This Diamond Terminology Guideline serves as a reference document for the diamond and jewellery trade when referring to diamonds and synthetic diamonds. It is built on two internationally accepted standards: the ISO 18323 Standard (“Jewellery – Consumer confidence in the diamond industry”) and the CIBJO Diamond Blue Book.


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Natural Diamonds

A diamond is a mineral consisting essentially of carbon crystallised in the isometric cubic crystal system, with a hardness on the Mohs scale of 10, a specific gravity of approximately 3.52 and a refractive index of approximately 2.42, created by nature. A diamond always means a natural diamond.


Synthetic Diamonds

Synthetic diamonds also commonly referred to as laboratory grown diamonds are artificial (man-made) products that have essentially the same chemical composition, crystal structure and physical (including optical) properties as diamonds.


Stones that might be confused with diamonds

There are a number of synthetic stones on the market that could be confused with diamonds. These are as follows:

  • Cubic zirconia (or CZ)
  • Zirconium oxide (ZrO2) is a mineral that is extremely rare in nature but is widely synthesized for use as a diamond simulant. This inexpensive, synthesized material is hard, optically flawless and usually colourless although it is also made in a wide variety of different colours.
  • Moissanite, which takes its name from the French scientist Dr Henri Moissan who discovered natural moissanite in Arizona in the 1890s, is also known by its chemical name, silicon carbide(SiC). The rarity of natural moissanite crystals large enough for jewellery prohibits their use. For years, scientists tried to re-create this extraordinarily brilliant material. Only recently, through the power of advanced technology has the US company Charles & Colvard, developed a way to produce large gem-quality crystals which can be faceted into near-colourless jewels with real fire and brilliance.
  • Diamonique® This is the brand name of a CZ diamond simulant, sold through the internet and television shopping channel QVC.



How good is your diamond?

A diamond’s value depends on four sets of characteristics – the famous 4Cs which are CLARITY, COLOUR, CUT and CARAT. The first two can be assessed by a skilled person using a universally acknowledged grading system.


CLARITY – refers to the number of visible imperfections or ‘inclusions’ in a diamond. These can be tiny fractures or minerals trapped within the stone. When viewed through a ‘loupe’ – the 10x magnifying tool jewellers use to look at diamonds – they may appear like minute clouds, crystals or feathers. The size and position of such inclusions in a diamond is important in terms of its value. If they are at the side they may be hidden by the mount and may have little effect on the stone’s beauty or brilliance. If they are at the top or in the middle of the diamond however they may impact upon the light dispersion and make the diamond less brilliant and less desirable. Clarity is graded on a scale from Flawless (FL) to Included (I). The grading is as follows:

  • FL Flawless - no inclusions or surface blemishes under 10x magnification
  • IF Internally Flawless – no inclusions and only insignificant surface blemishes under 10x magnification
  • VVSI – VVS2 Very, very, small inclusions – extremely difficult to see
  • SI1 – SI 2 Slightly included
  • I 1 - I 13 Included - inclusions visible to the naked eye (sometimes referred to as P1 – P3 or piqued.)

COLOUR – refers to how ‘colourless’ a diamond is. The scale used ranges from the most-coveted, icy white perfection of D (colourless) – to Z which describes the more brown/yellow diamonds. Colour differences are extremely subtle and to ensure like-to-like comparisons laboratories use a master set of stones and controlled lighting conditions to avoid ultraviolet light. The master stones mark the boundaries of the colour scale, so assisting the diamond grader to decide which colour grade to apply. Once you know what you are looking for, you will be able to see the subtle shifts in tone and what you choose is a matter of personal taste and affordability. Not all diamonds are white. Rare ‘fancy’ diamonds come in glorious canary yellow, soft blue, green, orange, pink, and red which is the rarest of them all. Black and browny/beige or ‘champagne’ diamonds as they a known, are currently particularly fashionable.


CUT – refers to the angles and proportions of a diamond and the way in which the diamond cutter has faceted the stone from the original ‘rough’ diamond to release its fire and sparkle. Diamond cutting is an art based on scientific formulas which seek to reflect the maximum amount of light from one ‘facet’ of the diamond to another. Diamonds that are cut too deeply or too shallowly ‘leak’ light from the sides and bottom rather directing it to the top of the stone and are thus less brilliant. Cut is often considered to be the most important element of the 4Cs but grading the quality with which a diamond has been cut is less well developed than grading clarity and colour. New software and techniques have been developed to introduce new standards for this but are not yet widely available. Cut also refers to the shape of the diamond. The most common is the round diamond which is also referred to as a brilliant cut because its shape reflects the optimum amount of light. Other shapes include square, pear, marquis, princess, trillion and heart and your jeweller will be able to explain the criteria for a good cut in each alternative.


Round Brilliant Diamonds

This shape has set the standard for all other diamond shapes and accounts for more than 75% of diamonds sold today. Its 58-facet cut, divided among its crown (top), girdle (widest part) and pavilion (base), is calibrated through a precise formula to achieve the maximum in fire and brilliance.

Oval Diamonds

An even, perfectly symmetrical design popular among women with small hands or short fingers. Its elongated shape gives a flattering illusion of length to the hand.

Marquise Diamonds

An elongated shape with pointed ends inspired by the fetching smile of the Marquise de Pompadour and commissioned by the Sun King, France's Louis XIV, who wanted a diamond to match it. It is gorgeous when used as a solitaire or when enhanced by smaller diamonds.

Pear Shaped Diamonds

A hybrid cut, combining the best of the oval and the marquise, it is shaped most like a sparkling teardrop. It also belongs to that category of diamond whose design most complements a hand with small or average-length fingers. It is particularly beautiful for pendants or earrings.

Heart Shaped Diamonds

This ultimate symbol of romance is essentially a pear-shaped diamond with a cleft at the top. The skill of the cutter determines the beauty of the cut. Look for a stone with an even shape and a well-defined outline.

Emerald Cut Diamond

This is a rectangular shape with cut corners. It is known as a step cut because its concentric broad, flat planes resemble stair steps. Since inclusions and inferior colour are more pronounced in this particular cut, take pains to select a stone of superior clarity and colour.

Princess Cut Diamond

This is a square or rectangular cut with numerous sparkling facets. It is a relatively new cut and often finds its way into solitaire engagement rings. Flattering to a hand with long fingers, it is often embellished with triangular stones at its sides. Because of its design, this cut requires more weight to be directed toward the diamond's depth in order to maximize brilliance. Depth percentages of 70% to 78% are not uncommon.

Trilliant Diamonds

This is a spectacular wedge of brittle fire. First developed in Amsterdam, the exact design can vary depending on a particular diamond's natural characteristics and the cutter's personal preferences. It may be a traditional triangular shape with pointed corners or a more rounded triangular shape with 25 facets on the crown, 19 facets on the pavilion, and a polished girdle. It is definitely for the adventurous.

Radiant Cut Diamonds

This square or rectangular cut combines the elegance of the emerald shape diamond with the brilliance of the round, and its 70 facets maximize the effect of its colour refraction. Because of its design, this cut requires more weight to be directed toward the diamond's depth in order to maximize brilliance. Depth percentages of 70% to 78% are not uncommon.

Cushion Cut Diamond

An antique style of cut that looks like a cross between an Old Mine Cut (a deep cut with large facets that was common in the late 19th and the early 20th centuries) and a modern oval cut.


CARAT – refers to the weight of the diamond, not as is frequently assumed, its size. One carat weighs 200 milligrams or a fifth of a gram. A Carat can be divided into 100 ‘points’ – which means that a diamond weighing ¾ of a carat can also be termed as having 75 points, a 75 pointer or being 0.75 ct. Given equivalent gradings for clarity, colour and cut, the factor which determines the scarcity of a diamond is its weight. Good quality large diamonds are scarce and hence highly prized.

Ask for a “Certificate”

Reputable retailers automatically supply customers buying larger diamonds with a certificate, more accurately described as a ‘diamond grading report’. This is your diamond’s own personal passport and is a report of its characteristics and authenticity, but not its monetary value. The report will usually contain information about the clarity and colour grades, plus the shape, weight and measurements of the diamond and a brief assessment of the quality of cut and finish. They will also plot any inclusions and imperfections in your diamond onto a diagram. Any identifying laser inscriptions on the girdle of the diamond may also be described.

What to look for?

There are many people who have been trained to grade diamonds – this is an essential skill for people who make a living from buying and selling diamonds but their grading may not be as reliable as that carried out by a specialist diamond grader working in one of the many independent, certified laboratories around the world offering diamond grading facilities. These bodies will have quality control procedures and grades will be cross-checked by more than one grader who will confirm where your diamond stands in relation to the 4Cs. A reputable diamond retailer will be able to ‘read’ such a report and will be able to explain to you exactly what it means.

Sometimes a jeweller or a customer will ask for a diamond to be graded when it is in its setting in a piece of jewellery – this is clearly less reliable than setting an unset diamond as it is more difficult to view accurately and it cannot be measured or weighed accurately. Look for signs of this in a reduced or shortened report. Some diamond jewellery brands offer their own ‘certificates’ or diamond ‘guarantees’, but if you are spending a large sum of money, you may prefer to ask for an independent assessment of the diamond before you commit to buying it. In some cases, this will require that the stone is removed from its setting. Some of the main bodies offering globally-recognised diamond grading services are:

  • The Gemological Institute of America (GIA) -
  • The Gem Testing Laboratory of Great Britain (Gem-A) –
  • HRD Antwerp NV –
  • Anchor-Cert ® Independent Diamond Certification –

Buy from a reputable source

It pays to go to a reputable and established retailer when buying diamonds. We recommend someone who has real knowledge of diamonds and is a member of a recognised trade association such as the National Association of Jewellers.

Buying diamonds can be complex - remember that when diamonds appear to be offered very cheaply, there are many factors which need to be considered. For a significant purchase, compare the stone with others in a well-lit environment. The fire and sparkle we expect to see from a good quality well proportioned and professionally cut diamond can outshine a larger diamond of poorer quality so decide what is important – a big stone or better quality. Your budget and your own eyes will help you to make the decision.

If you want to buy online and an advertisement refers to clarity, colour and weight, it is reasonable to ask about the cut quality. Check also whether the grading has been carried out by a reputable laboratory and do not be afraid to use your right to return under the distance selling regulations, remembering that you must send the item back within seven working days of receiving it.

Above all – do your homework, trust your eyes and be happy with your diamond!


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