You are here:

Buying Diamonds & Gemstones

Many people buy diamond jewellery just a few times in their lives, sometimes to mark a significant event - an engagement, a wedding, the birth of a child or an important anniversary - although more are now indulging in these fascinating stones simply because they love to wear them.   Whatever your motive for buying 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 inform your choice.

All 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.

How good is your diamond?
A diamond’s value depends on four sets of characteristics – the famous 4Cs,  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 in 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 they 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 two 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 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.

Some popular diamond cuts are as follows:

RoundRound 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.

OvalOval 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.

MarquiseMarquise 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.

PearPear 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 DiamondHeart 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.

EmeraldEmerald 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 color are more pronounced in this particular cut, take pains to select a stone of superior clarity and color.

PrincessPrincess 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.

TrilliantTrilliant 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.

RadiantRadiant 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 color 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.

CushionCushion 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?
In the diamond and jewellery industry 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 particular 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:

Buy from a reputable source
Because there are so many elements to consider, it pays to go to a reputable and established retailer when buying diamonds  - 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. Generally speaking, for a significant purchase, it is a good idea to see the stone and to compare it 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!

Synthetic  Diamonds
In recent decades we have developed the technology to create synthetic diamonds by replicating the high temperature/high pressure conditions under which natural diamonds were formed in the earth’s crust millions of years ago.  Until recently these have been solely for industrial drilling, cutting and polishing but now gem quality synthetic diamonds are being produced in the USA and Russia.  They exist generally in smaller sizes and not yet in the whiter colour grades but are chemically indistinguishable from natural diamonds.  However, under a microscope synthetic diamonds exhibit growth patterns and light distribution which can be distinguished from the real thing.

Stones that might be confused with diamonds

There are a number of made-made 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. 


Buying Coloured Gemstones
Until relatively recently coloured gemstones were divided into two categories – precious and semi-precious – but as some ‘semi-precious’ stones are extremely rare and expensive this distinction has been abandoned in favour of simply ‘gemstones’. This said, some gemstones do command much higher prices than others and if you are buying significant emeralds, rubies or sapphires it is sensible to get a gemstone identification report from a gemmological laboratory to identify any fake stones and to determine the quality of the stone you are buying in terms of its colour, cut and clarity. The report will also identify any treatments which may have been applied to the gemstone.

Gemstone treatments
In their cutting and polishing, coloured gemstones are subjected to a growing range of treatments designed to enhance their value.  Heat treatment is routinely used to develop more intense colours in rubies and sapphires and is often combined with diffusion treatments designed to actually fuse colour into the surface of the gemstone.  Irradiation is sometimes used to enhance the colour of gemstones such as topaz, tourmaline and fancy diamonds. Generally these treatments are permanent.

Surface cavities which would otherwise reduce the value of a gemstone can be filled with glass like substances, and surface reaching fractures, fissures and laser drill holes can be repaired with glass and plastic resins. Emeralds are routinely referred to as “oiled,” as coloured coatings are applied to enhance the intensity of the natural colour.  If a gemstone has been identified as having been treated in this way then care must be taken in the wearing and cleaning of the jewellery which contains them.  Extremes of heat and ultrasonic cleaning are not recommended and detergents may affect coatings.

A good gemstone laboratory will look for the signs of these treatments and include the information on the gemstone report.  Some of these treatments can be controversial – they enhance the beauty of gemstones which otherwise might not be suitable for jewellery and bring them within the reach of consumers who otherwise might not be able to afford them.  In some categories it is difficult to find natural untreated gemstones, which can attract a significant premium.

Tanzanite, a variety of zoisite, is a relatively new and expensive gemstone, having been discovered in 1967  in a remote corner of Tanzania.  The only known source is a 6km strip of land at the foot of Mount Kilimanjaro.   This blue-violet gemstone varies in colour and intensity and recently a colour grading system was introduced to help.  It has its own 4C’s grading system with the deeper coloured stones being the most prized. For further information visit or

For more detailed information about individual gemstones, visit the International Colored Gemstone Association at

The choice of pearl jewellery, both in terms of design and in relation to the type, size and colour of pearls employed has never been greater.

Stone Guides:

  Guide to Rubies
  Guide to Sapphires
  Guide to Emeralds

Buying Pearls

There are basically three main types of pearl:

Natural Pearls – these are pearls that grow naturally, at random, inside either oysters or mussels. In the old days all pearls were ‘natural’ but today such pearls are extremely rare and expensive and are not generally available.

Cutured Pearls– cultured pearls are produced in oysters or mussels but with the intervention of  man who introduces a foreign body or ‘nucleus’ into the creature which it then covers in ‘nacre’ or mother of pearl.  Cultured pearls can be grown in sea or freshwater and as the  table below demonstrates there are many different types.

Synthetic Pearls – these are simply ‘pearly’ beads which are entirely man-made and are not really ‘pearls’ at all.

Akoya  - The original cultured pearl from Japan.  Sizes are relatively small, 2-10 mm and colours tend to be pale – cream, white/pink and silver.

South Sea - These valuable pearls from Australia, Indonesia and the Philippines are larger 10-22mm and range in colour from silvery white and cream to champagne and gold.

Tahitian - Tahitian pearls from French Polynesia and the Cook Islands are naturally dark, colours include black/green, aubergines and violet as well as browns and gold Sizes are 8 – 18mm

Freshwater  - These generally nucleus free cultured pearls are mainly from China. They come in many different shapes and sizes and in colours from white, peaches, pinks and lavender. Sizes 2 -16mm or larger depending on the variety.

Keshi - Irregularly shaped ‘blobs’ of pearl that resemble hot metal dropped into water – Keshi can measure up to 20 mm across

PEARL QUALITY - the quality of a pearl depends on five criteria:

Lustre - This refers to the sheen of pearls. A good pearl should be deeply lustrous – the deeper the coating of nacre the better the lustre will be.

Texture - Good pearls should ideally be flawless without any blemishes or hollows                            

Shapes - Pearls can be many different shapes but the most common are button, drop, round, oval and baroque (or irregular). Shape does not influence quality but perfect examples of each shape are more highly prized but this is a matter of taste.

Size - The size of a pearl is measured in millimetres and tends to depend upon the size of the original nucleus and the time the pearl has had to develop.

Colour - Colour is a matter of fashion and personal choice. Deeper colours especially browns and greens are currently popular.


© 2017
The National Association of Jewellers
Head Office: Federation House
10 Vyse Street
Birmingham, B18 6LT, UK

London Office: 45 Britton Street, London EC1M 5NA

Birmingham Office: 0121 237 1110
London Office: 020 7613 4445
General enquries:
Education queries: