Diamonds are not the only stone for an engagement ring. They are not even a ‘traditional’ stone for the ring, but if you’ve done any research at all online, you’ll have found that there’s an awful lot written about them. Much of what is written is intended to ‘romance the ‘stone’ – create a story around the subject, getting you to buy into the ‘subtle complexity’ of the diamond and pay more for the privilege.

If you are still keen to have a diamond in your engagement ring, the following chapter covers pretty much all you will need to know. Applying that information to any individual diamond might require a bit more expertise.

Read on - or Download Chapter 8 as a pdf to read at your leisure.



• Diamond grading is an art, not a science. There is no such thing as an accurate description of a diamond, other than its weight and physical dimensions

• Decide on your own priorities. Key criteria are: size, colour, quality, cost, origin and certification

• Size is measured in carats (weight) as well as mm (dimensions). Sometimes the latter is more useful

• Colour is graded on different scales. For most people there is little visible difference between the top six GIA colour grades

• Fluorescence is irrelevant except in very special circumstances

• Quality includes things like cut and clarity, both of which are subjective assessments.



You may have read a lot about the ‘4Cs’ of diamonds – shorthand for colour, clarity, cut and carat. These are the supposed key criteria for judging a stone, and you might think that all you have to do is get the right certificate with the right letters on it and job done!

The concept of the 4Cs was originally devised by the GIA (Gemmological Institute of America) in part to provide some certainty to consumers and a recognised standard by which diamonds could be assessed. But it quickly became yet another marketing device promoted by the jewellery industry to segment the market and create the illusion that diamonds are somehow different from any other gemstone. As a means of describing a diamond, the 4Cs concept is useful up to a point – for example, to establish some minimum criteria. But given the variability of the standards applied by different laboratories, each description requires so many caveats that it can be more confusing than enlightening. Some diamond merchants even issue disclaimers with all certified stones, GIA or otherwise, to the effect that they do not offer any warranty or guarantee of the accuracy of the description in the certificate.

Diamond grading is an art, not a science. Apart from carat weight, which can be objectively measured, grading the remaining Cs – colour, cut and clarity – depends on the stringency of the criteria of the individual laboratories and certification bodies, and ultimately on the human being doing the grading. Whether any one diamond is a colour F or K, for example, may largely be a matter of opinion, and there is a wide variation in standards.

So be aware that, taken at face value, some of the ‘information’ available to you could be a touch misleading.

The strictly technical data is accurate (i.e. what can be objectively measured), but there is a strong tendency to try to persuade you that only certain colour grades and features are acceptable. Naturally these are the more expensive, and what constitutes the ‘best quality’ is a moveable feast.


The most important thing is for you to decide on your priorities. When you know what you want to get from your purchase, and why, you are less likely to be led into spending more than you need to achieve your goals.

You know what your overall budget is, and if diamond is your main stone, this will probably take up the largest part of that. So you want to aim for the best balance between your priorities within your budget. You may decide that diamond size is the most important element, and you may be prepared to compromise on the colour, clarity or cut, or a combination of all three. You can always find a diamond for your budget or fit your budget to the diamond, it is up to you.

Apart from cost, the key considerations are:

• Size – it usually matters here

• Colour – generally white rather than yellow, unless you are setting directly into yellow or rose gold or want a fancy coloured stone

• Quality – it should sparkle and not have any visible black bits (carbon inclusions)

• Origin and provenance – something you may not yet have considered

• Certification – there are a number of certification bodies to choose from, but not all apply the same standards.

Not as catchy as the 4Cs perhaps, but a more practical way to look at the problem.



The size of a diamond is described by its weight in carats (ct–UK, or kt–USA).

Do not compare the prices of a 1.0ct solitaire to a 1.0ct trilogy ring with three smaller diamonds. A single diamond of 1.0ct costs much more than three stones whose weights add up to 1.0tcw. This is because larger diamond crystals are less common than smaller ones so command a higher price per carat.

If a ring has more than one diamond, it will be described using its total carat weight. This should be expressed as ‘tcw’ or ‘ct (tw)’, but is often displayed just as ‘ct’, which can be confusing because it may lead you to believe that the main stone is a higher carat than it is.

For example, some retailers will describe a ring as 1.0ct when it contains a 0.5ct central diamond together with twenty-five diamonds of 0.02ct each in the halo and shank. To avoid confusing the consumer, the correct way to describe such a ring would be 1.0tcw because the total value of the diamonds is much less than a single 1.0ct stone.


An Explanations of ‘Carats’ (cts)

There are about five carats in a gramme, so 1ct = 0.20g

Carats are divided into ‘points’, so 1ct = 100 points

A half-carat diamond can be described as ‘50 points’, and ‘10 points’ is 0.01ct or 0.002g. The weights are tiny (and originally based on the weight of a carob seed, hence the name).

A 1.0ct diamond can cost ten times as much as a 0.33ct (otherwise of the same specification) for just three times the weight. In the example above, the 1.0ct trilogy ring might be half the price of the 1.0ct solitaire.

Assuming the same mount costs and based on prices for GIA certified FSI1 excellent-cut round brilliants at the time of writing.



If size is an issue, and it often is when we are talking diamonds, it may be more useful for your purposes to know the dimensions of a stone. There is a standard for the relationship between the carat weight and dimensions of any shape of diamond. This is based on the ‘ideal cut’ for that shape.

But stones are cut to maximise their value, which, more often than not, means their carat weight. So any reasonable quality of diamond is available in a wide range of dimensions. The quality of the cut is directly related to how much sparkle you will see in a stone. Both a very flat cut and a very deep cut diamond will lose brilliance so the ratio is important, but may be less noticeable than the impact of the size of the stone on the hand. Yet another reason why you do need to establish your priorities and why expert guidance will ensure you get the best value for your purchase.


Comparing sizes

This illustrates a comparison of the relative sizes of two actual GIA certified round brilliant 1.0ct diamonds - see image below.

Comparison of table sizes of two 1.0ct round diamonds

Diameter 1 5.92mm (Depth 1 4.27mm; ratio – 72.1)

Diameter 2 6.59mm (Depth 2 3.87mm; ratio – 58.8)

So, diamond #2 is 0.67mm (11) wider than diamond #1. This may not seem much, but the difference is visible. To put it into perspective: a standard 0.75ct brilliant is about 0.7mm wider than a 0.5ct, and a standard 1.5ct is about 1.0mm wider than a 1.0ct.




After the size of the diamond, the colour is usually the next most important consideration, and this is where opinion starts to come into the equation. When comparing data on graded diamonds, be aware that the opinion of one certification body may differ from that of another for the same stone.

Each diamond certification body sets its own standards, and any qualified diamond grader will use his or her judgement within the acceptable ranges permitted by the certification body. Many ready-made engagement rings do not come with an independent grading certificate, so the opinion on colour (and quality) is that of the seller. There is clearly an even greater potential for variation here.

Diamond colour is graded from D, the whitest of diamonds, down through the letters of the alphabet to fancy yellows and brown diamonds, all the way to black. For most practical purposes, diamonds are still considered ‘white’ in the range D to J. These are most suitable for rings set in platinum or white gold.

If your ring is to be yellow or rose gold, it is worth thinking about a colour K to M as these warmer tints sit well in gold and are much less costly than whiter stones. In fact, a K diamond is often half the price of an otherwise similar G diamond – as long as they have been certified by the same laboratory.

There is a fine distinction between each of the colours. Most people cannot detect differences between one colour and the next, and for a single diamond the distinction is even less obvious. Ice white is not everyone’s cup of tea, and there is a subtle beauty in the very faintly yellow tints. It is all down to personal preference, and unless you can compare two stones directly it is pretty difficult for the lay person to tell whether they are looking at a colour D or G anyway.

Fancy coloured diamonds. Almost all diamonds fall within the standard D to Z colour classification, but there are what are called ‘fancy coloured diamonds’ in blues, pinks, deep yellows and even green. Some coloured diamonds are treated as naturally occurring fancy coloured diamonds are very rare, much prized and a lot more costly. One of the best known mines for fancy pink diamonds is the Argyle Mine in Western Australia.

Colours can range from a subtle tint to strong, deep hues, and the deeper the colour, generally speaking, the more valuable the stone, if natural. In these stones, brilliance and fire are less of a consideration.

As with all diamonds, very small fancy stones are unlikely to come with their own grading certificate, but it is important to have a certificate for any coloured diamond over 0.25ct so that you can be sure of its provenance.


A Note on Fluorescence

The apparent colour of a white diamond can be influenced by ‘fluorescence’. This is natural in about 25 of diamonds seen under ultra-violet light, including daylight. It is the same effect as seen in white clothes or teeth when you stand under a blue or ultraviolet light (which anyone who has ever been to a nightclub will recognise).

In diamonds, fluorescence is the result of ultra-violet radiation causing electrons to move within the diamond’s crystal structure. So much for the science. There is no need to worry about fluorescence – in most cases there is no practical effect, and because the most common type is blue it will make yellowish diamonds look whiter, so improving their appearance.

If you are matching diamonds in a ring or pair of earrings and fluorescence is present, it is as well to make sure that the stones are broadly similar, otherwise they won’t match under UV light.

If that is not an isssue, the good news is that fluorescence can reduce the price of a diamond, as well as making a stone look a better colour than its grading might suggest. Win-win, I think.



Clarity. Clarity refers to the number, type and visibility of inclusions (bits of material and crystalline faults) in the stone. It determines how ‘sparkly’ any cut of diamond can be, as the higher the level of clarity, the fewer inclusions there are to get in the way of light passing through the stone.

As with all things diamond-related, it all depends what sort of inclusion, how big it is, whether it is faint and white or a black speck of carbon, and where it appears on the stone. Does the way the stone is cut help to reduce the appearance of the inclusion? For example, the inclusions in a 1.0ct emerald cut diamond are more apparent than the same inclusions in a round brilliant because the latter has more facets and throws light around in more directions, so obscuring minor inclusions.


How Clarity is described (GIA)

Clarity is graded by the GIA as follows:

• IF – Internally Flawless, which speaks for itself

• VVS 1 & 2 – Very, very slightly included. Inclusions can’t be seen with the naked eye and are very difficult to see even under 10x magnification

• VS1 & 2 – Very slightly included. Again, inclusions are not visible to the naked eye, but may be visible under 10x magnification

• SI1 & 2 – Slightly included. Inclusions are visible under 10x magnification and, rarely, to the unaided eye

• I1 & 2 – Included. You can see these inclusions with the naked eye. Sometimes this requires close inspection, and the smaller the diamond or the more facets it has, the less important that might be.


Cut. There are two aspects to cut – quality and type. The quality element of cut is highly complex, subjective and the most difficult for a non-specialist to assess.

The quality of cut is generally graded from excellent, through good to poor. The cut may also be described as ideal, shallow or deep. These describe the ratio of surface to depth.

A shallow cut will give you more surface area (i.e. the stone appears bigger) for a given carat weight, and a deep cut the reverse. As you can see from the image, the depth of the cut will also affect the apparent brilliance of the stone as light is reflected at a different angle. A ‘poor’ cut can spoil a stone, and an ‘excellent’ one can elevate it.

Most diamonds are cut to maximise carat weight and brilliance, so there is always a compromise between these elements, and the diamond will be priced accordingly.

How light is deflected in ideal, shallow and deep cut brilliants

The type of cut does make a difference to the sparkle factor as it determines the number of facets you can expect in a stone. Modern cuts, like the ‘brilliant’ cut, are designed to create the maximum sparkle for the stone. All other things being equal, the more facets you have, the more sparkly a diamond will be. New designs for cuts do come to the market from time to time, and these are usually trademarked.

Older pieces of jewellery sometimes have diamonds with antique styles of cut, like the ‘rose’ cut. These are more subtle and don’t have the brilliance of modern stones, so if you are using inherited stones and need to find a match to add to the design, this will require some care.



Diamond certification is often referred to as the ‘fifth C’. So what is it? And why is it important?

A diamond certificate is intended to provide third party information about the characteristics of a diamond, including grading its colour, clarity, cut and the carat weight. It is supposed to help you understand what you are buying and will tell you if a diamond has been treated to enhance it in any way, as this would affect its market value and price. There are also specific certificates for laboratory created diamonds.

I want to correct one common misunderstanding about diamond certificates and it is this: a diamond certificate is not a guarantee that a diamond has been mined in an ethical or ecologically sustainable manner. Certification is only about the physical characteristics of the stone, not its sourcing or the supply chain.

The GIA was the first to introduce what has become the best known and most trusted system of diamond grading and certification. The importance of a certificate for a diamond lies in the extent to which it offers you assurance that you are getting what you pay for. The danger in buying an uncertified diamond, or one which has been certified by the seller, is simply that without a certificate the seller can represent the diamond as being whatever he wishes it to be, and will charge accordingly.

You also have to ask yourself (and the retailer) why a diamond is not certified. Certified diamonds carry more value in the market than uncertified diamonds, so there would have to be a very good reason why a retailer had not had the diamond certified. Do not be put off by the claims that ‘it takes too long’ or ‘it’s too expensive to get a certificate’. The extra cost of certification is outweighed by the additional value having it confers.

You will also find that diamonds certified by different bodies have different prices. This is because the market discounts up to a point the differences in grading standards in the price which a stone can command. But if you don’t know which laboratories are the most lax, or can’t evaluate the diamond yourself, you could pay more than you should.

Do be aware that round diamonds smaller than 0.3ct are rarely certified because they are too small to warrant the cost of certification. For other shapes, such as oval and square, the minimum weight for certification can be higher, and very small diamonds, known as ‘mêlée’, are never certified.

For anything else, get one with a certificate.



A couple came to me for wedding rings by recommendation from one of their friends. At the same time they asked for my opinion on the engagement ring which they had bought only six months before in a shop in London’s jewellery quarter, Hatton Garden.

Not knowing where best to start when buying their ring, like many people they thought this would be the place to find it. They found a design they liked and were sold the ring as a 0.7ct DVS1 diamond at a price they thought was a very good deal. But there was no independent certificate to verify the grading of the diamond.

Even by eye it was clear to me that the diamond they thought was a colour D was actually nearer H or I. That is four or five grades of colour lower than they believed they had purchased! But because there was no independent certificate (and colour grading is then a matter of personal opinion), there was little they could do to remedy the situation.

While the price they paid would have been a good deal if the diamond were a GIA certified D colour, they had paid more than they should have done for a stone whose correct grade was H or I. Given the gross overstatement of the colour, it was not surprising to discover that the retailer had also graded clarity with equal laxity. So they lost out on both counts.


This story just underlines the need to be absolutely sure about the reliability of anyone from whom you buy an uncertified diamond. Why would a 0.7ct DVS1 diamond not be certified? If you are not sure, specify that the purchase is subject to testing and arrange for the stone to be independently certified by a reputable laboratory of your choice. If you can do this before you buy, even better. It will be worth the relatively small investment in the laboratory fees.


There is an argument that retailers, especially online, concentrate too much on the certificate and not enough on the diamond itself. This reflects the fact that, although certificates are intended to provide some certainty to the buyer, because diamond grading is so subjective, they are only a guide. Even with GIA certificates, you could line up four diamonds with the same certificated colour grading and they would be four different colours.

Recently, there has been a lot of concern within the industry about deliberate over-grading on diamond certificates. Grading largely determines price, so in some cases this practice is fraud and there have been arrests by US authorities. This fraud can be perpetrated precisely because so much reliance and confidence is placed in the certificate, particularly when diamonds are sold online.



There are a number of organisations which certify diamonds, the most well-known being the GIA (Gemmological Institute of America). The GIA is also the leading independent grading laboratory with offices around the world. It offers educational services and is the longest established of the grading organisations. Over time it has pretty much set the standards for diamond grading and established the concept of the 4Cs.

In the USA, the AGSL (American Gemmological Society Laboratories) is especially known for its in-depth scientific analysis of the technicalities of cut which are so important to diamond brilliance. AGSL uses a different scale to describe diamonds, but this can be compared directly with the more well-known GIA scale. Its standards on colour and clarity are directly comparable to GIA (AGSL uses a GIA graded master set of diamonds for colour grading), and its analysis of cut and light performance is better.

You will also come across IGI, HRD, and EGL, although there are others (see glossary for the full titles of these organisations). There is some dispute about the relative laxity of grading of the different laboratories, although GIA and AGSL are generally considered the strictest. As discussed earlier, there is always room for human opinion in the colour and clarity grading of diamonds. And there are so many potential variables it is difficult to conduct a definitive ‘test’ to identify which laboratories are stricter than others in all cases. Even within the same laboratory it is accepted that the same stone may be graded up or down by one grade of colour or clarity, depending on when or by whom it is graded, and this includes GIA and AGSL. Nevertheless, some jewellers will avoid certain of the grading laboratories.



Diamonds are a subject to which too much attention is paid and about which too much is written. My apologies for adding to that mountain of text.

Most of what is written is designed to make you believe that diamonds are special and create mystique around them.

There is no such thing as an accurate description of a diamond, other than its weight and physical dimensions. The truth is that unless you are trained or experienced in the subject of diamonds, you cannot know how accurate the description is on the certificate. That being said, you should ask why a diamond does not have a certificate as the fact of having one adds more to the price than the cost of obtaining one.

My only advice when it comes to buying diamonds, or any other gemstone, is treat online sellers with caution. If you want to be sure you are getting what you need and what you are paying for, consult a jeweller you know you can trust, and one you can look in the eye!

Read On – Chapter 9 looks at alternatives to diamonds for your engagement ring. We examine the pros and cons of the rare and beautiful coloured gemstones which have always traditionally been valued and used in betrothal rings.

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