A Diamond Held in Tweezers

The need to know guide on Diamonds!

This guide is designed to help guide you through the process behind the classification and relative values of diamonds. A once closely guarded secret technique by experts but we’ll tell you the secrets and tips behind diamond grading, the process known as the 'Four-C's'.

Each step within the Four-C's calculation will tally up to the final value of a diamond, biggest is not always best in the world of diamonds. Qualities of Cut, Colour, Clarity and Carat all are factors in the formation of the perfect diamond.

C1. Cut

Transforming rough diamonds into bright, sparkling gems with which we are so familiar did not begin until the fifteenth century and is nothing more than an art form. Even though modern technology has helped in the transformation of diamonds it is still very much a skill that takes years of training to truly master.

Rough diamonds are sorted into over 5000 different categories of shape, colour and clarity and in many cases more than one polished gem will be cut from a single piece of rough. There are six basic shapes of rough diamond. These are called: Stone, Shape, Macle, Cube, Flat, and Cleavage.

The prime object of the cutter is always to achieve the best sparkle or brilliance and the maximum size diamond or yield from the rough. The sparkle we all come to resemble with a diamond is called ‘refraction’ which produces the brilliant flashes we call the fire of a diamond.

Refraction is the reflection of light. White light will penetrate a diamond and bounce off the angles within, before the light passes back out and hits your eye, making the flashes of colour known as “Fire of a Diamond”.

Just like a piece of wood, diamonds have grains. An expert cutter must take great care when cutting a diamond to work with the grains to avoid shattering or splitting. The factors a cutter will also consider are the positions of any imperfections within the diamond and internal features. We will also consider the proportions to achieve maximum yield.

On average only 35% to 43% of a rough diamond will be used to create the finished cut and polished stone. Every piece of the rough diamond shall be used in some form however, nothing is wasted!

Today there are many different cuts or shapes of diamond but the most common are: Brilliant, Baguette, Oval, Marquise, Princess, Pear, Emerald, and Heart. You will often find these styles of diamonds in most stores you visit including our own.

Ideal Diamond Cut Diagram

C2. Clarity

Clarity is the second of the diamond characteristics and probably the most difficult to agree upon, when it comes to assessing the value of a diamond. This is because the clarity of a diamond is based on the subjective judgement made by an experienced grader against the industry standard.

Clarity is entirely down to nature and the formation of a crystal over thousands of years. The vast majority of diamonds have internal characteristics that indicate their growth. These inclusions may be small particles of other minerals trapped within the diamond or irregularities in the diamond structure itself, the hallmarks of nature.

There are two main international standards for judging clarity. The European standard: CIBJO and more universal scale set by GIA (Gemmological Institute of America). Both are very similar in classification.

The scale of clarity ranges from ‘Flawless’ at the very top of the scale down to ‘I3’. Flawless is observation under 10 x magnifications whilst I3 are internal marks that can be seen by the naked eye.

The standard tool used to look at the internal characteristics of diamonds is the chromatic loupe or glass with a 10x magnification.

You may come across times where two experts have given different grading to a diamond; this is down to the difficulty of assessing a diamond as no two are the same. The median standard of diamonds in the UK is ‘small inclusions’ – SI clarity.

It is also very hard to photograph diamonds in a way that show inclusions because of the way a diamond handles the light. Even under extreme magnification it can be difficult to pinpoint marks, which is why clarity can often vary between experts!

Inclusions should not be seen as faults, they are the result of nature. Though with all things the closer to perfection you get the more valuable an item becomes, which is why flawless diamonds command high prices!

Clarity Grade Number and size of inclusions Discernible with a loupe Discernible with the naked eye Influence on brilliance
FL – IF No inclusions Nothing to be seen Loupe clean
VVS (VVS 1 + 2) Very very small inclusions Very difficult to see Eye clean
VS (VS 1 + 2) Very small inclusions Difficult to see
SI Small inclusions Easily to see
I1 Inclusions Recognisable at once Difficult to recognise Not influenced
I2 Larger and/or numerous inclusions Recognisable Somewhere influenced
I3 Very easily recognised Definitely influenced

C3. Colour

The next C is colour, which together with quality of cut and clarity determines the value of a diamond. To the untrained eye most diamonds look colourless however this is not the case, with the best diamonds being completely colourless.

As with clarity there are two standards of classification for colours, the more accepted standard is GIA. At the top of this standard is D which is an exceptional white plus crystal within the CIBJO scale. From D the grading descends down the alphabet all the way to the lowest grade Z with is tinted with colour.

The judgement of a colour is also subjective and down to the individual experts who are grading the diamond although the grade will be compared with a ‘Master Set’ of stones which is matched to one of the international agreed standards.

Once a diamond reaches the grading of H it will only be then that trained experts will have the expertise to say where a diamond will sit in scale between D and H. Once more experts can sometimes come up with different grading for a diamond based on their own subjective judgement.

Whilst the majority of diamonds are colourless natural diamonds can be found in almost any colour. Pinks, yellows and black are the most widely used in jewellery making, some colours such as natural deep red are very rare and as of such command high prices.

There are many different colours of diamonds that can be found, some commanding higher prices than others due to the rarity and clarity of the diamond.

Exceptional White Plus D
Exceptional White E
Rare White Plus F
Rare White G
White H
Slightly Tinted White I
Tinted White K
Tinted Colour M
S – Z
Fancy Colours

C4. Carat Weight

The final C is carat weight. The carat is the unit of weight for the diamond. The term carat is derived from the seeds of carob bean, which are a uniform of weight that was adopted by early traders as a universal measure. In the 20th century carat become standardised to the metric weight of .20grams.

Most diamonds are considerably smaller than a carat so the measurement is divided into 100 points. One carat is equal to 100 points, half a carat is 50 points; a quarter of a carat is 25 points and so on in the same fashion.

The measurements from this are written in as follows: 1ct, 0.50ct, 0.25ct and so on…

A single diamond on its own is easy to gather the weight of, but a diamond that is set within a piece of jewellery requires specialist gauges that will give an accurate representation of the weight. These gauges measure the diameter squared x the depth x 0.0061 and finally an adjustment then has to be estimated based on how close the gem is to ideal proportions something only a real expert can do.

The visual size of a diamond represents has a link to the weight of the crystal however the correlation only applies to diamonds that ideal proportions when first cut!