About

The basics of diamonds are the ’4Cs’ — the four characteristics that are generally used to describe a particular diamond.

Just like people, no two diamonds are exactly the same, so the diamond industry uses some common terms which describe the key characteristics of each and every diamond.

The 4Cs of diamonds are:

Carat       Cut       Colour       Clarity

Taking each of these in turn…

Carat

Carat is the weight of the diamond.  One carat is equal to one fifth of a gram (0.2g) so a five carat diamond actually weighs one gram.  Carat is usually abbreviated to ‘ct’, and 1 carat is divided into 100 ‘points’, so a 0.16ct diamond can also be described as weighing 16 points.

Carat is also the unit of weight used for pearls, but carat is often confused with the word karat, which is a measure of purity used to describe gold (where 24 karat gold is maximum purity, 18 karat gold is 75% purity, 12 karat gold is 50% purity, etc).

We get the word carat from carob - a seed that was used as a reference weight for weighing out small objects of quantities of goods.  Carob seeds were used because of their apparant consistency, therefore leading to more precison in weighing.  Actually it turns out that carob seeds are no more consistent than other seeds, but it might have been easier to select a consistent weight of carob seed than was the case with other seeds.

Anyway, the carat weight of a diamond is almost universally quoted to two decimal places, for example, 0.32 carats or 1.59 carats.  Modern electronic scales weigh to a much more accurate degree than two decimals, with scales in high precision diamond operations (such as certification labs) weighing to 5 decimal places, eg. 0.32123 carats.  That’s a 100,000th of a carat!

Diamonds are priced by weight, and the industry uses some standard ‘size breaks’, so for example a 1.00 carat diamond is normally quite a lot more expensive than a 0.99 carat diamond of the same colour, clarity, and cut.  For this reason, diamond cutters try to get a diamond to be just over the size break rather than just under it, so long as they can maintain cut and clarity, because it gives them a better financial result.

There’s no way that you can tell the difference between 0.99ct and 1.00ct just by looking at a diamond, and once the stone is set into jewellery then it can’t be weighed with any accuracy anyway.  So unless you have your heart set on a diamond that is over half a carat or 1 carat or 2 carats or whatever, then it often makes economic sense to buy a diamond that is just below one of these thresholds, eg 0.95ct.

The range of possible diamond sizes is almost infinite, but in practice cut diamonds don’t come much smaller than about half a point (0.005ct).  The world’s largest faceted diamond is the Golden Jubilee diamond, currently in the Thai Crown Jewels, weighing in at 545.67 carats (just over 100g).

Cut

The cut of a diamond describes the basic shape but also the quality of the proportions, symmetry, alignment, finish etc of the facets.  The vast majority of all cut diamonds are round brilliant.  This is the classic diamond shape, featuring 57 facets: 33 on the top of the stone (including the table facet), and 24 on the bottom.  Sometimes the very tiny point where the bottom facets meet (the ‘culet’) is also considered to be a facet in its own right, in which case the total number of facets is 58.

The number of facets, the arrangement of those facets, and the proportions of the diamond all contribute to how ‘sparkly’ and attractive a diamond appears to be.  There are a number of different ways in which the ‘sparkliness’ or beauty of a diamond is described and defined, with attribute such as brilliance, scintillation, and fire being used to categorise the light performance of a diamond.  This can all get very technical, and to be honest not even the diamond industry can always agree on the technical specification that creates the most beautiful diamond.

In a way, that’s not a bad thing: it’s like trying to define what makes the perfect flower or the perfect snowflake.  Each and every one is unique and appealing to different people for different reasons.

Nonetheless, there is a broad consensus about the general proportions and attributes of a diamond that will maximise its light performance, and taking all sorts of technical details into consideration, diamonds are generally referred to as being in one of the following cut categories:  Excellent, Very Good, Good, Fair, Poor.

You might hear some other categories of cut for round brilliant diamonds, notably Ideal, Hearts & Arrows, and Signature.  These are further subdivisions at the very top end of the cut scale, and they usually have more to do with the diamond industry talking to itself rather than to the general consuming public.

Lastly on cut, although the vast majority of diamonds are round brilliant in shape, there are plenty of other variations on shape, with the most common being Princess (a square shape), Marquise, Pear, Heart, Oval, Emerald, Cushion, and Baguette.

Colour

Most diamonds are white or yellow or brown, with various shades in between white and yellow and brown.  Actually white is more accurately described as colourless, in the sense that white light can also be called colourless.

Perfectly colourless diamonds are given the colour ‘D’, and then the scale runs through the letters of the alphabet to Z, which is near colourless, with hints of yellow or brown.

Beyond Z we are getting into what are called fancy colours.  This can include the more intense yellows and browns, but there are also a number of other fancy colours which are extremely rare, and as such, extremely valuable.  Such colours include blue, pink, red, orange, and green.

Colour in diamonds is often caused by some sort of impurity, so the colourless ones are in fact the ‘purest’ diamonds (which adds to the appeal and value of ‘top colour’ diamonds – i.e. D colour stones).  But sometimes these impurities are also exceptionally rare as well as giving rise to unusual and attractive colours in diamonds.

Blue is caused by a tiny quantity of boron within the crystal structure – just a few parts per million – whilst a violet-blue occasionally seen in diamonds from the Argyle mine in Australia is thought to be the result of hydrogen.

Yellow is much more common in diamonds, and is caused by nitrogen.  Diamonds on the D-Z colour scale contain increasing levels of nitrogen as the yellow tint becomes more intense.

Other colours are not caused by impurities but by something physical that has affected the diamond.  The most common is brown, which is a product of plastic deformation of the crystal structure as the diamond was growing.  Brown diamonds are sometimes marketed as ‘champagne’ or ‘cognac’ diamonds.  Much rarer and more valuable, but thought also to be the result of plastic deformation, are pink, and most rare of all, red diamonds.  The Argyle mine in Australia is famous for its pinks and reds.

Lastly, a mention of black diamonds.  These have a black colour thanks to many microscopic inclusions within the diamond material.  These inclusions block the transmission of almost all light, but the finest black diamonds can still be attractive because they can be polished to give brilliantly smooth, glassy, facets, similar to ‘normal’ diamonds.  In recent years, black diamonds have become rather fashionable, and they are often set alongside colourless diamonds in order to provide an interesting contrast: a ‘night & day’ effect.

Clarity

Clarity is sometimes referred to as ‘quality’ or ‘purity’, but that messes up the concept of diamonds having 4Cs so we will stick to clarity.  Clarity grading is necessary because diamonds usually (in fact more or less always) contain some sort of inclusions or other structural imperfections.

A diamond that appears to be perfectly without inclusions or imperfections is categorised as Flawless.  Not surprisingly, these gems are very rare and they have a high value.

Inclusions can take many forms – for example small crystals, feathers, clouds, cavities etc – and a diamond’s clarity depends upon the location, size, number, and visibility of its inclusions.  There may also be surface features such as polishing lines, nicks and scrates, and these will also affect a diamond’s clarity.

The GIA (Gemological Institute of America) uses the following categories for diamond clarity, and most of the rest of the world now uses the same definitions:

FL: Flawless: No inclusions or blemishes are visible to a skilled grader using 10× magnification
IF: Internally Flawless: No inclusions and only blemishes are visible to a skilled grader using 10× magnification
VVS1 & VVS2: Very, Very Slightly Included: Inclusions are difficult for a skilled grader to see under 10× magnification
VS1 & VS2 – Very Slightly Included: Inclusions are clearly visible under 10× magnification but can be characterized as minor
SI1 & SI2 – Slightly Included: Inclusions are noticeable to a skilled grader using 10× magnification
I1, I2 & I3 – Included: Inclusions are obvious under 10× magnification and may affect transparency and brilliance

Most people can’t actually see any of the inclusions in diamonds that are VVS or VS clarity, especially once the diamonds are set in jewellery are seen in real everyday circumstances (i.e. without any kind of magnification), which begs the question: why would you pay a lot more money to have diamonds of VVS, IF or Flawless clarity?  Well, some people always want the very best, even if they can’t tell the difference between the very best and the next best thing.

The other factor to consider is rarity: Flawless diamonds are more appealing for some because they are so rare and exclusive.  But for most people buying diamonds or diamond jewellery in the UK, VS and SI diamonds will have the right balance of ‘quality’ and affordability.