If you’ve ever researched or embarked upon buying a loose diamond or diamond jewellery, you will do doubt be acquainted with the “4 Cs”. To the uninitiated, this represents:

  • Cut
  • Carat
  • Clarity
  • Colour

Each of these has a direct bearing on the appearance of a stone, and consequently its price. There are cultural, personal and budgetary influences which determine how these characteristics are prioritised. By compromising on one or more of these traits, you can arguably have more of the property that you prize most. But I would argue that one attribute impacts beauty more than the others.

Conventional wisdom has traditionally dictated that no one characteristic was more important than the other. However, I am going to throw the cat amongst the pigeons and challenge that view, because there is one “C” which reigns supreme. I would argue that contrary to accepted wisdom, one “C” is king, a cut above the others (pardon the pun), and without it, a diamond will never fulfil its potential. And that characteristic is quality of CUT. Unfortunately for a layman, this is also the most difficult to assess without training.

A well cut stone (most notably the round brilliant cut) recognises, respects and ultimately exploits the optical properties of diamond. It is fashioned within very specific and narrow pre-defined parameters to ensure that the maximum amount of incident light is returned to the viewer, enhancing the brilliance and liveliness of the diamond. These characteristics are not negotiable, so a poorly cut stone which neglects to conform to these strict constraints will always fail to do a diamond justice.

Familiarising yourself with the anatomy of a diamond is helpful, and this diagram illustrates a round brilliant cut diamond viewed in profile, and introduces some key terms:

Diagram provided with kind permission from Gem-A

If we concentrate specifically on the modern round brilliant cut diamond, there is an ideal cut which incorporates a number of criteria. Most notably, the angle of the pavilion facets (those underneath the stone) in relation to the girdle is critical. The role of pavilion facets is to act as mirrors so that light bounces around within the diamond and exits the stone through the crown (the top of the diamond). The ability of the pavilion facets to perform this function is dictated by the pavilion angle.

Diagram provided with kind permission from Gem-A

In poorly cut diamonds, it is usually the pavilion angle which is compromised, resulting in a diamond which is either too deep (resulting in a “nail head”- a dark reflection of the table facet dominating the pavilion) or too shallow (producing a “fish eye”- a circular reflection of the girdle visible through the table facet). It would be unreasonable to expect all light entering a diamond to be returned to the viewer, however, if a brilliant cut diamond has an excellent quality of cut, it is possible that it can return up to 97% of incident light, which is spectacular. This can mean the difference between an appealing stone and a dazzling diamond.

This diagram illustrates how different pavilion angles can affect the appearance of a diamond when viewed down through the table:

Diagram provided with kind permission from Gem-A

Cut, which is referred to as “make”in the trade, is a complex term which incorporates many attributes:

  • Style of cut: This describes the outline shape- for example, round brilliant, princess, pear, Asscher etc
  • Symmetry
  • Proportions: this includes a number of factors including the angles of facets to achieve the best combined effect of brilliance and fire (beautiful spectral colours), and the relationship of various parts of the diamond in relation to the diameter of the girdle.
  • Quality of polish

It is reasonable to query why a diamond manufacturer would consider compromising the quality of cut. The reality is that in optimising an excellent quality of cut, some diamond rough has to be sacrificed and the final weight of a diamond will inevitably be reduced. The primary objective of most cutters is to maximise the (carat) weight of diamond rough. The premium charged for producing a heavier stone will usually be greater than the discount applied to reflect a poorer cut… so within reason, the final weight of the cut stone will almost always take precedence over quality of cut.

Taking an educated view on quality of cut requires training and experience. If this leaves you feeling a little daunted then take some confidence in common sense and a good eye- they can tell you a lot. When you observe one stone next to another, one may exhibit more vibrancy and sparkle. You may not be able to explain exactly why, but it is almost inevitable that the more lively diamond has a superior cut than the other. Trust your judgement and instinct.

There is a temptation to explore seemingly cheap loose or set diamonds online. There is a reason why these articles are more affordable- the compromise which will almost certainly have been made is quality of cut. You wouldn’t buy a car without driving it first or checking its performance- the same care and due diligence should be undertaken when researching diamonds. These are often significant purchases which last longer than a lifetime, so if you are unsure, liaise with professionals who can guide you through the process.

So, take care when buying diamonds unseen- even if they are accompanied by a certificate. If a piece of jewellery appears substantially cheaper than comparable items, you may wish to consider why. Poorly cut stones are bought at a discount- for good reason. Not only are they less attractive, but their lack of uniformity can compromise their security in a setting. If you are buying a special piece of jewellery, take steps to ensure that you explore how well the stones have been cut.

There is little point in paying a premium for a diamond with good colour and free of visible inclusions if it has been poorly cut. It will forever look dull and lifeless, and lack the sparkle, liveliness and brilliance for which diamonds are sought and prized.