(A bespoke diamond engagement ring created by London Diamond & Emerald Exchange sparkles)
Gem cutters, polishers and jewellers have developed a number of techniques to bring out this most elusive of diamond qualities over many centuries and in this article we seek to shed some light on their closely guarded trade secrets to help you find a sparkling stone of your own. Diamonds sparkle due to the interaction of light with the stone's cut. Consequently the type, depth and quality of the cut dictates the manner in which the gem reacts to the light that enters it. The geometry of the diamond's facets and its proportions directly affect the path taken by the light that hits the stone. When gemmologists study a diamond's light characteristics they assess the way in which it enters and passes through the stone, reflecting and refracting on its interior surfaces, or facets. This light will then either leave the diamond as a white light, referred to as 'brightness,' or it may be split into any combination of the spectral colours (red, orange, yellow, green, blue and violet), known as 'fire.' The effects of this can be spectacular! As the stone, or the observer, moves the visible alternate flashes of white and coloured light contrasted with the dark and the light form an effect known as 'scintillation' - in essence this is what is more commonly known as 'sparkle.'
(A master jeweller at work)
Now that we have assessed some of the science behind this phenomenon, how does one go about finding a diamond with scintillating qualities? Due to the fact that we are dealing with the interplay of rays of light, the environment in which you view a stone will have a profound effect upon its sparkle, as will its cut. As a rule of thumb, gemmologists recommend that you view a diamond under at least four different light sources. Spot lights or a large number of smaller individual light sources are normally employed by jewellers when they are working with diamonds so that they can assess the amount of sparkle being produced within a piece. It is important to set the lighting level correctly so as to avoid any glare that may lead to a distortion in your observation. Next you should observe the stone under diffused lighting and a trick is to use fluorescent lights that reflect from a white ceiling. It is then worth trying a mixed light environment encompassing spotlights and diffused lights together. Finally, and most importantly, inspect the diamond in natural daylight. In general the more facets a diamond has the greater the opportunity there is for a ray of light to reflect from one of stone's surfaces and bounce or scatter. Round brilliant cut diamonds with 57 or 58 facets will often appear to sparkle much more than a single-cut cut diamond with just 17 or 18 facets.
(A diagram of a faceted diamond)
If you want to set a diamond that is not round, look for stones cut in the brilliant faceting style, including princess, radiant, oval, pear, heart and marquise. With diamond sparkle, as with almost every other aspect of buying a precious gem, certification is an invaluable friend. The world renowned GIA (Gemmological Institute of America) reports, for example, grade cuts as: "Excellent; Very Good; Good; Fair & Poor." Obviously Excellent is the best quality of cut, leading to a stone in which the cut grade is very bright, showing an even pattern and a good contrast between light and dark areas. This indicates the reflections will appear crisp and well balanced and that the cutter has created the best possible stone from the rough diamond. A Very Good grade means the stone has evenly distributed bright areas across its crown and few distracting areas. Good grade stones are not as bright, their reflections are not as sharp and there may be some dark or dull areas within the stone. A Poor cut grade stone will harbour more prominent dark or dull areas so it is clearly one to avoid. As with all things in life, size isn't everything! Some people think the larger the stone, the greater the sparkle but this isn't the case and diamonds with identical proportions, colour and clarity produce the same 'volume' of sparkle irrespective of their relative size.
(GIA cut grading profile)
Despite the fact that the size of a diamond does not improve the sparkle, the number of diamonds in a setting does. This is why diamond side (or flanking) stones and pavé settings are often incorporated into engagement rings and other jewellery items. The better the colour and the clarity of the diamond, the greater its scintillation will be. Experts believe that the 'brightness' of a stone lessens as you move from D-Z on the colour scale and the from Flawless (F) to Included 3 (I3) on the clarity scale. Prong setting can also have a positive impact as it allows more light to enter the diamond than bezel settings that cover more the top surface of the stone. This doesn't mean that you have to overcomplicate things, however, as many simple designs can incorporate the tricks of the trade that promote sparkle just as well as more intricate ones. One of the simplest and most obvious ways of maximising the sparkle of a diamond is to keep it clean - a dirty gemstone will not sparkle at all! Diamonds and coloured gems attract grease and dirt so regularly wipe the stones with a soft cotton cloth and occasionally clean the stone with warm soapy water. It is important to never use polish or chemical products on any precious stone or precious metal as they can cause them to deteriorate.
(Pavé settings of multiple diamonds enhances the sparkle)