The Round Brilliant Cut is arguably the most popular and most recognizable diamond cut of all the cuts available with over three quarters of all diamonds used in jewellery cut to this shape, this is because it achieves the greatest brilliance and fire. Thus is optically the most efficient. It was developed by Marcel Tolkowsky as late as 1919. This cut is certainly the most popular amongst buyers at the present time with the Princess Cut being a distant second.
The Round Brilliant Cut was developed from the Old European Cut which was the most advanced cut of the 19th century. The first brilliant cuts were introduced in the middle of 17th century and were known asMazarins or Double Cuts. They typically had 17 facets which by today's standards would mean they would be pretty dull as a brilliant round cut diamond has 58 facets. The next improvement was made by a Venetian polisher, Vincent Peruzzi, who increased the facet count from 17 to 33 it became known as the Peruzzi Brilliant or the Triple Cut, these also would look considerably dull as the bruting technique had not as yet been developed. This is the technique whereby two diamonds are set on to axels and set to spin in opposite directions thus grind together to give them rounded edges. The Peruzzi dramatically improved the fire and brilliance of the diamond compared to the Mazarin Brilliants. By the 19th century the Old European Cut had became the most popular cut, it had a shallower pavilion, more rounded shape and different arrangement of facets. This is the fore runner of the round brilliant.
The Russian mathematical genius Marcel Tolkowsky, a member of a large and powerful Diamond family, subsequently calculated the cuts necessary to create the ideal Diamond shape. As part of his PhD thesis in mathematics, Tolkowsky considered variables such as the index of refraction and covalent bond angles to describe what has become known as the Round Brilliant Cut. Thus maximising the fire and brilliance of the stone. Since this there have been minor developments as Tolkowsky's calculations were not perfect. Tolkowsky had not followed the path of the light rays that were reflected more than twice inside the diamond; this meant that the results were incomplete. Tolkowsky's guidelines, while revolutionary in their day, are not a definitive solution to the problem of finding the perfect proportions of a round brilliant cut diamond, which has to led to other attempts to do so. In the past few decades computers have been used to try to find the optimum standards for the round brilliant.
These proportions for the perfectionist in terms of the Round Brilliant Cut are a depth percentage of between 59.3% and 62% and a table percentage of 55% to 58% this would help to maximise the brilliance and scintillation as the gem appears to dance and sparkle in the light. Diamonds of such quality are hard to come by as there is such a huge demand for these.
The most popular of all cuts the Round Brilliant in its ideal proportions is designed to give maximum scintillation, beauty and fire. Rounds make up the vast majority of diamonds found in engagement rings and are popular as stud earrings and in pendants. The Brilliant cut follows more naturally the rough diamond crystal shape, and thus is most popular for cutting due to the beauty it returns. The Round Brilliant Cut also has the appearance of being larger than it actually is which means that a higher carat weight is not essential when purchasing the gem. The hearts and arrows phenomenon which can be seen in Round Brilliant Cutalso are attractive selling points. This phenomenon is seen when the top or table facet is exactly perpendicular to the bottom or pavilion of the diamond.