Aug 10th, 2015
by Mike Botha, RS & Master Diamond Cutter
The modern Round Brilliant has been around for over a century. Its genesis roughly correlates with that of the Model T Ford. Whereas the Ford Motor Company pursued innovation by improving their technology and designs, the diamond industry was content with the work done by Marcel Tolkowsky. I would like to point out that Marcel’s findings were empirical as much of the evaluation of the various parameters of cut was purely observational. `Do I want to minimize what Marcel has done? Not at all! Rather, I think the industry should have directed more energy to find out what really makes a diamond return light and how to improve on the Round Brilliant.
Coming back to the Model T: Just imagine if the Ford Motor Company were to stick with the Model T design, yet perfecting the fitting of body parts by using 3 D solid modelling techniques! They could also have added the following: Independent suspension with shock absorbers, electronic ignition, power steering, collapsible steering column, crumble zones, airbags, halogen head lights, L.E.D. tail lights, heated seats, climate control, remote start, entertainment system, navigation system and the list could go on. I am sure you get the picture. A Model T with all the modern bells and whistles would still be a Model T, with the same old power train and looks!
Rather than stepping outside of the constraints and shortcomings of the Round Brilliant, the diamond industry was and still is fixated on creating the most perfect Round Brilliant -‘Model T’. We have moved away from the Old European, to the ‘modern’ brilliant, to the Ideal, the New Yorker (60-60) and everything in between in the quest of creating the ‘best looking’ diamond. We have lately seen the quest for quality bringing about an abundance of Triple Excellent cuts, which is now becoming the industry standard for Round Brilliant. In the process of amelioration, the price advantage of the Triple Excellent cut has been eroded as a plethora of these diamonds are now available in the market. Triple Excellent has become the new norm and rightfully so, at least for Round Brilliants.
A FLAWED PARADIGM
Anybody who has done ray tracing on Round Brilliants will know that the best of them still leak some light. Experts do not always agree on how much light leaks out of the best cut Round Brilliants as some say 3% while others say up to 7%. You may think, ‘that is nothing’, but if a paradigm is flawed it should not serve as a paradigm. If we were to base our evaluation of a diamond cut based on scientific criteria, we might just start to question the status quo. One needs to ask; ‘Why has the Round Brilliant become the paradigm for cut and price? It boils down to laziness and apathy towards change. Just think about it, the Princess cut has been around for over thirty years, yet it is still referred to as a Modified Square Brilliant by some laboratories! There is nothing in a Princess cut that resembles the facet arrangement of a Round Brilliant, but this goes to show how lethargic the industry has become to accept change. For how long does a diamond have to be on the market before laboratories start calling it by its name? Why is the industry so besotted with the Round Brilliant? Okay, it is round, but is it that brilliant? Don’t get me wrong, the Round Brilliant is a way better diamond with regards to light performance and integrity (no sharp corners that could chip during setting) than many of the designs out there.
But, Round Brilliants at their best still leak light as demonstrated by the GemCad image below when light beams are directed perpendicular to the table and does not take tilt positions or angular light into consideration. Light beams were shot into the diamond in a 45 degree segment starting at the culet and then widening out towards the girdle. Experts differ in how much light leaks out of a Round Brilliant. Some say 3% while other say 7%. Whether the leakage is 3%, 5% or 7%, it doesn’t really matter. The paradigm is flawed and it is time we get just a little more scientific and creative!
Machines with cameras and other gadgets as well as presentation tools were developed to ‘prove’ the high quality of the diamonds sold by vendors. Some presentation tools are really good like the AGS Angular Spectrum Evaluation Tool (ASET), which is pure science based and an excellent evaluation tool.http://www.americangemsociety.org/aset-reg-tools
No client however, is provided with the ‘machine’ to boost his or her bragging rights. Once clients leave the store, they leave the gadgets and machines behind, after all diamonds are worn and are dynamic pieces of art and craftsmanship. Diamonds are worn by humans, viewed by humans having human eyes. No machine can rightfully render or evaluate that which the human eye observes in the light return of a diamond. Should we be against evaluation tools? Heaven forbid, but they should not be used at the exclusion of human perception. If the machines are using the best Round Brilliant as the paradigm, then the results would always be flawed.
HEARTS AND ARROWS
The Japanese ‘invention’ of Hearts and Arrows probably did the most for raising the bar on Round Brilliant symmetry. New tools and greater accuracy in the polishing process resulted in better quality Round Brilliants. I would like to add that Hearts and Arrows quality diamonds were produced by a select few master diamond polishers using a painstaking method of trigonometric profiling with extreme accuracy. This method of polishing was used long before anyone knew of Hearts and Arrows. A closer look at the arrows in well-cut Round Brilliants would reveal that they are none other than obscuration patterns, which are vividly recognizable in elongated traditionally cut fancies like oval, pear and marquise. Of course in the latter group, the obscuration patterns known as ‘bow ties’ are deemed undesirable, yet sought after in Round Brilliants – go figure. I have to admit though that the arrows are more pleasing to the eye than bow ties. Kudos to those brave souls who introduced offset polishing and French culets in traditional fancy shapes to eliminate the old bow tie effect.
In the quest to differentiate their product, some diamantaires have taken the bold step to create new designs, with many of them incorporating multiple tier pavilion and crown faceting arrangements. Some of the designers are onto something good, while a large number of these designs just do not ‘work’ and there are various reasons for that. Adding more facets to the crown of a Round Brilliant does not add to the light return of a diamond. The pavilion facets are the ‘work horses’ of a diamond. These are the facets that return light back to the viewer. This may sound like an oversimplification, and one needs to be aware of the fact that the angles of crown and pavilion facets are symbiotic. It is commonly known that shallower pavilions, would dictate a steeper crowns and vice versa for optimal light return. One needs to be cautious as to where additional facets are added. One could add facets that would ‘kill’ the diamond and some designs out there, which may perform very well in the ‘gadget criteria’, fail to appeal to the human eye, with too much obscuration or the lack thereof. Opening the parcel papers containing
some of these designs are like opening a can of sardines. They are all tightly and neatly packed together, but they are, you may have guessed it, ‘dead’. The reason for this is the lack of facet definition.
Let me preface this with an analogy. The numerals on an analog clock are radially spaced at 30 degrees. How do we get to that? Divide 360 (the face of the clock) by 12 (hours) and we get 30. The radial positions or angular definition of the numerals are therefore a minimum of 30 degrees or multiples thereof.
Let us use another example.
If one cuts a pizza in half it will have two segments (slices) of 180 degrees each. If we quarter it, it would have 4 segments of 90 degrees each. If we divide these 4 again, it would have 8 segments of 45 degrees each. If we divide these 8 again, it would have 16 segments of 22.5 degrees each. Divide them one more time and it would have 32 segments of 11.25 degrees each. Now we have a picture that resembles the segments of a Round Brilliant diamond. On a Round Brilliant all the facets relate to one another in a radial position for a minimum of 11.25 degrees or multiples of 11.25 degrees i.e. 11.25 x 2 = 22.5 degrees, 11.25 x 4 = 45 degrees etc. on a well cut Round Brilliant. The facet definition of a Round Brilliant is therefore a minimum of 11.25 degrees, seen in a radial context. The radial positions of facets on diamonds are referred to as the azimuth. The following diagram would explain the radial position (azimuth) of the facets on Round Brilliants.
A perfectly cut diamond would meet the following geometric criteria (facet definition):
1. Azimuth (radial positions) are the same for all the facets within a facet group (stars, mains and crown and pavilion girdle facets a.k.a. halves)
2. Angles are the same for all facets within a facet group
3. Maximum angular variance between facet groups (within the design parameters)
4. Equal azimuth between facet groups
SKEWED FACET COUNT
If we calculate the average surface area of the various sectors, i.e. table, crown and pavilion for an Ideal Round Brilliant (53% table, 40.9 degrees pavilion mains and 34 degrees crown main) the math looks something like this:
Table – 12%
Crown – 31%
Girdle – 4%
Pavilion – 53%
Now just think about it. The crown which represents only 31% of the surface area has 32 facets! Yet the pavilion which makes up 53% of the surface area has only 24! Do I knock the crown for having too many? Not at all, I want to speak up for the pavilion which only has 24. It is time we add some facets that will ‘work’ to the pavilion in an attempt to rectify the skewed facet count and make that which is good, even better. A good start would be to double the facet count by creating multiple tier pavilion configurations, keeping in mind that brilliance should not be compromised by too much scintillation. It is important to retain some ‘big flash’ in the pavilion.
Any transparent object (medium) has the ability to refract/bend light. The speed of light passing through a transparent medium is slowed down by the medium. The ratio at which light is slowed down is called the refractive index. Formula: Speed of light in air ÷ speed of light through medium= refractive index. The refractive index for diamond is 2.42. The net effect of refraction is that the disparity between the slower and faster light waves becomes discernable when the refracted light is shone onto an external surface. Refracted light is also momentarily discernable when the diamond is moved or oscillated, at a frame rate which is faster than the processing speed of our brains. Like with sunlight, once a diamond is stationary, our brains have the ability to recompose the refracted light into white light.
An optical law for transparent objects is that the angle of incidence of light would equal the angle of reflection, if the light falls outside of the critical angle of the medium. The critical angle of diamond is 24.41 degrees from perpendicular to any internal surface. If the angle of light falls inside the critical angle it would exit. Following is a diagram that illustrates what happens to light in a diamond. The angle of the blue beam is greater than the critical angle which is shown in red and therefore gets reflected. The angle of the yellow beam is less than that of the critical angle and therefore exits.
Following is a simplified rendering of the light path in a typical Round Brilliant diamond.
ANGLE OF LIGHT RETURN
The angle at which light leaves a diamond is of utmost importance. A shortcoming in Round Brilliants is that the angle at which the light leaves the crown is not large enough. By adding additional tiers of pavilion facets, a larger angle of light return is achieved. This has the net effect that the diamond appears larger than a Round Brilliant of the same diameter.As can be seen in the following comparative images, the angle of light return can be increased by at least 13 degrees as in the bottom image. The net result is that the diamond would be attractive to more persons in close proximity to the wearer.
To take the angle of light return a little further, compare the two images in the composite below. The light return angle is rendered as a ‘Light Cone’ created in 3D Solid Modelling.
New stunning designs have been and could be created by adhering to the principles of light return, and facet definition. These are sound scientific and mathematical principles which should form the paradigm in diamond design, rather than one of the products of this paradigm, which has been the Round Brilliant for so long. Having based all our criteria and research on the Round Brilliant instead of the principles mentioned has brought us to the cul-de-sac of the quality pursuit in Round Brilliants. After reaching the milestones of Triple Ideal and Triple Excellent, where do we go? In an attempt to de-commoditize diamonds, do we pursue Super Triple Ideal, Super Triple Excellent, or some other super-duper criteria yet to be formulated to try and get an edge in the marketplace? Or do we dare to be brave enough and step outside of the ‘Model T’ box and create real beauty with discernible differentiation? I place my money on the latter.
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