How to Determine an
Ideal Cut Diamond after January 2006
A very Brief History
Well... there is a lot of debate about what exactly is "ideal cut" but back in the beginning of the last century a gentleman by the name of Marcel Tolkowski (a mathematician) came up with what would be considered to be the "ideal" proportions for a diamond that would yield the most pleasing display of "brilliance", "fire", and "scintillation". His calculations resulted in the following proportions.
The research of Marcel Tolkowsky has been the foundation for many studies conducted on cut and a basis upon which the new cut grading systems have been implemented. In the early 60's the AGS (American Gemological Society) developed it's cut grading system for rounds and based it on a numerical scale ranging from 0-10. That same scale is used today and has been modified a few times over the course of the decades. The most radical modification came about in June 2005 when they changed from a proportion based system to a performance based system. The older proportion based system was based on the following proportions. The only modification they made to this was in the pavilion angles as they allowed them to range from 40.2°-41.2°.
At the present time numbers have basically been thrown out of the window to an extent as 3d modeling has taken precedence within their system. Also since measurements of the minor facets (40 out of 57) were never taken into account, THEY ARE NOW as these facets impact optical performance as well. So a basic Sarin Report which shows the above measurements is not enough to determine whether a diamond is "Ideal" or not. We'll delve further in Sarin Reports later in this tutorial but first lets get to the meat. :)
2 Standards for Ideal after 01/2006
Within the course of June 2005 and January 2006 we have seen the release of 2 cut grading systems by both GIA and AGS laboratories. Both labs are considered the more conservative of those currently out there (at least within the gold ol USA) and just about all the diamonds on our website feature a lab report by either. So before we begin a more in depth look at all the things that go into determing their cut grades it is vital to understand the *tools* each lab uses to determine their top grades. An understanding of the tools used will better help us understand the how's and why's behind each of their respective cut grading systems.
How a GIA Excellent is Determined
GIA Excellent cut grade next to a GIA Good
The science behind GIA's cut grading system was ultimately determined by human observation testing and is perhaps the greatest strength of their system. There are some critical elements to cut grading that observation testing does not see or anlayze but the basis for the GIA Cut Grading system is how a person sees, in the most common lighting environments, the optical characteristics of brightness, fire and scintillation. Any stone that displays a decrease in any of these optical elements contributes to a lower cut grade.
GIA's study took place over the course of 15 years. At the beginning of their studies they did indeed utilize technologies, the primary one being that of ray tracing software with which they could build a virtual diamond of any proportions and track how light behaves in such a stone. Over the last 5 years of their study the focus of their research was in conducting observation testing with people in the trade as well as consumers. GIA created a lighting environment which, in my professional opinion duplicates excellently the lighting conditions which most people find themselves in on a daily basis in which they can observe brightness, fire & scintillation.
Tools: The primary tool is GIA's DiamondDock. You can read about this in more detail in our "Technologies" section but the GIA Diamond Dock uses neautral gray walls, with the diamonds observed in a neautral gray backdrop (tray) with which any diamond can be observed in specially calibrated ...
1. daylight fluorescence, to observe brightness & patterned scintillation.
2. 5800 degree kelvin l.e.d. (light emitting diodes) to observe fire and sparkle scintillation.
3. You can turn on both fluorescent and l.e.d.'s and observe a nice mix of both brightness, fire and scintillation (both patterned and static).
After their observation testing was complete, GIA also developed the GIA FacetWare Software which is available for free online at this link. The FacetWare program is based on approx. 38.5 million proportion combinations in which "face up appearance" is determined. There are certain limitations to the software but a knowledge of the facets is required. We provide this analysis with each of our diamonds including the FacetWare results and GIA Cut Grade.
How an AGS Ideal is Determined
The science behind AGS new ideal cut is based on an advanced form of reflector technology called the ASET which is the abbreviation for "Angular Spectrum Evaluation Tool". For a full discussion of this tool I refer you to our chapter "What do Reflector Technologies Teach Us?". AGS Laboratories consulted the expertise of optical scientist Jose Sasian to determine light performance within diamonds based on the ASET technology. With this science and the ASET tool AGS has developed a cut grading system for square princess cuts, round brilliant cuts and is working on other fancy shapes as well. Rumor has it a system for square emerald cuts (also known as Asscher cuts) is in the works.
Through our own testing, through the use of many technologies combined with observation testing the ASET proves to be an excellent tool for evaluating diamond cut quality and light performance. There are instances however where ASET images do not always correlate to human observation. You'll read more about this in the upcoming chapters and what kind of images to look out for in an ASET to determine if it meets AGS "Ideal" qualifications.
In Summary:
GIA Excellent Cut Grade (not to be confused with polish and symmetry grades) must meet certain minimum criteria in appearance to make it's top grade plus a minimum of very good polish, very good symmetry and none to minimal painting and digging on the girdle facets (more on this in the upcoming chapters). While the appearance can be judged under their DiamondDock which shows the consumer accurate portrayals of brightness, fire & scintillation, many diffuse lighting environments can also be used for brightness and pattern. Fire is slightly trickier since adding spot lighting that is too intense can overwhelm the observer so that brightness and pattern are harder to observe (meaning a diamond that does not have as great of an appearance gets some help and its harder to see differences in spot lighting that is too strong). The Diamond Dock helps in this area, by adding spot lighting that is not too strong, yet fire is easily seen.
AGS Ideal Cut Grade must show a certain balance of colors in their ASET Reflector tool. A good distribution of blue, a superior amount of reds and minimal greens are needed in order to meet "Ideal" status for light performance. To meet Ideal grade, light performance must be tops as well as ideal symmetry, ideal polish and ideal proportion factors.
The following chapters examine the various optical characterics that comprise the most beautiful diamonds. While the greater majority of our inventory consists of diamonds that meet both labs qualifications for their top cut grades (helping to ensure your purchase is a safe one), and now that you've got your feet wet with this introductory to cut information ... you may as well take the plunge and read the rest of our chapters on cut. We promise you'll greatly benefit from them! 
Take me to the chapters on "The New Cut Grading"!  |
