Articles about Diamond Grading
This article will focus on the particular issues involved in light performance grading specific to princess cut diamonds. We will delve more deeply into the underpinnings of the AGS light performance based cut grading system and the round brilliant in a future article. For a look at the peer reviewed science behind the AGS system that was years in the making you can refer to the landmark study which appeared in 2007 in the journal Optical Engineering, entitled “Evaluation of Brilliance, Fire, and Scintillation in Round Brilliant Gemstones." Foundational work on the project was published in Optics and Photonics News in April of 2003 entitled “The Optical Design of Gemstones."
Garry Holloway1 was the first to suggest a meaningful explanation for this: he suggested that, because there is a small difference between pavilion main & half facet slopes (less than 2º in a typical round brilliant), this may cause one to be dark when the other is bright – producing contrast in the gem’s image. Studies of human optical response2 say that this is attractive to viewers; it may be why the people Tolkowsky polled chose the proportions they did.
Diamond clarity grading involves assessing how readily visible the inclusions are in a diamond and accounting for an extensive list of potential variables including the size, number, type, location, and relief of its inclusions. At the American Gem Society Laboratories (AGSL), clarity grading begins once color grading is completed.