Articles about Diamond Grading
Nineteen years ago the Gemological Institute of America, (GIA), published the results of a human experiment in the observation of diamonds with various amounts of blue fluorescence. The article was entitled “A Contribution to Understanding the Effect of Blue Fluorescence on the Appearance of Diamonds”. An introductory editorial indicated that this study “should bring into question the trade’s lower “bid” prices for moderate to highly fluorescent diamonds in the better colors”.
Ask 10 jewelers about one diamond and you might hear 10 different stories. Ask 10 independent appraisers and the clinical analysis may agree, but terminology and methodology can vary. But ask 10 PriceScope prosumers and you often see unanimous agreement. Curious, isn’t it? What could possibly cause a diverse group of thousands of consumer enthusiasts and pros alike, to use the same terms and uphold similar values when evaluating diamonds?
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.