Over Grading of Blue Fluorescent Diamonds Revisited

Nineteen years ago GIA published the results of a human experiment in the observation of diamonds with various amounts of blue fluorescence. 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”.

GIA was addressing the negative publicity concerning blue fluorescent diamonds, which began during the diamond investment craze of the late 70’s, early 80’s. Since then blue fluorescence has been an obstacle to marketing, leading to discounting compared to non-fluorescent diamonds of the same color grade.

25diamonddatabaseFigure 1. 25-Diamond Data Base photographed in typical artificial lighting

25diadatafluor2

2. 25-Diamond Data Base in Long Wave Ultraviolet “black-light” illumination. There are 5 rows of five diamonds with the five fluorescent strengths of None, Faint, Medium, Strong, and Very Strong blue fluorescence

There are several reasons for the concern and distrust by consumers and the trade of these gemstones that glow blue when excited in the dark by ultra violet (UV) radiation, Figure 2. The reasons are mostly due to misinformation and misguided publicity except for one valid concern. That is the overgrading of color that according to members of the diamond trade is too often observed. Overgrading results from the use of UV-containing, fluorescent lighting in color grading. …..Read full article here.

The Central Ideal

Have you heard of the ‘American Ideal’ or ‘Tolkowsky Ideal’ in diamond cutting? How about the ‘Morse Ideal’? Michael Cowing explains that because a majority of diamonds are fashioned as 57-facet round brilliants, many are familiar the ‘Ideal’ brilliant. Through their research GIA and AGS have both found ranges of angle combinations they believe retain the finest brilliance. However the two disagree over the extent of that range. Despite the controversy over these competing ranges, a surprising commonality—a Central Ideal—has been discovered, which we will explore here.

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Objective Diamond Clarity Grading

The diamond clarity grading scale used worldwide today was introduced by the Gemological Institute of America (GIA) in 1953. To help address varying interpretations and inconsistencies in clarity grading between laboratories (and even within some labs), this article introduces an objective system for diamond clarity grading. The determination of the clarity grade is influenced by up to five factors: size, number, contrast (colour and relief), position and nature of the inclusions. The proposed system assesses these factors (with emphasis on the first four) by using an objective metric that emulates the intuitive analysis done by experienced diamond graders. Using high-quality photographs of more than 100 randomly selected diamond examples, this article demonstrates a high degree of agreement between clarity grades obtained using this system and those determined by GIA and the American Gem Society Laboratories (AGSL). The system’s objective methodology may offer a means for improving inter- and intra-laboratory grading consistency.

Click to download the pdf: Objective Diamond Clarity Grading – published in The Journal of Gemmology, 34(4), 2014, pp. 316–332, http://dx.doi.org/10.15506/JoG.2014.34.4.316

The Overgrading of Blue-Fluorescent Diamonds

Michael D. Cowing FGA
AGA Certified Gem Laboratory
email: michaelgem@gmail.com

Abstract: Decades after the establishment in the mid-twentieth century of ultraviolet-free illumination for colour grading a diamond, an examination of diamond trade and laboratory grading practices finds nearly everyone employing some type of fluorescent tube lighting containing significant ultraviolet. This paper demonstrates and quantifies the over-grading of blue-fluorescent diamonds that often results. Simple methods are proposed that, by themselves or in combination, provide inexpensive and workable solutions to resolve this problem.

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Accordance in Round Brilliant Diamond Cutting

Photo realistic image of today's Ideal cut diamond

Photo realistic image of today’s Ideal cut diamond

Photo realistic image of the Ideal with pavilion cut in the antique style of the early 20th century

Photo realistic image of the Ideal with pavilion cut in the antique style of the early 20th century

Accordance in round brilliant diamond cutting

Michael Cowing, FGA

AGA Certified Gem Laboratory

 Abstract: Over more than 150 years, those involved in the diamond industry have worked to establish the ideal angles and proportions to cut the facets of the standard round brilliant (srb) cut diamond in order to produce the ‘Ideal’ gem. This paper reviews milestones in that work and demonstrates that the solutions by major contributors to this endeavour have surprising commonalities. These common aspects are in accord with the research and investigation of the author as well as that of the GIA and AGS and the knowledge of diamond cutters and the teaching of diamond cutting institutions.

Click to download the pdf: Accordance in Round Brilliant Diamond Cutting – published in Journal of Gemmology