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Posts by ACA Gemological Laboratory

Ideal Cut

The Ideal Brilliant Cut: Its Beginnings to Today Introduction Since its beginnings in the early 20th century to the present day, confusion and misunderstanding has frequently surrounded the use (or misuse) of the term “Ideal Round Brilliant Cut,” its defining properties and origin. Some have advocated eliminating its use altogether. Through the examination of the…

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What is the American Ideal Cut?

ACA Gemological Laboratory.

Question: What exactly is the American Ideal? Was it Americans who refined the cutting/proportioning process? The American Ideal Cut Ideal is defined as: “A standard of perfection, beauty, or excellence.” The standard of perfection and beauty in diamond cutting is embodied in the round brilliant, American Ideal cut. This concept of an ideal cut for…

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The Central Ideal

ACA Gemological Laboratory.

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.…

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Accordance in Round Brilliant Diamond Cutting

ACA Gemological Laboratory.

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 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…

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Identify the Ideal by the Eye of the Diamond

ACA Gemological Laboratory.

Here is a surefire way to recognize Ideal cut diamonds at a glance. Learn to look for the “eye of the diamond”. The mosaic pattern of reflections in the top portion (crown and table) of a brilliant cut diamond can be subdivided into three concentric rings—each of which corresponds to a part of the eye:…

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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…

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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…

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A Place for CZ Masters in Diamond Colour Grading

ACA Gemological Laboratory.

Figure 2. Complete set of GIA graded diamond masters from E through M. Over the last 20 years and despite recommendations to the contrary, many gemmologists and appraisers have gravitated to the use of cubic zirconia (CZ) master stone sets to assist in the colour grading of diamonds. This investigation revisits with new insight, diamond…

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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…

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