Carat

Diamonds and other gemstones are weighed in metric carats: one carat is equal to 0.2 grams, about the same weight as a paperclip. (Don’t confuse carat with karat, as in “18K gold,” which refers to gold purity.)

Just as a dollar is divided into 100 pennies, a carat is divided into 100 points. For example, a 50-point diamond weighs 0.50 carats. But two diamonds of equal weight can have very different values depending on the other members of the Four C’s: clarity, color and cut. The majority of diamonds used in fine jewelry weigh one carat or less.

Because even a fraction of a carat can make a considerable difference in cost, precision is crucial. In the diamond industry, weight is often measured to the hundred thousandths of a carat, and rounded to a hundredth of a carat.

Diamond weights greater than one carat are expressed in carats and decimals. (For instance, a 1.08 ct. stone would be described as “one point of eight carats,” or “one of eight.”)

The carat, the standard unit of weight for diamonds and other gemstones, takes its name from the carob seed. Because these small seeds had a fairly uniform weight, early gem traders used them as counterweights in their balance scales. The modern metric carat, equal to 0.2 grams, was adopted by the United States in 1913 and other countries soon after. Today, a carat weighs exactly the same in every corner of the world.

Cut

Cut refers to the shape and proportion of a diamond. Diamonds may be cut in a wide variety of shapes but the most popular are round, oval, marquise, pear, emerald, radiant, princess and heart. While other diverse cuts are available on the market, the round brilliant cut is still the top choice.

There are standards of cutting to produce the optimum of brilliance (light reflecting from the table) and dispersion (light refracting from the crown). Originally designed by mathematician Marcel Tolkowsky in 1919, his design became one standard for the modern brilliant cut today. In cutting to these proportions, a cutter must often be willing to sacrifice much more of the valuable rough to yield a diamond of superior beauty but of far smaller size.

Most diamonds are cut for weight retention, which often results in a deviation from “good proportions”. Often, the Diamond Cutter will sacrifice some of the beauty of the stone by cutting for a minimum of weight loss from the rough, which usually deviates from ideal proportions, but gets a larger finished stone. The truth is that less than 5% of all diamonds are cut to ideal proportions.

Care must be taken to avoid buying a stone that has been cut too far from the “excellent” proportions. When a stone has either a very shallow or very deep cut, light is lost through the sides and bottom of the stone (pavilion), reducing its brilliance. Cutting a stone that has “very good to good” cut or proportions usually results in a smaller carat weight stone.

Clarity

Most Diamonds contain inclusions. Sometimes they are incorrectly referred to as “carbon spot”. In reality they can be a myriad of things from other minerals such as carbon or even a garnet. There can also be minute fractures within the stone. What ever they are, they are the internal characteristics of the stone. It is what makes each diamond unique. You should learn to recognize the “birthmarks” in your stone as they are an easy means of identification.

The Clarity Grades as defined by the Gemological Institute of America are generally accepted throughout the world. Each has a very specific meaning. The grading takes place using 10x magnification using either a loupe or a gem microscope. As can be expected, the fewer inclusions, the rarer, thus the more valuable the stone.

Special Notes on the term “Ideal Cut”

The term “Ideal cut” is used to describe a range of dimensional tolerances that produce exceptional quality diamonds in terms of brilliance and dispersion. The term “Ideal Cut” does not intimate a single set of dimensions.

Care should be taken of the loose use of the term Ideal Cut as there is no universally accepted standard. There is some overlap in the dimensional criteria used by the recognized laboratories to establish a grade of “Excellent to Very Good. The major internationally recognized laboratories, HRD, GIA, EGL and IGI each grades cut as deviations from one of several standards and always within a range of tolerances.

It is highly unlikely that there will ever be a single set of dimensions that will be universally accepted as the “Ideal Cut” as there is a relatively large range of dimensional possibilities that produce exceptional diamonds.

ICE Brand diamonds are selected from a range of tolerances that are included in both American and European standards with a special emphasis on visual beauty.

Color

In the late 1950’s GIA (The Gemological Institute of America) introduced the colour grading system that is used today. The GIA grading system replaced grades such as Top Wesselton and Capes and is internationally accepted. In most cases, unlike all other gems, it is the absence of colour that makes the stone more valuable. With the exception of “Fancies”, or fancy coloured diamonds, which are rare, all diamonds are graded on the scale shown below. Most diamonds are either a light yellow, light brown or light gray. The separation between grades is almost undetectable to the untrained eye. An analogy would be five pieces of white paper of differing qualities. Looked at Individually they are all look white, but when placed side by side the distinction can be made.

When it comes to diamond colour grading, most people have difficulty distinguishing between two or even three full grades. When selecting Gemological Institute of America (GIA) master stones, though, graders must push the limits of visual tolerance, since two masters of the same grade are virtually indistinguishable. This section of the Winter 2008 Gems & Gemology article Color Grading D-to-Z Diamonds at the GIA Laboratory, by John King, Ron Geurts, Al Gilbertson and James Shigley, details how master stones are selected and used in the GIA diamond-grading process.

Making the grade

As the article explains, only diamonds whose colour lies at the upper limits of visual tolerance of a particular grade can serve as a master for that grade. Thus, a G master would be at the border of an F grade; all diamonds with slightly more colour would be graded as G, while those with slightly less colour would receive an F grade.

All master stones undergo the same grading procedure as commercial diamonds. Multiple graders independently assess them, and their consensus decision is supported by a colour measurement device.

While precision colour is the first criterion for a GIA master stone, there are other criteria as well. Masters must be well-cut round brilliants in a consistent size range. The common round brilliant shape provides the most consistent colour appearance, and 0.25 to 1 carat stones work well for grading the bulk of the stones seen in the marketplace. Graders have found that 1 carat masters can be used to accurately grade very large stones, even those 50 carats and above. Masters cannot have eye-visible inclusions, which distract the observer and often compromise apparent colour.

The standard for standards

GIA’s system for grading master stones preceded its commercial grading activities. The institute began to create such sets for American Gem Society retailers in 1941 using the GIA Colorimeter, a device with a standardized, specially filtered light source and a colour scale graduated from colourless down to the equivalent of the present-day P. This was the only diamond service offered by GIA for more than a decade.

Today, GIA uses working master sets of 10 stones to grade the most commonly submitted diamonds, which fall between D and N. Starting with O, the lab doubles up, with one stone per two-grade range, from O-P down to Y-Z. The GIA Laboratory also, however, uses a face-up Z master at the lowest end of that colour range to delineate the border between the D-to-Z scale and the start of the fancy-color scale.

Because dirt can accumulate on diamonds and affect their appearance, GIA boils each master set in sulfuric acid every two to four weeks. The authors reported that some master sets submitted to GIA for review had their colour altered by as many as four grades because of dirt that had accumulated on their bruted girdles. To avoid abrasions and chips that can also affect colour appearance, GIA lab graders use rubber-tipped tweezers to handle all master stones.

Fluorescence

The Valuing of diamonds, requires an assessment of each of the four Cs (cut, colour, clarity and carat weight). But a fifth factor-fluorescence-often plays a role in the pricing and marketability of diamonds.

Fluorescence is a trait that is greatly misunderstood. It’s often perceived by members of the trade and consumers as a negative trait, it is usually a positive one. Fluorescence almost always makes diamonds look better in overall colour appearance. Although this sounds like a good thing, some in the trade believe this means that they are paying for a higher grade than the true grade of the diamond. Sales have been lost, and unnecessary discounts given, on diamonds that possess only beautiful qualities.

Tracing the source

Fluorescence is the caused by trace impurities in the diamond. Approximately one- third of all gem-quality diamonds fluoresce, usually blue, But white, yellow, green, orange, and very occasionally red also may be witnessed. Pink diamonds may fluoresce a bright orange. Author of The Micro World of Diamonds, John Koivula states, In natural diamonds, the reaction on exposure to long-wave ultra-violet radiation is virtually always stronger than the corresponding short-wave reaction.

When a diamond is viewed in lighting that contains ultraviolet such as daylight the appearance is almost always improved by fluorescence. The excellent high-colour Russian diamonds which were highly publicized during the last two decades have a higher percentage of fluorescence in the medium-to-strong blue range than diamonds from other sources, which is one of the reasons they look so good.

Eric Bruton author of Diamonds discussed false white stones in his book: If a stone has blue fluorescence and a tinted yellow body colour, the colours being complementary may cancel each other so that in some conditions the stone appears white. The experienced grader will recognize such stones because their colour grade appears to vary in different light intensities. A white light free of ultra-violet will disclose the true body colour, and an ultraviolet lamp will disclose the fluorescence.

On GIA Gem Trade Laboratory grading reports, fluorescence is categorized by level of strength: None, Faint, Medium, Strong, or Very Strong. When fluorescence is faint, it’s listed without noting the colour of fluorescence while other levels of fluorescence are noted along with the colour. However, GIA lists fluorescence on grading reports as an identifying characteristic rather than a grading factor.

Fluorescence study

The 1997 winter issue of Gems & Gemology presented results of a visual observation experiment regarding fluorescence. Trained graders, trained professionals and untrained observers viewed diamonds in various lighting conditions and positions. They observed diamonds that fluoresced as well as those that were inert. Not surprisingly, most observers perceived the diamonds with strong blue fluorescence as having better color appearance.

The study, which also analyzed a large sampling of data on diamonds submitted to the lab, found that about 35% of all diamonds exhibit florescence. Of those that fluoresced, 62% were medium to very strong and of those 97% were blue.

Epilogue

Consider the absurdity of this statement: This diamond exhibits fluorescence. That means that in UV light such as sunlight, your diamond will look better. Therefore I have to charge you less. Actually, some in the trade believe a premium is justified on lower-colour diamonds improved by fluorescence. But if lower-colour diamonds deserve such a premium, why don’t white diamonds that look even whiter because of fluorescence deserve a discount?

In The Micro World of Diamonds, John Koivula writes, By far the most common ultraviolet fluorescence colour in diamonds is light blue, some-times referred to as a blue-white colour. Weak fluorescence reactions are relatively common, but strong blue fluorescence is much more unusual.