Diamond Buying Guide

                                                                                        Ever wonder…

                         …why some diamonds with high grades may not be good stones?
…why even a GIA certificate will not tell you all you need to know about a diamond?
…why diamonds graded by certain laboratories other than GIA appear to be cheaper?
This guide explains it all.


My purpose in writing this is to introduce you to diamonds and to take some of the mystery and confusion out of purchasing a diamond by making you a more informed consumer.  I will discuss the different qualities of diamonds using the grading system from the Gemological Institute of America.  When doing so, I will not only discuss the advantages, but also the disadvantages and limitations of this system.

If you have ever purchased a diamond, your jeweler might have mentioned what we call the four C’s of a diamond: cut, color, clarity, and carat weight.  In addition to the aforementioned, two more C’s should be considered.   “Cost,” of course, is of vital importance to every consumer.  The most important “C” of all, however, is “confidence” in the jeweler from whom you are buying.  Only an experienced and educated jeweler with the proper gemological credentials has the ability to properly guide you with your diamond purchase.

The majority of the world’s diamonds come from the mines of Australia, Russia, Canada, and various African countries.   Diamonds are formed approximately 100 miles beneath the surface of the earth, and it takes extensive mining to recover them.  Almost all of the rough diamonds mined are regulated by a company called De Beers Consolidated.  De Beers has a virtual monopoly on the world’s rough diamonds, controlling approximately 85% of the world’s distribution.   However, this industrial monopoly has proven to be beneficial, since controlling the supply of diamonds to world markets has caused the value of diamonds to steadily increase year after year.

Approximately ten times a year, De Beers Consolidated, based in London, convenes with a small number of diamond cutters from the major cutting centers of the world in Gaborone, Botswana. These meetings are referred to as “sights.”  It is during these “sights” that each cutter receives his allotment of rough diamonds.   Although De Beers may accommodate cutters who have certain needs, the cutters must unconditionally accept the rough diamond allotment that is offered to them.  Some of these rough diamonds are then sold to other diamond cutters who in turn cut and polish them.  (The majority of diamond cutting is now done in Mumbai, India, with Israel, New York, and Antwerp, Belgium also supplying stones.)  Cutters then sell their diamonds to wholesalers, such as M. Martin and Co., who are able to buy large quantities.  The wholesalers then sell them to retailers, who ultimately sell them to the consumer.                 

The irregularly shaped rough diamond that is mined from the earth bears no resemblance to the finished product that the consumer eventually sees.  To create a beautiful stone, the rough diamond must be cut and polished.  Originally, diamonds were worn virtually unfaceted.  Over the centuries, however, cutters experimented with different faceting patterns and proportions to try to create a diamond that radiated maximum beauty.  Around 1919, a man named Tolkowsky mathematically developed the proportions of the modern cut diamond.  First, he calculated the precise angles at which light is refracted (or bent) and reflected when traveling inside the diamond.  Second, he considered a property of gemstones called the “critical angle of light,” the maximum angle at which light can strike a facet of a diamond and still be totally reflected within the stone.  Precise angles of the facets and exact proportioning are essential if the diamond is to attain maximum beauty. 

Theoretical Proportions of a Modern Cut Diamond

A diamond that is beautiful to our eyes will have a balance of two components of light, namely brilliance and dispersion.  The brilliance of the diamond comes from light reflecting from the bottom, or pavilion, facets of the diamond.  The dispersion of the diamond comes from the upper, or crown, facets of the diamond as these facets act like a prism breaking the light into the colors of the rainbow.  Thus, when I say that a diamond is beautiful, I am saying that it has maximum brilliance as it gathers light and returns it to our eyes, and maximum dispersion as it shows a plethora of rainbow colors.  

There are a number of major shapes of diamonds that can be found on the market today.  These shapes can be divided into two categories: the round (brilliant) cut, and the fancy cuts, which include the marquise, pear, oval, heart, emerald, princess, radiant and cushion. Since each cut has its own special beauty and qualities, the shape that a person chooses depends only on personal preference.

Each diamond is cut with a specified number of facets.   The round diamond, which is also called the brilliant cut, has a total of 58 facets.  Thirty-two of these facets are above the girdle, and twenty-four facets are below it.  In addition, the largest facet, which is located on the top of the stone, is called the table.  The point at the bottom of the stone where the facets meet is called the culet.

  Why is it so critical that a diamond be properly proportioned?  As demonstrated in the illustration of a properly cut diamond, light entering through the table and crown facets of the diamond is reflected across the inside of the stone and back out the top of the stone. 
  If the stone is cut too deep, the light entering the diamond hits the pavilion facets at the wrong angle, and much of the light will leak out the sides of the stone.

Pictures courtesy of GIA Gem Instruments Corp.

If the stone is cut too shallow, much of the light may leak out the bottom of the stone.  The pictures of the deep stone and the shallow stone have been shown exaggerated for illustrative purposes only. 
  Diamond material varies from stone to stone affecting the transparency of the stone.  Poor density or grainy material will disperse light inside the diamond resulting in a weak looking stone.   GIA does not yet have a way to measure this characteristic, and thus there is nothing on the certificate that may indicate if a diamond is cut from sub-par material.

Although there are small variations allowed in the ideal cut stone, once a stone is cut outside of these limits, the brilliance of the diamond will be noticeably diminished.  (We are only discussing the round diamond here.  Although the same principles apply to the fancy shapes, their proportions are different and the subject is much too complex to be analyzed here.)  If you want maximum beauty and brilliance from the diamond you are about to purchase, you should select a stone that is extremely well cut.  A stone that is cut either too deep or too shallow cannot possibly give you maximum brilliance.

Next I will discuss the color and clarity of the diamond, using the grading scales of the Gemological Institute of America to evaluate each of these characteristics.  These scales for color and clarity were created in the early 1950’s and were intended primarily for use by jewelers.  It was not until the late 1970’s that they were promoted to the general public as people became interested in knowing more about how diamonds were judged and graded.

GIA’s color scale begins with the letter D and continues successively downward to the letter Z.  When we talk about the color grade of a diamond, we are referring to the body color of that diamond as seen from the side of the stone under certain lighting conditions.  As we move along the scale, the body color of a diamond may range from one having a very fine white color, to one having a very slight tint, to one having a very noticeable tint.  Generally, the tint will be of a yellowish color, although some stones may have a brownish, grayish, or green tint (green is the hardest color for even an expert to detect and is the color that affects the value of the stone most negatively.)   To determine the color grade of a diamond, the jeweler uses a master set of pre-graded diamonds.  The jeweler matches the body color of the stone he is grading against the stones in the master set.

Color Scale

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Clarity Scale

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Clarity grading is accomplished by inspecting the diamond under ten-power magnification, using either a microscope or a jeweler’s loupe.  The clarity grading scale begins with a rating of flawless.  A flawless diamond has no inclusions under ten-power magnification when viewed by a trained eye.  Other ratings on the scale include VVS-1 and VVS-2 (very, very, slightly included), VS-1 and VS-2 (very slightly included), SI-1 and SI-2 (slightly included), and I-1, I-2, and I-3 (imperfect). There is also an SI-3 grade between SI-2 and I-1 that is used by some laboratories.   When judging clarity, the jeweler considers the size, nature, number, position, and relief of the inclusions and then makes an educated decision as to where this diamond would fall on the scale.

Carat weight is the last major criterion that jewelers take into consideration when evaluating a diamond.  Today, digital scales make weighing diamonds both fast and accurate.  The weight of a diamond is expressed in carats and points.  There are one-hundred points to the carat.  A diamond that is 48 points, for example, is 48/100 of a carat — or slightly under one-half carat.  As diamonds increase in size, the price per carat goes up very rapidly.  A one carat diamond of a particular quality may be twice the weight of a half-carat diamond of the same quality, but it may cost three times as much.  The explanation for this is simple.  As stones increase in size, they become rarer and their price per carat increases.

These are the four basic characteristics of a diamond that will be discussed in this booklet.  In reality, however, there are many additional characteristics that the gemologist takes into consideration when evaluating a diamond.  These may include the quality of the polishing, the symmetry of the diamond, variances in the quality of the diamond material (which resulted from changing conditions of temperature and pressure in nature as the rough diamond crystal was being formed), and numerous other gemological factors.  As we learn how to use the GIA grading system, we will concern ourselves only with the four basic factors, but keep in mind that there are many intangible characteristics that cannot be measured and do not appear on the certificate.  One of the most important of these non-measurable characteristics is the transparency of the diamond material itself.  This refers to whether the material is “grainy” in nature or whether it is of the more desired “crystal” quality.

It is important that the consumer understand how to use the grading system in order to obtain the desired balance of characteristics in the diamond he wishes to purchase.  As we have already discussed, the beauty and brilliance of the diamond come from the cutting, the proportioning, and the quality of the diamond material.   The color and clarity scales refer only to the rarity of the material from which the stone is cut.  Although a diamond may have a high color and clarity grade on the GIA scale, unless it has an excellent cut, it will not be a beautiful stone.  Therefore, if you want your stone to have maximum beauty and brilliance, we suggest that you buy a finely cut and polished diamond.  You should then vary the color grade, clarity grade, and weight of the diamond to stay within your budget.

Some important observations should be made with respect to the different grading systems.  On the color grading scale, differences in adjoining color grades are extremely slight.  The average consumer will have difficulty observing differences in the color grades of diamonds unless they are three or four grades apart.  As a matter of fact, if a gemologist is trying to grade the color of a mounted diamond, he may put the diamond into a three-grade range instead of attempting to pinpoint the exact grade of the diamond.  It is necessary to remember that a diamond is color graded from its side, and that when mounted the diamond will only be viewed in the face-up position.  Many times diamonds that have a very slight body tint and are very well cut will not show any color when viewed from the top of the stone.  With regard to the clarity grading system, although diamonds may be classified within the same clarity grade, they can still be very different.  No two diamonds can possibly have identical inclusions, or identifying characteristics.  Each clarity grade is a range within itself; it is not an absolute point on the scale.  For example, there may be two diamonds which have each been classified as SI-1.  However, if one stone borders on being a VS-2, and the other stone borders on being an SI-2, then even though the stones are both classified as SI-1, they will look very different inside.

Even an experienced and trained gemologist may encounter limitations when using the grading system.  It is not uncommon for two gemologists to examine the same stone and grade it slightly differently (though the grading should be close).  Borderline situations of color and clarity may prove to be particularly troublesome, and a judgment call must be made.  The most difficult of all these judgment calls, however, is the determination of the quality of the cutting and the proportioning of the diamond.

Ninety-five percent of all diamonds cut today are not cut to achieve optimal brillance.   The rough diamond that is mined from the earth is generally a very irregularly shaped crystal that must be cut and polished.  We stated earlier that the ideally cut diamond must be cut with very precise angles to emit maximum beauty.  The rough diamond does not have these proper angles. Aside from the fact that not every cutter has the experience or ability to cut a quality diamond, with modern technology, a highly skilled cutter can cut a stone to achieve its optimal beauty, assuming the rough diamond accommodates this procedure. However, when a cutter cuts a diamond to ideal proportions, he will have a greater weight loss from the rough diamond than if he cuts the diamond too deep, too shallow, or with shifted crown and pavilion angles.  In other words, the cutter can cut the rough diamond to achieve either maximum weight or maximum beauty, but not both.  Diamonds that are cut in “off-make” proportions have a greater weight yield from the original rough diamond.  By cutting a diamond to obtain the maximum weight yield, the cutter can cause a consumer to believe that he is obtaining a better value for his money.  As an example, from a specific rough diamond a cutter might have the option of cutting a perfectly proportioned .85 carat diamond or leaving extra weight on the diamond by cutting a high crown, thick girdle, and/or deep pavilion, thereby creating an “off-make” diamond weighing one carat.  By cutting the diamond to the weight of one carat, the cutter is unable to maintain ideal proportions for the diamond, and the diamond loses much of its brilliance and beauty.  This practice proves to be advantageous for the cutter, however, because the increased weight on the stone enables him to receive a higher price in the marketplace.  Unfortunately, it is the consumer who ultimately pays for this excess weight.

Many jewelers, especially in the United States, promote only the color and clarity grades of the diamonds that they sell, while ignoring the quality of the cut.  By purchasing cheaper, “off-make” stones, a jeweler can give the customer the impression that his stone is a better deal than the stones of the same size and grade that may be offered to the customer by other jewelers.  This is a very common practice, and as long as it continues, there is little incentive for the diamond cutter to cut ideally proportioned diamonds.  Many consumers are being taught the improper practice of shopping for diamonds by color and clarity grade alone.  Often, their shopping consists of going from jeweler to jeweler, writing down the color grades, clarity grades, and prices of the diamonds that they are shown, and then incorrectly assuming that the highest color and clarity grade at the lowest price is the best deal.  Frequently, the “best deal” is just the diamond that has the poorest cut. In the case of the round diamond, which now has a cut grade, consumers have added a cut grade to their criteria, but may be unaware of the fact that diamonds that rank low in even the highest cut class may not have the optimum beauty they desire for their diamond. For all the other shapes, although cutting parameters have been established by various organizations in the industry (and not all agree), it is unlikely GIA will be able to establish a workable system for grading these diamonds due to the many intertwined variables involved in determining cut quality.

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