The factors that determine the value of a diamond: color, clarity, cut, and carat weight.

Color:
The most sought-after diamonds are completely colorless in natural light, with absolutely no undertones of any color. Oddly enough, this is often tested by exposing the diamond to ultraviolet light, where it should fluoresce blue. The most colorless diamonds are called D grade, with the range of increased color going on through the alphabet to Z.

Clarity:
Diamonds are rated for clarity by their appearance under a 10x (10 times magnification) jeweler's loupe. This finds flaws that cannot be seen by the naked eye. A diamond with no inclusions is graded FL for flawless; most of those available in jewelry stores are between SI2 (slightly included) to I2 (included).

Cut:
Cutting a gemstone makes an irregular pebble into a brilliant finished stone. The quality and symmetry of the cut can change a stone's value by up to 50 percent. A cut can mask flaws in the stone or make them more obvious; it can make light appear to burst out of the stone or make it look flat and dull. Certain cuts, such as the brilliant cut with at least 58 facets, will make a cut stone more valuable than something like a seventeen-facet single cut.

Carat weight:
Though people say things like "Look at the size of that rock!" about some jewelry, the weight of the stone is the least important factor in its value. A larger diamond will be worth more than a smaller one of the same quality, but a small, flawless, colorless diamond will be worth more than a large one with inclusions and a slight color. And of course, a "one carat ring" with a cluster of small diamonds will cost much less than a "one carat ring" with only one stone in it -- a lot of jewelry stores make pieces sound more impressive by giving the combined carat weight of all the stones in them.

Shopping for Diamonds

There are, of course, the four C’s, the basics of understanding what the jeweler is telling you about the diamond.

Cut:

An absolutely critical feature. First, I'll describe some types of shapes to choose from:
  • Round brilliant (most common)
  • Marquis (Oval with points at the top and bottom)
  • Oval
  • Princess (square)
  • Pear
  • Heart
  • Trillion (triangular)
  • Emerald (rectangular)
  • Cabochon (green diamonds usually appear as cabochon's but otherwise this is rare)
All of these shapes have several different cuts, but most new diamonds are given a brilliant cut. With antique gems, you might hear about other cuts which usually have fewer facets, like old mine or single cut.

Next, the parts of a faceted gemstone.
  • The table is the flat surface at the very top of the diamond. Like every other part of the diamond, there are guidelines in terms of ratios about exactly how large this table should be. It is also important that the table be symmetrical.
  • The crown is the mass of facets between the table and the girdle. Different cuts will have different quantities of facets here, and the different facets have different names.
  • The girdle is the skinny band around the widest part of the diamond. Usually, the girdle is not faceted, but it can be in very high quality stones. When the girdle is faceted, its facets are not counted in the stone's total facet count.
  • The pavilion stretches from the girdle all the way to the very bottom point, called the culet.
  • The culet is usually faceted, but when it is not, the diamond will be marked as having one fewer facets and having a culet of “none” (other marks include small, medium, and large, medium being the most desirable). It is important in judging cut that the culet be in the center of the stone when looking downward through the table.
There are many extremely dry statistics involved in describing the round brilliant and still other types of cuts. I provide here a sampling of the guidelines GIA set forth for thepurposes of grading the cut of a standard round brilliant cut.
  • There are 8 star, 8 bezel, and 16 upper girdle facets on the crown, and the uniformity of these facets is graded.
  • The pavilion should contain 16 lower girdle and 8 pavilion facets.
  • The table diameter should be 52.4-57.5% of the average diameter of the girdle (GIA also grades the roundness of the girdle).
  • The height of the girdle should be between .7-.9% of the diamond’s total height.
  • Amongst the other things that are measured are pavilion depth, pavilion angle, and crown angle.
All those statistics fall into categories such as symmetry, proportion, and make. How closely the diamond’s cut follows the GIA guidelines greatly affects the stone’s value.

What happens when the diamond doesn’t quite follow those very specific guidelines? Horrific stuff, like the diamond won’t sparkle and light escapes out the sides of the diamond. A well cut diamond takes light from all around and shoots it straight up out of the crown and table, creating all sorts of wondrous things such as brilliance (total light reflected), dispersion (the tendency of the diamond to create rainbows), and scintillation (how much it sparkles when moved).

The cut of a diamond, being the most important and least cut-and-dried of diamond attributes, doesn’t have the same pretty rating systems that color and clarity get to have. For example, on a diamond certificate, the girdle is rated from “extremely thin” to “extremely thick,” the culet from “none” to “large,” and symmetry and proportion in terms of some mind-boggling statistics. Pear, marquis, and oval shaped diamonds are graded also on the presence of the undesirable bowtie effect. These shapes have a tendency to show a unattractive dark spot in the shape of a bowtie across the center of the diamond; this reduces the stone's value.

Color:

Diamonds are rated D-Z by the GIA (Gemological Institute of America) or 0-10 by the AGS (American Gem Society) as follows:

0  0.5  1  1.5  2  2.5  3  3.5  4  4.5  5  5.5  6  6.5  7  7.5  8  8.5  9  9.5  10

D E F G H I J K L M N O P Q R S T U V W X Y Z

Colorless Near Colorless Light Yellow Yellow


It’s important to note the difference between the yellow in the scale and a fancy yellow diamond. The color in both actually occurs the same way (nitrogen), only a fancy “canary” is so yellow it is off the scale. In other words, a Z diamond will be quite yellow, but is not categorized by the GIA as a fancy.

The biggest price jumps here are near the top of the scale, with a rather significant jump between F and G, since F is categorized by the GIA as “Colorless” and the luxury of being able to officially say you own/wear a colorless diamond commands a price. However, it is nigh impossible to see the difference in color between an F and a G stone without removing the stones from their settings and holding it up to reference stones. In my experience, most people begin to notice color around H and I, with near 100% recognition at color J. In other words, unless the recipient of the stone really genuinely cares which letter comes on the piece of paper which certifies the diamond rating, it isn’t worth the money chasing a D stone, or perhaps even an E. A good target for the ordinary consumer would be F-H.

Fluorescence occurs in about 35% of gem-quality diamonds, and is most frequently blue. Avoid any other color of fluorescence (and they do occur: orange, purple, green…). In very white stones, fluorescence can actually appear milky or cloudy and detract from the beauty of the stone; meanwhile, fluorescence can make a more yellow diamond appear whiter. The key is to test the stone under every type of light possible and determine for yourself whether the presence of fluorescence, if any, bothers or delights you.

The type of metal used for the setting of the diamond is crucial in that differently colored metals will treat the diamond differently. If you bought a very white stone and wished to showcase that color, platinum is an excellent choice, or white gold. I tend not to recommend white gold since it contains a good deal of nickel, and many people are allergic to it. Yellow gold is kinder to a stone’s color and gives it the illusion of being whiter. Moral of the story is this: what the GIA decides the color is when they hold it up to their lights and white paper and reference stones isn’t, in stark, somebody-will-be-wearing-this-on-their-body reality, half so important as the way it looks as a piece of jewelry. If the stone looks fabulous in yellow gold and it happens to be cheaper, more power to you. Just make sure you know what you are paying for.

In addition to white, diamonds occur in every color of the rainbow, naturally and artificially. Natural yellow diamonds usually contain nitrogen; blue diamonds, boron. When the diamond is affected by naturally occurring radiation, we get the extremely rare natural green diamond.

One question to ask the dealer is whether the color in the stone (or lack thereof) occurred naturally or artificially. There are many techniques used to whiten or color diamond; here I describe only a couple of them, and many more are found under the node Gem Enhancement:
  • Irradiation – The use of radiation to create various types of fancy color diamonds.
  • High Pressure/High Temperature (HPHT) – Use of (guess what?) high pressure and high temperature in a process developed by General Electric. Diamonds treated with HPHT are detectable, but at high cost.
  • Some irreputable jewelers will paint the culet of the stone blue to make a yellow stone appear whiter, and then set the stone in such a way that you can't see the bottom of the stone. Yet another reason to shop for loose diamonds, rather than pre-set ones.

Clarity:

Rated FL-I3 by the GIA as follows. IMPORTANT: All ratings are determined at 10x magnification; the GIA does not permit any further magnification for the purpose of rating. Reason? You could take the most perfect diamond in the world, and if you magnified it enough, you would find blemishes and inclusions. Tiny crystals, bits of black carbon, miniscule feathers, etc. When the GIA says “free of inclusions,” they mean “free of inclusions at 10x magnification.”
FL - Flawless
Free of all blemishes and inclusions
IF - Internally Flawless
No inclusions visible, only minor blemishes.
VVS1 - Very Very Slightly Included 1
Minute inclusions extremely difficult to locate.
VVS2 - Very Very Slightly Included 2
Minute inclusions extremely difficult to locate.
VS1 - Very Slightly Included 1
Minor inclusions difficult to locate.
VS2 - Very Slightly Included 2
Minor inclusions somewhat easy to locate.
SI1 - Slightly Included 1
Noticeable inclusions easy to locate.
SI2 - Slightly Included 2
Noticeable inclusions very easy to locate.
I1 - Imperfect
Obvious inclusions usually easy to locate with the unaided eye.
I2 - Imperfect
Obvious inclusions easy to locate with the unaided eye.
I3 - Imperfect
Obvious inclusions very easy to locate with the unaided eye and which may threaten stone's durability.

Note: Neither the GIA nor the AGS acknowledges the so-called SI3 clarity grade, which was designed to further differentiate a clarity area at which many people buy their diamonds. It is simply an unofficial term meaning “low SI2” or “high I1.”

Blemishes are less serious, as they are usually caused by human error or mishandling.
  • Abrasions on a diamond’s surface are caused by wear or contact with other diamonds.
  • One interesting blemish is a natural. A stone which has a natural sports part of the diamond’s original crystalline surface, usually around the girdle area. Often, a gemcutter will leave a natural if s/he is trying to minimize some other inclusion or move that inclusion away from the center of the stone, where it is most noticeable. As there is usually a reason for leaving a natural (improving the stone’s value by removing/reducing another inclusion), and since the girdle of the stone is generally not visible when the stone is set into jewelry, a natural is not considered a serious flaw, and can actually add to the stone’s “character” or uniqueness.
  • A stone might also have extra facets which were cut to remove some inclusion from the stone. These are quite different from “added facets” which are designed into the cut to improve a diamond's brilliance or scintillation.
  • Other blemishes which are minor, and sometimes can even be removed, are polish lines and marks, which occur during polishing. The marks may sometimes appear like clouding on the surface of the diamond.
  • The girdle might appear pitted or grainy as a result of poor workmanship.
Inclusions are irregularities within the stone itself, and can actually render the stone less durable if they are in the wrong place.
  • Feathers, for example, are tiny fractures in diamond which look, surprisingly enough, like feathers. A canny cutter will make sure these feathers, if they must be there at all, are completely inside the stone. If the feather touches the outside of the diamond, the diamond’s durability is thrown into question.
  • Laser drill holes are found when a laser was used to remove a more unsightly inclusion. On the surface, there will be a tiny pit, and the tube will look like a needle, either under magnification or to the unaided eye. GIA will grade stones with a laser drill hole in them, but will not grade those stones where the laser hole has been filled with some other material. Much like the color-enhancing procedures described above, this practice of filling laser holes is frowned upon.
  • Cavities and chips are openings in the stone’s surface and, depending on the severity and location of the cavity or chip, can be very detrimental to the stone’s value.
  • Included Crystals: there could be tiny bits of other mineral crystals in the diamond, which are sometimes even precious or semi-precious minerals.

Carat Weight:

1 carat = 200 milligrams. 100 points = 1 carat. Widely regarded as the least important of a diamond’s features, the carat weight is simply that - the stone’s weight. This measurement can even be misleading – imagine a diamond where the pavilion ran way too deep. There’s a lot of diamond down there which is actually hindering the stone’s ability to reflect light properly, yet it weighs more and sounds more impressive than a well-cut stone which is lighter. Conversely, some stones are given a “spread” cut to look larger than they should. Sounds fantastic, but they often look lifeless and dull.

Much like the color, there tend to be large price breaks around the various categories jewelers tend to use to categorize their diamonds, especially at the half- and whole-carat measurements (1/2 carat, 1 carat, 1 1/2 carat, etc.). Moreover, there’s a margin of error in what the jeweler gets to call a half-carat stone. I’ve forgotten all that by now, but my memory hints at 46-55 points counting as a half carat. I found a 45-point stone for a customer once that looked nearly identical to the half-carat ring he’d been looking at, but since the store had to label it a “3/8 carat ring,” it was $200 cheaper. Categories are completely irrelevant, especially once you get out of the store. It matters how beautiful the ring is, and more power to you if you can trade 5 measly points for $200.




Mandi’s opinion section: While you do need to verify all the technical stuff and make sure you’re not being lied to, the most important thing is how beautiful it is to your eye and in the manner it will be worn. Did it grab your attention in the case amongst 30 other diamonds? Does it “look great” outside of the case? Outside of the store? Did you pick an appropriate setting for the diamond, or does it come with an appropriate/flattering setting? Is it “just really cool?” Then, if it’s a solid stone and priced fairly, you’ve got your diamond.




I had held jobs in jewelry stores for 18 months and the vast majority of this information stems from the training programs at these companies. I had some remaining pamphlets and notes from the first of my jobs, but they didn't have any references on them except "Sears." I assume most of their information comes from the GIA, however, since Sears uses the GIA to certify all of their engagement diamonds (yes, Sears sells fine jewelry!).

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