Buying a diamond, whether online or through a brick and mortar store can be hard and trying experience. Similar to other significant purchases, which one may make, there are so much technical details, so many differing opinions and so much to learn.

Often first time buyers get there education about diamond jewelry from the seller at the time of purchase. One might argue, to get the best value or your money’s worth, it is very importance to learn about diamond jewelry separate and apart from the process of acquisition.

Because diamond are so valuable, the GIA adopted a universal grading system for comparing their quality. In the 1940s and ’50s, GIA developed the 4Cs (carat, color, clarity, cut) and the GIA International Diamond Grading System™ to objectively compare and evaluate loose diamonds, plus the diamonds set in jewelry like diamond.

diamond 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 diamond 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 diamond 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 oh eight carats,” or “one oh eight.”)

How did the carat system start?

The carat, the standard unit of weight for diamond 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.

Diamond Color

Diamond color is all about what you can’t see. Diamonds are valued by how closely they approach colorlessness – the less color, the higher their value. (The exception to this is fancy-color “diamond», such as pinks and blues, which lie outside this color range.)

Most diamond found in jewelry stores run from colorless to near-colorless, with slight hints of yellow or brown.

GIA’s color-grading scale for diamond is the industry standard. The scale begins with the letter D, representing colorless, and continues with increasing presence of color to the letter Z, or near-colorless. Each letter grade has a clearly defined range of color appearance. Diamonds are color-graded by comparing them to stones of known color under controlled lighting and precise viewing conditions.

Many of these color distinctions are so subtle as to be invisible to the untrained eye. But these slight differences make a very big difference in diamond quality and price.

Why does the GIA color grading system start at D?

Before GIA developed the D-Z Color Grading Scale, a variety of other systems were loosely applied. These included letters of the alphabet (A, B and C, with multiple A’s for the best stones), Arabic (0, 1, 2, 3) and Roman (I, II, III) numerals, and descriptions such as “gem blue” or “blue white.” The result of all these grading systems was inconsistency and inaccuracy. Because the creators of the GIA Color Scale wanted to start fresh, without any association with earlier systems, they chose to start with the letter D—a letter grade normally not associated with top quality. 

Because diamonds are formed deep within the earth, under extreme heat and pressure, they often contain unique birthmarks, either internal (inclusions) or external (blemishes).

Diamond Clarity

Diamond clarity refers to the absence of these inclusions and blemishes. Diamonds without these birthmarks are rare, and rarity affects a diamond’s value. Using the GIA International Diamond Grading System™, diamond are assigned a clarity grade that ranges from flawless (FL) to diamond with obvious inclusions (I3).

Every diamond is unique. None is absolutely perfect under 10× magnification, though some come close. Known as Flawless diamond, these are exceptionally rare. Most jewelers have never even seen one.

The GIA Clarity Scale contains 11 grades, with most diamond falling into the VS (very slightly included) or SI (slightly included) categories. In determining a clarity grade, the GIA system considers the size, nature, position, color or relief, and quantity of clarity characteristics visible under 10× magnification.

Flawless (FL) - No inclusions or blemishes are visible to a skilled grader using 10× magnification
Internally Flawless (IF) - No inclusions and only blemishes are visible to a skilled grader using 10× magnification
Very, Very Slightly Included (VVS1 and VVS2) - Inclusions are difficult for a skilled grader to see under 10× magnification
Very Slightly Included (VS1 and VS2) - Inclusions are clearly visible under 10× magnification but can be characterized as minor
Slightly Included (SI1 and SI2) - Inclusions are noticeable to a skilled grader using 10× magnification
Included (I1, I2, and I3) - Inclusions are obvious under 10× magnification and may affect transparency and brilliance

How did the GIA Clarity Scale come about?

Like the color scale, GIA’s clarity grading system developed because jewelers were using terms that were easily misinterpreted, such as "loupe clean," or "piqué." Today, even if you buy a diamond in another part of the world, the jeweler will likely use terms such as VVS1 or SI2, even if her language is French or Japanese instead of English.

Diamond Cut

Diamond Cut is the factor that fuels a diamond’s fire, sparkle and brilliance.

The traditional 58 facets in a round brilliant diamond, each precisely cut and defined, are as small as two millimeters in diameter. But without this precision, a diamond wouldn’t be nearly as beautiful. The allure of a particular diamond depends more on cut than anything else.

Though extremely difficult to analyze or quantify, the cut of any diamond has three attributes: brilliance (the total light reflected from a diamond), fire (the dispersion of light into the colors of the spectrum), and scintillation (the flashes of light, or sparkle, when a diamond is moved).

An understanding of diamond cut begins with the shape of a diamond. The standard round brilliant is the shape used in most diamond jewelry. All others are known as fancy shapes. Traditional fancy shapes include the marquise, pear, oval and emerald cuts. Hearts, cushions, triangles and a variety of others are also gaining popularity in diamond jewelry.

As a value factor, though, cut refers to a diamond’s proportions, symmetry and polish. For example, look at a side view of the standard round brilliant. The major components, from top to bottom, are the crown, girdle and pavilion. A round brilliant cut diamond has 57 or 58 facets, the 58th being a tiny flat facet at the bottom of the pavilion that’s known as the culet. The large, flat facet on the top is the table. The proportions of a diamond refer to the relationships between table size, crown angle and pavilion depth. A wide range of proportion combinations are possible, and these ultimately affect the stone’s interaction with light.

In early 2005, GIA unveiled a diamond cut grading system for standard round brilliants in the D-to-Z color range. This system, the product of more than 15 years of intensive research and testing, assigns an overall diamond cut grade ranging from Excellent to Poor.

The distance from the bottom of the girdle to the culet is the pavilion depth. A pavilion depth that’s too shallow or too deep will allow light to escape through the sides or the bottom of the stone. A well-cut diamond will direct more light through the crown.

Diamond Hardness

The diamond is the best known and the most heavily marketed gemstone. Like graphite, Lonsdaleite ("hexagonal diamond"), and the fullerenes, a diamond is an allotrope of carbon and, no matter what its size, each diamond can be considered to be a single molecule of carbon.

Diamond is the hardest natural substance (while carbon is one of the softest). The word diamond derives from Greek adamas or "hardest steel". Pliny the Elder (A.D. 23 to 79) wrote that "the best way to test adamas is upon the anvil; strike even upon the point of the adamas with a hammer as hard as you can, it defies all blows and instead of the stone yielding, the hammer flies into pieces and even the anvil splits in half." This experiment, however, is not recommended: though hard, a diamond is brittle, and can crack under the shock of a sudden, sharp blow.

Diamond has an isometric crystallography. The crystal structure of a diamond, called a face centered cubic lattice, derives from the way each carbon atom joins four other carbon atoms in regular tetrahedrons (triangular prisms). It is possible to cleave, or split, a diamond, along its crystal face (grain), such that each side of the cleavage remains smooth.

The adamantine luster (the brilliance and "fire") of a diamond is due to its high dispersion and its high refractive index (a measure of how far it can bend light). Commercial gem diamonds are colorless or pale, steely blue. Strongly colored gem diamonds, called "fancies," are extremely rare and valuable (especially red, pink, and blue). Diamonds can also be gray, yellow, brown, green, orange, lavender, and even black. Diamond crystals frequently contain inclusions of other minerals. Many diamonds fluoresce blue to violet and the effect is sometimes strong enough to be seen in daylight. Some blue-fluorescing diamonds phosphoresce yellow (afterglow reaction).

Diamond has a high specific gravity. A diamond does not conduct electricity well (it is a semiconductor), but conducts heat extremely well. At a high enough temperature in the presence of oxygen, diamond can burn.