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The 4Cs of Diamond Quality

According to the GIA (the Gemological Institute of America), “Every diamond is a miracle of time, place and chance. Like snowflakes, no two are exactly alike. Until the middle of the twentieth century, there was no agreed-upon standard by which diamonds could be judged. GIA created the first, and now globally accepted, standard for describing diamonds: Color, Cut, Clarity and Carat Weight.”

Today, the 4Cs of Diamond Quality is the universal method for assessing the quality of any diamond, anywhere in the world. The creation of the Diamond 4Cs meant two very important things: diamond quality could be communicated in a universal language and diamond customers could now know exactly what they were about to purchase.


The color evaluation of diamonds is based on the absence of color. Diamonds are valued by how closely they approach colorlessness – the less the color, the higher the value. GIA’s D-to-Z color-grading scale measures the degree of colorlessness by comparing a stone under controlled lighting and precise viewing conditions to master stones of established color value.

GIA’s D-to-Z color-grading scale is the most widely accepted 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.

Many of these color distinctions are so subtle that they are invisible to the untrained eye, but these slight distinctions make a 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, including 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, to descriptive terms like “gem blue” or “blue white,” which are notorious for misinterpretation. The creators of the GIA Color Scale decided to start fresh, without any association with previous systems, thus the scale begins with the letter D.


Cut is a crucial factor to each diamond’s final value and beauty. We often think of a diamond’s cut as shape (round, oval, pear, heart), but a diamond’s cut grade depends on how well a diamond’s facets interacts with light. Fueling a diamond’s fire, sparkle and brilliance, cut is also the most complex and technically difficult to analyze of the 4Cs.

To determine the cut grade of the standard round brilliant diamond – the shape seen in the majority of diamond jewelry – GIA calculates the proportions of the facets that play a part in the diamond’s face-up appearance. These proportions allow GIA to evaluate how successfully a diamond interacts with light to create the desired visual effects such as:

  • Brightness: Internal and external light reflected from a diamond
  • Fire: Dispersion of light into the colors of the spectrum
  • Scintillation: Flashes of light, or sparkle, when a diamond is moved

GIA’s diamond cut grade also considers the craftmanship and design of the diamond, including its weight relative to its diameter, its girdle thickness, the symmetry of its facet arrangement and the quality of polish on those facets.

In early 2005, GIA unveiled a diamond cut grading system for standard round brilliant diamonds 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.

How Does Pavilion Depth Affect a Diamond’s Cut?

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 bottom of the stone. A well-cut diamond will direct more light through the crown, adding to the radiance of the diamond.


Diamonds are the result of carbon exposed to tremendous pressure and heat deep in the earth. This process results in a variety of internal characteristics called “inclusions” and external characteristics called “blemishes.”

Evaluating diamond clarity involves determining the number, size, relief, nature and position of these characteristics, as well as how these affect the overall appearance of the stone. While no diamond is perfect, the closer it comes, the higher its value.

F – No inclusions or blemishes are visible to a skilled grader.

IF – No inclusions and only blemishes are visible to a skilled grader.

VVS1-VVS2 – Inclusions are difficult for a skilled grader to see.

VS1-VS2 – Inclusions are clearly visible but can be characterized as minor.

SI1-SI2 – Inclusions are noticeable to a skilled grader.

I1-I3 – Inclusions are obvious and may affect transparency and brilliance.

*All diamonds are viewed through a 10x magnification lens by diamond graders.

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 “pique.” Today, even if you buy a diamond in another part of the world, the jeweler will likely use terms such as VVS1 or SI2, regardless of langue barriers.


Diamonds are weighed in metric carats: one carat is equal to 0.2 grams – roughly the same weight as a paperclip. Just as a dollar can be divided into 100 pennies, a carat is divided into 100 points. The higher the carat weight, the increase in the diamond’s price.

Two diamonds of equal weight can have very different values depending on the other members of the 4Cs. When it comes to carat weight, even a fraction of a carat can make a considerable difference in cost – precision is crucial.

How Did the Carat System Start?

The carat, the standard unit of weight for diamonds and other gemstones, takes its name from the carob seed. Since 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. Today, a carat weighs exactly the same in every corner of the world.