Beneath the Surface: Colorless Diamonds

Beneath the Surface: Colorless Diamonds

When it comes to the third “C” of “the 4 Cs”, color is often glossed over because it can be counterintuitive to understand that 98% of diamonds are color graded on their lack of color. Most diamonds on the market that you will see in jewelry stores are graded on a scale called the “D to Z scale”, which means they range from perfectly colorless at the top of the scale (D color) to hints of yellow, brown, or gray, at the other end of the scale (Z) color.

Diamond Types

Why are 98% of diamonds graded this way? The reason is that when most natural diamonds are formed over a hundred miles beneath the Earth’s surface, they incorporate the element nitrogen into the diamond crystal as they grow. In fact, diamonds are even characterized by “type” based on the way the nitrogen is arranged in the diamond crystal lattice (at the atomic level!) and even if there is nitrogen present in the crystal.

Certain diamond types have such low amounts of nitrogen, they are classified as a rare “Type IIa” which means they have no detectable amounts of nitrogen in their crystal lattice and save any other causes of color like plastic deformation of the crystal lattice, or external causes of color like irradiation, they are perfectly colorless, like a drop of water. These rare Type IIa diamonds are only about 2% of diamonds in jewelry.

Why this is important is that nitrogen causes the yellow color in diamonds. The way the nitrogen atom interacts in the diamond crystal lattice causes the diamond to absorb the blue parts of white light (remember – white light is made up of each of the colors of the visible spectrum, as we learned in school, ROYGBV). When the diamond absorbs blue light, it means our eye perceives the diamond as yellow. Even the smallest trace of nitrogen can cause a diamond to look yellow, so truly colorless diamonds are much rarer than their yellow counterparts.

Diamonds can often occur with hints of brown or gray. These diamonds are usually colored by other factors, that may or may not include the presence of nitrogen but are also a part of the natural diamond formation process. For example, we mentioned plastic deformation. This means the diamond crystal has been put under stress or strain while still in the Earth. The pressure of the earth is enough to very slightly cause the diamond crystal lattice to shift, just like if you were to squeeze modelling clay, except diamonds are much harder. What happens is the diamond crystal’s atomic structure is rearranged slightly which changes how light is absorbed and reflected by the diamond. This can cause brown diamonds, but also rare, and coveted pink and red diamonds.

In short, most diamonds are yellow or have tones of brown or gray because of how they are formed. Truly colorless diamonds are rarer than those that are not.

Why a scale from D to Z?

Before the D-Z scale was developed, diamonds were traded using terms such as “AA” and “AAA”. In order to avoid confusion, the industry adopted a scale that started with “D” to circumvent the other more confusing terms using the first three letters of the alphabet. D-to-Z diamonds are usually called “near colorless” diamonds. This is in contrast to another group of diamonds called “fancy color”, which are diamonds that are yellow, brown, or gray past the “Z” grade, or other colors such as red, orange, green, blue, purple, black, or white. As a note, near-colorless diamonds are also incorrectly referred to as “white” diamonds, which can be confusing as there are fancy white diamonds.

Beneath the Surface: Colorless Diamonds

When it comes to the third “C” of “the 4 Cs”, color is often glossed over because it can be counterintuitive to understand that 98% of diamonds are color graded on their lack of color. Most diamonds on the market that you will see in jewelry stores are graded on a scale called the “D to Z scale”, which means they range from perfectly colorless at the top of the scale (D color) to hints of yellow, brown, or gray, at the other end of the scale (Z) color.

Master diamonds must be consistent in size, proportions, have faceted girdles, and have no modifying hues, other than yellow. This ensures the master diamonds are consistent in appearance. Diamonds are graded for color in the face-down orientation in order to eliminate any reflections from facets. Diamond graders look through the body of the diamond and judge the saturation of color. Just like a glass of water with one drop of food coloring is less saturated than a glass of water with five drops of food coloring, this difference in saturation serves as a starting point for the evaluation of the diamond’s color grade. The sample diamond is then flipped to the face-up position where it is also evaluated against the master diamond face-up, to ensure the cut of the diamond, or any other potential impacts on the final appearance of the diamond (such as color zoning) are considered.

Diamonds are also graded in a color-neutral environment (usually a gray background), with a daylight equivalent lamp that is calibrated to a color temperature of 6,500 K. The trays used to hold the master diamonds and sample diamond are special material that do not fluoresce, so they won’t inadvertently impact the color grade of the diamond. Diamonds are examined at precise viewing angles and distances from the light source. Diamond graders are assessed for their proficiency and color acuity and are limited to the amount of time they color grade to prevent eye fatigue. At GSI, the color grading procedures are carefully controlled so every diamond is assessed consistently and accurately.

Colorimeters are devices that are used to measure diamond color and can also be a helpful tool in evaluating diamond color. However, there are important limitations, many related to the cause of color in diamonds and the diamond type. Colorimeters are best used for diamonds from the D to J range but tend to have issues with diamonds that are more saturated, and diamonds that exhibit strong fluorescence, which can also be related to nitrogen in diamond. Colorimeters tend to have a higher degree of error for diamonds with modifying hues that modify the yellow color, such as “greenish yellow”. This is why GSI uses a mix of diamond assessment technology and the acuity of the human eye and expert graders to assess the color of your diamond.

To ensure the color grading of your diamond, request that your diamond is accompanied by a GSI report. Each diamond is independently verified as natural and graded to the highest standards and level of integrity by GSI’s leading team of expert diamond graders.