Diamonds naturally occur in every imaginable color – white, pink, yellow, green, blue, brown and black, to name a few – with an infinite number of hues, tonality and saturation levels. Basically, humans perceive the color of an object as the color of the light leaving its surface. For example, white (colorless) diamonds do not absorb any specific colors from a light spectrum, while blue diamonds absorb all colors except blue. In a diamond, natural and synthetic alike, the color is determined by imperfections at the atomic level originating during diamond crystallization, such as dissolved non-carbon atoms and growth defects. These imperfections distort the diamond lattice and in many cases create so-called "color centers" which absorb specific wavelengths of the visible light spectrum–giving the diamond a specific color. A variety of different color centers, their interactions and concentrations, coupled with variable levels of absorption gives us an abundant number of resulting colors.

Based upon two main impurities, nitrogen (N) and boron (B), diamonds are classified into four types:

Type I: Nitrogen is present in the diamond lattice.

  • Type Ia: Nitrogen atoms are clustered together. Resulting color centers absorb blue light to a certain extent. These diamonds may come in a range of shades from pure white to pale yellow (cape) color. 97% of natural diamonds are Type Ia. No Type Ia synthetic diamonds exist.
    • Type Ib: Isolated nitrogen atoms replace single carbon atoms in a diamond lattice. Resulting color centers absorb both green and blue light. These diamonds usually come in a range of yellow and orange colors in a variety of tone and saturation levels, depending on the actual concentration of nitrogen atoms. All yellow synthetic diamonds and less than 1% of natural diamonds belong to Type Ib.

Type II: Nitrogen is not present in the diamond lattice.

  • Type IIa: These diamonds contain no or trace amounts of nitrogen as well as no other impurities. In most cases, they are colorless. Certain lattice defects may lead to a creation of color centers that may result in pink, red, or more often, brown color. All white synthetic diamonds and 1-2% of all natural diamonds belong to Type IIa.
    • Type IIb: These diamonds contain no nitrogen (or trace amounts) but do contain boron as the main impurity. Resulting color centers absorb red, orange and yellow light. These diamonds are usually blue and come in a variety of tone and saturation levels, depending on the actual concentration of boron atoms. All blue synthetic diamonds and less than 0.1 % of all natural diamonds belong to Type IIb. All of them are electroconductive, unlike diamonds of other types.

Color Grading

Gemological laboratories grade white and colored diamonds differently. For white diamonds, laboratories have adopted a relatively simple system based on the "whiteness" of stones. The most common nomenclature use letters from D (colorless) to Z (light yellow) to describe color.

Colored diamonds are usually graded using a system based on the combination of hue, tone, and saturation.

  • HUE: aspect that gives a color its name, like yellow, blue or purplish pink
  • TONE: the lightness to darkness aspect of a color.
  • SATURATION: the intensity or strength of a color.

Every gemological laboratory employs its own proprietary methods to determine those parameters and derive a resulting color grade, so results produced by different laboratories for the same stone may vary.

Color is the primary distinctive feature of an AOTC created diamond. We produce diamonds in a wide variety of colors, however, in our production we focus on three highly sought after colors–blue, yellow and white. All those colors are as-grown–in other words, created during diamond crystallization, without any post-growth treatment. Those intrinsic colors are permanent and do not change or fade with time or exposure to higher temperatures. On a relatively small scale, AOTC Group also produces other colors - pink, purple, green, red, etc. These colors are created by applying various post-growth treatments to our lab-grown diamonds.