Colored diamonds, known as Fancy Color Diamonds, are extremely rare when found in nature, representing a fraction of all mined diamonds. Their vibrant hues result from unique conditions deep within the Earth or through human intervention. Because a diamond’s color significantly impacts its value, understanding the origin—natural, treated, or laboratory-grown—is paramount for consumers.
How Diamonds Acquire Color Naturally
The development of color in a natural diamond is a geological accident, determined by the presence of trace elements or defects in the crystal structure during formation. The most common color, yellow, is primarily caused by nitrogen atoms trapped within the carbon lattice. These nitrogen impurities absorb light in the blue spectrum, causing the stone to reflect a yellow hue.
Blue diamonds owe their color to the presence of boron atoms, which replace some carbon atoms in the crystal structure. This trace amount of boron absorbs light in the red and yellow spectrums, allowing the blue color to be transmitted. These unique chemical signatures occur under intense heat and pressure deep within the Earth’s mantle.
Other colors, such as pink, red, and purple, are caused by structural defects known as plastic deformation, not chemical impurities. Extreme pressure during the diamond’s ascent to the surface causes the internal crystal planes to slip or distort. This distortion changes how the diamond absorbs light, resulting in these non-elemental colors. Green diamonds result from exposure to natural radiation over geological time, creating tiny defects near the surface that selectively absorb light to produce the green shade.
Methods for Creating Non-Natural Color
Since natural Fancy Color Diamonds are scarce, the industry uses laboratory methods to introduce or enhance color in existing natural diamonds. One common technique is irradiation, where a diamond is exposed to a particle accelerator to alter its atomic structure. This process creates color centers that produce blues or greens, often followed by annealing (heating) to stabilize the color or shift the hue to yellows, oranges, or pinks.
Another established method is High-Pressure/High-Temperature (HPHT) processing, which mimics the intense conditions of the Earth’s mantle. HPHT is often used to treat brownish diamonds, a common starting material, by changing the state of nitrogen impurities to produce yellow or near-colorless diamonds. This process requires temperatures reaching thousands of degrees Celsius and pressures up to 70,000 atmospheres.
Colored diamonds can also be entirely manufactured in a lab using methods like HPHT or Chemical Vapor Deposition (CVD). In these processes, specific trace elements like nitrogen or boron are intentionally introduced into the growth chamber. The resulting synthetic diamond crystals grow with the desired color under controlled, accelerated laboratory conditions.
Identifying the Origin of a Colored Diamond
Determining whether a colored diamond is natural, treated, or synthetic requires sophisticated gemological testing. Professional gemological laboratories rely on advanced analytical instruments to detect subtle differences in a stone’s composition and structure. These differences are often too small to be seen with a standard jeweler’s loupe.
One primary tool is spectroscopy, which analyzes the way a diamond absorbs and emits light. Techniques like Photoluminescence (PL) spectroscopy can detect specific atomic-level defects or foreign elements that serve as tell-tale signs of a diamond’s origin, such as characteristic spectral peaks left by lab irradiation.
Microscopy is also employed to look for physical evidence, such as color distribution patterns that reveal a diamond’s history. Natural color resulting from plastic deformation, for instance, often appears as colored graining or bands. In contrast, color induced by irradiation may show a patchy or “umbrella-like” pattern on the surface. Identifying these microscopic signatures allows experts to definitively separate the Earth-grown from the lab-enhanced or lab-created.