Diamonds are prized for their clarity and sparkle, but some people desire colored diamonds for their unique beauty. Though diamonds naturally form in different colors, most are colorless. Is it possible to add color to a clear diamond? The answer is yes, but it requires advanced techniques.
Natural Diamond Colors
Diamonds form deep within the earth under intense heat and pressure. Impurities present during their formation determine their final color. Here are some of the natural colors diamonds can exhibit:
| Color | Cause |
| Yellow | Nitrogen impurities |
| Blue | Boron impurities |
| Pink | Structural defects |
| Green | Radiation exposure |
| Purple | Hydrogen and plastic deformation |
| Red | Crystal lattice defects |
| Orange | Nitrogen impurities |
| Brown | Lattice defects |
The most common impurity in diamonds is nitrogen, which produces yellow or brown shades when present in large enough quantities. Structural imperfections like cracks and vacancies also alter light absorption to create pink, purple, and red diamonds. Trace elements like boron account for blue diamonds. Green diamonds get their color from radiation exposure.
Color Grading System
The Gemological Institute of America (GIA) uses a grading system to classify diamond colors:
| Grade | Color Description |
| D-F | Colorless |
| G-J | Near colorless |
| K-M | Faint yellow |
| N-R | Very light yellow |
| S-Z | Light yellow |
The rarest and most valuable diamonds fall into the top color grades of D-F and are described as colorless. They transmit white light without any noticeable tinting. As more impurities are present, letters descend through G-J, K-M, N-R, and finally S-Z for light yellow diamonds. Fancy colored diamonds are graded separately on the intensity of their color.
Methods to Add Color
Since most diamonds extracted from mines are colorless or pale yellow, methods have been developed to turn these into colored diamonds. Here are ways color can be added:
HPHT Treatment
Diamonds can be placed under high pressure and high temperature (HPHT) to alter their atomic structure. The intense conditions mimic the environment diamonds formed in within the earth. HPHT treatment can remove nitrogen impurities to make some yellow diamonds colorless. It can also rearrange crystal lattices to potentially produce pink, red, purple, or brown colors.
Irradiation
Exposing a diamond to radiation can add color. Neutron, electron, or gamma radiation can displace carbon atoms to produce crystal defects that alter light absorption. Green diamonds result from prolonged exposure to radiation. Lab irradiation can also enhance existing faint pink or blue hues to make them more vivid. The irradiation process is limited by how much radiation diamonds can absorb before they become too structurally damaged.
Coatings
Diamonds can be coated with a thin translucent layer of material to produce surface colors. Common coatings include silicon dioxide for blue, gold for pink or purple, and silver for aqua. The coatings refract light to present certain colors. However, coatings wear away over time with cleaning and wear, needing reapplication every few years. Only irradiation and HPHT treatment create permanent color change to the diamond itself.
Effects on Value
Adding color to naturally colorless diamonds generally lowers their monetary value among jewelers and collectors. A few reasons why enhanced colored diamonds are worth less:
– The color is not natural, only created through artificial treatment
– The color is not stable long term like a naturally occurring color
– There are many more colored diamonds available in the market driving prices down
– The diamond has been damaged from exposure to high pressure, heat, or radiation
However, treated colored diamonds cost a fraction of naturally occurring colored diamonds. For those desiring colored diamonds on a budget, enhancement creates more affordable options.
Detection
Color enhanced diamonds should always be disclosed as such when selling. Testing can reveal if a diamond has been artificially colored:
UV Light
Many HPHT or irradiated diamonds will fluoresce under ultraviolet light, unlike natural diamonds. The color of the fluorescence can indicate if a diamond has been treated.
Spectrometer
A spectrometer measures optical properties. Artificially colored diamonds will show different absorbance spectra than equivalent natural diamonds. Labs can keep databases of the spectral signatures of various treated diamonds.
Microscopy
Powerful microscopes may reveal structural anomalies around inclusions that indicate artificial treatment. Fingerprints, bubbles, and dark dots around crystal defects can give away HPHT and irradiated diamonds.
Summary
While natural fancy colored diamonds are exceptionally rare, science has found ways to create similar colors in abundantly available clear diamonds. High pressure and heat treatments, irradiation exposure, and applied coatings can all add color. However buyers should be aware these colors are not natural and can fade or need reapplication over time. For diamond lovers who dream in color, treated diamonds offer beautiful options at accessible prices, as long as they honestly represent their enhanced origin.
