There are several shades of lab-grown diamonds, ranging from red, brown, green, pink, yellow, or blue, but only a few buyers know this fact. Apart from these, naturally colored diamonds are extremely rare which makes them very expensive and extensive to find in jewelry stores. Because no two stones have the same makeup of color combinations, these gems are sold at auction, often fetching millions of dollars per carat.
With the advent of production technologies like HPHT and CVD, the market for laboratory-grown diamonds has changed immensely. These technologies have made almost all colors attainable in a real diamond. As a result, these stones are no longer priced in millions of dollars per carat but are valued similarly to grown D-colored colorless stones (+10-20% from Rapaport).
The different colors of lab-grown diamonds would be unnecessary if not for the precedent set by their natural “older brothers.” In the 20th century, diamond color ranges were studied with natural stones.
Eventually, scientists found a way to create lab-grown stones by replicating the control and environment that nature had naturally created over millions of years. The scientific claim that the color of mined and lab grown diamonds is homogenous. The only difference is that natural diamonds were formed deep within Earth’s mantle and have been stored there for millennia, while lab-grown stones are created by humans under similar but artificial conditions over just two weeks.
A diamond’s color is identified by the amount of defective impurities present in its crystal lattice. A pure diamond is crafted only with carbon atoms, but once atomic impurities or defects enter the structure, a shade appears.
A 1934 study by Robertson, Fox, and Martin, later expanded by many other scientists, is still widely used to define diamonds. It is based on the presence of the main impurities in diamond crystals—nitrogen and boron—which usually dictate the diamond’s color. Nitrogen creates over 15 different defect centers in the diamond structure, while boron is incorporated only as a single atom into the diamond lattice. FTIR spectroscopy is used to identify the present value of nitrogen and boron impurities in diamonds.
Let’s explain diamond classification in more detail. The criteria apply equally to both natural and grown diamonds. However, all diamonds were divided into two types according to the presence of nitrogen impurities within them:
I — with nitrogen
II — without nitrogen.
Type I was further subdivided due to the various nitrogen defects in diamonds:
- Ia — diamonds with aggregated nitrogen atoms:
- IaA — diamonds with A defects (a pair of nitrogen atoms).
- IaB — diamonds with B1 defects (four nitrogen atoms + vacancy).
- IaAB — mixed type, diamonds with A and B1 defects.
- Ib — diamonds with single nitrogen atoms in the structure (C defects), typically yellow.
Type II was split into two subtypes:
- IIa — pure diamonds, colorless or brownish.
- IIb — diamonds with single boron atoms in the structure, typically blue.
Different Vibrant Colors of Lab grown Diamonds
In the market of lab-grown diamonds, we can simplify the classification into three types based on physical characteristics: IIa-colorless, IIb-blue, and Ib-yellow. It’s important to note that naturally occurring diamonds of all three types are rare, with about 95% of natural diamonds being type Ia. This distinction is a key difference between natural and lab-grown diamonds and is often used by experts to identify them.
These colors are described with a brief analysis below:
- Yellow: The Shade featured by nitrogen atoms entering the diamond structure, Type Ib.
- HPHT technology: Common product with well-controlled color. Nitrogen is captured from the air or regulated by the catalyst metal alloy composition.
- CVD technology: Less common, harder to control color, with nitrogen included in the gas mixture.
- Colorless: No impurities, Type IIa.
- HPHT technology: Common product with good color control, using “getters” (gas absorbers) in the metal-catalyst alloy.
- CVD technology: Common product but less controlled color, often with a light brownish tint.
- Green: The shade occurred by vacancies in the diamond structure.
- Both technologies: Typically achieved by irradiating Type Ib or IIa diamonds with a fast electron beam (1-3 MeV).
- Pink and Red: Result from nitrogen-vacancy (NV) centers.
- HPHT technology: Grows low-saturated yellow diamonds (Type Ib) and then irradiates them with a fast electron beam. They are annealed at 800-1200°C to form NV centers.
- CVD technology: Either follows a similar process to HPHT or forms NV centers directly during growth.
- Brown: Caused by deformation disturbances or nickel-nitrogen centers.
- HPHT technology: Rarely produced due to low demand, resulting from nitrogen-rich crystals with nickel impurities in the catalyst metal alloy.
- CVD technology: Often produced when synthesis quality is poor, leading to dislocations and structural disturbances.
- Blue: Caused by single boron atoms in the diamond structure, Type IIb.
- HPHT technology: Common product with well-controlled color, achieved by adding boron to the metal catalyst alloy.
- CVD technology: Less common and harder to control color, with boron added to the gas mixture.
Dependency of Color Saturation of Lab Grown diamond
The color saturation of a lab-grown diamond depends on the number and density of defect-impurity centers. Diamonds have a very particular atomic structure, so even a tiny concentration of impurities can change their color. These impurity amounts are measured in ppm (parts per million) and even ppb (parts per billion).
For instance, one nitrogen atom for every million carbon atoms is represented by the 1 ppm of nitrogen that may give a diamond its yellow color. The concentration of impurities in a diamond is determined using complex spectroscopic research methods, such as IR Spectroscopy, Optical Spectroscopy, and Photoluminescence.
Therefore, the color of a lab-grown diamond is significant because it depends on the defect-impurity structure within the crystal lattice.
