Artificial diamonds, also known as lab-grown diamonds, are pure carbon crystals created by advanced technological processes rather than geological ones. These manufactured stones possess the exact same chemical composition, crystal structure, and physical properties as diamonds mined from the Earth’s mantle. They are grown in a controlled laboratory setting over a period of weeks, replicating the natural conditions required for carbon atoms to crystallize. These techniques produce gems that are optically and chemically identical to their natural counterparts.
High-Pressure High-Temperature Method
The High-Pressure High-Temperature (HPHT) method is the older process, directly mimicking the conditions deep within the Earth where natural diamonds form. This technique requires massive mechanical presses, such as a belt press or a cubic press, to generate the necessary forces. The interior of the press contains a growth chamber where a small diamond seed crystal is placed, serving as the template for growth.
Surrounding the seed is a carbon source, typically high-purity graphite, and a metal solvent-catalyst mixture, often an alloy of iron, nickel, or cobalt. The chamber is heated to temperatures ranging from 1,300 to 1,600 degrees Celsius. Simultaneously, the press applies extreme pressure, generally between 5 and 6 gigapascals.
Under these intense conditions, the metal solvent melts and dissolves the carbon source material. The dissolved carbon then migrates through the molten metal toward the cooler diamond seed crystal. As the carbon atoms precipitate out of the solution, they bond onto the seed, atom by atom, to form a newly grown diamond crystal. The entire process is maintained for several days to a few weeks until the rough diamond reaches the desired size.
Chemical Vapor Deposition Method
The Chemical Vapor Deposition (CVD) method is a newer technique that operates under significantly lower pressures and temperatures. This process involves placing thin slices of diamond seed material inside a vacuum chamber, which is then heated to temperatures between 700 and 1,200 degrees Celsius.
A mixture of carbon-containing gases, typically methane and hydrogen, is introduced into the chamber at a low pressure. Microwave energy is applied, which breaks down the gas molecules into a plasma cloud of chemically active carbon atoms. Hydrogen gas selectively etches away non-diamond carbon, ensuring the purity of the final product.
The pure carbon atoms deposit from the plasma onto the seed substrate, building the diamond structure layer by layer. This deposition results in a diamond with a columnar growth structure. The process can be paused periodically to polish the surface of the growing diamond and remove any non-diamond carbon impurities.
Post-Growth Enhancement and Finishing
Once the rough crystal is harvested from the growth chamber, a series of finishing steps are required to transform it into a faceted gemstone. The initial step involves laser cutting, which precisely separates the rough diamond into preliminary shapes for polishing. Technicians then polish each facet to maximize the stone’s brilliance and fire.
Many lab-grown diamonds, particularly those produced by the CVD method, undergo post-growth treatment to improve their color. CVD diamonds often exhibit a brownish or grayish tint due to structural defects created during rapid growth. These stones are subjected to a secondary HPHT annealing treatment. This involves heating the diamond to high temperatures under high pressure to rearrange the atomic lattice and remove the brown hue.
Other treatments, such as irradiation followed by low-pressure high-temperature (LPHT) annealing, may be used to alter the diamond’s color. This process can produce “fancy” colors, such as pink, blue, or green, by manipulating the defects and impurities within the crystal structure.
Key Differences Between HPHT and CVD Diamonds
The two methods of diamond synthesis result in stones with distinct crystallographic signatures. HPHT diamonds typically exhibit a cuboctahedral crystal structure, growing along multiple directions simultaneously. In contrast, CVD diamonds grow in a layered, tabular fashion, primarily in one direction, which leaves behind parallel growth striations.
The inclusion types present in each stone differ due to the manufacturing environment. HPHT diamonds are characterized by microscopic metallic inclusions, derived from the iron, nickel, and cobalt solvent-catalyst used in the growth chamber. These metal inclusions can cause the HPHT diamond to be weakly magnetic, which is a key identification feature for gemologists.
CVD diamonds, grown in a gas environment without a metal solvent, do not contain metallic inclusions. Their common impurities are often minute traces of non-diamond carbon or graphite. Gemologists rely on advanced spectroscopic analysis, like photoluminescence and specialized UV imaging, to distinguish between the two types.
From a production standpoint, HPHT requires massive, costly presses and a high energy input to maintain extreme pressure. Conversely, the CVD process is more scalable and allows for the growth of large-area films, though it often requires a post-growth HPHT treatment to achieve a colorless grade. These differences in equipment and process result in distinct characteristic markings that allow laboratories to determine the specific method of a lab-grown diamond’s creation.