How are Lab-Grown Diamonds Grown?

At the end of the 1800s, two French scientists made independent discoveries that would, over the course of a century, revolutionize the gemstone trade. In 1883, Auguste Verneuil produced lab-grown corundum (the mineral form of ruby and sapphire) using a flame fusion technique now known as the Verneuil process, and ten years later, Henri Moissan grew the first lab-grown diamonds using an electric-arc furnace that could reach temperatures of 3500°C.

Though by the early 20th century the Verneuil process was yielding gemstone quality rubies and sapphires, the technology behind lab-grown diamonds was not yet advanced enough to create gemstone-quality diamonds. That is, the diamonds these early methods yielded were too small, too dark, and too opaque to use as gemstones. But research continued, only briefly halted by the outbreak of World War II.

A major breakthrough occurred in 1954, when a General Electric engineer named Tracy Hall invented the belt press. His invention allowed GE to grow diamonds by subjecting carbon to higher levels of heat and pressure than had been previously possible. These diamonds, however, were still not gemstone quality. But that doesn’t mean these diamonds were useless. Lab-grown diamonds found use in industrial applications, whether as an abrasive or as a coating for saw blades.

Today, there are primarily two methods for producing lab-grown diamonds: Chemical Vapor Deposition (CVD) and High Pressure, High Temperature (HPHT). Both of these methods were developed shortly after World War II, and by the 1990s, both methods were growing diamonds of the highest quality. At Primo Diamonds, we use the HPHT method, which mimics the way diamonds are grown inside the Earth. 

Chemical Vapor Deposition

The CVD method is used in a variety of manufacturing settings, from polymers to electronics. Growing a diamond using the CVD method involves placing a diamond substrate or “seed” inside a low-pressure chamber. The chamber is filled with hydrocarbon gas and flooded with heat in the form of microwave energy or electricity. The heat then breaks the hydrocarbon gas into atomic hydrogen and carbon. The hydrogen from the gas gives the diamond a stable environment in which to grow, while the carbon bonds with the diamond seed, adding layer after layer of pure carbon, growing a diamond crystal one atom at a time.

Success using this method was first reported in the 1950s, though the process was not replicated until the 1960s and was unable to grow gemstone quality diamonds until the 1980s. Until recently, results using the CVD method were inconsistent, but changes to the types of gasses and seed crystals used have vastly improved the quality of CVD lab-grown diamonds.

High Pressure, High Temperature

Once 18th and 19th century geologists discovered how heat and pressure formed minerals deep inside Earth’s crust, scientists such as Moissan set out to replicate those conditions in the laboratory. The HPHT method used today is a further development of the original method pioneered by Moissan. After Hall’s invention of the belt press, GE continued to research lab-grown diamonds, finally growing gemstone-quality diamonds using the HPHT method in 1970.

Over the years, different types of presses capable of producing higher temperature and pressure environments have been developed, but the concept behind them remains the same. Just as in nature, graphite (carbon) is subjected to extreme heat and pressure, which crystalizes as a diamond. The process takes millions of years in nature, but only a few weeks in the lab.

The acronym “HPHT” can be a source of confusion in the context of diamonds. There is also a treatment process called HPHT, in which a mined diamond is subjected to heat and pressure to enhance its color. This is entirely different from HPHT as a method for growing a diamond. Primo Diamonds sells only “as-grown” HPHT lab-grown diamonds. That means our diamonds undergo no post-growth treatment.

CVD, HPHT…Which One Grows Better Diamonds?

Though the above processes are based on vastly divergent principles, there’s nothing in their results that immediately suggests that one method is better than the other. Generally, the HPHT method can grow diamonds in a wider range of color, and HPHT typically produces a better "colorless" diamond, while CVD diamonds tend to have a more brown-to-dull pink color. It is for this reason that Primo Diamonds chooses to sell only HPHT diamonds that are "as-grown," which means there are no post-growth treatments. Both methods are capable of producing D color (almost colorless) diamonds of the highest clarity, identical in color, clarity, and hardness to the finest diamonds that can be mined.

Diamonds, like all gemstones, are judged on the 4 Cs: color, clarity, cut, and carat, and both methods produce diamonds that score high in all categories. No one can tell a CVD lab-grown diamond from an HPHT lab-grown diamond from a mined diamond with the naked eye. Even an experienced gemologist might not be able to tell the difference under magnification. The only way to tell a lab-grown diamond from a mined diamond is with an expensive procedure that tests the amount of nitrogen inside the diamond. Whatever the method, today’s lab-grown diamonds are consistently high in quality. When you buy a Primo lab-grown diamond, you can request an IGI grading report so you know exactly what you’re getting.