How Are Lab-Grown Diamonds Made?

With temperatures reaching 2700 degrees Fahrenheit (1500 degrees Celsius) and pressure of 1.5 million pounds per square inch, the high pressure high temperature (HPHT) method of producing lab-grown diamonds was the first method utilized and is the most well-known.

The HPHT method begins with a tiny piece of diamond, called a diamond seed. The diamond seed comes from a natural, mined diamond or from a previously grown HPHT diamond. The seed is placed in a sealed chamber in pure carbon and then exposed to high pressures and temperatures. This process exactly mimics the conditions deep within the Earth’s crust that produce diamonds over billions of years.

During this process in the lab, the carbon melts and dissolves under the heat and then solidifies from the pressure, turning into a diamond as it cools. Once done, a completed diamond has formed around the original diamond seed. The whole process takes less than a month.

Once removed from the machine, the newly created diamond is sent to be cut and polished, following the exact process that natural diamonds go through. Cutters optimize the features of each diamond to create a beautiful gemstone.

The chemical vapor deposition (CVD) method relies on carbon-based gases instead of high temperature and high pressure to grow and form diamonds. Beginning with a diamond seed, the CVD method typically uses a tiny sliver of diamond that has been created through the HPHT method, but can also use small pieces of natural diamond instead.

Inside a sealed chamber, methane and hydrogen gases are introduced to the diamond seed. The chamber’s environment is then heated up to 2200 degrees Fahrenheit (1200 degrees Celsius) causing the gases to ionize into plasma. The technology used then breaks down the molecular bonds of the gas.

As they break down, the carbon atoms released from these gases begin to build around the diamond seed. This process repeats over and over again to replicate the crystal structure of the diamond seed in three dimensions.

In about 21-28 days, the diamond will be ready to be removed from the reactor. At this point, the diamond is ready to be sent out for cutting in the same way as a natural diamond to maximize its unique features.

Diamonds ready to be cut and polished

While neither process necessarily produces a better diamond than the other, there are a few marked differences between the two methods. The CVD method was more recently developed and is less costly than HPHT since the machinery used is smaller and requires less power. The HPHT method has been around longer and has experienced more innovations as a result.

Optically, there will be no noticeable difference between a diamond grown through the HPHT method or one through the CVD method. However, gemologists using sophisticated equipment are able to discern what method was used by examining their growth morphology.

Growth morphology describes how growth conditions influenced the shape of the resulting diamond crystal. Diamonds grown through the HPHT method create a cuboctahedron shape that has growth in 14 directions. Diamonds grown through the CVD method create a cube and have growth in one direction.

While this describes the shape of the diamond rough which is lost after being cut and polished, a gemologist could make these identifications by looking for fluorescence patterns that result from each specific growth morphology. This is also how cut and polished natural diamonds are differentiated from lab-grown diamonds, since a natural diamond grows in an octahedron shape in 8 directions.

While there’s a case to be made for HPHT diamonds being of better quality, that’s not universal, since exceptional diamonds can be made by both methods. However, it’s often the case that CVD diamonds need to go through an additional treatment process, using heat or irradiation to enhance their colors after the growth process. Oftentimes, CVD diamonds will be finished off with HPHT treatment to enhance its color.

The two methods may also vary somewhat on price, but that’s not an indicator of a lesser or more high quality diamond. Since CVD is the less expensive process by which to grow a lab diamond, that is reflected in the price. The HPHT method is simply more costly because it requires larger and more robust equipment and higher amounts of energy.

Also, it has only recently changed that certification labs will include information about which method was used to grow the diamond. Before then, it was hard to come by the information. While policies have been updated, it’s still not entirely consistent as to when the IGI (International Gemological Institute) and the GIA (Gemological Institute of America) will include that designation on the official report. In many cases, lab reports will include when the diamond was grown using the HPHT method, and lesser so with the CVD method.

We carry lab grown diamonds produced under both methods, as long as they are beautifully grown and cut. Because we prefer to carry DEF color diamonds, most of our inventory is HPHT made.  

Not even two decades ago, no one could have predicted that technology would allow us to create diamonds grown in a lab that have the same properties as mined diamonds. And it only takes weeks to grow them. With technological advances and greater awareness and interest, lab-grown diamonds will continue their rise in popularity, carving out their role as a permanent fixture in the market.