HPHT vs. CVD Lab-Grown Diamonds

The high pressure high temperature method is the original method created for growing diamonds in a lab. Gem quality HPHT diamonds were introduced to the market in the 1950s and this method is often used to enhance the color of diamonds, making them appear more colorless or adding depth and saturation to pink, green, blue, and yellow diamonds.

To grow a diamond through the HPHT process, a small diamond seed is placed in carbon, the element that makes up a diamond’s crystalline structure. The seed is then exposed to extreme heat and pressure, replicating the conditions in the earth’s crust that create mined diamonds. Temperatures reach 2,000 degrees Celsius and pressure of 1.5 million PSI (parts per square inch). As the carbon melts, it forms a diamond around the seed and then it cools in a process that takes roughly 6-8 weeks.

HPHT diamonds form in a cuboctahedron shape, growing in a total of 14 different directions. These diamonds are known for their high quality clarity and color. HPHT uses heavy-duty equipment and highly-trained professionals to manage and complete the process.

CVD stands for chemical vapor deposition and was invented much more recently, in the 1980s. In this process, diamonds are grown from a hydrocarbon gas mixture, similar to how diamonds form in interstellar gas clouds. The equipment used and the type of process require much less energy than the HPHT method.

To make a CVD diamond, a tiny slice of diamond seed is placed in a sealed chamber and heated to 800 degrees celsius. Once it reaches that temperature, the chamber is filled with other carbon gases like methane. These gases are then ionized into plasma using microwaves, lasers, and other techniques. This ionization process breaks down the gases to release carbon pieces allowing the carbon to merge with the diamond seed.

As the diamond seed grows layer by layer, a cubic shape is created with growth occurring in one direction only. The CVD process produces beautiful lab-grown diamonds, but it’s a common practice to finish the process with HPHT to bring out the best in the diamond, especially the color.

Choosing one growth process over another is often based on a preference for purity in the method. Since the HPHT method so closely resembles the growth process for mined diamonds while also producing lovely, high quality stones, it is often the preferred method. While our primary goal is always a great looking diamond, we will normally choose an HPHT diamond for their superior color and clarity gradings.

We prefer HPHT diamonds because they are generally more colorless than CVD diamonds. For lab-grown diamonds, we typically provide D or E color options which means they are either HPHT diamonds, or they are CVD-grown diamonds that have been treated with HPHT at the end of the growth period. CVD diamonds on their own are normally F or G color or lower. Both processes are supposed to be stable, meaning that an HPHT-treated diamond will not lose its benefits and revert back to the original look of a CVD-grown diamond.

When it comes to the growth process, the HPHT method is more difficult, requires larger equipment, more energy, and generally costs more because of that. The CVD method is not as nuanced or complicated and the price will reflect that. However, because the highest quality CVD diamonds are finished off with the HPHT method, cost tends to even out.

Whether grown through the HPHT method or CVD, the high cost of mining and the rarity of earth-grown diamonds push lab-grown diamonds to be generally around 40% less expensive than mined diamonds. They also offer a transparent supply chain and can be entirely sustainable when grown with renewable energy sources.

The most beautiful and high quality diamonds we see are either HPHT grown or HPHT treated when originally grown through the CVD method. However, as long as you’re choosing a diamond that looks great and fulfills your diamond priorities, the growth process doesn’t need to be your determining factor.