An In-Depth Look at CVD vs. HPHT

May. 06, 2024

An In-Depth Look at CVD vs. HPHT

Lab-grown diamonds are at the center of constant debate in engagement ring circles, although the oldest of those discussions is officially put to rest. Lab-grown diamonds are real diamonds. However, just because they are created in a laboratory doesn’t mean they’re all created using the same process. Introducing CVD vs. HPHT.

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There are some major differences between the two main types of lab-grown diamonds, so keep reading to explore what sets them apart. If you’ve chosen to go the lab-grown route, this blog aims to help you understand the two growing methods, and perhaps use that knowledge to decide which type of lab-grown stone you prefer.

Chemical Vapor Deposition (CVD)

CVD, which stands for “chemical vapor deposition”, is a less intense approach to creating lab-grown diamonds. CVD is the newer of the two methods, as it was developed in the 1980s, and aims to recreate the way diamonds form in gas clouds. CVD relies on a hydrocarbon gas mixture to mimic the conditions of interstellar gas clouds.

One of the major differences between CVD and HPHT is the amount of necessary pressure. CVD diamonds require far less, and the equipment and machinery needed to complete them are smaller, too.

The CVD Process

In CVD, a slice or wafer of real diamond (sometimes referred to as a diamond seed) gets placed into a sealed vacuum chamber. After the chamber fills with carbon-heavy gas (like methane), it’s heated to a high temperature of around 1500 degrees Fahrenheit. The high temperatures convert the gas into plasma, which releases pieces of carbon.

Those carbon pieces build upon the diamond seed originally placed in the chamber. Eventually, a full diamond forms after layer and layer of carbon pieces attach to the seed. The whole process produces incredible, chemically-pure diamonds free of most impurities. They don’t contain metal inclusions, either.

The whole process for a CVD diamond takes somewhere between 6 to 12 weeks, depending on the size of the diamond, and CVD diamonds tend to grow in a sort of cube-like shape as they form. At Lauren B, most of our lab-grown diamonds are CVD diamonds.

High Pressure High Temperature (HPHT)

HPHT was the first major method for creating lab-grown diamonds. It was developed in the 1950s before the debate about mined vs lab-grown diamonds reached the crescendo we’ve seen as of late.

The acronym stands for “High-Pressure High-Temperature,” which says a lot about the method itself. Unlike CVD, which works with lower pressure and relatively low temperatures, HPHT more closely mimics the natural conditions that form diamonds. While most of our lab-grown diamonds were created through the CVD process, we do have some in our inventory that were created using the HPHT process.

The HPHT Process

The basics of HPHT are contained in the acronym itself. It relies on high pressure and high temperatures. Of course, the reality is a bit more complex than that.

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A diamond seed, like the one mentioned in the CVD process, gets placed into a special press with carbon. The area is heated with heating machinery until it reaches a temperature of around 1600 degrees Celsius (or about 2900 Fahrenheit)—greatly exceeding the numbers necessary for CVD. The chamber exerts pressure up to and over 870,000 pounds per square inch.

Molten metal (typically from a source like graphite) in the chamber then dissolves the carbon source, and a diamond begins to form and build around the diamond seed. HPHT diamonds typically have both cubical and octahedral faces.

Similarities and Differences Between CVD & HPHT

Armed with a basic understanding of how each process works, you’re probably asking yourself why any of that makes a difference. How does it change the diamond you’ll actually be getting and are there visible differences between these two types of diamonds?

Color Distribution - CVD diamonds tend to have a more even color distribution and in general achieve higher levels of clarity and color than HPHT diamonds. In the past, HPHT diamonds were prone to developing yellowish color, due to the presence of nitrogen, but the technique has grown and developed over the years.

Fluorescence - HPHT and CVD diamonds show higher incidences of fluorescence, which is a type of glow seen in ultraviolet light. Fluorescence is widely misinterpreted as a bad thing but does not actually have any effect on the appearance of a diamond unless under UV or blacklight. Its presence is noted during grading, but its existence (or lack thereof) doesn’t affect the grade. HPHT diamonds tend to have higher instances of fluorescence than diamonds formed with the CVD method, but it’s possible in both.

Graining - HPHT diamonds show graining patterns based on their growth structure. CVD diamonds have no growth patterns.

Inclusions - Both types of diamonds may have inclusions, but they come from different sources. CVD diamonds may have dark pinpoint inclusions, whereas HPHT could develop metallic flux inclusions.

Strain Patterns - CVD diamonds display banded strain patterns, while HPHT diamonds usually don’t (or have very minor ones). Notably, natural, mined diamonds also tend to display strain patterns.

Aside from internal makeup and appearance, there are also price differences to consider. HPHT diamonds tend to cost more than CVD stones. Creating them takes more time, effort, and space, as the process is more intense and laborious. Both cost less than natural diamonds, but CVD is the more budget-friendly option when choosing between the two.

Overall, the HPHT process offers greater control. They’re often more colorless than CVD diamonds. Some CVD diamonds are even treated with the HPHT method to finish the stone, as the tighter control allows for color adjustments.

Lab-Grown Diamonds at Lauren B

As with most debates in gemstones and jewelry, there’s no clear-cut winner between CVD and HPHT-grown diamonds. Both methods produce beautiful diamonds, which easily rival natural, mined diamonds in all of the Four C categories. No one will be able to tell the difference between any of these diamonds with the naked eye, regardless, as it takes specialized equipment and skill to spot the differences between them.

If you’re ready to take the plunge, schedule an appointment with one of our dedicated design consultants who can custom design the engagement ring of your dreams! Your perfect ring is just one click away…

If you want to learn more, please visit our website 6mm diamond studs.

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