How Lab Diamonds Are Made: CVD vs HPHT Explained Simply

Lab-grown diamonds aren't fake or synthetic in the way most people think. They're real diamonds, created using advanced technology that replicates the natural processes happening deep within the earth. If you're curious about how scientists grow diamonds in a lab, this guide breaks down the two main methods in plain language.

The Basics: What Makes a Diamond a Diamond

Before we dive into the processes, let's establish what makes a diamond unique. Diamonds are pure carbon atoms arranged in a specific crystal structure. This arrangement is what gives diamonds their exceptional hardness and brilliant sparkle.

Natural diamonds form over billions of years under extreme heat and pressure deep in the earth's mantle, about 100 miles below the surface. Lab-grown diamonds achieve the same result in a matter of weeks by recreating those conditions in a controlled environment.

The key point: lab diamonds have the identical chemical composition and physical properties as natural diamonds because they're made of the exact same thing—carbon atoms in the same arrangement.

HPHT: High Pressure High Temperature

HPHT was the first successful method for creating lab diamonds, developed in the 1950s. As the name suggests, it mimics the natural conditions deep underground where diamonds form.

How It Works

Scientists place a small diamond seed (a tiny piece of diamond) in a specialized chamber along with pure carbon. The chamber is then subjected to extreme conditions:

• Temperatures reaching 2,700-2,900°F (about as hot as molten lava)
• Pressures of approximately 870,000 pounds per square inch (equivalent to the weight of a jumbo jet pressing down on your thumbnail)

Under these extreme conditions, the carbon melts and begins to crystallize around the diamond seed, slowly forming a larger diamond. The process typically takes several weeks, depending on the desired size.

The Equipment

HPHT requires massive industrial presses that can generate and maintain these extreme conditions. These machines are engineering marvels, often standing several stories tall and weighing hundreds of tons. The precision required is extraordinary—temperatures and pressures must be carefully controlled throughout the entire growth process.

What HPHT Diamonds Look Like

HPHT diamonds often have a cubic or octahedral shape when they come out of the press. They're then cut and polished just like natural diamonds to create the familiar shapes we recognize—round brilliant, princess, emerald, and so on.

Advantages of HPHT

HPHT can produce diamonds relatively quickly and is particularly effective for creating fancy colored diamonds, especially yellows and blues. It's also been around longer, so the technology is well-established and refined.

CVD: Chemical Vapor Deposition

CVD is the newer method, developed in the 1980s and perfected over recent decades. It takes a completely different approach to diamond creation.

How It Works

CVD starts with a thin diamond seed placed in a sealed chamber. The chamber is filled with carbon-rich gases, typically methane and hydrogen. Here's where it gets interesting:

The chamber is heated to around 1,500-2,000°F (hot, but much cooler than HPHT). Microwaves or other energy sources break apart the gas molecules, causing pure carbon atoms to separate and slowly fall onto the diamond seed like snow. Layer by layer, atom by atom, these carbon particles build up and bond to the seed, gradually forming a larger diamond.

The process happens at much lower pressures than HPHT—close to normal atmospheric pressure. It takes several weeks to grow a diamond of significant size.

The Equipment

CVD reactors look more like high-tech ovens than the massive presses used in HPHT. They're smaller, more precise, and easier to control. Scientists can monitor and adjust the growth process in real-time, which allows for greater consistency.

What CVD Diamonds Look Like

CVD diamonds typically grow in flat, tabular shapes that look like thin squares or rectangles. These are then cut and polished into traditional diamond shapes. The flat growth pattern is why CVD is particularly efficient for creating certain shapes and sizes.

Advantages of CVD

CVD offers greater control over the diamond's properties during growth. It's more energy-efficient than HPHT and produces diamonds with very few metallic inclusions. CVD has become increasingly popular in recent years due to these advantages and the ability to produce high-quality colorless diamonds.

Key Differences Between HPHT and CVD

While both methods produce real diamonds, there are some practical differences worth understanding.

Growth Conditions HPHT uses extreme pressure and heat, mimicking deep earth conditions. CVD uses moderate heat and low pressure, relying on chemical processes instead.

Growth Rate Both take weeks to grow diamonds, but the specific timeline varies based on size and quality. Neither is dramatically faster than the other.

Equipment and Energy HPHT requires massive presses and significant energy for pressure generation. CVD uses smaller reactors with energy focused on maintaining temperature and breaking down gases.

Final Product Characteristics HPHT diamonds sometimes contain tiny metallic inclusions from the growth process, though these are often microscopic. CVD diamonds rarely have metallic inclusions but may occasionally show evidence of their layer-by-layer growth under specialized testing.

Color and Clarity Both methods can produce colorless, high-clarity diamonds. HPHT is traditionally better for creating certain fancy colors, while CVD excels at producing colorless stones.

Can You Tell the Difference?

Here's the bottom line: once cut and polished, HPHT and CVD diamonds look identical to each other and to natural diamonds. You cannot tell them apart with the naked eye or even under standard magnification.

Advanced gemological testing can sometimes identify the growth method by examining microscopic growth patterns or trace elements, but this requires specialized equipment. Even then, the distinction doesn't affect the diamond's quality, beauty, or durability.

Grading labs like IGI and GIA may note the growth method on the certificate, but both HPHT and CVD diamonds receive the same quality grades based on the 4Cs.

Does the Method Matter for Your Purchase?

For most buyers, whether a lab diamond was created using HPHT or CVD doesn't matter. Both methods produce genuine diamonds with identical properties.

What actually matters is the diamond's quality as measured by the 4Cs—cut, color, clarity, and carat weight. A well-cut CVD diamond and a well-cut HPHT diamond with the same specifications will look identical and perform identically.

Some people find the science interesting or prefer one method's environmental profile, but functionally, the choice between HPHT and CVD doesn't impact your diamond's appearance or longevity.

From Lab to Ring

Regardless of the method used, once a lab diamond is grown, it follows the same path as natural diamonds:

1. The rough diamond is extracted from the growth chamber
2. It's evaluated and planned for cutting
3. Skilled cutters shape and facet the diamond
4. The diamond is polished to maximize brilliance
5. It's graded by gemological labs using the same standards as natural diamonds
6. Finally, it's set into jewelry

The cutting, polishing, and grading processes are identical for lab and natural diamonds. A master diamond cutter can't tell the difference between rough HPHT, CVD, or natural diamonds—they all require the same expertise and careful work.

The Future of Lab Diamond Technology

Both HPHT and CVD technology continue to advance. Growth times are decreasing, quality is improving, and costs are coming down. Some facilities now use renewable energy to power the growth process, further reducing environmental impact.

Research continues into new variations and improvements on both methods. The goal is always the same: create diamonds more efficiently while maintaining or improving quality.

Making Your Choice

When shopping for lab-grown diamonds, the growth method is just a small piece of the story. Focus on what really matters: the diamond's graded quality, the reputation of the seller, the certification provided, and whether the diamond fits your budget and aesthetic preferences.

Both HPHT and CVD produce beautiful, real diamonds. The method is simply the scientific process that got you there—what matters is the stunning result.