What Is The Difference Between HPHT And CVD?

Gem-quality lab-grown diamonds are more available in today’s market than ever before.

And while shopping for a synthetic diamond, you’re likely to come across the terms HPHT and CVD, which refer to different methods of growing diamonds in a lab.

So, now you might be wondering: What is the difference between HPHT and CVD?

HPHT method uses high pressure and high temperature to replicate natural conditions in which diamonds are made. CVD uses a hydrocarbon gas mixture subjected to medium temperatures and pressures in a vacuum chamber.

But can you differentiate these two, and what are the benefits of synthetic diamonds anyway? In this article, we’ve covered answers to these – and many more – questions, so, without further ado, let’s dive in.

Lab-Grown Diamonds: Introduction

Scientists first managed to grow diamonds in a lab in the mid-1950s. However, these stones were too small to be set in jewelry. Production of bigger, gem-quality diamonds began in the mid-1990s – and it continues to this day with more and more companies producing lab-grown diamonds.

Lab-grown or synthetic diamonds are grown in several countries for jewelry and industrial purposes. On that note, industrial use is the primary use of these stones.

With the traditional diamond growth process, HPHT – short for high-pressure, high temperature – synthetic diamonds are manufactured from carbon in instruments that can mimic high-pressure and high-temperature conditions.

Natural diamonds are formed this way below the Earth’s crust, too.

Learn More: Lab-created Diamond Vs. Natural Diamond

The more modern method, CVD – short for chemical vapor deposition – involves filling a vacuum chamber with gas that contains carbon, which is then crystallized on an artificial diamond seed.

This method uses lower pressures and temperatures than HPHT.

Nevertheless, both of these processes are currently popular methods of diamond growth in labs.

The CVD diamond growth process requires a lower upfront apparatus cost than HPHT, but CVD may need subsequent treatment to improve the grown diamond’s color.

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What Is HPHT Diamond?

HPHT is short for high-pressure, high-temperature and is one of the primary methods utilized to grow diamonds in a laboratory.

This diamond growth method puts carbon atoms through extreme pressures and temperatures, which is meant to replicate great heat and pressure conditions deep below the Earth’s surface – where natural diamonds form.

The HPHT Diamond Growth Process

Let’s get into the details, shall we?

The HPHT diamond growth method takes place in a small capsule inside a specialized rig that produces high pressures. Carbon starting material dissolves in a molten flux made out of metals like iron, nickel, or cobalt within this tiny capsule.

This process lowers the pressure and temperature required for diamond growth. After that, the carbon moves through the flux to the cooler diamond seed and crystalizes on its surface to form a diamond.

While natural diamond crystals usually form as octahedrons, HPHT diamond crystals commonly have cubic facets – in addition to octahedral facets.

Since natural and HPHT diamond crystals are different in their structure, their internal growth patterns differ, as well. These patterns are the most reliable way to tell natural from lab-grown diamond crystals.

The resulting faceted synthetic stones often show the distinctive color distribution and graining patterns related to their growth-sector structure. In some cases, the material even showcases fluorescence and phosphorescence – glowing after being exposed to blacklight.

Growing colorless HPHT diamonds was once a challenge.

For one, nitrogen had to be kept out of the growth environment since it turns diamonds yellow. Additionally, growing colorless diamonds with high purity called for longer growth times and greater control over pressure and temperature conditions.

However, recent technological advancements have allowed laboratories to produce colorless crystals.

By adding boron to the growth process, scientists are now able to produce blue gems. Other colors such as red and pink can be made by following the growing process up with a method involving heating and radiation.

What Is CVD Diamond?

Another method used for growing diamonds in a lab is CVD, which, as we explained, stands for chemical vapor deposition.

Diamonds grow from a hydrocarbon gas mixture exposed to moderate-level temperatures and pressures in a vacuum chamber.

The CVD Diamond Growth Process

CVD diamond growth takes place inside a specialized vacuum chamber filled with carbon and hydrogen-containing gas – methane, for example.

A source of energy – like a microwave beam – breaks down the molecules of the gas. The carbon atoms diffuse to the colder diamond seed plates. Crystallization happens for several weeks, and crystals grow at the same time.

The number of crystals is based on the chamber’s size and the number of seed plates. It’s also worth noting that the arranged crystals often develop a rough edge of graphite that needs to be cut away.

The crystals also tend to show a brown color removed before faceting.

Most CVD-grown colorless stones on the market were most likely once brown gems that have been decolorized – which is done by HPHT annealing.

Like the HPHT method, the CVD method constantly improves and allows manufacturers to offer bigger sizes with improved clarity and color.

How To Identify A HPHT And CVD Diamond

Although synthetic gems have the identical chemical makeup as natural diamonds, they have identifying makers caused by the conditions in which they are grown. Scientists can use these makers to tell apart synthetic diamonds and natural diamonds.

These makers even allow scientists to identify which process has been used to grow a diamond – that’s how significant they are.

HPHT diamond	CVD diamond
Uneven color distribution	Even color distribution
Unique fluorescence colors	Unique fluorescence colors
Fluorescence color patterns	Fluorescence color patterns
Graining patterns	No graining patterns
Occasional phosphorescence	Occasional phosphorescence
Metallic flux inclusions	Occasional dark pinpoint inclusions
Possible inscription on girdle	Possible inscription on girdle
No strain patterns	Banded strain patterns

The table above outlines some notable characteristic features of synthetic diamonds. That said, not every faceted lab-grown diamond will show all of the listed markers.

For instance, a particular lab-grown diamond may not exhibit fluorescence. Thus, it’s vital to use as many diagnostic characteristics as possible when identifying diamonds.

In particular, color zoning is a significant diagnostic feature. HPHT-colored lab-grown diamonds usually display geometric color zoning because of the concentrated elements within the crystal.

Natural diamonds will sometimes showcase color zoning – but they won’t feature any geometric patterns seen with HPHT lab-grown gems. On the other hand, CVD synthetic diamonds usually have even coloration.

HPHT diamonds usually contain metal flux inclusions that appear black in transmitted light but have a metallic shine. That’s because the metals used as catalysts during the growth process sometimes enter the diamond crystal.

These flux metal inclusions contain elements such as nickel, iron, and cobalt.

On that note, lab-grown diamonds with bigger metallic inclusions can thus sometimes be picked up with magnets.

On the other hand, CVD synthetic diamonds don’t have metallic flux inclusions. Instead, these diamonds often contain inclusions of dark graphite or some other minerals resulting from their distinctive growth process.

Graphite inclusions look different from metallic inclusions; they don’t have the same shine.

When examined between two polarizing filters that are angled at 90 degrees, natural diamonds usually exhibit a bright mosaic or crosshatched pattern of interface known as strain colors.

These interface colors emerge from the diamond being put through incredible stress of high pressures and heat. CVD lab-grown diamonds tend to showcase banded strain patterns – a marker that aids scientists in telling them apart from HPHT diamonds.

In contrast, HPHT lab-grown gems – made in environments with uniform pressure where they aren’t subjected to stress – don’t display any strain patterns.

The fluorescence of lab-grown diamonds is also helpful for distinction.

Lab-grown diamond fluorescence is usually stronger under short-wave than under long-wave UV light, while the opposite is true for mined diamonds that exhibit fluorescence.

Moreover, synthetic diamond fluorescence occurs in a distinctive pattern. HPHT diamonds tend to exhibit a cross-shaped fluorescence pattern on their pavilion or crown after being cut. On the other hand, CVD diamonds may show a striped pattern when viewed through pavilion facets.

Standard fluorescence colors include yellow, yellow-green, green, red, and orange.

What’s interesting is that some lab-grown diamonds might glow for a couple of minutes after the UV lamp is turned off. That’s known as phosphorescence – and is usually only seen in lab-made diamonds.

How Long It Takes To Grow A Diamond In A Lab

Unlike the millions of years needed to create natural diamonds, synthetic diamonds usually take less than a month to grow. Colorless diamonds take the longest time to develop. It takes roughly two weeks – or more – to produce a 1-carat colorless synthetic diamond.

On the other hand, blue and yellow diamonds take between five and ten days to develop. The growing process mustn’t be rushed when creating diamonds, though. Otherwise, the crystal will fracture.

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Benefits Of Synthetic Diamonds

Diamonds made in a lab feature several benefits that add their value. And yes, they are equally gorgeous as natural diamonds formed beneath the Earth’s surface.

However, beauty isn’t the only thing synthetic diamonds have going for them.

Socially Responsible

One of the significant benefits of synthetic diamonds is knowing where the diamonds came from – and here’s why that’s a big deal: Many traditional natural diamonds come from conflict regions.

That has raised ethical and humanitarian concerns – the diamond industry has been connected with child labor, human rights violations, poor working conditions, and funding armed conflicts.

You can have peace of mind with synthetic diamonds since your diamond wasn’t involved in the conflict diamond trade.

Smaller Environmental Impact

Mining for diamonds has an enormous impact on the environment. Water usage is one of the most significant areas where lab-grown and mined diamonds differ.

A natural stone consumes more than 550 liters per carat. On the flip side, synthetic diamonds consume just 67 liters per carat.

Mined diamonds also lead to a constant discharge of wastewater and pollutants in surface water bodies.

When it comes to energy, natural gems use 539 million joules per carat, while lab-grown stones use 250 million. And to add to it, much of the energy used in growing diamonds in laboratories is renewable.

The difference in carbon emotions between natural and lab-grown diamonds is staggering, too. While mined diamonds produce more than 57 kilograms of carbon per carat, lab-grown gems emit around 2.5 kilograms.

Natural diamonds also produce more than 14 kilograms of sulfur oxide; synthetic diamonds produce none.

For every carat of diamond that gets mined, nearly 9.3 square meters of land is disturbed, and more than 2640 kilograms of mineral waste is created. By comparison, synthetic gems disrupt just 0.006 square meters of land per carat and only 0.4 kilograms of mineral waste.

Less Expensive

With synthetic diamonds, you’ll be able to get a larger gem or higher quality for your budget, as lab-grown diamonds can be up to 40% less expensive than their natural counterparts.

And as these processes of growing diamonds in labs continue to improve, the difference in price between natural diamonds and synthetic diamonds is likely to continue to grow.

Good news for your wallet, huh?

Better Quality For Price

Synthetic diamonds are produced in a controlled environment, even though each stone differs in quality – just like natural diamonds.

And yes, every lab-grown diamond is graded on the 4C’s of diamond quality – carat weight, cut, color, and clarity. The diamond’s price is determined by how it performs in terms of each one of these factors.

So, while no two diamonds are the same, whether synthetic or mined, you can get better quality for the same price you would pay for a mined diamond.

Conclusion

You now know that HPHT stands for high-pressure, high-temperature and that CVD is short for chemical vapor deposition – but what is the difference between HPHT and CVD?

HPHT is one of the leading methods used to create diamonds in a laboratory. This process exposes carbon atoms to immense pressures and temperatures – it’s meant to replicate the extreme conditions in which natural diamonds are formed.
CVD is also used for growing diamonds in a laboratory. Diamonds made using this method grow from a hydrocarbon gas mixture exposed to moderate-level temperatures and pressures within a vacuum chamber.

Both of these methods of diamond growing are currently pretty popular – and are continuously being improved.

So, if you’re not a fan of natural diamonds, be sure to consider these synthetic alternatives!