What’s the Difference Between CVD and HPHT Diamonds
13th February 2022
When it comes to producing lab-created diamonds, there are two different processes, CVD and HPHT. CVD refers to chemical vapour deposition, while HPHT stands for high-pressure, high temperature. Although both of these methods produce quality synthetics diamonds, it's important to understand the differences between the two and how these processes affect the diamond quality before making a purchase.
What are High Pressure High Temperature (HPHT) Diamonds?
HPHT diamonds mimic the natural process of diamond growth. Natural diamonds are formed deep underground where the conditions of high pressure and high temperatures are found. This is why so many use the HPHT method to grow diamonds. While there are several techniques of the HPHT method, the end goal is the same, to create an environment of pressure over 1.5 million pounds and a temperature over 1400°C where diamond growth can occur.
Since 1954, when the first HPHT lab-grown diamond was produced, technology has greatly advanced and now, we are able to efficiently produce large, gem-quality diamonds. You may find in HPHT diamonds metal inclusions such as iron, nickel and cobalt as these are typically used during the growing process and sometimes enter the diamond. These tiny metallic inclusions are actually what helps experts identify whether it’s a natural or lab-grown diamond as natural diamonds rarely capture metals while being formed. HPHT diamonds also often have yellowish or brownish tints to them as they would’ve been exposed to nitrogen while forming.
Outside of growing diamonds, HPHT is a method that can be used to enhance the colour of natural diamonds. Using HPHT the diamonds can turn either colourless, yellow, orange-yellow, yellowish-green, green, pink and blue.
What are Chemical Vapour Deposition (CVD) Diamonds?
CVD diamonds, or Chemical Vapour Deposition diamonds, is a fairly recent growing technique that was created in the 1980s. This method is able to grow a diamond from a hydrocarbon gas mixture that mimics the forming of natural diamonds in an interstellar gas cloud. The process involves introducing a gas into a vacuum chamber and is heated to around 800°C. Then, it activates and breaks down the molecules of the gas with microwaves. This causes the atom carbons to accumulate and grow a gemstone atom by atom, layer by layer until you have a fully formed diamond.
As the high pressure and extreme high temperatures are not needed, this process is much less costly than HPHT. While the diamonds can be grown colourless, as the chamber only contains carbon and some hydrogen, and they won’t contain metal inclusions, they can sometimes have a brown hue to them when produced quickly at the lower temperature.
However, over the years, researchers have found that changing the gas in the chamber and treating the material at higher temperatures and pressures can remove the brown colouration and make them colourless. If nitrogen or boron is also introduced to the chamber, then yellow or blue diamonds can be produced.
CVD vs HPHT Diamonds: Which is Better?
When comparing CVD and HPHT diamonds, there is no difference other than how they were grown. Both processes produce real diamonds that are chemically, physically and optically identical to natural diamonds and you won’t be able to tell which is a CVD or which is a HPHT diamond.
CVD, HPHT and natural diamonds all made from crystallised carbon, measure a 10 on the Mohs scale of hardness which makes them the hardest minerals on earth, the colour and clarity of the stones are permanent and will not fade or lessen and each will be certified by gemological institutes. CVD and HPHT lab-grown diamonds will be the more sustainable and ethical choice than natural diamonds as tonnes of earth won’t be extracted to produce them. They’re also excellent value for money as they are made in larger quantities and so aren’t as rare but still just as magnificent.
Learn more about why you should choose lab-grown diamonds over natural diamonds.