Lab diamonds have made the luxury of diamond jewelry more available, but finding one is often a lesson in unknown abbreviations. Two common terms encountered while comparing lab diamonds are CVD and HPHT. These both refer to distinct growth processes rather than whether the stone itself is a real diamond.
Knowing the differences between CVD vs HPHT enables you to make more informed choices about cut, color, clarity and ultimately value, instead of getting confused buying a diamond based on technical jargon.
Both methods are used to create crystalline diamond material, which shares similar chemical and physical properties on the atomic scale as a mined diamond. They are not to be confused with simulant stones like cubic zirconium and moissanite. The main differences involve the crystal structure formation processes and the growing conditions. These differences often lead to variation in optical characteristics and gemological quality that are detectable by trained professionals.
For most buyers, the visual inspection (ideally with a loupe) along with objective laboratory test results will provide much more useful information than trying to determine the manufacturing process.
CVD Diamonds: How they are created
CVD stands for Chemical Vapor Deposition. In this process, a miniscule diamond seed is placed into a chamber with carbon rich gas, usually methane.
With the addition of energy, reactions break down some of the gas molecules, adding carbon atoms to the seed. Less pressure is involved in the CVD production, reports the GIA, while modern equipment allows the production of visually perfect stones using this method.
It is common for CVD diamonds to be further treated after growth in order to enhance color. The added treatment should not be considered a negative factor, so long as a buyer is aware it has occured.
CVD vs HPHT: How HPHT Growth works
HPHT stands for High Pressure High Temperature. Using a mix of heat and pressure plus a carbon source and diamond seed, carbon atoms are bonded together to form a crystal structure around the seed in a growth process.
According to the GIA, pressues are between 5-6 GPa and temperatures around 1300-1600 degrees Celcius during HPHT production.
Modern equipment can allow the producion of colorless and near-colorless diamonds as well as colored precious stones for jewelry using the HPHT process.
CVD vs HPHT: Quality, Beauty and Appearance
One process is not inherently better than the other. Two stones grown through the same method can show very different qualities. It is advised to compare lab diamonds using the 4 Cs: cut, color, clarity and carat weight. Cut affects a diamonds ability to interact wth light, with better cutting allowing a bigger proportion of light to refract back in to a viewer’s eye as sparkling white light. For most viewers, color is easily noticed and has a large impact on the appearance. Two diamonds with the same cut may not be the same, with the higher grade color diamond appearing whiter. With clarity, different inclusions will affect a diamond’s personal appeal to a buyer.
Carat weight is a direct measure of a diamond’s weight, but actual size will also depend on the cut. Looking at a grading report is another useful comparison tool between two diamonds, looking at the objective information provided about those factors mentioned above.
To the untrained eye, the difference between high-quality CVD vs HPHT diamonds will not be easily visible. In fact, the right equipment in a professional lab can see beyond appearance to indicate differences in growth process.
CVD vs HPHT: Which method is best?
In most cases, the choice between CVD vs HPHT growth process should be less important than considering the 4 Cs and an overall assessment of value. A well-cut CVD diamond will often be far preferable to a poorly-cut HPHT diamond. Likewise, an equally well-cut HPHT diamond could be a better choice if it has superior color, clarity or carat weight. Looking at the grading report, appearance, cut and price will allow you to decide which of these makes more sense for your budget and preferences.