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Lab-Grown Diamond Treatments: What Are They, and Why Should I Care?

You’ve probably been seeing more mention of the term “as-grown” as it relates to lab-grown diamonds. This is because many members of the jewelry industry are pushing for greater disclosure and transparency as it relates to lab-grown treatments, much as we work for full disclosure in all other gem categories.

When a lab-grown seller promotes their diamonds as “as-grown,” they are telling you that the diamond was grown, cut, and polished - without any post-growth processing. In other words, these growers haven’t treated their diamonds to enhance their appearance. 

In general, CVD diamonds tend to have a slight brown undertone in their raw form, and HPHT diamonds tend to have a slight blue or grayish tone. Post-growth treatment can make them appear whiter. It is said that as much as 90% of CVD diamonds receive some sort of post-growth treatment, and that some diamonds grown with HPHT also receive post-growth touchups for color enhancement.

HPHT Post-Growth Annealing

So, what are these post-growth treatment methods? The primary treatment method is HPHT (high pressure, high temperature), in which the already grown diamond (CVD or HPHT) is subjected to additional time in an HPHT chamber. For the CVD diamonds, a post-HPHT treatment can help close microscopic voids that are created during growth. 

Why would a grower do an HPHT post-growth treatment on an HPHT-grown diamond? Well, unlike CVD diamonds — which have graphitic inclusions — HPHT diamonds tend to have black flux inclusions. Further time in the high pressure chamber following growth can reduce the appearance of those inclusions.

There is some question about whether an HPHT “touch-up” on an HPHT diamond should be considered a treatment at all, though at the moment both GIA and IGI list them as such.

LPHT Post-Growth Annealing

Another post-growth treatment used on lab-grown diamonds is Low Pressure High Temperature (LPHT). LPHT is a form of annealing. According to the GIA, “HPHT annealing can be achieved at temperatures ranging from 1800–2500°C and pressures greater than 5 GPa. High pressure is required in order to prevent graphitization, especially in natural diamonds. In contrast, LPHT annealing is performed at temperatures 1400–2200°C and pressures below 300 torr.” Reduction of the defects related to nitrogen and nickel in HPHT diamonds does not rely on pressure, so LPHT can be an effective method for improving color. But the risk of LPHT in HPHT diamonds is that annealing without stabilizing pressure can contribute to luminescence and lattice distortions around point defects. Nitrogen vacancy and hydrogen complexes in CVD diamonds are what contribute to their common brown undertone, so LPHT is a method that can also be effective for improving color in CVD diamonds. 


The next post-treatment method is irradiation. Irradiation has long been used on color gemstones and color diamonds to enhance optical properties (it’s important to note that all mined color diamonds and some color gemstones have been exposed to natural radiation over millennia, and it is this radiation that has led to their colorful hues). But the irradiation of gemstones is an artificial process achieved by bombarding the gems with subatomic particles and electromagnetic radiation. This is done using either a nuclear reactor, a particle accelerator, or a gamma ray facility. High levels of ionizing radiation actually change the atomic structure, or the “crystal lattice” of a gem, which affects its optical properties. In the case of lab-grown diamonds, this can cause the color to be altered, or it can cause the visibility of inclusions to be reduced.

So What’s the Fuss?

As far as whether or not a treatment must be disclosed legally, the rules still aren’t very clear. According to Sara Yood, JVC Senior Counsel, in an interview for JCK Online, “Under the (Federal Trade Commission) guides, treatments that significantly affect the value of a stone must be disclosed to the consumer. Post-manufacturing treatment might fall into that prong of the treatment disclosure requirement. Certainly, HPHT treatment of natural diamonds does, and I see this treatment functioning in exactly the same way for the laboratory-grown diamond.” But at this time the FTC has not ruled on this topic. Nevertheless, the labs are disclosing treatments.

Some lab-grown experts argue that being able to promote lab-grown diamonds as “as-grown” is a testament to superior growing methods, signaling that the technology used is more advanced, so the diamonds do not need post-growth treatment. On the other side of the argument, many consider post-growth treatment a non-factor, considering that lab-grown diamonds are a product of technology to begin with.

So What Should You Do?

Whether you buy and sell post-growth treated lab-grown diamonds or not is an entirely personal decision that should be driven by your brand and your sales strategy. If your brand is about “only the best … of whatever …” then you may want to tout the fact that you only sell high color as-grown lab-grown diamonds. If your brand is about choice, then you may want to offer all the different choices and price-points to fulfill your brand promise. And if your brand is about telling fascinating stories, then the stories of how diamonds are grown and further improved may be of great interest to your customers.

The bottom line is that there is no “right” answer. There’s only your brand, your merchandising and selling strategy, and your relationship with your customer. However you decide to play it, as long as you are engaging and transparent, you simply can’t go wrong.