GIA Guest Lecture Featuring Ada Diamonds Founders
Lindsay Reinsmith and Jason Payne

There are Two Ways to Grow Lab Diamonds:

Lab diamonds are not a brand new technology. The first CVD and HPHT diamonds were grown in the 1950’s. De Beers has been selling lab diamond for industrial purposes for over 60 years. GIA first graded a lab diamond gemstone in 1971: a 0.30ct J VS1! It then took over 45 years of research and development for the technologies to mature enough for widespread consumer adoption. 

In reviewing US Customs Data, there is a clear inflection point for lab diamonds in 2016. According to the Knot’s Annual Wedding Survey, 36% of US couples chose a lab diamond for their engagement ring in 2022.

For years, the trade has repeated the above sentiments. That lab grown and natural diamonds are identical and unable to be distinguished without advanced gemological tools. These are just a few quotes from multi-billion dollar luxury corporations that sell lab diamonds. The decision to use such conclusive and definitive language comes from the desire to differentiate lab diamonds from diamond simulants, like cubic zirconia or moissanite.

We believe the correct way to speak about lab diamonds, relative to natural, is how GIA has framed it. Lab diamonds are not identical. Lab diamonds are not indistinguishable. Lab diamonds are essentially the same. And this is not just about semantics. This is an important distinction. 

There are minute chemical and structural differences between lab grown and natural. They are not identical products. And it is for this reason that lab diamonds cannot evade detection. It’s not possible to “fool” GIA’s testing equipment. Yes, we have the technology to tell the difference.

Some lab diamonds are indeed indistinguishable from natural diamonds with just a loupe and tweezers. Some lab diamonds do require specialized gemological equipment to determine a manmade origin.

Some lab diamonds possess obvious enough crystal defects that they can look different, even to an unaided eye.

Lab Diamonds Are Better and More Pure

Most CVD diamond gemstones graded by GIA are about 30% harder than natural diamonds.

Not only are lab diamonds harder than natural diamonds, they’re also more pure! There are approximately 500 trillion non-carbon atoms trapped in the average 1ct lab diamond. However, there are 1.6 Quintillion non-carbon atoms in the average natural diamond, according a recent article in GIA’s Gems and Gemology.

To put that in perspective, if a single Sour Patch Kid represents all the atomic defects in an average 1ct lab diamond, it would take 3,000 Sour Patch Kids to represent all the atomic defects in an average 1ct natural diamond.

GIA categorizes diamonds as Type I or Type II. Type I has detectible amounts of nitrogen trapped in the crystal, whereas Type II diamonds are more pure, with no detectible nitrogen. According to GIA, only 1-2% of natural diamonds are Type II, whereas virtually all lab diamonds are Type II. Natural diamonds have impurities measured in the parts per million, whereas lab diamonds have impurities and defects measured in the parts per billion. In other words, lab diamonds are more pure.

Some Defects in Lab Diamonds are Visible Without Any Special Tools

Lab diamonds are rapidly gaining adoption, yet there remains a significant knowledge gap among both retailers and consumers. Most consumers choose a lab diamond thinking and believing that it will look like a natural diamond, because that’s what they’ve been told. And for some consumers, that will certainly be the case. However, with the rise of consumer interest has come the rise of quality defects, many visible without any special tools at all.

What Should You Look For in Evaluating Diamonds?

In natural diamonds, the trade regularly uses the term “BGM” to describe commonly occurring quality characteristics beyond the 4Cs: brown, green, milky. These characteristics in natural diamonds are not something a human being can control and happen to exist in some diamonds mined from the earth.

In CVD and HPHT, the characteristics we recommend you be on the look out for are BGS: brown, gray, and strain/striations in CVD and BGP: blue, gray, and phosphorescence in HPHT.

Many aspects of these crystal defects are intentional, not accidental and deliberately caused by the actions of humans.

How Did We Get BGS and BGP?

At the start of the commercialization of lab diamonds, there was a strong desire to produce a product indistinguishable from natural, but with higher purity. Over the last 3 years, the lab diamond industry has seen an explosion in demand as well as a significant increase in the number of CVD growers around the world. Nascent, aspirational growers purchased disadvantaged tech reactors to get in on the action. People who had no business being in this business entered the market, and many of them still don’t know what they’re doing.

The manufacturing side of diamonds couldn’t get enough. COVID-19 disrupted diamond mining far longer than it disrupted diamond growing. Existing CVD growers began getting pressured (pun intended) to produce more and more with their existing equipment without reinvestment. The goal: produce as much as possible for as cheaply as possible.

To satisfy demand without increasing costs, growers started using shortcuts: accelerated growth cycles by adding or neglecting to remove catalysts like nitrogen, running the machines hotter and faster; using and re-using cheap seeds; and introducing masking agents like compensating boron to hide nitrogen.

Lab diamonds got faster and cheaper to produce, but not better. The technology didn’t improve. In fact, these shortcuts came with consequences like color tinges, crystal strain, and lackluster material. To be clear, many growers are capable of producing nicer material and are actively choosing not to.

This has effectively created two completely different lab diamond markets. One is full of lower cost material that is subsequently sold at wholesale for steep discounts, and the other has incredible quality high purity crystal material that rivals some of the best natural diamonds out there. The pricing for higher quality, lower defect crystal can be 3-5x higher than material that is produced with shortcuts.

Steep discounts at wholesale spill over into the retail market. Diamond manufacturers used to operating on low profit margins have run into a problem: a reduction of demand combined with increasing operating and maintenance costs has exacerbated the amount of poor quality rough being produced. As wholesalers, retailers, and even consumers have gotten more educated about these quality issues, it’s left a glut of bad inventory without a home, mostly in the 2-3ct range.

This has forced some vendors to panic sell their existing inventory, causing a sudden impact on pricing at the wholesale level. This kind of liquidation will leave many vendors with little to no ability to re-invest in quality inventory in the future, and it will likely lead to industry consolidation. We predict in the medium to long term there will be fewer growers than there are today.

Lab diamonds are only going to grow in popularity as consumers become more aware of it as an option. However, consumers, and the retailers they purchase from, need better education and information, especially for quality characteristics beyond the 4 C’s.

The rise of internet buying is leaving many open to risk that they purchase a lab diamond that doesn’t look like a natural diamond. Indeed, this is just as much about striving for quality as it is about protecting the consumer.

Sentiments like these harm consumer confidence in lab grown as a whole. But there are absolutely stunning and gorgeous lab diamonds out there that aren’t gray and aren’t brown. Consumers deserve that information and transparency to make better decisions.

How CVD is Grown

The first step of CVD diamond growth is preparation of the seeds. Great care needs to be taken to ensure the seed is as perfect as possible, as the quality of the seed determines the quality of the diamond. The seeds are strategically arranged on the growth platform in the reactor, and the all the air is sucked out of the reactor. A high power microwave generator is activated, and ultra pure methane is fed into the reactor. The microwave energy causes a plasma to form above the seeds, which turns the seeds a bright red color.

In the plasma, the methane begins to break apart, and the carbon from the methane attaches to the diamond seeds, growing vertically, atom by atom, for weeks at a time. On the edges of the diamonds, black polycrystalline material begins to form. That black material is removed with a laser, and the gemstone can be cut from the rough CVD.

Approximately 80% of CVD diamonds undergo post-growth treatment, which is a final stage of refinement. The CVD diamond is loaded into an HPHT press for a quick 15-30 minute heat treatment to improve the crystallographic structure and appearance of the diamonds.

Video courtesy of ALTR Created Diamonds

Since 2009, GIA has seen a steady increase in CVD grown diamonds to approximately 80% of the total lab diamond grading reports in the latest published data.

Why is CVD outpacing HPHT? It’s a more efficient technology. The equipment is substantially smaller and does not require a specialized facility. It generally produces Type IIa completely inert under SW and LW light and does not test as moissanite (for the most part) on cheap diamond handheld diamond testers. It’s also possible to observe diamond growth and restart growth when problems arise

What are the drawbacks and limitations of CVD? It has slower growth rates than HPHT, requires expensive seeds from third parties, and quality can vary. CVD is more prone to crystal strain, which can cause blurriness. It’s also less economical than HPHT for melee sized diamonds, also known as accent diamonds. Most HPHT melee is high color, which means pairing a much warmer CVD with bright white side stones can be visible to the naked eye.

These are all G color CVD lab diamonds. As you can see the color tinges can vary in hue, saturation, and severity, even within the same color grade.

In evaluating CVD diamonds, we recommend looking for BGS:

B = Brown

Brown hues in CVD diamonds can be more of a pinkish brown or more grayish brown. Both of those diamonds are from the same grower! Brown tinge also occurs in natural diamonds, though the reason for brown in natural diamonds is sometimes due to a completely different type of defect (plastic deformation).

In CVD diamonds, brown is caused by two main things:

1. Empty voids in the diamond and

2. Nitrogen atoms trapped in the crystal.

Nitrogen defects can be accidental, leaking into the reactors past faulty seals, or nitrogen can be intentionally added as a catalyst to speed up the growth process.

Small amounts of nitrogen allow you to grow diamonds 200-300% faster. However, the faster you grow CVD diamonds, the more that can go wrong. As the atoms stack on top of each other, sometimes there are stacking faults, or glitches in the matrix of carbon atoms. One of the issues that can arise are voids of missing carbon in the crystal, like bubbles trapped in ice.

To demonstrate a void in CVD diamond, we’ve effectively sliced the carbon lattice in half and painted the cut line green. You can see that atoms are missing from the center of the lattice – that’s the void. When light hits a void in a diamond, the result is a brown coloration of the diamond.

Nitrogen Defects

Nitrogen can also give CVD diamonds a brown tone. Even though there is far less nitrogen in a CVD diamond than an average natural diamond, the optical consequences of said nitrogen can be more obvious to the naked eye in CVD than in natural. Single substitutional atomic nitrogen is actually more apparent and brown in tone than aggregated nitrogen.

Brown can also mean brownish pink, and this is primarily caused by nitrogen vacancy defects resulting from low pressure, high temperature treatment. 

If the color of as-grown CVD diamond is brown, it can be made colorless through post growth treatment. That treatment can remove the voids from the crystal structure and also aggregate the nitrogen atoms, reducing the amount of brown they create.

G = Gray

The most prevalent color tinge is gray and it can have several causes. It may also be accompanied by lifeless material. Gray is also possible in natural diamonds, but for the most part not at the same level as in lab grown and certainly not for the same reasons. Gray tinge can be seen as high as D color.

Both F Colors

The diamond on the right has a gray tinge over the diamond on the left.

Both D Colors

The diamond on the left has a gray tinge over the diamond on the left.

Causes for Gray: Silicon Vacancy Defects

Silicon trapped in the crystal can cause gray tinges. Silicon is very rare in natural diamonds, but common in CVD diamonds. Most frequently, the silicon is from the inside of the quartz window of the CVD reactor literally burning off into the vacuum chamber from the plasma.

Causes for Gray: Boron Compensating for Nitrogen

Adding nitrogen speeds up the diamond growth, but it leaves an undesirable brown tinge. You can compensate for the nitrogen by adding boron to your recipe – the pairs of atoms find each other and cancel out the properties of each other. But if you add too much boron, the nitrogen is overruled, and the diamond can present with a gray tinge/tone.

Causes for Gray: Graphitic Nanoclusters

Gray can also be the result of graphite nanoclusters, which is essentially carbon forming inside the crystal as little chunks of graphite instead of as diamond. The faster you run your reactor, the more likely it is you get graphite clusters trapped in the diamond. Graphite cannot be treated out. Moreover, graphite provokes formation of more graphite at high temperatures. Thus, if gray color component is present, this gray color can get worse after high temperature treatment.

Gray Can Get Worse with Treatment

In this example a diamond has a void with a small graphite nanoclusters nearby. You can see the graphite nanoclusters are highlighted with black.

When the void collapses, the graphitic inclusion nearby can expand into the space that used to be occupied by the void, causing a stronger gray tinge. Bottom line: removing the brown and/or strain from a CVD diamond can make it more gray!

S = Strain

CVD Strain Often Looks Like Streaks on Glass

Strain presents as blurriness in the crystal, and it looks almost like you can never get it fully clean.
The closest approximate natural characteristic is graining.

CVD Strain Causes Light to Scatter

You can see the “shimmer” on the CVD rough as the light hits the strain.

Strain is Not a Binary

Strain is not measured as a binary but rather exists on a scale of good to bad. There’s little to no consensus in the industry as to what is light or faint and what is strong. Strain is not a clarity setting feature, meaning it does not appear in inclusion maps or change clarity grades. All of the above diamonds are VVS in clarity.

Crystal Strain Looks Different Depending on the Type of Diamond

Another reminder that lab diamonds are not identical to natural and can be detected! It’s worth noting that HPHT has little to zero strain when viewed under cross polar filters.

Strain Starts with Seeds

The quality of seeds can vary significantly and build either a strong or weak foundation for CVD diamond growth on top. Seeds viewed through an x-ray (at right) can show faults or uneven surfaces.

One CVD reactor can have varying degrees of quality seeds. The quality of the material of the grown CVD can vary significantly for the same grower and even in the same growth run!

Seeds deteriorate with each use and the diamonds grown on top of them get worse and worse. Replacing seeds is very expensive. Many growers will use and reuse seeds far past their prime.

Post-Growth Treatment Heals Strain

Strain Accumulates Until Polycrystalline Nucleates

As strain builds, it can eventually explode, almost like a volcano, and form into polycrystalline inclusions. That does impact clarity. The diamond on left is CVD and diamond on right is HPHT. Both got the same clarity grade of I1.

So What Do You Do When Polycrystalline Forms?

You stop your machine, take the crystal out, laser off the polycrystalline layer, and put the diamond back into the reactor. What forms: striations.

S = Striations

The impact of starting and stopping the CVD reactor are rings of diamond growth known as striations. Nearly all CVD diamonds have some striations, it’s not a binary.

The image at left shows 8 growth cycles, designated by obvious rings. It’s not just the presence of these growth rings. How far apart or close together the rings are represent a timetable showing how long the growth cycles lasted in between stops. Striations can make a diamond look out of focus and lackluster.

The diamond on the bottom has over 8 growth cycles and is more heavily striated. The diamond on the top has a cleaner crystal material. Note the difference in contrast between the two diamonds.

Every time a CVD reactor is stopped and restarted, contaminants get into the plasma, which cause the rings of diamond growth to look dark gray, further contributing to color tinge face up.

Gray & Striation Case Study

This was a G color CVD diamond we sent for additional analysis to GIA’s researchers. It has a very obvious gray tinge. After spectral analysis, we concluded this was likely due to a combination of silicon defects and graphitic nano inclusions. The silicon and silicon vacancy defects were too significant to have been from the CVD viewing glass, and were likely the result of intentionally added silicon during growth. The zoning and clear growth line (shown in bright green) indicate that this diamond was likely moved from one reactor to another generation CVD reactor with a different chemistry profile. It’s possible one of the reactors was being used for R&D purposes.

Approximately 80% of GIA graded CVD diamonds are HPHT treated. Why? Proper HPHT treatment makes the diamonds better. Period.

We believe the resistance to post growth treatment is a hangover effect from the natural diamond market where there’s legitimate concern about undisclosed manmade treatment being done to a natural product. But in lab grown, the product is manmade throughout the entire process. And what one grower considers treatment another may consider simply part of the growth process.

Untreated CVD has some flaws. It’s less durable and has more crystal material issues like brown and strain. Post-growth treatment effectively heals brown and strain. Not all treated CVD is good, and not all of it is bad. 

How HPHT is Grown

Small diamond seeds are placed at the bottom of a growth cell. Catalytic metal material is placed on top. Graphite is added into a gasket. This growth cell is then placed at the center of a hydraulic press where six different anvils exert pressure on six different sides (which is why it’s called a cubic press). The press is heated to 1500 degrees Celsius and subjected to 1 million psi of pressure. The graphite is heated to the point where it melts into liquid carbon. A convection is created. As the press cools, the carbon affixes to the diamond seeds and grows atom by atom, crystalizing into diamond. The seeds with which the diamonds are grown in the rough HPHT are visible upon removal.

HPHT is Prone to Unique Color Tinges

In evaluating HPHT diamonds, we recommend looking for BGP:

B = Blue

Blue tinge in HPHT diamonds is a very common crystal defect. This is due to trace boron that is intentionally added during the growth process to compensate for nitrogen. Measurable levels of boron are considered Type IIb. 75% of HPHT diamonds submitted to GIA for grading are Type IIb, but that doesn’t necessarily mean that they all have blue tinge! Type IIb is more likely to have blue tinge, but it’s not definitive.

In the video above, the D, F, and H color HPHT diamonds have a blue tinge, but notice that the E color does not. Color is measured for the presence of any color, not just yellow.

While there certainly exist blue natural diamonds, they are exceptionally rare, making up less than 0.1% of the gemstone market and fetching significantly higher prices per carat than traditional natural or lab diamonds. It is not feasible that a member of the public would “accidentally” purchase a large Type IIb natural diamond. So having a blue tinge diamond may make someone question whether the material was diamond or something else like aquamarine or moissanite.

While a blue tinge may be a consumer’s personal preference, it is technically a crystal defect.

Why Blue Happens

For years, HPHT diamonds were yellowy orange due to the presence of nitrogen. Added boron helps to compensate for the nitrogen. In some cases you can end up with excess nitrogen, just the right compensation, or too much boron. While this practice also exists in CVD, it’s much more common and at a more significant level in HPHT.

Blue is Variable

During HPHT growth, you can have some diamonds that are blue and some that aren’t, and even within the diamond you can have some parts of the diamond that are blue and some that are not.

This is the spectral analysis of a single grower of HPHT. You can see in some cases the boron spikes are very low and in others quite high. Even though nitrogen is more likely to be dispersed throughout a diamond’s crystal lattice, boron can be growth sector dependent and quite concentrated. In other words, boron is very difficult to control.

This type of boron zoning would not be present in a natural Type IIb diamond.

Green Tinge Case Study

In some cases you can have both a growth sector of nitrogen and a growth sector of boron. In this case, this greenish tinge pear had both, resulting in blue + yellow = green. Despite having enough nitrogen to modify the color, this HPHT diamond is still Type IIb based on the boron content as there is more boron than nitrogen. This is NOT a high enough concentration to be a fancy color diamond. It received an “I” color grade.

G = Gray

There are lots of reasons why HPHT can look gray. For some, it’s simply that it has a blue tinge that looks gray in certain lights. Others can be irradiated or have elements like aluminum, titanium, nickel, or other trace metals. Some can have metallic inclusions.

The exact formulas that keep out nitrogen are tightly held trade secrets. Those secrets can determine if HPHT diamonds are grayish blue or bright white.

Gray Tinge Case Study

This is a fascinating diamond we shared with GIA. In our conversations with GIA researchers, we’re not 100% certain why it has this super obvious gray tinge. One theory is that it’s due to the presence of growth tubes, seen here under SW light as uniform streaks or claw marks. This diamond is also Type IIb, had strong phosphorescence, but does not appear blue in person. This is honestly one of the ugliest lab diamonds we’ve ever seen. Super interesting.

P = Phosphorescence

Phosphorescence is:

• an orange or blue glow seen in a diamond after exposure to long wave UV light, sunlight, or full spectrum light bulbs

• not the same thing as fluorescence

• due to boron, but it’s not necessarily seen only in blue tinge

• able to make a diamond look hazy or milky in low light environments

• able to last for a few seconds or several minutes.

We’re only discussing phosphorescence under long wave UV light and sunlight. Shortwave light is filtered by our atmosphere and using it at high power can be dangerous and should only be done by trained professionals.

Here are four HPHT diamonds. On the far left, there’s one that has a blue tinge and one that has a yellowy tinge. The yellowy tinge emerald cut is Type IIb despite not having a blue tinge. On the right there’s a blue tinge as well as a yellowy tinge HPHT stone.

The four diamonds are moved from the paper tray to a perforated tray. After just a few seconds of long wave UV light using a handheld light from Amazon (you can buy for $5) being applied, the main light is turned off. The two diamonds on the left had very strong and moderate phosphorescence and the two diamonds on the right are inert, with no reaction to long wave UV light.

Phosphorescence is not just seen in blue tinge or avoidable in yellowy tinge. It is connected to boron at an atomic level, not an optical one.

Well, That’s Interesting

These same four diamonds were left in the office for about an hour. Once the light was turned off, the diamonds glowed again. We concluded this was not, in fact, prolonged phosphorescence, but merely phosphorescence that had been activated by the office lighting. So it doesn’t take special equipment, gemological tools, or even sunlight to activate phosphorescence. You just need darkness to see it.

Why This Matters

Phosphorescence is not disclosed on a grading report and is only something that can be tested for in person. It’s also not a great “surprise.” Imagine walking into a dark movie theater and suddenly seeing your diamond glow, without warning. Consumers believe that lab diamonds are chemically identical to natural diamonds, but the number of natural diamonds that have phosphorescence under normal indoor lighting? Fewer than 0.1%. The presence of glow-in-the-dark diamonds has the potential to erode consumer trust in HPHT lab diamonds if consumers don’t know that it exists. Medium to strong phosphorescence can also make a lab diamond look cloudy/hazy in low light environments.

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