G&G in a Flash: The Latest on Laboratory-Grown Diamonds
December 2, 2024
Laboratory Growth and Treatment Methods
Most laboratory-grown diamonds passing through GIA’s laboratories are grown by CVD (chemical vapor deposition), with most undergoing post-growth HPHT (high-pressure, high-temperature) treatment to remove their color.
CVD Diamonds
When the first CVD diamonds were produced in 1952, the crystal quality and sizes were not suitable for jewelry. Some gem-quality diamonds began appearing in the 2000s. In recent years, however, rapid advancements in technology have resulted in vast quantities of high-quality CVD-grown gem diamonds.
CVD diamond growth is based on a chemical process very different from natural diamond formation. This technique involves a reactor in which hydrogen and hydrocarbon (typically methane) gases flow over one or more diamond substrates. Microwaves are used to activate a plasma, triggering a series of reactions necessary to deposit diamond material on the seeds. Hydrogen, accounting for 90–99% of the gas mixture, suppresses the growth of graphite or non-diamond carbon, which would hinder high-quality diamond formation.
This ring features a 2.14 ct heart-shaped laboratory-grown diamond with E color and VS1 clarity as well as 2.12 cts of D–F, VVS–VS laboratory-grown melee diamonds.
HPHT Diamonds
While the CVD method was developed earlier, the first gem-quality laboratory-grown diamonds were produced using the HPHT method. The HPHT method mimics some of the conditions in which natural diamonds form. A solid carbon source, typically graphite powder, is subjected to pressures of 5–6 GPa (equivalent to a depth of 150–190 km within the earth) and temperatures of 1300–1600°C, higher than those for natural diamond formation (~1040–1250°C), allowing for rapid growth. HPHT growth takes place inside a capsule that includes a carbon source, a metallic flux for dissolving the carbon to aid in growth, and a diamond seed to start the process. The temperature of the diamond seed is lower, so that carbon supersaturates and crystallizes out of the metal solution. An HPHT diamond usually takes an hour to a few weeks to grow, depending on the desired size and quality.
For both methods, a diamond substrate (often referred to as a “seed” in HPHT growth) is used to create the crystal blueprint from which the new diamond is created. The quality, size, and preparation of the substrate can have a significant impact on the resulting diamond.
These CVD-grown diamonds vary from 9.52 to 12.06 carats. Their color ranges from E to G and their clarity from VS2 to SI1. Large laboratory-grown diamonds like these have become more common in recent years.
Color, Clarity, and Carat Weight
Color
Prior to 2020, most CVD-grown diamonds were “near-colorless,” with color grades from G to N. During the mid-2010s, many CVD-grown diamonds also had gray coloration. The year 2020 saw a significant increase in the submission of colorless-grade diamonds (D, E, or F), likely due to improvements in growth and treatment procedures. Manufacturers are constantly—and successfully—refining their growth and treatment procedures to produce large, colorless diamonds.
Most early HPHT-grown diamond submissions observed at GIA starting in 2007 were yellow-orange due to nitrogen impurities or blue due to boron. Over the past 10–15 years, manufacturers have successfully eliminated nitrogen, the main cause of yellow-orange color, from laboratory-grown diamonds. There has since been a sharp decline in submissions of yellow-orange HPHT-grown diamonds, with colorless samples now representing the vast majority of submissions. In the years 2021–2023, more than 90% of HPHT-grown diamond intake was colorless—a trend that likely reflects consumer preferences.
Some CVD-grown diamonds have a brown coloration after growth. As with natural brown diamonds, CVD-grown diamonds can be enhanced using HPHT treatments to reduce or remove the brown coloration. Although similar equipment can be used for HPHT treatment and HPHT growth, the underlying methods are different. HPHT treatments are conducted at higher temperatures than those used for HPHT growth (>1600°C) and do not result in additional diamond material. Low-pressure, high-temperature (LPHT) treatment, in which samples are annealed at similarly high temperatures under a vacuum or an inert gas, can also be used to change the color of CVD-grown diamonds.
Manufacturers of CVD products can thus use recipes that promote rapid growth of diamond layers, even if it results in a brown coloration, and subsequently improve the color grade through post-growth annealing. This approach may be faster, easier, or more cost-effective than directly producing a colorless diamond using CVD. Over time, the percentage of CVD-grown diamonds exhibiting signs of annealing treatment has consistently increased. Since 2020, approximately 80% of the CVD-grown diamonds submitted to GIA have undergone post-growth processing.
These 2.00 ct Fancy Deep orange (left) and 3.00 ct Fancy Vivid orangy pink (right) CVD-grown diamonds underwent multiple treatments, including HPHT processing, irradiation, and low-temperature annealing to achieve their final color grades.
Clarity
The growth of large, colorless HPHT-grown diamonds with high purity is particularly challenging, as it requires complex ingredient and recipe development to minimize nitrogen content, as well as the ability to carefully control conditions over extended periods of time. Nitrogen speeds diamond growth, so its absence reduces growth rates. Whereas CVD-grown diamonds can be created over a series of growth steps, HPHT-grown diamonds are produced in a single uninterrupted run, making a highly controlled environment much more necessary.
Carat Weight
The size of gem-quality CVD-grown diamonds has seen a dramatic increase over time. From 2000 to 2010, most CVD-grown diamonds submitted to GIA were under half a carat. Today, the majority of them exceed 3 ct. This change in size reflects improvements in CVD methods as well as the availability of larger diamond substrates. The years since 2010 have seen a very rapid increase in size. By January 2022, the largest faceted CVD-grown diamond was 16.41 ct. Since that time, the benchmark has more than quadrupled to 75.33 ct.
Some HPHT-grown diamonds surpass 100 carats in size. The largest recorded laboratory-grown diamond is a 150.42 ct HPHT-grown crystal with good quality, created in November 2021.
These cuboctahedral near-colorless HPHT-grown diamond crystals are commonly grown up to a few carats in size.
Global Laboratory-Grown Diamond Producers
One industry report estimated that 6–7 million carats of gem-quality laboratory-grown diamonds were produced globally in 2020. China produced approximately 3 million carats (mostly HPHT), followed by India with about 1.5 million carats (mostly CVD) and the United States with about 1 million carats (mostly CVD).
Market leaders in China use the HPHT method to mass produce small, melee-size goods and diamond grits and powders for abrasives. Chinese CVD producers also grow high-quality gemstones, including large, untreated colorless diamonds and pink and blue diamonds.
India has an estimated 4,000–6,000 CVD reactors based in Surat in the state of Gujarat, which is also the world’s leading diamond cutting and polishing center. A company there produced the largest known faceted CVD diamond to date, a 75.33 ct square emerald cut displayed at the 2024 JCK Las Vegas show. The original crystal reportedly took nine months to grow. In 2023, Indian Prime Minister Narendra Modi presented a 7.50 ct F-color, VVS2-clarity CVD-grown diamond to First Lady Jill Biden during a visit to the White House, showing the increase in prestige and importance of laboratory-grown diamonds.
CVD diamond production in the United States arose due to the semiconductor industry. Diamond’s remarkable properties—including high hardness, high thermal conductivity, low thermal expansion, wide optical window, biocompatibility, and high resistance to corrosion, acid, and radiation—have a wide range of engineering applications.
Tens of carats of near-colorless HPHT diamonds are grown in single runs and faceted into melee gems like these.
Did you know that the vast majority of colorless to near-colorless laboratory-grown diamonds are type II, meaning they have no detectable nitrogen impurities? In contrast, only about 1% of natural diamonds are type II. Therefore, most diamonds submitted for extensive analysis to determine whether they are laboratory-grown are type II.
To learn more about identifying laboratory-grown diamonds, especially melee, read the full article.
