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146 UPDATE ON LABORATORY-GROWN DIAMONDS GEMS & GEMOLOGY SUMMER 2024
The introduction of laboratory-grown diamonds
to the consumer market has expanded the va-
riety of products available but also increased
the complexity of identification for many in the
trade. Laboratory-grown diamonds that are colorless
to near-colorless share many gemological and physi-
cal properties with their natural counterparts (figure
1), which presents a challenge for independent
gemologists and appraisers in distinguishing these
gems from natural diamonds. Consequently, gemol-
ogists have needed to invest in powerful analytical
testing equipment or depend on gemological labora-
tories for accurate identification.
Colorless to near-colorless laboratory-grown dia-
monds are type II, meaning they have no detectable
nitrogen impurities (Breeding and Shigley, 2009). By
contrast, only about 1% of natural diamonds are type
II (Smith et al., 2016; Eaton-Magaña et al., 2020). De-
spite the increasing prevalence of laboratory-grown
diamonds within the trade, their volume remains
small compared to that of natural diamonds submit-
ted for grading. Therefore, only those diamonds that
test as type II require extensive analysis to determine
whether they are laboratory-grown. These can be pro-
duced by high-pressure, high-temperature (HPHT) or
chemical vapor deposition (CVD) processes.
This study summarizes the wide range of labora-
tory-grown diamonds submitted to GIA over the
years, allowing these stones to tell the story. Over the
past 20 years, advances in diamond growth processes
have substantially altered the color and size of gem-
quality stones submitted to GIA. In addition, this sur-
vey emphasizes some new laboratory-grown products
that could become more common in the future.
LABORATORY-GROWN DIAMONDS:
AN UPDATE ON IDENTIFICATION AND
PRODUCTS EVALUATED AT GIA
Sally Eaton-Magaña, Matthew F. Hardman, and Shoko Odake
FEATURE ARTICLES
Over the past two decades, GIA has documented a rapid evolution of laboratory-grown diamonds; this article provides
a comprehensive overview of these developments and summarizes novel laboratory-grown diamonds that may become
more common in the future. The industry has seen a significant increase in the quantity, size, and quality of labora-
tory-grown diamonds, making them viable for commercialization on a larger scale. Nevertheless, there have been rel-
atively few changes in laboratory-grown diamonds during the last five years, indicating that developments have largely
stabilized for now. This overview summarizes the two diamond growth processes: high-pressure, high-temperature
(HPHT) and chemical vapor deposition (CVD). It explores the major trends observed by GIA since 2007, the year it
began issuing synthetic diamond grading reports. CVD products now dominate the supply of laboratory-grown diamonds
submitted for grading reports, with the majority of these also undergoing post-growth HPHT treatment to remove their
color. This article discusses methods and strategies for identifying laboratory-grown diamonds by providing their distin-
guishing gemological characteristics as well as results from recent developments in advanced testing approaches.
In Brief
• HPHT- and CVD-grown diamond size, quantity, and
color grades have rapidly improved over the decades.
• A small number of laboratory-grown diamonds show
that high concentrations of impurities and post-
growth treatments can produce a variety of unusual
colors.
• While identification criteria have remained largely the
same through time, some laboratory-grown diamonds
require experienced gemologists and advanced ana-
lytical techniques to confirm laboratory-grown origin.
See end of article for About the Authors and Acknowledgments.
GEMS & GEMOLOGY, Vol. 60, No. 2, pp. 146–167,
http://dx.doi.org/10.5741/GEMS.60.2.146
© 2024 Gemological Institute of America
OVERVIEW OF LABORATORY-GROWN
DIAMOND MANUFACTURE
Although the mechanisms for laboratory growth of
diamonds are well established (e.g., Eaton-Magaña
and Shigley, 2016; Eaton-Magaña et al., 2017; D’Hae-
nens-Johansson et al., 2022), this article provides a
brief summary of the CVD and HPHT growth
processes. 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 prepa-
ration of the substrate can have a significant impact
on the resulting diamond (D’Haenens-Johansson et
al., 2022). Substrate availability—previously a limit-
ing factor for commercial production—has dramati-
cally improved to meet demand.
A report by Bain & Company (Linde et al., 2021)
estimated that 6–7 million carats of gem-quality lab-
oratory-grown diamonds were produced globally in
2020. China led the way with approximately 3 mil-
lion carats (mostly grown using HPHT), followed by
India with about 1.5 million carats (mostly CVD) and
the United States with about 1 million carats (CVD).
Laboratory-grown diamond production has contin-
ued to expand as public perceptions of its use in jew-
elry have evolved. In October 2021, industry analyst
Paul Zimnisky estimated that laboratory-grown dia-
mond jewelry accounted for approximately 3.4% of
the global diamond jewelry market by value in 2018.
He forecast an increase to 7.5% in 2021 and 11.5%
by 2025. In January 2024, he revised the 2025 projec-
tion to ~20% (Zimnisky, 2021, 2024).
HPHT-grown diamonds are the market leaders in
China, including the mass production of small,
melee-size goods by both private and government-
funded companies such as Zhengzhou Sino-Crystal
Diamond Co., Zhongnan Diamond Co., and Henan
Huanghe Whirlwind Co. (Linde et al., 2021). HPHT
technology has long been used to manufacture dia-
mond grits and powders for the abrasives industry,
setting the stage for the rapid development of gem-
quality materials. Chinese CVD producers have also
demonstrated the ability to grow high-quality gem-
stones. Shanghai Zhengshi Technology Co. produces
large, untreated colorless CVD-grown diamonds
(Myagkaya and Johnson, 2021; Wang et al., 2022),
while Ningbo Crysdiam Technology Co. creates col-
orless, pink, and blue CVD products (Lu et al., 2019).
India’s output of laboratory-grown diamonds
using the CVD method has accelerated dramatically
in recent years, supported by an estimated 4,000–
6,000 CVD reactors (Rego, 2023). Many of these
manufacturers are based in Surat in the state of Gu-
jarat, which is also the world’s leading diamond cut-
ting and polishing center. Ethereal Green Diamond
produces CVD-grown diamonds in very large sizes,
including the largest faceted example to date, a 75.33
ct square emerald cut displayed at the 2024 JCK Las
Vegas show. The crystal from which it was fashioned
reportedly took nine months to grow (Ord, 2024).
Greenlab Diamonds attracted global attention when
Indian Prime Minister Narendra Modi presented one
of their CVD-grown products to First Lady Jill Biden
during a 2023 visit to the White House. This 7.50 ct
UPDATE ON LABORATORY-GROWN DIAMONDS GEMS & GEMOLOGY SUMMER 2024 147
Figure 1. This 10.02 ct
E-color, VS1-clarity emer-
ald-cut diamond is an
example of the great
strides made in HPHT
growth technology in the
past two decades, as lab-
oratory-grown diamonds
have become an impor-
tant sector of the gem
diamond market. Photo
by Johnny Leung. The
as-grown CVD diamond
plate (1.24 ct, 8.41 ×
8.60 × 1.26 mm) was
manufactured by GIA
at its New Jersey re-
search facility. Photo by
Adrian Chan.
F-color, VVS2-clarity diamond was faceted from a 17
ct crystal that took 40–45 days to synthesize (Fedow,
2023). The 75 ct and 7.50 ct weights for these CVD-
grown diamonds were both intended to commemo-
rate the 75th anniversary of India’s independence.
This high-profile gift demonstrated the dramatic
change in attitudes toward laboratory-grown dia-
monds in recent years.
CVD diamond production in the United States
arose as a byproduct of the semiconductor industry,
which harnessed them for a range of technological
uses. Indeed, diamond’s remarkable combination of
properties—high hardness, high thermal conductiv-
ity, low thermal expansion, wide optical window,
biocompatibility, and high resistance to corrosion,
acid, and radiation—has sparked a wide range of en-
gineering applications (e.g., De Wit, 2018; Markham
and Twitchen, 2020). Some of the players that pro-
duce both engineering-related and gem products have
included Washington Diamonds, Diamond Foundry,
and Plasmability.
CVD Growth. CVD diamond growth is based on a
gas-phase chemical process that bears almost no re-
semblance to natural diamond formation. This tech-
nique involves a reactor in which hydrogen and
hydrocarbon (typically methane) feed gases flow over
one or more diamond seeds. Microwaves are used to
activate a plasma, creating a mixture of molecular,
radical, and ionic species that are involved in 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 di-
amond formation.
For many decades after the first growth of CVD di-
amond in 1952, the crystal quality and sizes were not
suited for gem applications. Only limited quantities
of these diamonds were available in the early 2000s
(Wang et al., 2003, 2005, 2007; Martineau et al., 2004;
Angus, 2014). Since then, there have been notable im-
provements to CVD growth techniques (e.g., Butler
et al., 2009; Liang et al., 2009; Nad et al., 2015, 2016;
Tallaire et al., 2006, 2017), which have yielded sub-
stantial amounts of high-quality CVD-grown gem di-
amonds (e.g., Wang et al., 2010, 2012; Linde et al.,
2021; Smith, 2023), including the large specimens
mentioned earlier.
HPHT Growth. The HPHT method mimics some of
the essential conditions under 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 tempera-
tures of 1300–1600°C. These temperatures are higher
than those for natural diamond formation of ~1040–
1250°C (Stachel and Luth, 2015), allowing for rapid
growth. HPHT growth takes place inside a capsule that
includes the carbon source, a metallic flux for dissolv-
ing the carbon to aid in growth, and a diamond seed to
initiate the process (Stoupin et al., 2016; Tallaire et al.,
2017; D’Haenens-Johansson et al., 2022). The diamond
seed is at a lower temperature, so that carbon super-
saturates and crystallizes out of the metal solution. An
HPHT-grown diamond can usually be grown in a time
frame ranging from an hour to a few weeks, depending
on the desired size and quality (Sumiya et al., 2015;
D’Haenens-Johansson et al., 2015a).
While the CVD method was developed earlier
(Angus, 2014), the first gem-quality laboratory-grown
diamonds were produced using the HPHT method
(Shigley et al., 2002, 2004). Most early HPHT prod-
ucts had saturated fancy colors, often yellow-orange
or yellow due to isolated nitrogen impurities or blue
due to boron. Over the past 10–15 years, there has
been a significant shift toward colorless to near-col-
orless products (D’Haenens-Johansson et al., 2014;
Eaton-Magaña et al., 2017). Additionally, large
HPHT-grown diamonds have been created, with
Meylor Global reporting crystals surpassing 100 ct in
size produced by Alkor-D (“Meylor Global…,” 2020;
D’Haenens-Johansson et al., 2022). The largest
recorded laboratory-grown diamond is a 150.42 ct
HPHT-grown crystal (28.55 × 28.25 × 22.53 mm) with
good quality, created in November 2021. To date,
there are no documented reports of faceted HPHT-
grown diamonds larger than 100 ct.
DISTRIBUTION OF QUALITY FACTORS
AMONG LABORATORY-GROWN PRODUCTS
GIA maintains a comprehensive database of all types
of gemstones submitted to the laboratory, including
natural, treated, and laboratory-grown diamonds, both
fancy-color and colorless. This resource provides a
unique opportunity to review historical data and ana-
lyze submission trends over time. The results of GIA’s
examination of tens of thousands of HPHT-grown and
CVD-grown diamonds are documented in figures 2–6
and box A. These include updates to articles that dis-
cussed data from years prior (Eaton-Magaña and
Shigley, 2016; Eaton-Magaña et al., 2017, 2021b).
GIA has documented the color distribution of
CVD-grown diamonds per year (figure 2). Through-
148 UPDATE ON LABORATORY-GROWN DIAMONDS GEMS & GEMOLOGY SUMMER 2024
out the first decade of the 2000s, CVD submissions
to GIA were relatively low, so the submissions for
some years had to be aggregated graphically. For
many years, most samples were “near-colorless,”
with color grades from G to N. Prior to 2020, only a
small percentage of CVD submissions had colorless
grades (D, E, or F). However, 2020 saw a significant
increase in the submission of colorless CVD-grown
diamonds, likely due to improvements in growth and
treatment procedures by established diamond man-
ufacturers and the emergence of additional growers
with new approaches. Moreover, a significant num-
ber of CVD-grown diamonds during the mid-2010s
were observed to have a gray coloration (e.g., Ardon
and Eaton-Magaña, 2014), possibly produced unin-
tentionally through defect contamination during
growth—an effect that may be even more evident fol-
lowing the annealing treatments commonly used to
decolorize brown-hued CVD-grown diamonds. Gray
color in CVD-grown diamonds has been linked to the
presence of non-diamond inclusions referred to as
“carbon nanoclusters,” whose introduction is af-
fected by growth conditions (Zaitsev et al., 2020).
The conditions causing gray-colored CVD-grown di-
amonds have been mostly eliminated, as these
stones are no longer being produced and submitted.
These trends indicate that manufacturers are con-
stantly—and successfully—refining their growth and
treatment procedures to produce large, colorless dia-
monds in response to consumer tastes.
UPDATE ON LABORATORY-GROWN DIAMONDS GEMS & GEMOLOGY SUMMER 2024 149
Figure 2. The color dis-
tribution of CVD-grown
diamonds submitted to
GIA, 2003–2023. Several
early years with low
submission numbers are
combined. Updated
from Eaton-Magaña and
Shigley (2016).
2003–2008
2010–2011
2009
2012
2013
2014
2015
2016
2017
2018
2019
2020
2021
2022
2023
0
100
80
60
40
20
Brown
Green-blue
Gray
Yellow
“Pink” (brown-pink,
purple-pink, etc.)
“Near-colorless”
(G–N)
Colorless (D–F)
YEAR
RELATIVE PROPORTION (%)
COLOR DISTRIBUTION OF CVD-GROWN DIAMONDS
Figure 3. The color distri-
bution of HPHT-grown
diamonds submitted to
GIA, 2007–2023. Up-
dated from Eaton-Mag-
aña et al. (2017).
2007
2009
2008
2010
2011
2012
2013
2014
2016
2015
2017
2018
2019
2020
2021
2022
2023
0
20
40
60
80
100 Brown to black
Green
Blue
Orange
Yellow- o ran ge
Yellow
Pink to red
“Near-colorless”
(G–N)
Colorless (D–F)
YEAR
RELATIVE PROPORTION (%)
COLOR DISTRIBUTION OF HPHT-GROWN DIAMONDS
150 UPDATE ON LABORATORY-GROWN DIAMONDS GEMS & GEMOLOGY SUMMER 2024
Type IIb CVD-Grown Diamonds
In recent years, HPHT-grown diamonds have been notable
for their lack of bodycolor and low boron content. Fancy-
color blue HPHT-grown diamonds deliberately doped
with boron were some of the earliest gem laboratory-
grown diamonds reported (e.g., Shigley et al., 2002). In col-
orless HPHT-grown diamonds, boron is usually
incorporated accidentally, with concentrations typically
<20 ppb (D’Haenens-Johansson et al., 2014, 2015a; Eaton-
Magaña et al., 2017). Analysis of HPHT-grown D-to-Z dia -
monds submitted to GIA since 2020 reveals that more
than 80% contain boron concentrations detectable by in-
frared spectroscopy (uncompensated boron at 2800 cm–1),
meaning they are type IIb. Notably, the boron detected by
IR is not the total boron present in the diamond, as high
amounts of compensating defects can render boron unde-
tectable (Gaillou et al., 2012). Trace amounts of boron are
associated with the phosphorescence often observed in
these materials (Watanabe et al., 1997).
Meanwhile, colorless to near-colorless CVD-grown
diamonds often have had a brownish coloration and were
classified as type IIa, without detectable boron impuri-
ties. Type IIb CVD-grown diamonds were quite rare until
the start of the 2020s, when the number of colorless to
near-colorless CVD-grown diamonds with a low concen-
tration of uncompensated boron, evidenced by the 2800
cm–1 peak in their IR spectra, began to increase (figure A-
1). Since 2020, ~5% of CVD-grown diamonds have
shown detectable levels of boron, typically at low con-
centrations of <10 ppb, which are too low to produce a
noticeable difference in diamond color.
The proportion of type IIb CVD-grown diamond sub-
missions increased substantially in 2020–2021. Since
then, the percentage of type IIb CVD-grown diamond
submissions for many quarters has been greater than 5%
(figure A-1A). It is important to note that this chart per-
tains to GIA laboratory submissions only, and global sta-
tistics may differ. Additionally, the increase in type IIb
CVD diamonds could be limited to a few producers and
might not represent a consistent increase across all man-
ufacturers. The data is further subdivided into type IIb
CVD-grown diamonds weighing <4 ct and ≥4 ct, indicat-
ing a smaller percentage of type IIb CVD-grown dia-
monds submitted in 2022–2023, but also a dramatic shift
to larger sizes among type IIb material. One notable ex-
BOX A: RECENT TRENDS IN LABORATORY-GROWN DIAMONDS
Figure A-1. Statistics for CVD-grown diamond submis-
sions identified as type IIb are illustrated in this series of
plots. A: The dataset of all CVD-grown diamonds identi-
fied as type IIb from 2018 through 2023 shows a signifi-
cant increase in type IIb diamonds larger than 4 ct (the
percentages across all years in the plot sum to 100%). Be-
fore 2018, only 17 type IIb CVD-grown diamonds were
submitted. B: Color grade distribution of type IIa and type
IIb submissions. The type IIb diamonds are shifted toward
higher color grades than their type IIa counterparts. C: A
box and whisker plot comparing the photoluminescence
(PL) intensity of the NV0 center between type IIa and type
IIb CVD-grown diamonds. The solid horizontal line corre-
sponds to the median value, the boxes correspond to the
interquartile range (IQR; 25th–75th percentile), and the
dashed “whiskers” extend 1.5× IQR. Samples beyond the
whiskers are considered outliers. The NV0 center is notice-
ably more intense in many type IIa stones.
10
0
2018 2019 2020 2021 2022 2023
8
6
4
2
2024
40
20
0
15
10
5
35
30
25
104
101
10–2
100
10–1
103
102
IIbIIa
DE FGH I J K LMN
575 nm peak area
(Raman-normalized)
A
B
C
<4 carat s
≥4 carats
Type IIa
Type IIb
YEAR
TYPE IIb CVD-GROWN DIAMONDS
COLOR
COLOR GRADE DISTRIBUTION
DIAMOND TYPE
PL INTENSITY
NV0 PEAK INTENSITY
RELATIVE PROPORTION (%)RELATIVE PROPORTION (%)
UPDATE ON LABORATORY-GROWN DIAMONDS GEMS & GEMOLOGY SUMMER 2024 151
ample of larger type IIb CVD material is a 34.59 ct emer-
ald-cut diamond grown by Ethereal Green with a measured
uncompensated boron concentration of ~2 ppb (Tam and
Poon, 2023).
Among CVD-grown diamonds submitted to GIA, ~80%
have been subjected to post-growth HPHT treatment to im-
prove their color grade (Eaton-Magaña et al., 2021b); among
the type IIb CVD-grown diamonds, the percentage of color-
less to near-colorless samples that have undergone HPHT
treatment is slightly higher (~85%). Additionally, the type
IIb submissions tend to have a slightly higher color grade
than type IIa CVD-grown diamonds (figure A-1B). Statistical
analysis of prominent PL features (NV0, NV–, and SiV–) indi-
cates negligible differences in SiV– concentrations between
type IIa and type IIb CVD-grown diamonds. Conversely, the
type IIb population has lower median NV0 and NV– concen-
trations than type IIa (figure A-1C). Although there is signif-
icant overlap between the two diamond types, the median
of the normalized peak area for NV0 is noticeably larger in
type IIa material than in type IIb. The normalized peak area
in NV– is also greater in type IIa material, but this distinction
is less pronounced.
The incorporation of boron into CVD-grown diamonds
remains uncertain—it could be incidental during the
growth process or limited to doping by a few producers.
Additionally, uncompensated boron (i.e., not electrically
Figure A-2. Statistics of all laboratory-grown diamond submissions 4 ct or larger, the majority of which are CVD-grown.
A: The distribution of the dataset plotted by year shows that most have been submitted since 2021. B: The distribution
by color grade reveals that most HPHT-grown diamonds are D-color, while most CVD-grown diamonds (and laboratory-
grown diamonds overall) are E-color. C: The majority of large laboratory-grown diamonds weighed between 4 and 5 ct.
D: Although round diamonds outnumber the other shapes, there is a relatively even distribution of shapes compared
with natural diamonds, in which rounds are a heavy majority.
70
60
50
40
30
20
10
0
45
0
5
10
15
20
25
30
35
40
70
60
50
40
30
20
10
0
30
25
20
15
10
5
0
2016 2017 2018 2019 2020 2021 2022 2023 D E F G H I J K L M N
Round
Cushion
Oval
Pear
Heart
Emerald
Marquise
Rectangle
Square
Other
4–4.99
5–5.99
6–9.99
10–14.99
15–19.99
20–29.99
30+
HPHT CVD
AB
CD
YEAR
LABORATORY-GROWN DIAMOND SUBMISSIONS ≥4 ct
RELATIVE
PROPORTION (%)
RELATIVE
PROPORTION (%)
RELATIVE
PROPORTION (%)
RELATIVE
PROPORTION (%)
COLOR
WEIGHT (ct) SHAPE
compensated by other defects or impurities) is the only
known boron-related defect that is consistently de-
tectable by IR or PL spectroscopy in CVD-grown dia-
monds. This means that other boron-related defects may
be present, but they cannot be directly detected by these
methods. Furthermore, some CVD-grown diamonds
may have comparable total boron concentrations but be
classified as type IIa due to higher amounts of compen-
sating defects (e.g., nitrogen).
Large (≥4 ct) Laboratory-Grown Diamonds. In recent
years, GIA has seen an increase in the quantity of large
(defined here as 4 ct or larger) laboratory-grown dia-
monds produced by both CVD and HPHT processes. Fig-
ure A-2 plots some of the parameters for large D-to-Z
laboratory-grown diamonds submitted to GIA, illustrat-
ing the quantity of submissions and the distribution of
color grade, carat weight, and shape. Most of the large
laboratory-grown diamonds submitted since 2021 have
been CVD (figure A-2A), consistent with the submission
trends among laboratory-grown diamonds in general (see
figure 7).
The majority of large CVD-grown diamond submis-
sions are colorless, falling in the D–F range (figure A-2B).
The highest proportion of CVD-grown submissions (and
laboratory-grown diamonds in general) are E-color dia-
The color distribution of HPHT-grown diamonds
over the years (figure 3) is much different. Most early
HPHT-grown diamond submissions, starting with
the introduction of synthetic diamond reports at GIA
in 2007, were yellow-orange (e.g., Shigley et al.,
2004). With advances in HPHT growth processes,
manufacturers successfully eliminated nitrogen from
the lattice in growing diamonds—the main cause of
their yellow-orange color. There has since been a
sharp decline in submissions of yellow-orange
HPHT-grown diamonds. Colorless samples now rep-
resent the vast majority of submissions, particularly
in the years 2021–2023, when >90% of HPHT-grown
diamond intake was colorless—a trend that likely re-
flects consumer preferences.
The size of gem-quality CVD-grown diamonds
has seen a dramatic increase over time. There has
been a consistent trend toward larger sizes (figure 4).
In the first decade of the 2000s, most CVD-grown di-
amonds 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 large diamond substrates.
Figure 5 shows milestones in record size for CVD-
grown diamonds, illustrating the rapid evolution in
gem-quality CVD growth. Starting from 2003, when
GIA received its first faceted CVD-grown diamond
for research purposes, specimens remained small
(and mainly brown) until about 2010 (Wang et al.,
2007, 2010). The years since then have seen a very
rapid increase in size. By January 2022, the largest
faceted CVD diamond was 16.41 ct (Wang et al.,
2022). Since that time, the benchmark has more than
quadrupled to 75.33 ct. Now that manufacturers
have demonstrated the ability to produce large CVD-
grown diamonds, future production will be guided by
demand and profitability.
Figure 6 shows the annual weight distribution of
faceted HPHT-grown diamonds. The majority of the
larger HPHT-grown diamonds were in the less-mar-
152 UPDATE ON LABORATORY-GROWN DIAMONDS GEMS & GEMOLOGY SUMMER 2024
monds. Among HPHT-grown submissions, D-color dia-
monds represent the largest share. Among natural dia-
monds, the highest proportion fall in the F–G color range
(Eaton-Magaña et al., 2020).
As expected, most of the submissions larger than 4
ct are between 4 and 5 ct, with the submissions decreas-
ing at progressively higher weights (figure A-2C). While
70% of D-to-Z natural diamonds are round (Eaton-Ma-
gaña et al., 2020), there is a much more even distribu-
tion of shapes among laboratory-grown diamonds (figure
A-2D). This is likely due to efforts to maximize weight
retention from the laboratory-created crystal shape,
which is distinctly different from that of natural dia-
mond rough.
Figure 4. The weight
distribution of CVD-
grown diamonds sub-
mitted to GIA,
2008–2023. The trend
lines show an increase
in median values for
three weight categories:
the smallest 10% each
year (bottom), all dia-
monds submitted each
year (middle), and the
largest 10% each year
(top). Updated from
Eaton-Magaña and
Shigley (2016).
2008
2009
2010
2011
2012
2013
2014
2015
2016
2017
2018
2019
2020
2021
2022
2023
0
10
8
6
4
2
Median (largest 10%)
Median (all)
Median (smallest 10%)
YEAR
WEIGHT (ct)
WEIGHT DISTRIBUTION OF CVD-GROWN DIAMONDS
ketable yellow-orange color range. The growth of
large, colorless HPHT-grown diamonds with high pu-
rity is particularly challenging, as it requires complex
ingredient and recipe development to minimize ni-
trogen incorporation, as well as the ability to care-
fully control conditions over extended periods
(D’Haenens-Johansson et al., 2022). Nitrogen has a
catalytic effect on diamond growth, so its absence re-
UPDATE ON LABORATORY-GROWN DIAMONDS GEMS & GEMOLOGY SUMMER 2024 153
Figure 5. Size milestones over the past two decades for CVD-grown diamonds. The current record holder is a 75.33
ct emerald cut announced in May 2024. Updated from Eaton-Magaña and Shigley (2016).
First faceted CVD
larger than 1 carat
First round brilliant
CVD larger than 1 carat
First client-submitted
larger than 1 carat
First near-colorless
larger than 1 carat
submitted by client
0
50
40
100
80
90
70
60
30
20
10
2002 20 04 2006 2008 2010 2012 2014 2016 2018 2020 2022 2024
1.11 1.14 1. 25 1.05 2.16
3.23 5.19
9.04 12. 75 14 .6 0
16.41
27.27
30.18
34.59
75.33
50.25
2.51
YEAR
SIZE MILESTONES FOR CVD-GROWN DIAMONDS
WEIGHT (ct)
Figure 6. The annual
weight distribution of
HPHT-grown diamonds
submitted to GIA,
2008–2023. The trend
lines show the change
in median values for
three weight categories:
the smallest 10% each
year (bottom), all dia-
monds submitted that
year (middle), and the
largest 10% each year
(top). Updated from
Eaton-Magaña et al.
(2017).
2008
2009
2010
2011
2012
2013
2014
2015
2016
2017
2018
2019
2020
2021
2022
2023
0
6
4
2
Median (largest 10%)
Median (all)
Median (smallest 10%)
YEAR
WEIGHT (ct)
WEIGHT DISTRIBUTION OF HPHT-GROWN DIAMONDS
duces growth rates. Whereas CVD diamonds can be
created over a series of growth steps, alleviating some
process control requirements, HPHT-grown dia-
monds are produced in a single uninterrupted run.
Since 2016, there has been a shift toward colorless
material (figure 3) and an increase in size, with the
majority exceeding 2 ct (figure 6).
Figure 7 shows the cumulative submissions of
HPHT- and CVD-grown diamonds to GIA since
2007, when GIA began receiving them. This figure
indicates that the vast majority of both HPHT- and
CVD-grown diamond submissions have been since
2021. Initially, most of these were created using the
HPHT method. Over the ensuing years, however, the
CVD population consistently increased and eventu-
ally outnumbered HPHT-grown submissions by
around 2016. At present, GIA averages more CVD-
grown diamond submissions per day than it once did
during an entire year.
Some CVD-grown diamonds have a brown col-
oration after growth, associated with the presence of
vacancy clusters and/or nitrogen-related defects
(Barnes et al., 2006; Jones et al., 2007; Mäki et al., 2007;
Khan et al., 2013; Zaitsev et al., 2020, 2021). As with
natural brown diamonds (e.g., Fisher et al., 2009), CVD-
grown diamonds can be enhanced using HPHT treat-
ments to reduce or remove the brown coloration (Wang
et al., 2003, 2012; Charles et al., 2004; Mäki et al.,
2007). Although similar equipment can be used for
HPHT treatment and HPHT growth, it is important to
note that the underlying methods are distinct. Further-
more, HPHT treatments are conducted at higher tem-
peratures than those used for HPHT growth (>1600°C)
and do not result in the synthesis of additional dia-
mond material. Low-pressure, high-temperature
(LPHT) treatment, in which samples are annealed at
similarly high temperatures under vacuum or an inert
gas, can also be used to change the color of CVD-grown
diamonds (Meng et al., 2008; Liang et al., 2009; Johnson
et al., 2023). Manufacturers of CVD products can thus
use recipes that promote rapid growth of diamond lay-
ers, even if it results in a brown coloration, and subse-
quently improve the color grade through post-growth
annealing. This approach may be faster, easier, or more
cost-effective than directly producing a colorless dia-
mond using CVD. Over time, there has been a consis-
tent increase in the percentage of CVD-grown
diamonds exhibiting signs of annealing treatment
(Eaton-Magaña et al., 2021b). Since 2020, approxi-
mately 80% of the CVD diamonds submitted to GIA
have undergone post-growth processing.
IDENTIFICATION AND MELEE DIAMONDS
The gem trade has been facing challenges in identi-
fying laboratory-grown diamonds due to the rapid in-
crease in production as well as mixing (both
accidental and intentional) with natural diamonds.
154 UPDATE ON LABORATORY-GROWN DIAMONDS GEMS & GEMOLOGY SUMMER 2024
Figure 7. The cumula-
tive increase in labora-
tory-grown diamond
submissions, 2008–
2023. Most of the sub-
missions have been in
the last few years,
marked by a dramatic
rise in CVD-grown dia-
monds. For the years
2008–2021 (inset), the
vast majority of sub-
mitted stones were
HPHT-grown.
2008 2010 2014 2016 2018 2020 2022 20242012
0
100
80 5
4
3
2
1
0
60
40
20
2008
2009
2010
2011
2012
2013
2014
2015
2016
2017
2018
2019
2020
2021
CVD
HPHT
YEAR
CUMULATIVE PROPORTION (%)
LABORATORY-GROWN DIAMOND SUBMISSIONS
While HPHT and CVD growth processes have been
refined, many of the gemological criteria and strate-
gies have remained consistent. Prior publications
have documented the detailed gemological charac-
teristics of HPHT- and CVD-grown diamonds (e.g.,
Eaton-Magaña and Shigley, 2016; Eaton-Magaña et
al., 2017; D’Haenens-Johansson et al., 2022), and the
reader is referred to those review articles for details
on gemological characteristics. The conclusive iden-
tification of a laboratory-grown origin typically re-
quires a combination of gemological features, yet
simple visual inspection can still be valuable. For in-
stance, a “LABORATORY-GROWN” inscription or
manufacturer-specific marking to support trans-
parency and traceability is commonly found on the
girdle of commercial-size products.
Although certain gemological features strongly
suggest a laboratory-grown origin, there are exceptions
due to the wide range of growth recipes and treat-
ments. Phosphorescence—the emission of light from
a sample after exposure to UV—is often used as a key
indicator for colorless and near-colorless HPHT-grown
diamonds, which generally exhibit intense, long-lived
blue-green phosphorescence. Only a few natural type
IIb diamonds and some CVD-grown diamonds exhibit
a comparable reaction. However, low-dose irradiation
can reduce or eliminate the phosphorescence response
in HPHT-grown diamonds, as initially reported by
Robinson (2018) and confirmed by subsequent exper-
iments (e.g., figure 8 and Gao et al., 2021). Relying on
a phosphorescence observation or any other single
gemological observation in testing colorless HPHT-
grown diamonds is not advisable.
Melee Diamonds. Identifying melee-size diamonds
as laboratory-grown presents a particular challenge.
Due to their small size, they are difficult to handle
and not suited for testing using certain laboratory in-
struments; they also require higher magnification for
detailed microscopic inspection and often lack mark-
ings from a manufacturer or gemological laboratory
(Choi et al., 2020). A tiny melee stone can take two
to three times longer to analyze than a half-carat di-
amond. Most melee-size laboratory-grown diamonds
come from manufacturers in China, where the
HPHT growth method is preferred for growing small
diamonds economically, allowing the simultaneous
production of thousands of nearly colorless diamonds
using microscopic seed crystals.
Given the small size and abundance of melee,
screening instruments are particularly important in
analyzing them. But because there are significant dif-
UPDATE ON LABORATORY-GROWN DIAMONDS GEMS & GEMOLOGY SUMMER 2024 155
Figure 8. These ~0.4 ct HPHT-grown diamonds remained colorless after low-dose laboratory irradiation. Prior to ir-
radiation, these samples displayed observable phosphorescence to deep UV. Images by Diego Sanchez (top) and
Sally Eaton-Magaña (middle and bottom).
Phosphorescence
before irradiation
Color after
irradiation
Phosphorescence
after irradiation
ferences between HPHT and CVD growth methods,
as well as various types of post-growth treatment,
there is no cost-effective or rapid screening tool that
can definitively identify all laboratory-grown dia-
monds. Instead, the majority of screening tools avail-
able in the consumer market provide a “pass” or
“refer” result for colorless to near-colorless diamonds
(Tsai and D’Haenens-Johansson, 2019), with “pass”
indicating the test sample is natural. Diamonds that
produce a “refer” result may be natural or laboratory-
grown. These require further testing for conclusive
identification, which involves a combination of
gemological techniques or examination by a labora-
tory (e.g., D’Haenens-Johansson et al., 2022). Depend-
ing on the method of testing, some screening devices
may not be able to refer simulants, incorrectly pass-
ing them as natural. Users must understand a screen-
ing instrument’s scope and limitations (e.g., color
range, size, and simulants). The Natural Diamond
Council reports on independent testing of popular
screening equipment under the ASSURE program
(Natural Diamond Council, 2023).
Many screening approaches for colorless or near-
colorless diamonds are based on the diamond’s type.
Diamond type, as described by Breeding and Shigley
(2009), is a valuable classification for scientific analy-
sis. To summarize briefly, a type II diamond contains
no nitrogen detectable by infrared (IR) spectroscopy,
while a type Ia diamond shows the presence of aggre-
gated nitrogen. Figure 9 illustrates the clear differ-
ences between natural type Ia and laboratory-grown
type II diamond populations. The overwhelming ma-
jority of natural diamonds in the D to N range are
type Ia, while all colorless laboratory-grown dia-
monds are type II. This distinction provides a solid
basis for various screening approaches and an effi-
cient first step in the identification process. How-
ever, there are some caveats to advanced testing,
which will be discussed in the next section.
ADVANCED TESTING CHALLENGES AND
NEW TECHNIQUES
CVD-grown diamonds often have distinctive gemo-
logical and spectroscopic features that make their
identification straightforward using the tools avail-
able in a gemological laboratory (e.g., Eaton-Magaña
and Shigley, 2016; D’Haenens-Johansson et al.,
2022). This section will discuss some of the current
challenges with advanced testing, as well as addi-
tional spectroscopic and imaging instrumentation
used.
The spectroscopic characteristics of laboratory-
grown diamonds, especially the defects identified
through photoluminescence (PL) spectroscopy, have
been thoroughly documented (Wang et al., 2012;
D’Haenens-Johansson et al., 2014, 2022; Eaton-Mag-
aña and Shigley, 2016).
The silicon vacancy (SiV–) peak at 736.6/736.9 nm
has long been a consistent indicator of CVD-grown
diamonds. Silicon incorporation is often caused by
156 UPDATE ON LABORATORY-GROWN DIAMONDS GEMS & GEMOLOGY SUMMER 2024
Figure 9. Distribution of
diamond types (type Ia
and type II) among col-
orless to near-colorless
diamonds. Adapted
from Eaton-Magaña et
al. (2020).
0
100
80
60
40
20
Natural
99.1%
0.9%
100 % 100%
HPHT-grown CVD-grown
Typ e Ia
Type II
GROWTH METHOD
DISTRIBUTION (%)
DISTRIBUTION OF DIAMOND TYPES
accidental doping due to silicon-containing compo-
nents such as quartz windows in the reactor cham-
ber. However, silicon-related defects are also detected
occasionally in natural diamonds (Breeding and
Wang, 2008; Lai et al., 2020). Furthermore, an in-
creasing number of CVD-grown diamonds do not ex-
hibit detectable SiV– peaks in their PL spectra. In
recent years, the GIA laboratory has noticed a higher
percentage of CVD-grown diamonds that have only
a very weak or undetectable SiV– feature in the PL
spectra. Through the years, there has been a pro-
nounced decrease in SiV– intensity when detected
(figure 10A). In the future, the absence of a detectable
SiV– peak could become more common in CVD-
grown diamonds, reducing its value as a diagnostic
feature.
Similarly, the fluorescence of CVD-grown dia-
monds when excited by deep UV using the Dia-
mondView instrument (excitation wavelength <225
nm; Welbourn et al., 1996) is often very distinctive
and recognizable. Growth layering, corresponding to
defects at growth interfaces, is commonly visible
when a diamond is exposed to deep UV (e.g., figure
11, top left). Recently, however, we have seen some
examples of CVD-grown diamond that do not exhibit
traditional features and patterns (e.g., Eaton-Magaña
UPDATE ON LABORATORY-GROWN DIAMONDS GEMS & GEMOLOGY SUMMER 2024 157
Figure 10. A: This semi-
logarithmic plot shows
the decrease in SiV– in-
tensity among available
CVD-grown diamonds
examined by year using
514 nm excitation; over
the ten-year period
shown here, the average
SiV− concentration de-
creased by two orders of
magnitude. The peak
area of the silicon dou-
blet at 736.6/736.9 nm is
normalized to the unsat-
urated diamond Raman
line and then averaged
for each year; the error
bars correspond to the
standard deviation. Al-
though the SiV– feature
is often listed as a reli-
able indicator of CVD
growth, it is not ob-
served in all such stones.
B: This 2.22 ct G-color
marquise proved to be a
CVD-grown diamond
with post-growth HPHT
treatment, based on
spectroscopy and imag-
ing. However, the deep-
UV fluorescence image
appears nominally simi-
lar to deep-UV fluores-
cence images often seen
in natural diamonds (C).
Recently submitted CVD Natural diamond
10–1
100
101
102
103
104
2014
2015
2016
2017
2018
2019
2020
2021
2022
2023
A
BC
YEAR
NORMALIZED SiV– PEAK
AVERAGE SiV– IN CVD-GROWN DIAMONDS
and Shigley, 2016; D’Haenens-Johansson et al., 2022).
Instead, they display a fluorescence that closely re-
sembles what we often see in type II natural dia-
monds (figure 10, B and C). The ambiguity of
deep-UV fluorescence patterns occasionally requires
the use of more specialized imaging technologies
such as cathodoluminescence (CL) imaging. While
CL imaging is not commonly applied even at gemo-
logical laboratories, it has successfully revealed
growth features diagnostic of CVD growth that were
not reliably identified with deep-UV imaging alone
(figure 12).
Recently, several new analytical techniques have
emerged. Photoluminescence mapping enables the
rapid collection of PL spectra across a diamond’s sur-
face, generating a map of PL intensities (Eaton-Magaña
et al., 2021a). This method can automatically collect
thousands of spectra in situ for a crystal in less than
10 minutes while the stone is held at liquid nitrogen
temperature (–196°C). The size of each pixel in the col-
lected spectrum can be as small as a few microns, en-
abling the determination of PL spectra and diamond
defects at the micron scale.
For example, silicon-related defects are commonly
introduced in CVD-grown diamonds by plasma etch-
ing of reactor components (Robins et al., 1989; Barjon
et al., 2005). The negatively charged SiV– defects emit-
ting at 737 nm can be easily detected by PL, and their
distribution can reveal changes in growth conditions.
In a CVD-grown diamond produced using a series of
158 UPDATE ON LABORATORY-GROWN DIAMONDS GEMS & GEMOLOGY SUMMER 2024
Figure 11. Top: The DiamondView’s deep-UV fluorescence imaging of a 2.02 ct near-colorless as-grown CVD dia-
mond is presented along with the results for PL mapping of the pavilion facets using 532 nm excitation and sub-
mersion in liquid nitrogen. This sample shows multiple growth layers, with the highest concentrations of SiV– near
the growth interfaces. Bottom: A 0.50 ct D-color HPHT-grown diamond shows different growth sectors through
deep-UV fluorescence imaging and PL mapping using 633 nm excitation and liquid nitrogen. The SiV– concentra-
tion is confined to the {111} growth sectors. A metallic rod inclusion is visible in the deep-UV image, and its pres-
ence is also displayed in the PL map as an area of lower SiV– concentration (red arrow in both images).
CVD-grown
diamond
HPHT-grown
diamond
Deep-UV Fluorescence Imaging PL mapping of SiV– defect
High
Low
growth steps, these interruptions lead to distinct spa-
tial differences in SiV– concentration (figure 11, top)
that reflect the layered growth of CVD diamonds.
These variations may be more pronounced than for
other commonly observed defects such as nitrogen va-
cancy (NV) centers.
PL mapping can also reveal the distinctive
cuboctahedral growth pattern in HPHT-grown dia-
monds, in which SiV– defects are confined to the
octahedral {111} growth sectors. PL mapping of var-
ious other defects in both CVD- and HPHT-grown
diamonds has also been reported (e.g., Loudin,
2017; Eaton-Magaña et al., 2021a). Given the het-
erogeneity of defects in the diamond lattice for
some stones, PL mapping offers advantages over
single-point analyses using traditional, non-map-
ping PL spectroscopy. PL mapping can show the
impurity distribution and growth pattern and, with
thousands of spectra collected, increases the prob-
ability of defect detection compared to a single-
point PL spectrum.
Despite the changes in laboratory growth
processes and post-growth treatments over time, the
combination of distinguishing features can still con-
firm a diamond’s natural or synthetic origin. This re-
inforces the importance of not relying on only one
gemological or spectroscopic feature. Instead, it is es-
sential to evaluate a range of characteristics.
UNCONVENTIONAL LABORATORY-GROWN
DIAMONDS
With the influx of laboratory-grown diamonds sub-
mitted to gemological laboratories in recent years,
we have been able to observe a subset of products
that are atypical. Many of these appear to be experi-
mental prototypes created by a combination of novel
growth and/or post-growth treatment methods made
possible by readily available and inexpensive labora-
tory-grown material. We have collected several ex-
amples of uncommon laboratory-grown diamonds
submitted to GIA, some of which may become more
prevalent in the future.
UPDATE ON LABORATORY-GROWN DIAMONDS GEMS & GEMOLOGY SUMMER 2024 159
Figure 12. A: A deep-UV fluorescence image of a 1.83 ct
treated CVD-grown diamond with a Fancy Intense
orangy pink color. The red fluorescence is due to high
concentrations of NV centers. B: A deep-UV fluores-
cence image with a short-pass filter eliminates the red
fluorescence so that underlying fluorescence colors, and
often additional details, can be revealed. While the very
strong NV-related fluorescence is filtered out and glows
green due to H3 fluorescence, diagnostic growth fea-
tures are not distinguishable. C: A CL image shows the
striations that were not displayed by fluorescence imag-
ing. Strong fluorescence can sometimes obscure CVD-
specific features, and CL is occasionally needed to
unambiguously identify the diamond.
A
B
C
CVD Overgrowth on Natural Diamonds. In 2017,
GIA encountered the first client-submitted CVD
overgrowth on a natural faceted gem diamond (also
called a “hybrid”) (Moe et al., 2017; see figure 13,
left). With these hybrids, the manufacturer places a
natural diamond in the CVD reactor as the seed plate
rather than a CVD-grown or HPHT-grown diamond,
which is standard for the CVD process. Both the seed
and the overgrowth layer are retained in the faceted
gem. CVD overgrowth diamonds are generally de-
signed to add weight or produce a different color. The
overgrowth described in Tang et al. (2018) success-
fully increased the weight of the original diamond
such that the 0.11 ct finished gem hybrid diamond
was 64% CVD-grown. Other hybrid diamonds re-
ported were generated with the intent to achieve a
fancy blue color (Fritsch and Phelps, 1993; Moe et al.,
2017; Ardon and McElhenny, 2019).
The CVD overgrowth layer has a limited thick-
ness when deposited on a faceted natural diamond.
In order to reduce non-diamond carbon formation
during the CVD process, seed plates are often cut
within 2° of the cubic {100} direction (Berdermann et
al., 2004). The faceted diamond surfaces would devi-
ate significantly from the desired {100} direction, lim-
iting the potential thickness of a deposited CVD
layer. Only a small amount of weight can be added,
and the table facet is the most likely growth face for
these cases of CVD overgrowth (Tang et al., 2018).
To achieve a blue color with a boron-doped CVD
diamond overgrowth, only a thin film (<0.1 mm) is
needed to significantly influence the stone’s color.
The deep-UV fluorescence image in figure 13 (right)
shows a marked color change at the interface be-
tween the natural diamond substrate and the CVD
overgrowth layers, resulting in a Fancy grayish green-
ish blue color (Ardon and McElhenny, 2019). Only a
small number of these CVD overgrowth diamonds
have been documented by gemological labs. Al-
though their identification is straightforward, it is
worth noting that some hybrid diamonds may go un-
detected by standard screening equipment if the un-
derlying natural diamond is type Ia, as many
screening instruments are based (either directly or in-
directly) on differences between type Ia and type II
diamond (figure 9). Kitawaki et al. (2023) produced
hybrid diamonds by growing colorless CVD diamond
on top of natural colorless type Ia diamonds. As ex-
pected, these hybrid diamonds passed standard
screening tests using UV transparency, N3 defect de-
tection, and bulk Fourier-transform infrared (FTIR)
measurement. However, deep-UV imaging and PL
spectroscopy identified them as natural diamonds
with a CVD diamond layer. Growing colorless CVD
diamond on natural type Ia diamond substrates re-
quires precise control of the temperature around the
natural diamond used as a substrate, and its applica-
tion currently offers little economic advantage.
Color Changes in CVD-Grown Diamonds. Advances
in laboratory growth techniques have enabled manu-
facturers to produce unique diamond products for
which there is no known natural equivalent. In some
photochromic diamonds, for example, defect concen-
trations and thus color can be temporarily modified
by exposure to certain lighting conditions. CVD-
grown diamonds that have been deliberately doped
with high levels of silicon may show an interesting
photochromic effect. The doping typically results in
a prominent absorption peak at 737 nm caused by the
160 UPDATE ON LABORATORY-GROWN DIAMONDS GEMS & GEMOLOGY SUMMER 2024
Figure 13. Left: This 0.64 ct Fancy grayish greenish blue stone proved to be a hybrid. Photo by Robison McMurtry.
Right: The majority of the sample is natural type Ia diamond, causing a deep blue fluorescence, but boron in the CVD
overgrowth layer creates its greenish blue fluorescence.
CVD
Natural
SiV– defect. These diamonds may have a gray or pink-
ish brown to pink appearance when observed in am-
bient lighting conditions. With UV excitation,
however, the concentration of the neutrally charged
defect counterpart (SiV0, with absorption at 946 nm)
increases due to charge transfer from SiV– centers, re-
sulting in a more bluish color (figure 14; D’Haenens-
Johansson et al., 2015b; Breeze et al., 2020). This color
change is temporary, and the diamond will revert to
its original stable color when exposed to white light.
UPDATE ON LABORATORY-GROWN DIAMONDS GEMS & GEMOLOGY SUMMER 2024 161
Figure 14. Top: This 0.65 ct CVD-grown diamond has a stable color of Fancy brown-pink but converts to a Fancy
Intense blue with deep-UV excitation. The visible/near-infrared (Vis-NIR) absorption spectrum for the stable
brown-pink color shows a dramatic but temporary shift with a decrease in the SiV– centers at 737 nm and an in-
crease in SiV0 at 946 nm. (D’Haenens-Johansson et al., 2015b). Bottom: Additional examples of photochromism
seen in other high-silicon CVD-grown diamonds.
Fancy brown-pink
Faint pink
Fancy Light pink
Fancy violet-gray
Fancy Dark pinkish brown
Fancy Intense blue
Fancy Light grayish blue
Fancy grayish blue
Fancy grayish blue
Fancy Dark grayish blue
White light
UV
400 500 600 700 800 900 1000
SiV–
830.4
857.5
870
SiV0
946
After white light
After UV light
WAVELENGTH (nm)
VIS-NIR SPECTRA
ABSORBANCE
Because the unstable blue color in CVD-grown di-
amonds can potentially revert to a stable pinkish
brown or gray color, it is important to confirm the
color stability of blue or gray CVD-grown diamonds
by exposing them to white light for at least 30 min-
utes during testing. Such diamonds can also change
color when heated (e.g., 550°C for 20 minutes in the
dark; Breeze et al., 2020). Heating causes electron
donors to convert SiV– into SiV2–, which does not ab-
sorb light (Breeze et al., 2020). The application of heat
can cause the pinkish brown or gray diamond to ap-
pear colorless—this change is also temporary, and the
diamond will revert to its stable color as it cools and
is exposed to white light.
An additional form of reversible color change can
be produced in CVD-grown diamonds, unrelated to
silicon defects. Exposing some CVD-grown diamonds
to UV radiation can cause the bodycolor to darken,
while heating to temperatures above 450°C can de-
crease a stone’s color saturation (Khan et al., 2010).
These color changes are only temporary and fully re-
versible, though the unstable color can be maintained
if the stone is kept in the dark or inside opaque stone
papers. Khan et al. (2009) attributed the color change
in these diamonds to electron transfer from isolated
nitrogen atoms to electron acceptor defects such as
NVH0. NVH0 is a defect that exhibits IR absorption
at 3123 cm–1 and can be detected in some as-grown
CVD diamonds. Similar to the SiV– ↔ SiV0 color
change, the original color can be fully restored using
white light.
Although there have been some concerns in the
trade (Bates, 2019), all photochromic and ther-
mochromic color changes observed in laboratory-
grown diamonds submitted to GIA have been
temporary and fully reversible, without any perma-
nent or long-term color changes. Furthermore, analy-
sis of CVD-grown diamonds that were submitted
multiple times showed no significant or systematic
change in color grade, even with stones that were
submitted to the GIA laboratory at intervals of sev-
eral months to a few years.
Unusual Fancy-Color Diamonds. Due to their vastly
different growth conditions and chemistries, labora-
tory-grown diamonds can have unique colors. In
HPHT-grown diamond, doping with high amounts of
nickel produces an attractive green coloration that is
quite distinct from the greenish appearance created
by post-growth irradiation. By incorporating large
amounts of nickel in the diamond lattice, an absorp-
tion band develops in the red portion of the visible
spectrum, centered at about 685 nm, thus forming a
transmission window in the green portion of the
spectrum. To date, only a few HPHT-grown dia-
monds with saturated green coloration have been
submitted to GIA (figure 15, left; Johnson and
Myagkaya, 2017), along with a few dozen having
Faint to Fancy Light green bodycolor due to high
amounts of nickel defects (e.g., Eaton-Magaña, 2019).
Some natural diamonds also have a greenish color
caused by nickel impurities (Breeding et al., 2018),
though generally at far lower concentrations than
what is possible in laboratory-created versions, and
they often have nitrogen-related defects that create a
green-yellow color instead.
In HPHT-grown diamond, distinctive color zon-
ing can occur as a result of growth sectoring (Howell
et al., 2019). These growth sectors are detected in
most HPHT-grown diamonds under deep-UV imag-
162 UPDATE ON LABORATORY-GROWN DIAMONDS GEMS & GEMOLOGY SUMMER 2024
Figure 15. Left: A 0.42 ct
Fancy Deep green HPHT-
grown diamond that owes
its color to high amounts
of nickel doping (Johnson
and Myagkaya, 2017).
Right: A 2.20 ct Fancy
Deep brownish orange
treated HPHT-grown dia-
mond with different de-
fect concentrations
created in the various
growth sectors. Photos by
Jian Xin (Jae) Liao (left)
and Diego Sanchez (right).
ing due to the various concentrations of defects in-
corporated into each sector (Shigley et al., 2004). In
some HPHT-grown diamonds, the defect concentra-
tions are high enough and distinct enough between
the growth sectors to create dramatic color zoning
(e.g., figure 15, right; Eaton-Magaña and Linzmeyer,
2023). Another recent example is a 4.32 ct HPHT-
grown diamond with pronounced blue and yellow
color zones (due to boron and single nitrogen, respec-
tively) that are visible face-up; these colors were in-
tended to evoke the Ukrainian flag (Jeffay, 2023).
CVD-Grown Diamonds with Invisible Markings. A
small subset of laboratory-grown diamond submis-
sions have distinctive features that are only revealed
using deep-UV excitation. Two CVD-grown dia-
monds—0.60 ct and 1.93 ct, both enhanced by HPHT
treatment—had no identifying patterns when ob-
served visually or with the microscope. When ex-
posed to deep UV, however, logo marks and numbers
appeared (figure 16; Odake and Kadam, 2023). These
markings were not visible on the 1.93 ct sample
when PL mapped with 455, 532, 633, or 830 nm laser.
The different font styles and marking positions sug-
gest that these two examples were produced by dif-
ferent methods. Although the method of creating
these markings is unknown, they were likely in-
tended as a tracking and security measure.
HPHT-Grown Diamonds with Strain. In general,
colorless and near-colorless HPHT-grown diamonds
have low impurity concentrations and uniform
pressure is applied during growth, resulting in high
crystalline perfection and very weak or almost no
strain levels, except around inclusions and cracks
(D’Haenens-Johansson et al., 2022). Though rare,
HPHT-grown diamonds with strain have been previ-
ously reported (Ardon and Batin, 2016). Recently, the
GIA laboratory received five stones showing two un-
usual features for HPHT-grown diamonds: a GR1 de-
fect [V0] detected by PL spectroscopy, as well as the
presence of strain (indicated by anomalous birefrin-
gence when examining the diamond through crossed
polarizers; figure 17). GR1 defects are not usually de-
tected in HPHT-grown colorless diamonds submitted
to GIA laboratories. Analysis of the GR1 distribution
using PL mapping in these strained HPHT-grown dia-
monds shows that the defect is limited to the {110}
sector (figure 17C), consistent with previous reports
(Loudin, 2017). Although this feature is currently rare,
it is likely that these stones were distorted during syn-
thesis, introducing the strain, and that GR1 was cre-
ated by subsequent irradiation treatment.
CONCLUSIONS
With the advancement of CVD and HPHT growth
processes, gem-quality laboratory-grown diamonds
have become a significant part of the global gem
trade. The rapid evolution of both HPHT and CVD
diamond growth is driven by manufacturers’ efforts
to develop innovative new products for both engi-
neering applications and gem purposes. As manufac-
turers refine their growth methods, they can better
tailor these products to satisfy consumer tastes and
UPDATE ON LABORATORY-GROWN DIAMONDS GEMS & GEMOLOGY SUMMER 2024 163
Figure 16. Left: This 0.60 ct I-color CVD-grown diamond shows a logo mark on the star facet that is only visible
with fluorescence imaging. Right: The DiamondView image of a 1.93 ct F-color CVD-grown diamond shows num-
bers on the table facet. Images by Jemini Sawant.
create niche products. In the coming years, we expect
that most products will be in the colorless range and
increasingly larger (e.g., figure 18). With the addi-
tional supply, we will likely see a greater variety of
stones with a range of colors.
If the submissions to GIA are an accurate repre-
sentation of the products on the market (excluding
melee diamonds), then the data in this study indi-
cates that the market for laboratory-grown diamonds
has shifted dramatically toward colorless and near-
colorless products (figures 2 and 3). There are a few
exceptions, such as the fancy-color laboratory-grown
diamonds treated by some producers (Bates, 2021).
Based on current trends, the quantity of HPHT-
grown diamonds is expected to increase most signif-
icantly at the extreme ends of the weight scale: both
small melee-sized stones and larger samples exceed-
ing 4 ct. CVD-grown diamonds are being submitted
at commercial sizes (i.e., non-melee) in far greater
quantities than their HPHT-grown counterparts, and
this trend is expected to continue.
Many manufacturers worldwide have committed
significant capital investment toward their labora-
tory-grown diamond facilities (Lu et al., 2019; De-
164 UPDATE ON LABORATORY-GROWN DIAMONDS GEMS & GEMOLOGY SUMMER 2024
Figure 17. A: Unlike most HPHT-grown diamonds, this 1.60 ct D-color pear shows the presence of strain and
anomalous birefringence when viewed through crossed polarizers. B: The deep-UV fluorescence image shows a
common fluorescence color for colorless HPHT-grown diamonds. The various growth sectors are indicated. C: PL
mapping of the peak area for the GR1 center using 633 nm excitation indicates it is largely limited to the {110}
growth sector.
High
Low
{110}
GR1
ABC
Figure 18. Large laboratory-grown diamonds such as these CVD-grown diamonds have become increasingly com-
mon the last few years. From left: a 12.06 ct G-color, VS2 emerald cut; an 11.36 ct E-color, SI1 round brilliant; a
10.42 ct G-color, VS2 heart brilliant; a 10.19 ct F-color, VS2 emerald cut; and a 9.52 ct E-color, VS2 oval brilliant.
Photos by Gaurav Bera.
Marco, 2020) and developed marketing efforts pro-
moting these stones as a readily available or environ-
mentally friendly commodity (e.g., Lu et al., 2019;
Bates, 2021). Although beyond the scope of this arti-
cle, there are indications that in recent years labora-
tory-grown diamonds have begun to complement
and, in some cases, replace sectors of the natural dia-
mond market (Bates, 2023), especially as their prices
have fallen. The long-term impact of laboratory-
grown diamonds on the industry will continue to be
assessed in the coming years.
This article has summarized many of the develop-
ments in laboratory-grown diamond production, based
on submissions to GIA over the last two decades. Be-
yond providing a snapshot of the current range of prod-
ucts seen at GIA, this also allows us to project trends
into the future as technological advances enable the
controlled production of stones with specific sizes and
colors. Even with the rapid progress of the past decade
and ongoing developments, GIA’s advanced analytical
techniques, backed by decades of research, can easily
identify and characterize laboratory-grown diamonds.
UPDATE ON LABORATORY-GROWN DIAMONDS GEMS & GEMOLOGY SUMMER 2024 165
ACKNOWLEDGMENTS
We thank Dr. Ulrika D’Haenens-Johansson for her excellent feed-
back and proofreading and the peer reviewers for suggestions
and comments that improved the content of this article. We also
thank Elina Myagkaya for collecting the cathodoluminescence
image in figure 12, Adrian Chan for his assistance with photogra-
phy of CVD diamond plates, and the analytic technicians who
collect the spectroscopic data and fluorescence images daily at
all of GIA’s global laboratories, whose consistency, reliability, and
vigilance make such studies of our GIA database possible.
ABOUT THE AUTHORS
Dr. Sally Eaton-Magaña is senior manager of diamond identifica-
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Carlsbad, California. Dr. Shoko Odake is senior manager of dia-
mond identification at GIA in Tokyo.
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