Feature

Man-made Diamonds: Questions and Answers


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A natural faceted diamond, on the left, and a man-made faceted diamond on the right. Photo by GIA

If it looks like a diamond and sparkles like a diamond, it’s a diamond – right?

These days it’s not so easy to pick out a natural diamond from among the assortment of colourless, shiny stones on display at a jewellery counter. Synthetic diamonds (also known as man-made and lab-grown) and imitation gem materials may also have a spot among the natural diamonds mined around the world. It can be confusing to know what you are looking at and what best fits what you want in a piece of jewellery.

Natural diamonds are one of nature's wonders. They can be several billion years old, made of a single element (carbon), and are formed deep in the earth under extreme pressure and high temperature. These intense geological conditions produce the physical properties – transparency, optical appearance and hardness – valued in a cut and polished diamond.

“When it comes to a natural diamond, we are looking at something that is really a rarity and a treasure from Earth,” says Brenda Harwick, manager of on campus and lab gemmology instruction for GIA. “But man-made diamonds have a place in the market as long as consumers know exactly what it is that they are buying. There are other synthetics out there – such as synthetic ruby, emerald and sapphire – so it’s not something new for the jewellery industry to have a synthetic alternative.”

A group of 10 colourless rough crystals on a black background.
A factory in Shandong, China, is producing a large number of colourless HPHT man-made diamonds for the jewellery industry. These colourless crystals are up to 3.5 carats. Jinan Zhongwu New Materials Company Ltd. Shandong, China. Photo by Jian Xin Liao/GIA

The jewellery industry uses special terms for manufactured and look-alike materials: synthetic (man-made, lab-grown or lab-created) and imitation (simulants).

Man-made diamonds are grown in a laboratory or factory. Their growth structure and atomic level defects allow them to be readily separated from natural diamonds by a well-equipped laboratory such as GIA. Because natural diamonds and man-made diamonds have some of the same physical and other properties, even a skilled jeweller or trained gemmologist cannot distinguish them by sight alone. It takes specialist equipment and trained staff in a gemmological laboratory to conclusively identify a diamond.

A colourful group of cubic zirconia set in jewellery - rings, earrings and bracelet – and loose.
Cubic zirconia can be created as colourless or with colour, such as these large pieces. From left: 44.49 cts, 29.86 cts and 56.60 cts. Photo by Tino Hammid

Diamond imitations only mimic the look of natural diamonds. Common simulants include colourless sapphire, colourless zircon, synthetic cubic zirconia (zirconium oxide, CZ) and synthetic moissanite (silicon carbide). Cubic zirconia and synthetic moissanite are the most important in the market. They may be natural or made in a lab, but do not share the chemical composition or physical properties of natural or man-made diamonds. Because simulants do not share those properties with diamond, they are more easily distinguished by gemmologists.

A group of 11 pieces of cut and polished moissanite. All round brilliants, except for one emerald cut.
Near-colourless synthetic moissanite is marketed for jewellery purposes as a diamond imitation. The faceted pieces shown here, weighing from 0.09 to 0.57 ct, illustrate the appearance of this material. Photo by Tino Hammid.

Man-made diamonds are a more common topic of discussion at the jewellery counter these days because they are being used more frequently in jewellery.

“They may be an option for some jewellery buyers as long as they are correctly identified,” says Dr James Shigley, a long-standing member of GIA’s research team who has studied and published research on man-made diamonds for decades.

It is important that you have some basic information about man-made diamonds and know what questions to ask before you shop.

What are man-made diamonds? Are they real diamonds?

Man-made diamonds have been produced for industrial purposes since the 1950s and are used in a wide variety of applications: telecommunications, laser optics, healthcare and more. In 1970, researchers at General Electric created the first, small, gem-quality synthetic diamonds that could be faceted as gems. By the mid-1980s, other manufacturers were able to grow them. Initially, they were mostly small and yellow, but the quality steadily improved, and today both colourless and coloured gem-quality man-made diamonds are available to use in jewellery.

A pink round diamond, a yellow round diamond, a colourless cushion-cut diamond, a blue heart-shaped diamond and a yellow heart-shaped diamond.
The identification of natural, man-made and treated diamonds has been the principal focus of the gem research programme at GIA for more than 60 years. This is a group of natural coloured diamonds (0.38 to 1.04 cts). Photos by Robert Weldon, composite by Kevin Schumacher/GIA

Robert Crowningshield, one of the pioneers of GIA’s research on diamonds and vice president of GIA for many years beginning in 1950, was able to examine some of GE’s man-made diamonds in 1970. He reported on them in a Gems & Gemology article titled “General Electric’s Cuttable Synthetic Diamonds”in 1971.

“Based on his examination of a few of these first experimentally grown synthetic diamonds, it’s amazing to me that he was able to recognise some of the distinctive visual gemmological properties of synthetic diamonds – and that those are the same visual features we look at today to identify them,” Shigley says.

The material ‘diamond’ is defined as carbon atoms in a cubic structure; both natural and synthetic diamonds are made of this material.

“The vastly different conditions under which natural diamonds and synthetic diamonds form result in differences in their growth structure and in atomic level defects, so to say that they are identical is misleading,” says Tom Moses, executive vice president and chief laboratory and research officer for GIA. “If they were identical, we would not be able to tell them apart.”

But because they share essentially the same physical and optical characteristics of natural diamonds, man-made diamonds have the shine and sparkle of a natural diamond when fashioned as gems.

“One of the beautiful aspects of a polished diamond is the way light interacts with it, and it has superior hardness on the Mohs scale (which means that polished surfaces are not easily scratched or damaged),” Harwick says. “A synthetic diamond has those properties as well.”

What are they called?

Many different terms are used to describe diamonds grown artificially. Look for the use of the terms synthetic, man-made, laboratory-grown or laboratory-created. These and other terms are listed in the US Federal Trade Commission (FTC) guidelines on diamonds.

“The industry uses many terms to describe them, so if you see any of these terms it’s an indication that it is synthetic,” Harwick says. “But they probably won’t use the term synthetic.”

From left: a photo of a piece of material in the centre of growth chamber and press, an illustration of cubic surfaces and a photo of rough man-made crystal.
In HPHT synthesis, a press (left) applies extremely high pressures and temperatures to a central growth chamber that contains the necessary ingredient. This results in man-made diamond crystals with combinations of cubic and octahedral faces (centre and right). Illustration by Peter Johnston for GIA Education.

How are they made?

Man-made diamonds are produced in two ways:

High Pressure, High Temperature (HPHT): A man-made diamond is produced in a laboratory or factory by mimicking the high-pressure, high-temperature conditions that form natural diamonds in the Earth. Within a growth chamber, a source of carbon dissolves in a molten metal, and carbon atoms travel through the metal to a small man-made or natural diamond seed to produce a distinctively shaped man-made diamond crystal.

Chemical Vapour Deposition (CVD): A man-made diamond is produced in a laboratory utilising carbon-rich gas (such as methane) in a vacuum chamber. The CVD process involves breaking down the molecules of methane gas into carbon and hydrogen atoms, which then are deposited on diamond seeds to produce a square-shaped, tabular man-made diamond crystal.

Like natural diamonds, synthetic diamonds can be subjected to treatments to change their colour, or to improve their face-up appearance and clarity,” Shigley says.

From left: an illustration of a plate with man-made diamonds tabular crystals on it, an illustration of the CVD cube and a photo of rough CVD crystals.
In CVD synthesis, deposition of man-made diamond occurs from a carbon-rich gas onto a flat diamond seed surface. The man-made diamond grows in thin layers, and its final thickness depends on the amount of time allowed for growth (left). This results in flat, tabular crystals (centre and right) with exteriors coated in black graphite crystals. Illustration by Peter Johnston for GIA Education.

How long does it take to make a diamond?

It typically takes a few weeks to make a man-made diamond in the laboratory. This is a much shorter period than a natural diamond spends in the Earth, which can be millions or billions of years.

Where are they made?

“We believe that commercial production of synthetic diamonds for jewellery use is taking place in China, Ukraine, Russia, Japan, the United States and perhaps elsewhere,” Shigley says.

What’s the difference?

Natural diamonds display differences in their properties from man-made diamonds due to the different growth conditions in which they form.

Crystal Shape: The temperatures for natural diamond crystal growth and diamonds made in the laboratory are similar, but diamonds grow as octahedral (eight equilateral triangular faces) crystals and man-made diamonds crystals grow with both octahedral and cubic (six equivalent square faces) crystals.

From left: an illustration of CVD, HPHT and natural diamond shapes.
Natural and man-made growth environments result in diamond crystals with distinctive shapes. From left is a comparison of CVD, HPHT and natural diamonds. Octahedral faces are shown as yellow and cubic faces as blue. Most natural diamonds grow as octahedral (right), but HPHT diamonds (centre) typically show a combination of cubic and octahedral faces. Octahedral faces are completely absent in CVD diamonds (left). Directions of crystal growth are shown by arrows. Dotted lines represent the position of the seed crystal in the HPHT diamond and the edges of the crystal in the CVD diamond. Illustration by Peter Johnston.

“Cube faces grow more quickly than octahedral faces," Shigley says. “They are preserved on synthetic diamonds, but they are not preserved on natural diamonds.”

Diamonds grow differently, depending on the growth environment:

  • Natural diamonds grow outwards on the octahedral faces
  • HPHT synthetic diamonds grow outwards on the octahedral and cube faces
  • CVD synthetic diamonds grow mainly upwards in one direction (a cube face)
One natural and one man-made diamond crystal, side-by-side.
A comparison of rough diamonds shows a 0.83 ct natural diamond crystal on the left and a 1.02 ct HPHT crystal on the right. Both crystals are from the GIA Research Collection. Photo by Orasa Weldon.

Inclusions: Natural and man-made diamonds can exhibit various inclusions (fractures, breaks, other crystals, hollow tubes), so they are not always diagnostic tools for gem identification, Shigley says.

Colour: Man-made diamonds are commonly colourless, near-colourless, light to dark yellow or yellow-brown; they are less commonly blue, pink red or green. Man-made diamonds can be subjected to the same colour treatments as natural diamonds, so any colour is possible.

Clarity: Man-made diamonds can vary from low to high clarity.

Cut: The cut of a man-made diamond is the same as that of a natural diamond – any cut is possible. Round brilliant is the most common shape and cutting style for colourless man-made diamonds.

Coloured man-made diamonds and larger man-made diamonds are more often fashioned into a fancy shape to retain more weight from the original crystal. The shape of the crystal also influences the choice of faceting styles.

How big are they?

Man-made diamond producers are capable of growing all different sizes, from melee up to 10 carats or more, Harwick says. Typically, most commercial sizes are less than 2 carats, except for melee-size, which can be abundant.

Man-made polished diamonds fall into three size categories, according to Shigley:

  • Large size (approximately 5-10 carats or more): These cut stones attract media attention, but they are quite rare and are likely to have been examined and correctly identified by a gem-testing laboratory.
  • Commercial size (approximately 0.25 to 2.5 carats): These cut stones are more abundant, but again, they are likely to be submitted to a gemmological laboratory for evaluation where they should be recognised.
  • Small or melee size (approximately 0.10 carats or smaller): These cut stones are the most abundant, and because of their small size, they will be more difficult to detect and are not often tested – this is the real identification challenge facing the jewellery industry
A variety of large, commercial and melee cut man-made gemstones are available in the market. These HPHT diamonds, from left, are 0.41 ct, 0.31 ct and 0.50 ct. and three melee-sized stones.
A variety of large, commercial and melee cut man-made gemstones are available in the market. These HPHT diamonds, from left, are 0.41 ct, 0.31 ct and 0.50 ct. and three melee-sized stones. Photo by Orasa Weldon/GIA

How does GIA identify and grade man-made diamonds?

Man-made gem diamonds have been extensively studied by gemmological researchers for the past 30 years, and much is known today about how they are grown and how they can be identified (there is a lot of published information that has been widely distributed).

“Synthetic diamond identification means distinguishing a natural diamond that formed over a long time, and very long ago, from a synthetic diamond that formed very quickly and very recently,” Shigley says.

GIA has screened every diamond submitted to its laboratory for grading for more than a decade to determine if it is natural or potentially man-made or treated. Following the initial screening, any diamond that is potentially man-made or treated undergoes rigorous examination to confirm if it is natural or man-made, and what treatments – if any – have been applied.

GIA can definitively identify both HPHT and CVD-created man-made diamonds.

A woman sits in front of GIA’s Diamond Check machine and a computer.
All items submitted to GIA for diamond grading services are examined using the GIA DiamondCheck™ to determine if the material is a natural diamond; a diamond that may require further testing for treatments or may be man-made; or non-diamond material. Photo by Jian Xin Liao/GIA.

What will a GIA grading report tell me?

GIA began to offer a report service for synthetic diamonds in 2006. These Synthetic Diamond Grading Reports, which GIA continues to offer, are distinct from GIA grading reports for natural diamonds in both their appearance and the information provided. They clearly identify that the diamond is man-made or laboratory-grown, and they evaluate colour and clarity using descriptive ranges rather than the specific grades of the colour and clarity scales.

“When these reports were introduced, there was a range of opinion in the trade about GIA grading synthetic diamonds,” Shigley says. “Since synthetic diamonds continue to be rare, and to differentiate them from what is reported on grading reports for natural diamonds, only colour and clarity ranges are used.”

In addition, the man-made diamond’s girdle is laser inscribed with its report number and a statement that the stone is laboratory- grown. GIA does this for every man-made diamond identified in its labs.

“The inscription on the girdle can be key to its identification,” Harwick says.

The reports also use the other US Federal Trade Commission (FTC) approved terms – man-made and lab-grown – for synthetic diamonds.

Three men look at diamond jewellery and paperwork at a jeweller’s counter.
There are legal and ethical requirements that a jeweller must disclose a gem’s identity at the time of sale. This helps ensure consumer confidence in what they are purchasing.

Considering a man-made diamond … what to expect?

Make sure you go to a reputable jeweller with a professionally educated gemmologist to purchase any diamond jewellery. They can act as your guide as you look at natural and man-made diamonds.

“A sales associate should articulate or represent and disclose accurately what they are presenting to you. If they are calling it ‘diamond’, you are assuming it is natural,” Harwick says. “[If it’s not natural] they need to be forthcoming in their description and are required by the FTC to call it laboratory-created, synthetic, laboratory-grown or manufacturer-created.”

Ask the sales associate if it is a natural or man-made diamond and how they know this information.

“Synthetic diamonds may be difficult for a jeweller or a trained gemmologist to recognise, but they do not present an identification challenge for GIA,” Shigley says. “There are a variety of instruments being offered to jewellers so that they can check for synthetic diamonds, but GIA does not use them so it is not appropriate for us to comment on their operation or accuracy.”

Ask for a diamond grading report from a recognised gemmological laboratory – these clearly disclose the identity of the diamond. GIA reports for natural and synthetic diamonds look very different.

“When you’re making an investment in something as precious as this, you should ask for a grading report,” Harwick says.

How much do man-made diamonds cost in relation to their natural counterparts?

Russell Shor, senior industry analyst for GIA, says that producing man-made diamonds, either by HPHT or CVD methods, is quite costly.

“The fact they can be sold for a third or less than a natural diamond suggests they are often priced relative to natural diamonds, rather than priced in a way that reflects a true market for synthetics,” Shor says. Like most technologies, however, he notes that innovations may bring down production costs and, accordingly, the demand for them will increase.

A group of nine round brilliant cut man-made diamonds on a black background.
Colourless gem-quality CVD-grown synthetic diamonds such as these (0.22-0.31 ct) are now commercially available, making proper identification important. Photos by Jian Xin Liao, composite by Kevin Schumacher/GIA.

What is the future potential of man-made diamonds?

No one knows for sure if man-made diamonds will become a popular choice for shoppers long-term. There are personal choice issues for each buyer to consider before they purchase one.

“It is up to the preference of the consumer whether they purchase a natural or synthetic diamond, however, proper disclosure about the nature of their stone is paramount,” says Wuyi Wang, director of GIA’s research and development. “As long as the origin of the diamonds is fully disclosed, consumers and the market will determine the future for synthetic diamonds.”

Amanda J. Luke is a senior communications manager at GIA. She is the editor of the GIA Insider and Alum Connect and was the editor of The Loupe magazine.