SYNTHETIC or MAN-MADE DIAMONDS?
PART 1: INTRODUCTION
First synthetic diamonds
Diamond was discovered to be carbon in 1796, and it took more than 150 years from that time until a method of diamond synthesis was invented. The secret was pursued by many scientists but not unlocked until the 1950s, when diamond was synthesized almost simultaneously by Swedish and American researchers. Pressures of over 55,000 atmospheres and 1400C, plus molten iron to facilitate the change from graphite to diamond, were necessary.
Over the past 50 years, the uses for diamonds are multiplying and advances in synthetic production have opened the floodgates to ever more innovative applications.
The first synthetic diamonds (diamond grit) were produced in the early 1950s by researchers at the Allmanna Svenska Elektriska Aktiebolaget Laboratory in Stockholm, Sweden The possibility of high-quality synthetic diamonds being produced for jewelry purposes, and the potential for their misidentification, have worried members of the jewelry trade since General Electric produced its first synthetic diamond in 1954. GE went on to become the largest producer of synthetic diamond; De Beers follows, with many other manufacturers also contributing to the
annual output of synthesized diamonds.
The diamond industry is now facing a “new diamond age” in which synthetic diamonds have chemically, physically and scientifically become identical to a natural diamond. From what is already being man-made now, it is clear that there will be lots of uses of diamond as a material over the next 50 years. De Beers estimates the potential market for industrial diamond applications at $50 billion, nearly as much as the $60 billion worldwide gem diamond jewelry sales and several times the $16.7 billion worth of diamonds in that jewelry.
The latest attempt to replicate the diamond is a product called moissanite. In 1893, Nobel Prize-winning French scientist Dr. Henri Moissan discovered minute quantities of a new mineral, natural silicon carbide. The mineral was located in an ancient meteorite found in the Diablo Canyon in Arizona and was later named moissanite.
It has only been recently produced synthetically, because it does not occur in sufficient quantities naturally to be commercially viable, so it was necessary to devise a way to synthesise to make it available in jewelry. Some jewelers cannot tell the difference between the colorless moissanite being sold today and a colorless diamond, so there's worry that fraudulent or inaccurate sales could take place after an initial moissanite purchase. There is a need for testing in gemological centers that have the respective lab instruments to help jewelers and others in the industry to distinguish these and other types of stones that are fraudulently represented as diamonds.
The density of synthetic moissanite is sufficiently different from diamond as to be a conclusive means of identifying it. Diamond has a density of 3.52 grams per cubic centimetre (SG = 3.52) whereas synthetic moissanite has a lower SG of 3.22. This means that by using the ‘heavy liquid’ called methylene iodide which has an SG of 3.33, diamonds will sink when dropped into the liquid whereas synthetic moissanite will float. This may provide a useful method of identifying a mixed parcel of diamonds and synthetic moissanites.
Another way to distinguish synthetic moissanite from diamond is to look for double refraction, or ‘doubling'. Diamond is an isotropic (singly refractive) material, so it does not exhibit ‘doubling.’
The synthesis of diamond at high pressures and high temperatures was first demonstrated by ASEA in Sweden in 1952 and at GE in 1955.
De Beers established the Adamant Research Laboratory in 1956 to intensify research into diamond synthesis. In 1958 De Beers produced its first synthetic diamond, and commissioned a synthesis plant in 1959.
Commercial production of synthetic diamonds
While General Electric pioneered the diamond-creation process and has since been selling HPHT-created diamonds for industrial uses, the diamonds were not sold as gemstones until Gemesis simplified the process and was able to create much higher quality diamonds. Several companies in the US – Gemesis Corp., Chatham Created Gems and Lucent Diamond – and Sumitomo Electric, have started to produce HPHT synthetic diamonds for the jewelry market. High-quality crystals up to 3.50 ct and faceted stones up to 1.50 ct are being produced commercially. In 1990, scientists at the De Beers Diamond Research Labaratory (DRL) synthesized a 14.2 ct industrial monocrystal diamond. In 1992, De Beers scientists grew the largest HPHT synthetic diamond of 34.80 carat for research purposes. Most HPHT synthetic diamonds are type Ib, but other types can be produced with the help of nitrogen and/or boron.
Large-scale commercial production of synthetic diamonds for jewelry has not been fully seen yet. However, the expansion of production capacity for high-quality yellow laboratory grown diamonds by the Gemesis Corp may alter the situation. Using “BARS” diamond growth equipment and expert Russian technicians, scientists and engineers from the University of Florida, the company redesigned the growth apparatus, commercialized the production and established a pilot plant in Gainesville, Florida in 2002. Over the next few years, this facility could be expanded to more than 300 “BARS” units.
According to the Diamond Trading Company (DTC), the marketing arm of diamond giant De Beers, some 200 tons of tiny synthetic diamonds, or grit, are used by the industry each year – several times total mined production. Almost all are colored crystals of up to 2ct with faceted material of up to 1ct. Synthetic diamonds are now produced with little nitrogen and as a result might not be strongly colored.
The largest crystal examined to date is a 10-carat, half-inch thick single-crystal diamond manufactured by Carnegie Institution’s Geophysical Laboratory in May this year. Researchers at the Carnegie Institution’s Geophysical Laboratory announced that for the first time they had succeeded to produce a 10-carat, half-inch thick single-crystal diamonds at rapid growth rates using a chemical vapor deposition (CVD) process. The Carnegie process growth rate is about 100 micrometers per hour and can reach up to 300 micrometers per hour.
This size is approximately five times that of commercially available diamonds produced by the standard high-pressure/high-temperature (HPHT) method and other CVD techniques. In addition, the team has made colorless single-crystal diamonds, transparent from the ultraviolet to infrared wavelengths with their CVD process.
“High-quality crystals over 3 carats are very difficult to produce using the conventional approach,” commented Dr. Russell Hemley who leads the diamond effort at Carnegie. “Several groups have begun to grow diamond single crystals by CVD, but large, colorless, and flawless ones remain a challenge. Our fabrication of 10-carat, half-inch, CVD diamonds is a major breakthrough.”
To increase the size of the crystals, the Carnegie researchers grew gem-quality diamonds sequentially on the 6 faces of a substrate diamond plate with the CVD process. By this method, three-dimensional growth of colorless single-crystal diamond in the inch-range (~300 carat) is achievable.
The synthetic diamond revolution could be damaging to both the consumer confidence in the integrity of the natural diamond and the diamond industry as a whole. As the technologies for the manufacture of synthetics and the treatment of diamonds becomes more sophisticated and widespread the diamond industry requires multiple solutions for the development of easy-to-use instruments, mainly for use at gemological laboratories designed for the disclosure of synthetics, treated diamonds and diamonds simulants. The challenge to the industry itself remains the awareness of gemologists and laboratories to keep up with the latest machines and instruments and for individual players to be aware of the need for gemological testing.
COLOR TREATED DIAMONDS AND MAN-MADE DIAMONDS
TREATMENTS AND IDENTIFICATION
Color treated diamonds
The diamond market has seen an ever increasing number of natural diamonds and diamonds types that have been subjected to some form of color changes through High Pressure High Temperature annealing or irradiation. The awareness of the market to HPHT color treated diamonds started when General Electric and Lazare Kaplan, in early 1999 introduced a technology to process certain type IIa diamonds and to convert them from brownish colors to a much more marketable colorless range or pink color. As a result of the treatment, the color of a diamond can be improved by several color grades. General Electric is producing colorless diamonds, called Bellataire, from type IIa diamonds that are nitrogen-free.
The HPHT color enhancement can also be suitable for converting brownish colored diamonds to fancy colored diamonds. Type IIb brownish diamonds can be enhanced to blue. HPHT can also change Type IaA/IaAB to yellow/orange or yellow-green
Synthetic diamonds: HPHT and CVD grown diamonds
Synthetic diamonds are made of carbon atoms, organized in the same crystal lattice as their natural counterparts. As such, both have the same basic physical and chemical properties. The only way to differentiate between natural and synthetic diamonds is studying their impurities both at the microscopic and atomic level.
Today, high-quality synthetic and treated diamonds can be created in a laboratory using two methods. One method is growing a diamond under the High Pressure High- Temperature (HPHT) technique and the other more recent method is the Chemical Vapor Deposition (CVD). The DTC Research Centre has been at the forefront of experimental diamond treatments and the manufacture of HPHT grown and CVD synthetics to identify potential challenges for identification.
HPHT grown diamonds
Although most HPHT synthetic diamonds are yellow, some have in recent years also shown large variation in color and saturation available in colorless, blue, green, orange-yellow, yellow-orange and most recently in pink. HPHT techniques can also improve the color of natural-color fancy blue and fancy pink diamonds by removing detrimental brownish undertones and thus, intensifying the color.
The HPHT method uses equipment, which tries to imitate the pressure and heat-filled environment that natural diamonds are found in the depths of the earth. The HPHT method converts carbon to diamond at high temperature and pressure using a molten metal catalyst in an environment where oxygen is not allowed. The method is sometimes also used to change or enhance the colors of some rare natural diamonds, thus making them more valuable on the market.
HPHT starts with a tiny diamond seed. In washing-machine-sized diamond growth chambers, each seed is bathed in a solution of graphite and a metal-based catalyst at very high temperatures and pressures. Under highly controlled conditions, the small diamond seed begins to grow, molecule by molecule, layer by layer, emulating nature's process.
CVD grown diamonds
One of the major advances in synthetic diamond technology is the CVD method, which forms diamonds through a chemical reaction between gases. In the early 1980s, a major breakthrough was made in Japan by Matsumoto, researchers at the National Institute of Research in Inorganic Materials (NIRIM) who reported CVD growth rates of over 1 µm/hour. The development led to initial interest in CVD processes and its potential industrial applications. In the late 1980s, De Beers started research into CVD diamond synthesis and fast become a leader in the field.
The CVD process involves the use of hydrocarbon and hydrogen gases and a source of energy. The growth of synthetic diamond by CVD techniques, which do not require the extensive apparatus to generate high pressure, has been drawing increased attention worldwide. As such CVD is also a more economical method of production.
Most CVD grown diamonds are type IIa. CVD can be manipulated to make particular shapes of diamond much more effectively than the HPHT method which compresses carbon into diamond using molten metal as a catalyst. That means wafer-thin layers of diamond can be produced for use in microprocessors, or thicker diamonds for other purposes.
But the CVD process gives the producer more control over the diamond produced and, vitally, can produce colorless stones. According to Apollo Diamond, CVD will eventually produce diamonds to compete openly in the market with mined stones. Apollo started in 2004 the commercial production of CVD synthetic diamond.
The producer has reported that, initially, 5,000-10,000 carats of faceted CVD synthetic diamond will be available. Most of these goods will be quarters and thirds, but by the end of 2004, stones as large as a full carat would be on the market.
While larger sizes will be able to be identified by a selected number of professional gemological laboratories, which have the necessary testing equipment, smaller diamond sizes under a carat are often not sold with grading reports, which raises some concern. The majority of synthetic diamonds now being produced are colored stones. Most CVD diamonds are brown, limiting their optical applications. It takes longer to grow a colorless diamond than a colored diamond and as such they are less cost-effective.
Most recently, the diamond market has also seen CVD grown diamonds, which have also been subjected to HPHT color annealing for color enhancement. Treating type IIa brownish CVD grown diamonds with HPHT can produce lighter to colorless and sometimes pinkish results.
HPHT color treated diamonds
Gemological laboratories today are required to be able test whether a diamond is suitable for HPHT annealing, ie. color improvement and whether a diamond has undergone color treatment.
Currently, the recognition of HPHT-treated diamonds involves the determination of various visual properties (such as color and features seen with magnification), as well as characterization by several spectroscopic techniques. HPHT-treated diamonds were introduced into the jewelry trade in the late 1990s, and despite progress in their recognition, their identification remains a challenge. While some detection methodologies have been established, the large number of diamonds requiring testing with sophisticated analytical instrumentation poses a logistical problem for some gemological laboratories.
Color treated HPHT diamonds are highly fluorescent and contain easily observed absorption characteristics as well as inclusion. The majority of color treated diamonds are type IIa diamonds, which are very rare in nature. They are almost free of nitrogen transparent in part of infrared and have irregular shapes.
HPHT will continue to be a controversial topic, with grading labs trying to perfect ways to detect the always-improving process so that consumers can receive full disclosure about the diamonds they purchase. The Federal Trade Commission recommends that HPHT is disclosed. It has become common practice for gemological laboratories to clearly indicate on diamond grading reports if the diamond is "HPHT annealed" or "artificially irradiated". At the Gemological Institute of America (GIA), diamonds are laser-inscribed with the words "HPHT PROCESSED" or "IRRADIATED" on the girdle.
Type IIa diamond is the rare type of diamond that can be transformed from brownish to colorless of a higher value — up to D in color — by HPHT treatment. Thus the first step to detect color treated is to determine whether the sample is type IIa. This can easily be done by using the SSEF Diamond Spotter, which is based on the transparency of these diamonds to short-wave ultraviolet radiation (SWUV).
The SSEF diamond spotter provides an inexpensive and convenient first test to determine whether it is not one of these rare types that are suitable for HPHT treatment, but if it is one of the rare types other infrared spectrometric tests must be performed.
The SSEF Diamond Spotter determines whether or not a diamond is one of the rare types that could be treated to produce colorless, near-colorless, pink and blue diamonds. It allows an easy separation into two groups of diamond types: type IaA, IaAB and Ib versus IIa and IIb. The technology is based on the fact that Type II diamonds are transparent to SWUV light, whereas the vast majority of Type I diamonds block SWUV light.
However, it does not determine whether the diamond has been HPHT treated or not.
By placing a diamond into the spotter and switching on the SWUV light source, the diamond will react by transmitting or absorbing the SWUV light, thus fluorescence or no fluorescence on the screen of the spotter
Green fluorescent light spot on the screen during testing with the SSEF diamond spotter identifies the diamond as type IIa or IIb and at the same provides indication that a colorless diamond may have been “discolorised” by HPHT treatment. Further analysis is required within a specialized gemological laboratory. . In this case, the second step is to look for subtle luminescence features related to N-V centers in the type IIa diamonds with a Raman spectrometer.
If no fluorescence reaction shows on the screen in the SSEF diamond spotter, the diamond is of type Ia or Ib, which means that the colorless diamond has not been HPHT treated for discolorisation.
Synthetic diamonds have a number of gemological properties by which they can be identified more reliably. However, this requires from professionals in the industry and jewelers to look at diamonds more carefully than they traditionally have with the usage of standard gemological equipment. Particularly problematic for gemologists and jewelers are small stones. It is easier, faster and cheaper to grow synthetic diamonds in the form of melee. The small size though means that the visual identifying features usually are more difficult to see with the microscope.
Another concern is that the CVD technique could yield larger synthetic diamonds that might lack, for example, growth sector-related color and UV fluorescence zoning patterns. The absence of these features would make identification in most gemological laboratories more difficult.
Here are some of the most recent distinctive featurs to identify gem synthetic diamonds:
The morphology and growth structure of natural diamond crystals is different from HPHT laboratory– created diamond crystals. Natural diamonds have an octahedral crystal structure. HPHT grown diamonds in turn form in a cubo-octahedral structure with possible dodecahedral and traphezohedral faces depending upon the temperature and pressure used during growth.
None of these signs are definitive, but they can serve as an indication that further gemological lab testing is recommended.
An ultraviolet lamp has found to be one of the most useful pieces of equipment for identifying HPHT-grown diamonds. A microscope fixed with an UV lamp positioned overhead is necessary. When viewed under short wave UV light, yellow to orange laboratory grown diamonds usually display a yellowish green pattern with inert areas. Under long wave UV light, the intensity of the fluorescence is much weaker or inert.
CVD grown synthetic diamonds show a weak but characteristic orange with sometimes yellow-green luminescence.
The absorption and luminescence of diamonds provide key knowledge about the atomic defects present in the diamond, and is very important for detecting treated as well as synthetic diamonds.
For this purpose, a combination of spectroscopic methods – including infrared spectroscopy and photoluminescence spectroscopy – has become paramount to gemological laboratories to distinguish synthetic gems from naturally occurring ones.
Physical and optical properties in many well-grown synthetic diamonds are identical to natural diamonds. Spectroscopic properties of synthetic diamonds, however, are different from the properties a natural diamond would show. Spectrophotometers provide a way to analyze a wide range of the spectrum and objectively and quantitatively record the data by plotting a graph of results. The spectra of most natural diamonds differ from those seen in synthetic diamonds. But today, high-quality synthetic diamonds are grown, which produce graphs, that are more and more similar to the ones natural diamonds would show.
Fourier Transform Infra Red (FTIR) spectroscopy studies the absorption of infrared light. Infrared spectroscopy measures how much light a gemstone absorbs or transmits at wavelengths from 12,000 to 400 wavenumbers (1,000 to 25,000 nanometers).
In infrared spectrometry analysis, the nitrogen content and its way of existence can be detected, which is an important indication for identification for the type of a diamond (ie. Ia, IIa, etc.). The instrument is used for the determination of the colour authenticity of diamond, and proves whether it’s a diamond or not.
In UV-VIS spectroscopy ultraviolet and visible light illuminates a stone and the absorption of certain colours is analysed. In principle, the UV-VIS absorption spectrum is the scientific representation of the diamond’s color. VIS spectroscopy measures how much light a gemstone absorbs or transmits at wavelengths from 400 to 1000 nm. Furthermore, the absorption graph gives indications whether a diamond has been heat treated or irradiated.
Raman spectroscopy involves illuminating a sample with a laser of a specific wavelength and a spectrophotometer is used to analyze the light scattered by the
sample. Optical centers are excited by the laser and emit a measurable amount of luminescence. The spectrophotometer shows the changes to the light as a graph. The luminescence phenomena appear as peaks in the spectrum. Photoluminescence detects certain color centers with much more sensitivity than other spectroscopic methods and is therefore especially useful for the detection of synthetic and HPHT treated diamonds.
De Beers has developed two machines, which are easy to use and can tell even colorless synthetic gem diamonds from the real thing, to prevent synthetic diamonds being passed off as mined gems. DiamondSure is a rapid screening instrument that’s been designed to pass natural diamonds, whilst at the same time referring all synthetic diamonds to further testing. Diamond Sure works by analysing the way light is absorbed by a diamond. It’s down to how nitrogen impurities form within the crystal. Nitrogen atoms occur in clumps in ninety eight percent of all natural diamonds. This causes light to be absorbed in a specific way, and provides the key to their detection. With a pass result, the user can be confident that this is a natural diamond, and requires no further testing. If the Diamond Sure machine gives indication for further testing the diamond is then referred to the DiamondView instrument.
Diamond View shines ultraviolet light on to the diamond and generates a surface fluorescence image from which synthetics may be unambiguously identified. Under ultraviolet light both natural and synthetic diamonds will glow to some degree, this is called fluorescence. But it’s the patterns that are revealed by this glowing fluorescence that can tell the two apart. Strong blocky blue fluorescence patterns indicate that this is a synthetic. Such strong shapes of blue florescence would not be seen in a natural diamond.
The new DiamondPlus is a compact instrument for high-sensitivity, low-temperature photoluminescence measurements on polished stones immersed in liquid nitrogen. It consists of two solid-state lasers and two miniature spectrometers. Each measurements takes 20 seconds and results are displayed on the screen.
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