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Similar processes are used in major gem testing laboratories around the world to detect diamonds, although each laboratory may use different methods and machines to determine if they are natural, synthetic, diamond-like or artificially processed diamonds.
All colorless diamonds were first screened and tested to see if they were Type I, and Type I diamonds accounted for 98% of all natural diamonds.
Any tests identified as Type II diamonds require further testing. There are many methods for screening including infrared spectroscopy (IR), ultraviolet absorption spectroscopy (UV), and ultraviolet transmission light broadband induced luminescence imaging analysis (photoluminescence spectroscopy) (PL). These machines accurately identify approximately 97% of natural diamonds, and approximately 3% of the diamonds will be marked for further testing. If it is a dark yellow and brown Ib diamond, it will be transferred directly to the final determination.
Diamonds marked for further testing will go through a more detailed process for final confirmation. These processes include the detection of impurity elements, crystal structure, electromagnetic wave absorption, phosphorescence, and fluorescence by a person.
Infrared spectroscopy can measure electromagnetic radiation of different wavelengths absorbed by different elements in the diamond. Different types absorb infrared light of a specific wavelength.
UV absorption, similar to the infrared spectrum, type I diamonds absorb specific wavelengths in the ultraviolet light and can be detected by this.
UV transmission is to see if light in certain bands can pass through diamonds. Natural Type Ia diamonds are opaque under UV light, while colorless Type IIa diamonds are UV permeable.
Ultraviolet transmitted light broadband induced luminescence imaging analysis (photoluminescence imaging technology) can test the fluorescent color, phosphorescent color intensity and duration of diamonds. When the ultraviolet light source that ignites the diamond is cut off, it is seen whether the diamond continues to emit light. Natural Type Ia diamonds tend to be blue fluorescent but not phosphorescent, and further testing is required when other phosphorescent or persistent phosphorescent diamonds are observed.
Second, the diamond type
The test instrument first tests whether the sample is of type Ia, because the current synthesis method, whether high pressure high temperature synthesis (HPHT) or chemical vapor deposition (CVD) can not synthesize type Ia diamond. Natural diamonds are likely to be of any type Ia and Ib, IIa and IIb, but HPHT diamonds may only be of type Ib, IIa or IIb, and CVD synthetic diamonds may only be IIa and IIb. Type I diamonds contain nitrogen and Type II diamonds contain no nitrogen.
As mentioned earlier, most natural white diamonds are of type Ia, and a few natural white diamonds are type IIa, although this is extremely rare. Similarly, chemical meteorological precipitation methods for the synthesis of diamonds, the diamonds synthesized by this method usually do not contain nitrogen.
Branko Deljanin, president and chief gemmologist of the CGL-GRS Swiss and Canadian Gemological Laboratory, said that in the near future, synthetic diamond producers will gain greater diamond discourse rights as synthetic technology advances and production increases, and Affects the type of synthetic diamonds, which will result in a large number of instruments that can be used to distinguish synthetic diamonds by screening diamond types. But he is also not sure when this will happen.
Third, available equipment
A wide range of equipment is available for laboratories to analyze and observe synthetic diamonds, ranging from simple hand-held to sophisticated professional equipment that automatically screens and packages for further analysis. The ability to analyze natural diamonds or equipment that requires further confirmation is as follows:
1, DiamondSure, from De Beers, through the principle of UV absorption, can quickly filter colorless or nearly colorless diamonds, weighing from 0.10 carats to 10 carats, whether inlaid or loose diamonds, can distinguish whether the diamond is natural or After processing or imitation, it takes several seconds to measure each diamond.
2, DiamondPlus, from De Beers, mainly to detect high temperature and high pressure diamonds, of course, it can also detect chemical vapor deposition of synthetic diamonds, laser-excited photoluminescence imaging analysis. Capable of detecting samples from 0.05 to 10 carats, diamond samples must be immersed in liquid nitrogen.
3, the automatic package automatic screening instrument (AMS), from De Beers, through the principle of ultraviolet absorption can quickly screen out synthetic diamonds and imitation diamonds, weighing from 0.01 carats to 20 carats, the instrument supports up to 500 carats of diamond samples It can detect about 360 samples per hour.
4. DiamondCheck, from GIA, uses infrared spectroscopy to quickly screen 0.01 to 10 carat diamond samples. Other devices can only detect colorless or nearly colorless diamonds, but DiamondCheck can filter pink diamonds. DiamondCheck can also filter high temperature and high pressure treated diamonds or imitation diamonds.
5. D-Screen, an HRD from Antwerp, uses UV absorption spectroscopy to distinguish whether a diamond is natural or a high temperature, high pressure diamond or synthetic diamond. D-Screen cannot screen out imitation diamonds and only filters diamonds from D to J.
6. M-Screen, from the HRD of Antwerp, uses UV absorption spectroscopy to screen colors from D to J, weighing from 0.01 ct to 0.20 ct. It can distinguish between natural diamonds, synthetic diamonds, imitation diamonds and artificially treated diamonds. According to HRD, the device can screen 7200-10800 diamonds per hour.
7. GV5000, Broadband Induced Luminescence Tester, National Jewelry Quality Supervision and Inspection Center (NGTC) from China, screens bare diamonds or diamonds by UV-transmitted broadband induced luminescence imaging analysis, weighing from 0.002 carats to 8 carats (diamonds) The diameter can be from 1mm to 25mm).
In addition to screening small diamonds that cannot be screened by other devices, the GV5000 can also screen a variety of fluorescent diamonds or set diamonds. The device is capable of screening diamonds with a size of 0.01 ct approximately 12,000 capsules per hour.
Whether these samples that have not been screened are natural diamonds needs to be finalized by a gemologist, and the equipment commercially available for final testing includes:
1. DiamondView, from De Beers, was detected by observing the broadband induced luminescence image produced by the sample under short-wave UV illumination. The device is capable of detecting diamonds weighing from 0.05 carats to 10 carats, as well as weights ranging from 0.01 ct to 0.20 ct. This equipment is mainly used for loose diamonds, but some diamonds can be tested if they meet the requirements.
2. The Alpha Diamond Analyzer, from the HRD in Antwerp, uses infrared spectroscopy to analyze diamond types – such as Type I and Type II. The device can also test whether the diamond is a synthetic diamond, a diamond or a diamond.
Fourth, the difference in classification
Gemological laboratories around the world not only provide diamond testing services, but also provide grading reports on synthetic diamonds. GIA Lab's grading reports on synthetic diamonds are generally described using a larger range. For example, color grading writes "colorless", "near colorless", and the netness writes "VS", "SI", which is not sub-level. It is different from the regular diamond grading report. This is explained on the GIA website. The reason why the synthetic diamonds are graded is because the amount of synthetic diamonds at this stage is too small. Tom Moses, GIA's executive vice president and chief laboratory researcher, added that synthetic diamond dealers are less interested in synthesizing diamonds with lower color grades. “If we see that the market needs more and more synthetic diamonds, synthetic diamond dealers can continue to increase production and quality to a certain level, we may also change the existing synthetic diamond grading report, but it is not necessary at this stage. "But other laboratories have the same rating for synthetic diamonds and natural diamonds received.
Five, the naked eye and magnifying glass observation
“Synthetic diamonds cannot be distinguished by the naked eye. A synthetic diamond may be found under a magnifying glass, provided that it contains visible inclusions, especially high temperature and high pressure synthetic diamonds,†Moses said, explaining that high temperature and high pressure synthetic diamonds Some metal inclusions may be left in the process. However, the quality inspectors of synthetic diamond dealers also know that others are looking for these characteristic inclusions, so they will be cut off or shaded as much as possible during the cutting of HPHT synthetic diamonds. Moses also said that the magnifying glass does not help the detection of CVD synthetic diamonds because CVD synthetic diamonds have no similar inclusions.
There are also some basic tools that can be used to detect synthetic diamonds. These tools range from simple magnets to handheld "diamond test" devices that test thermal and electrical conductivity, density and refraction. Additional methods include the use of conventional UV lamps, cross-polarization filters, microscopes, and a simple combination that still yields accurate results, but is often overlooked by jewelers, Deljanin said. These methods can quickly detect some of the characteristics of synthetic and imitation diamonds. However, Moses also pointed out that "most of the testing of synthetic diamonds relies on some specialized instruments. After all, such equipment can provide a better guarantee for the accuracy of detection."
6. High temperature and high pressure synthetic diamond VS chemical meteorological precipitation method for synthesizing diamonds
In order to accurately detect whether a sample that needs to be further tested is a natural diamond or a synthetic diamond, which method is a synthetic diamond, this requires a large amount of equipment to detect all aspects of the sample. A machine is usually designed to focus on detecting the characteristics of a certain aspect of a diamond. "There is no magic machine, everything you can do at one time." Deljanin wrote.
HPHT synthetic diamonds and CVD synthetic diamonds differ in the following ways:
1. Crystal structure: HPHT synthetic diamonds grow in a cubic octahedral structure, and under the special illumination, they show an "hourglass" shape, while CVD synthetic diamonds are layered and can be observed under special illumination. Natural diamonds grow in a circular ring shape, also known as a "triangle texture." When a diamond fluoresces under high-intensity ultraviolet light, or illuminates after absorbing radiation, the way the diamond grows can be observed under such light. The “hourglass†structure is considered to be an identifying feature of HPHT synthetic diamonds, but in 2013, GIA showed an extremely rare natural diamond that also exhibited this cubic octahedral structure.
2. In addition to observing the growth type, it is also possible to detect some crystal distortion characteristics by cross-polarization observation. These crystal distortions result in the occurrence of birefringence of light. HPHT diamonds usually have no crystal distortion or very small. Natural diamonds usually show a "tatami" shape, or a mottled pattern, that is produced during the formation. However, CVD diamonds can also exhibit distortion characteristics similar to natural diamonds.
3. Luminous features: Most natural white and nearly white diamonds emit blue fluorescence without phosphorescence. Very few diamond colors These natural diamonds also emit green to yellow fluorescence. White and near-white HPHT diamonds tend to exhibit blue-green fluorescence and exhibit strong blue-green phosphorescence from three seconds to one minute after the UV source is turned off. According to Lan Yan, director of the NGTC Shenzhen Jewelry Research Institute, all the white and nearly white HPHT synthetic diamonds he saw in his research were able to fluoresce and phosphorescence. CVD synthetic diamonds can emit green, blue, green, red, orange and other fluorescence.
4. Inclusions: Under the microscope, HPHT synthetic diamonds can be seen as rod-shaped metal inclusions, which may also be plate-shaped or irregular shapes. These inclusions are typically by-products of the metal solvents used during the growth process. CVD synthetic diamonds often have no inclusions because they can better control the growth environment, but there may be black carbon inclusions on the growth surface. GIA has reported inclusions of CVD synthetic diamonds, sometimes like natural diamond inclusions.
Seven, the future of synthetic diamonds
Although synthetic diamond technology has come a long way since its inception in the 1950s, it has indeed made great progress in recent years. According to GIA data, until 2014, IIa / b type HPHT synthetic diamonds had an impact on the market. Over time, Deljanin believes that the industry will be able to see larger, cleaner synthetic diamonds. He concluded: "The synthetic diamond technology will develop with the development of the jewelry industry." (Author: Shuan Sim; translation: National Jewelery Quality Supervision and Inspection Center Tae Jin Lu, Zhang sail, Liu Yang)
Abstract "As technology advances, synthetic diamonds can be made larger and better, and better, and these diamonds need to be better tested. Some people worry about illegal traders trying to impersonate synthetic diamonds in the diamond trade. Natural diamonds, because in the laboratory...
“As technology advances, synthetic diamonds can grow bigger and better, and better diamonds are needed. Some people worry about illegal traders trying to fake synthetic diamonds in the diamond trade. Diamonds, because diamonds grown in the laboratory, have grown whiter and cleaner now. However, gemologists are confident that there are ways to detect any synthetic diamond. This is not to say that gemmologists think synthetic diamond producers want to Escape test in the game of cat and mouse. IGI gemologist David Weinstein said: "I believe they are working hard to make it more perfect and make it as beautiful as possible, not to confuse us. "."