Before describing these methods, let's make a list of the properties of diamonds and their substitutes and see what are the differences between them:
In the table, the possible substitutes (and fakes) of diamonds are divided into three categories: the first category includes cubic zirconia, GGG and so on. Their optical properties, that is, refractive index and dispersion, are similar to those of diamonds, and they have no refraction in isotropic bodies. Therefore, the polished gem products are very similar to diamonds in appearance. In order to distinguish them, only by hardness, specific gravity and thermal conductivity; The second category includes zircon and synthetic rutile, whose finished products are similar to diamonds (but not as good as the first category), but because of their high birefringence, obvious double shadows can be seen in the finished products, which are easy to distinguish from diamonds. Of course, their hardness, specific gravity and thermal conductivity are also very different from those of diamonds; The third category includes colorless sapphires and crystals, which are characterized by low refractive index and unlike diamonds in appearance. Therefore, if conditions permit, their refractive index can be measured by refractometer. By measuring the refractive index, you can immediately know that it is a substitute rather than a diamond. Of course, their hardness and thermal conductivity are also very different from those of diamonds.
Generally speaking, the biggest difference between diamonds and all substitutes (or imitations) is two points, one is hardness, and the other is thermal conductivity. Therefore, according to these two differences, instruments can be made to quickly and accurately distinguish diamonds from all substitutes or fakes.
Diamond tester
Thermal conductivity refers to the ability of a substance to conduct heat. Any substance with strong thermal conductivity can transfer heat quickly, such as the well-known gold foil, copper and aluminum. When people touch copper and aluminum with their hands, they will feel that these metals are "cold" because they will quickly spread heat to their hands. Another example is wood, which has weak thermal conductivity, so people's hands feel warm.
The strength of thermal conductivity can be expressed by numbers. The larger the number, the stronger the thermal conductivity. For example, the relative thermal conductivity of copper is 0.927 and that of aluminum is 0.485. As can be seen from the table, the thermal conductivity of diamond is very strong, even exceeding that of copper and aluminum, and the relative thermal conductivity is as high as 1.6-4.8. Substitutes for diamonds have much weaker thermal conductivity than diamonds. As can be seen from the table, the thermal conductivity of most substitutes is lower than 0.0 1, that is, more than 0/00 times that of diamond bottom. Like glass, the thermal conductivity is the worst, which is more than 1000 times lower than that of diamond. Although sapphire has high thermal conductivity, it is 10 times or even dozens of times lower than diamond.
In this way, if you make an instrument that can quickly measure the thermal conductivity of gems, it is really easy to distinguish real diamonds from fake diamonds. This instrument is already available. Its English name is "Diamond Master" and Chinese can be translated into "Diamond Tester". The picture below shows a photo of a diamond tester. It is shaped like an electric meter with an external wire. The front end of the wire is like a pen, and the top of the pen is a "probe" When in use, turn on the switch, turn on the power supply (9v battery is generally used), and contact the probe with the gemstone to be measured (the gemstone must be cleaned in advance without oil stain). At this time, the pointer on the instrument began to turn. When the rotation angle is large and exceeds the calibrated area on the instrument, the measured gem is a real diamond. If the deflection angle of the pointer is too small to reach the calibrated area, then the measured gem is a fake diamond.
The simplest diamond tester can only show whether the tested gem is a real diamond or a fake diamond; With a more complex diamond tester, we can also estimate which diamonds are fake, such as cubic oxide or YAG. Due to different manufacturers, this instrument has various improvements, such as canceling the wire and pointer, installing the probe on the short tube protruding from the instrument, displaying the determination results with different colors of led, indicating the real diamond when the green light is on, and indicating the fake diamond when the red light is on.
The diamond tester is very small, almost like a pack of cigarettes, and can be easily put into clothes.
Standard hardness tester
It is of course the most ideal to use a diamond tester to distinguish between genuine and fake diamonds, but this instrument is more expensive, and we can use another effective method, that is, to test the hardness of gems. As we know, diamond is the hardest substance in the world, and its hardness is 10. You can scratch anything with a diamond, but nothing can scratch a diamond. According to this principle, people made a "standard hardness tester", which is a square box with the size of 65×55×23mhl. After opening the lid, there are four tablets with standard hardness embedded in it, all of which have been finely ground and the surface is as smooth as a mirror. The Mohs hardness of the four standard hardness tablets is 6, 7, 8 and 9 respectively.
The standard hardness tester is used to measure the hardness of precious stones. Find a sharp edge of the gem to be tested (whether it is polished finished product or uncut rough stone), gently carve a standard block with hardness of 6, and then observe it with a magnifying glass. If there is no scar on the standard part, it means that the hardness of the gem is lower than 6, and it is not necessary to measure it again. If there are indelible thin line scars on the surface of the standard piece, it means that the standard piece with a hardness higher than 6 or 7 should continue to be carved. If you can't scratch (no scar), it means that the hardness of the gem is between 6 and 7 (including 7). If it can be scratched, continue to scratch the standard piece with hardness of 8. In this way, the hardness of all gems can be divided into five categories, that is, the hardness is less than 6; The hardness is between 6 and 7 (inclusive); The hardness is between 7 and 8 (inclusive); The hardness is between 8 and 9 (inclusive); Hardness is higher than 9. It is very convenient to determine the authenticity of diamonds with a standard hardness tester. As long as the standard block with hardness of 9 is lightly scratched with precious stones, if scars can be drawn, it is a real diamond; If you can't row, it is a fake diamond. When scoring hardness, the surface of the standard film should be wiped clean first. No matter whether it is scratched or not, it feels different. If you can't move, you will feel "slippery". The standard hardness tester has simple structure and low price.