1, sensory recognition
It must be pointed out that sensory recognition must be based on professional knowledge and practical experience, both of which are indispensable. Sensory recognition can be summarized as "seeing, touching, weighing and listening".
Look: look at the characteristics, structure, color and flaws-the characteristic of jadeite is its "emerald" (commonly known as flying wing), that is, the starlike flash produced by the cleavage of granular, flaky or fibrous spots inside; The structure of jadeite jade is characterized by the interweaving of variegated crystals, and the translucent granular variegated crystals are surrounded by fine fibrous mineral crystals. Structural density and crystal thickness are the basis for evaluating the geological quality and grading of jadeite. Jade products generally have glass, sub-glass or semi-glass luster, and the color is uneven, while nephrite, jadeite and other jade similar to jade often have waxy luster and oily luster, and the color is mostly uniform. An experienced appraiser or merchant can tell whether this jade is jadeite or not by its color. With the help of lighting or natural light, it is the purpose of "checking for defects and filling leaks" to see if there are impurities and cracks. In the jadeite entity, the quality and grade of jadeite are estimated by combining other indicators.
Touch: jade can quickly transfer heat and dissipate heat, and it will feel cold in a short time if it is attached to the face or placed on the back of the hand. Emerald has a high hardness and a compact and delicate structure. After polishing, it can have a high surface finish, and it feels slippery by hand.
Yunnan: The density of jadeite is 3.34g/cm3, which is higher than that of nephrite, dushan jade, Xiuyu, Australian jade, Ma Laiyu (dyed quartzite), jadeite and grape jade. But lower than Cui (almandine) and Tesavoshi (hydrogrossular). Experienced people can preliminarily judge whether a jade material or jade piece is jadeite by weighing.
Listen: Listen carefully to the sound of collision between finished products, and you can roughly judge whether this piece of jade is jade or not, and what kind of jade it is (whether it has been pickled or treated). Natural jadeite jade pieces, especially those with good texture, make a pure and pleasant "steel sound" when struck. Listen, you must have a comparative hearing, or have some experience as the basis, in order to roughly judge the quality of jade according to the sound quality.
2, instrument testing
Although high-tech equipment and instruments such as electron probe, infrared spectrum and Raman spectrometer are also used in the identification of jadeite. These high-tech instruments (identification means) will only be used when encountering complex and difficult problems. In the inspection and appraisal work, we use more conventional instruments. Generally, jewelry inspection and appraisal workers often use the following instruments to identify jadeite:
Gem microscope: The magnification of gem microscope is usually 10 ~ 80 times. It can clearly observe the surface structure and internal tissue characteristics of jadeite, judge whether the detected object is jadeite, whether it is natural jadeite or treated jadeite (jadeite B and C), clearly observe the surface or internal defects of jadeite, and also observe the joint surface of composite stone.
Spotlight flashlight and hand-held magnifying glass: Use spotlight flashlight and hand-held magnifying glass when there is no gem microscope or it is inconvenient to carry a microscope. Spotlight flashlight mainly uses transmission method or reflection method combined with magnifying glass to observe the transparency, texture, color and defects of jadeite. Sometimes Charles filter is used to distinguish and observe whether the detected object is jadeite or dyed jadeite. There are 5 times, 8 times, 10 times, 15 times and 20 times for hand-held magnifying glasses, among which 10 times and 20 times are more suitable, and 10 times is the most useful. It can not only observe the internal situation and other defects of jadeite and other jewelry, but also observe jewelry defects (such as cracks and black spots) in jewelry trading.
Refractometer: Refractometer is one of the most direct and effective instruments to identify the authenticity of jewelry. The refractive index of jadeite is 1.650— 1.680, and the point measurement method is 1.65 ~ 1.67. Usually 1.66. However, it should be pointed out that the natural jadeite has the same refractive index as the treated jadeite.
Spectrometer: absorption. When white light passes through a gem, it will absorb some wavelengths of light. Different gemstones have different light absorption conditions, and the selective absorption of gemstones is related to the types of chromogenic elements. Therefore, spectroscope is the most powerful means to identify the true and false colors of gemstones, and it is often used to identify true and false jadeites and dyed jadeites in practice.
In the absorption spectrum of cr-colored gem-grade green jadeite, there are three thin absorption lines in the red light regions of 630, 660 and 690nm. Generally, jadeite has obvious black absorption line only at 437nm in the purple light region; The jadeite dyed green by hand has a dense absorption band near the red light region of 650nm.
Polarizer: Block aggregate, consisting of monoclinic mineral jadeite and biaxial crystal positive light. So if it doesn't go out under the polarizer, it is all bright.
Specific gravity scale: most of them use electronic scales with high accuracy. The density of jadeite measured by hydrostatic method (density method) is 3.34 g/cm3 (+0.06, -0.09), which is an important index to distinguish jadeite from other jadeites of the same kind.
Standard hardness tester: 5 ~ 7, which can be scraped with the hardness of crystal (hardness 7), but not with the hardness of feldspar (hardness 6). This attribute can be used as a reference for identification.
Charles filter: nothing that turns red under Charles filter can be natural jade; On the other hand, what doesn't turn red is not necessarily the real thing, because some dyed jadeite, coated jadeite and laser jadeite are all filtered in Charles.