Identification method of jade
First of all, we should read carefully and read more monographs on ancient jade. These academic works are rich in knowledge. For example, The Examination of Ancient Jade in the late Qing Dynasty, The Complete Works of China Fine Arts Jade edited by contemporary editors, The History of Jade Edited by editors, The Discrimination of Ancient Jade edited by Hong, etc.
Secondly, direct contact is very important. The real ancient jade has a long history, heavy feel, soft and smooth appearance, natural color, neat knife work and moist patina. Xinyu doesn't have these feelings. Antique jade appeared in the Song Dynasty. At that time, someone used rainbow grass to fake chicken blood infiltration. After the Qing dynasty, there were more and more forgeries and unprecedented creations, such as? Dog jade? 、? Sheep fat jade? 、? Yu Feng? Wait, attract people.
The quality of jadeite is generally judged from five aspects: texture, hardness, transparency, specific gravity and color. The texture of jade refers to the delicate and moist degree of jade. One of the differences between jade and stone is that jade is delicate, moist and hard, translucent and glossy as fat; Stone, on the other hand, is rough and dry, lacking luster and opaque. Hardness refers to the ability of jade to resist external forces (such as pressing, engraving and grinding). The higher the hardness, the more difficult it is to process and the better the quality of jade. Although the hardness index of jade can be known by detecting its internal crystal structure with instruments, the method of scraping hardness is generally used in operation. The hardness of common jade in China is between 46 degrees, higher than copper and lower than glass. In other words, jade may not be able to carve marks on glass.
People often distinguish gems, jade and colored stones according to their hardness. Generally speaking, the Mohs hardness of gemstones is above 7, such as diamonds, rubies, sapphires and jadeites, but Opal gemstones are an exception, with Mohs hardness of 5.5; The Mohs hardness of high hardness jade is between 6 and 7.5, such as Hetian jade, Nanyang jade and jadeite. The hardness of low-hardness jade is 4-6, such as turquoise and jadeite (the hardness of some serpentine jade is lower, as low as 2.5). The minerals below 4 are generally not called jade, but called colored stones.
In addition to describing hardness, there is also a hardness standard called compressive hardness, or indentation hardness, that is, absolute hardness, which refers to the ability to resist external impact, and is also called toughness in the jade industry. The highest compressive hardness in nature is black diamond, marked as 10 degree, followed by Hetian jade, with compressive hardness of 9 degrees, jadeite, ruby and sapphire of 8 degrees, diamond, crystal and aquamarine of 7-7.5 degrees and so on. On the other hand, the compressive hardness of Hetian jade is 1000, that of jadeite jade is 500, that of Xiuyu jade is 250, and that of agate is only 5. Hetian jade has such high toughness because its crystal distribution is woven like a blanket, and the intermolecular force is very large.
In practice, a jade craftsman usually looks at jade by observing craters. Generally, he cuts a small piece, breaks it with a small hammer, and observes the fracture, which is glassy compared with strength and toughness. Jade with strong toughness is not easy to break, even if it does, the fracture is uneven; And the glassy jade fracture, through the bright section, is called? Bright slag? , similar to the shape of a shell. Jade between toughness and glassy, usually called? Not good? 、? Fleshy? Its slag mouth is granular, parallel bundle, needle-like and so on. Through this observation, we can also observe whether jade has cleavage characteristics. If there is cleavage or crack, the jade will break in the direction of cleavage or crack when knocking.
It can be seen that jade and hetian jade with excellent toughness have strong plasticity in processing. Among the gems with the same Mohs hardness or higher, Hetian jade will never crack when carving, so its texture is delicate, moist and smooth. Of course, toughness and hardness will also be affected by jade impurities, and impurities can also be understood by measuring toughness and hardness. This is a major factor that determines the use of a piece of jade. For example, jade magazine is not strict in making jade mountain seeds and utensils, but it requires pure and uniform jade materials when making jewelry.
Yufu Workshop suggested that the hardness of jade is one of the important criteria for identifying jade, and the luster of gemstones is also the basic criterion for identifying the authenticity and grade of gemstones.
Generally speaking, the luster of gems can be simply classified as? Residual light? 、? Burning light? 、? Flash? And then what? Weak light? Several kinds. But light is the strongest brightness, and people must squint. For example, the polished diamond total reflection surface has such brightness; Burning brightness is also very high, dazzling and high-hardness gems generally have burning brightness after polishing; Flash is the brightness of ordinary glass, which is divided into strong flash and weak flash. Jade with high hardness is generally strong flash, while jade with low hardness is weak flash. However, the light intensity of the stone surface with lower hardness is weak after polishing.
In addition to brightness, luster is also one of the identification characteristics of gems. It is also divided into four categories: semi-metallic luster with refractive index between 2.6 and 3, such as goethite; Diamond luster, with refractive index between 1.9-2.6, such as diamond; The refractive index of glass luster is between 1.3- 1.9, such as jadeite; Grease luster, like animal fat, the most famous is the sheep fat white jade in Hetian jade. Every specific gem has a specific refractive index, and it is difficult to keep consistent with it under various conditions such as hardness, density, refractive index and brightness. Therefore, through the identification of these standards, the identity and initial value of gems can be confirmed.
At present, fake jade synthesized from jade powder by artificial high pressure has appeared in the market, and its color and hardness are similar to Hetian jade, so we should be especially careful when identifying it. The real ancient jade includes soil infiltration, lime infiltration, mercury infiltration, corpse blood infiltration, cinnabar infiltration, copper infiltration, surface oxide layer and so on. Some of the fake mud spots are fried, some are baked by fire, and some are etched by chemicals. It is important to find out the differences and differences between true and false products in color, luster, thickness and so on. The scribed lines on the jade surface have different sections such as V-shape, semicircle and U-shape, and U-shape is an important feature of modern processing. Carved lines, notches and shiny surfaces are true in color and patina. Is the hairline cracking on both sides of the line notch modern? Mechanic? The characteristics of.
Identification of jade
1. color: the white of white jade is often slightly blue, and few people are extremely white and pure white, while nitrate is even white and pure white. After the light is on, nitrate still has a slight orange light.
2. Jade: One of the characteristics of jade is that it is moist and even, like cream. Although the feeling of nitrate is bright and naked, it feels like a thief's light flashing in the bright and moist.
3. Fracture: This is an obvious feature. The fracture of white jade is stony, dull, serrated or serrated, while the fracture of nitrate is material, bright and shiny, and shell-shaped. Although jewelry appraisal can't be destructive, it can be observed through some accidental bumps, unpolished grinding surfaces and corners.
4. Impurities: There are no bubbles in jadeite, but there are bubbles in nitrate. Sometimes it is difficult to be observed because of its translucent color, and sometimes it is rare because of its good quality. But as an appraisal, you can't stop without finding evidence. Sometimes we can check from the surface. If there is trachoma, that is, there are bubbles on the surface, it can also be proved to be nitrate, because white jade does not have this characteristic, and the bubbles inside can also be checked under strong light.
5. Specific gravity: the specific gravity of jadeite is between 2.9-3. 1, and nitrate is about 2.5, which is lighter than nitrate.
6. Voice: The voice of jade is dignified, and the voice of nitrate is crisp. In some cases, it can be identified by the sound difference between jade and nitrate through a gentle impact.