China's most unique beauty jade – Dushan jade
Dushan jade is named after Dushan, which is produced in Nanyang City, Henan Province. It is also known as the unique jade. According to historical materials, as early as the Neolithic Age more than 6,000 years ago, people began to use and sculpt Dushan jade. With a long history and good quality, after the liberation, the development and utilization of Dushanyu has been highly valued, and significant progress has been made in mineral deposit research, mining, carving and processing, and market sales, especially since the reform and opening up, the prestigious Nanyang The jade carving industry has attracted a large number of people from outside the industry, so that Dushan jade can be understood, appreciated and accepted by more people.
Compared with other jade, due to the complexity of the genesis of the Dushan jade deposit, the appearance of Dushan jade is more complicated, which makes some understanding of jade not deep or the identification of beginners in Dushan jade and the differentiation of similar varieties. Confused, it is not easy to grasp the quality. In view of the situation in market trade and jewelry teaching in recent years, the author has collected more than 50 pieces of Dushan jade specimens of different varieties, and conducted systematic analysis and testing on the mineral composition and gemological parameters of typical varieties. Shanyu's gemological classification and detailed identification parameters, establish a series of standard samples of typical varieties, and should have a more comprehensive understanding of the complexity of Dushan jade and its evaluation of crafts, thus facilitating communication and better serving Market and gem teaching work.
1. Inherit commercial and process classification standards to determine gemological classification
Like most jade, the classification of Dushan jade gemology should follow the commercial and process classification standards, inherit some of the principles of customary conventions, so that it is easy to promote and exchange. On the other hand, it should be summarized and improved according to the market and the latest research results. Strive for objective, accurate and scientific. Dushan jade is characterized by rich colors, different shades and different distributions. The same jade often has multiple colors coexisting due to different mineral combinations. It is consistent with the process classification standard, and the gemological classification should also be color. In order to divide the mark, Dushan jade is divided into the following eight varieties or subspecies.
(1) Bai Duyu: The overall white, milky white, often translucent to slightly transparent or opaque, according to the transparency and texture, there are three kinds of water white, oil white, dry white, of which the best for permeable white , Bai Duyu accounted for about 10% of the entire Dushan jade.
(2) Red jade: often expressed in pink or hibiscus, varying in depth, generally micro-transparent to opaque, and a transitional relationship with white jade. The content of such jade is less than 5%.
(3) Green pure jade: including green, gray-green, blue-green, yellow-green, often accompanied by white jade, the color distribution is uneven, mostly in the form of irregular band, filament or agglomerate. Transparency varies from translucent to opaque. The translucent blue-green jade is the best variety of Dushan jade. It is also known as "Tianlan Jade" or "Nanyang Jade" in business. In the mining of mines in recent years, the output of such high-quality varieties has gradually decreased. Most of them are gray-green opaque green jade.
(4) Huang Duyu: It is a yellow or brownish yellow with different depths. It is often semi-transparent, often with white or brown agglomerates and a transitional color.
(5) Brown jade: dark brown, gray-brown, yellow-brown, uneven in depth, such jade is often translucent, often in transition with gray and green jade.
(6) Qingyu jade: cyan, gray cyan, blue cyan, often expressed as block, band, opaque, is a common species in Dushan jade.
(7) Black only jade: also known as "墨玉", black, dark green, opaque, coarser particles, often blocky, clumpy or point-like, accompanied by white jade, the variety is Dushan jade The worst variety.
(8) variegated jade: often appears in the same specimen or finished product as the above two or more colors, especially in some large Dushan jade raw materials or carvings often appear four to five or more Multi-color varieties, such as green, white, brown, cyan, ink and other colors, are dipped or gradually transitioned to the same block, and even brown, green and white may appear on the ring less than 1cm. Coexistence of color, this complex color combination and distribution characteristics have important guiding significance for the identification of Dushan jade. The variegated jade is the most common variety in Dushan jade, accounting for more than 50% of the total reserves.
In the above classification, except for the green jade and the variegated jade, the color distribution area of ​​the main body of other varieties should account for more than 90% of the whole block. For green jade, the green part is immersed in white jade. When the green part is more than 20~30%, it can be called green jade. Two or more colors other than this are called variegated jade.
Second, determine the main gemological properties for different varieties
The mineral composition of Dushan jade is the most complex of all jade. It is usually simply called altered plagioclase or shale petrochemical plagioclase. The main components of most varieties are plagioclase and zoisite, and attapulgite. More than 20 kinds of minor minerals and trace minerals such as actinolite, chrome mica, pyroxene, sericite and vermiculite are the changes in the content and proportion of these minerals, which make their properties changeable and difficult to identify. Many gemological reference books or textbooks generally summarize the main identification parameters of Dushan jade as relative density: 2.73-3.18, refractive index is 1.56-1.70, obviously, this large range of interval values ​​for different varieties of Dushan jade The identification lacks specific guiding significance. Here, the author systematically tested the composition, relative density and refractive index value of the important varieties of Dushan jade collected. The results are shown in Table 1.
In the above table, the main and minor mineral compositions are observed under a polarizing microscope. The relative density is determined by the hydrostatic weighing method. The solution is determined by carbon tetrachloride, and the refractive index is an approximation of the point measurement. The above results indicate that the color refractive index and relative density of Dushan jade depend on the composition and content of minerals in jade. Among them, a few dry white jade, the content of zoisite is high, and the RI value and SG value are as high as 1.70 and 3.15 respectively. The opaque green and white varieties in Qingyu jade and green jade also exhibit higher relative density values. For all samples of other varieties, the spot index value was 1.58, the relative density was between 2.70 and 2.80, and most of them were 2.75-2.76. Of course, it is not certain that the above results include the transition types of all varieties, but these common varieties identification parameters should have a positive guiding role.
Third, the identification of Dushan jade should be heavy appearance, Xiao nature, knowledge mechanism
The identification of Dushan jade is one of the difficult points in the identification of jade. Due to the complexity of its composition, the variety of species, the similarity of appearance and some properties to other jade, it strives to be meticulous, comprehensive and accurate. Paying attention to the meticulous observation of the appearance of Dushan jade is an important aspect of distinguishing the jade. Many experienced jade merchants or jewelers can determine the type of jade by relying on the intuitive judgment of the appearance of a certain jade.
The observation of the appearance of jade usually depends on the naked eye or 10 times the mirror. The observations mainly include four main aspects: gloss, color, transparency and texture. The fracture and some surface features also have important hints. Dushan jade products often show glass luster to grease luster, translucent to opaque, mostly micro-transparent, and very few high-quality products are nearly transparent. And transparency and different color varieties often have a certain matching relationship, such as gray green and yellow green and white jade, often opaque, brown jade and blue green jade are often translucent. Color observation should pay attention to four aspects, namely color type, concentration, distribution, and combination. As long as you pay attention to these aspects of different colors, the identification of Dushan jade is basically in mind. Dushan jade texture is mainly reflected in the change of grain size. Most of the varieties are fine-grained (granular) structure or cryptocrystalline structure, the average particle size is less than 0.05mm, and the polished finished surface is fine and smooth, only part of Hei Dushan Jade has a coarser grain size and is uneven. For some varieties that are confusing, the main physical properties should be tested. For example, translucent blue-green Dushan jade is similar in appearance to high-quality jade, but it is easy to distinguish between the two by RI value, SG value and spectrum test. And this unique jade color is caused by chrome-containing mica, which turns red under the Charles filter. In addition, the Dushan jade is greenish blue, often with black spots of dark minerals. These characteristics are also distinct from similar jadeite. Bai Duyu is easily confused with quartz jade in similar appearance and white jade in nephrite. It is not difficult to distinguish them by some routine tests such as RI value, SG value, and microstructure observation. At the same time, when we identify the jade, we should have a comprehensive understanding of the causes and mechanisms that produce the different properties of the above aspects, so as to objectively grasp the nature of Dushan jade to achieve the purpose of accurate identification.
Fourth, the evaluation of Dushan jade crafts: material quality is the foundation, the process is guaranteed, design is the key
Similar to most jade, the quality evaluation of Dushan jade is still based on color, transparency, texture and block. Commercially, the raw materials are divided into five grades: special grade, first grade, second grade, third grade and other grades. The high-quality Dushan jade requires dense, delicate, no cracks, no white gluten and impurities. The color is single and uniform, and the green is similar to emerald. Transparency is semi-transparent and near-transparent. The bigger the block, the better.
There are many kinds of handicrafts processed with Dushan jade, and the content is rich. The raw materials of fine varieties are small, and they are often processed into small pendants, bracelets and ring faces due to market needs. Other processing of adult objects, landscapes, flowers, birds and beasts, furnace smoked, utensils, bonsai, antique jade and other types of crafts. Each category has dozens of themes or products, totaling more than 100 product types. In addition to paying attention to the grade of jade and the advantages and disadvantages of the engraving process, the design ideas and aesthetic effects of the products are important factors that cannot be ignored.
Dushan jade is rich in color, and the combination of color and depth is rich. On the one hand, it provides designers with a wide range of imagination spaces, and also puts forward higher requirements for designers. Different materials must have different design ideas. Or static or moving, or ancient or modern, or simple or complex, depending on the material. A good work should achieve the harmony of the subject matter and the quality of jade, the unity of form beauty and color beauty, and conform to the basic aesthetic principles of contrast, symmetry, balance and unity. In order to achieve the artistic level of "smart, pretty, and absolutely", that is, the design ideas are clever, the use of the pretty colors is reasonable, and the craftsmanship is superb. For example, Dushan jade carving "iron fan princess", the work uses the white, black, green, red and other colors in the variegated jade, the white part is used as the face of the character, the green part is used as the body, and the piece is thick. The green area is cleverly designed as a banana fan, the edge of the blush part is used as a flame, and a large red dot is designed as a Sun Wukong. The whole picture structure is reasonable, the shape is lively, the lines are smooth, and it can be said that it is selected in materials, design, color and workmanship. A rare masterpiece. Another example is the variegated jade product "Jade Jade Eagle Snake", the black part is mixed stone and dead wood, the green flower is designed as grass and shrub, the green is carved into a mighty eagle, and the snake body is white with black spots. In the gravel grass. The work is unique in design, natural in shape and lifelike. Obviously, an excellent craft is closely related to the delicate design. The evaluation of these handicrafts not only requires the judges to know jade, is familiar with the craft, but also has considerable artistic accomplishment and aesthetic taste, which is the quality that many people in the industry pursue and must have.
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