1, mineral composition of jadeite
The composition minerals of jadeite are mainly jadeite or other pyroxene minerals (such as jadeite and omphacite) in clinopyroxene cluster. ) and jadeite molecule (NaAlSi206). The mineral composition of jadeite is considered to be the product of high-pressure and low-temperature metamorphism, which has been confirmed by jadeite synthesis experiments. For example, NaAl in jadeite is largely replaced by calcium, magnesium, iron and chromium. , beyond the scope of jadeite composition, become other pyroxenes (such as jadeite, omphacite, diopside, aegirine, etc. ). Jade composed of diopside and aegirine can also be called "pyroxene jade", but it is not jadeite. The national standard "GB/T 16553— 1966 Jewelry and Jade Identification" has made more accurate provisions on the identification of jadeite jade. However, the commercial scope of jadeite is larger than that of jadeite. Because jadeite is a polycrystalline aggregate, the more accurate method to determine whether jadeite and jadeite are mineral components is electron probe image composition analysis, but it is limited by instruments and equipment, and the cost is high. The rapid change is the micro-powder oil immersion method. As long as an ordinary polarizing microscope and a few bottles of refractive oil are used, the samples taken are very small, and even the high-grade torus will not affect its beauty and value.
2. The color of jadeite
Emerald jade is regarded as a treasure, and it is said that "the price of color is ten times higher". Therefore, green additive technology is also constantly innovating. Besides adding red and purple, there are at least four green varieties on the market. It looks like a natural emerald, and its value is only 1% to11000 of that of goods A, even lower than that of goods B. Dyeing colorless jadeite into brilliant green jadeite and selling it as high-grade jadeite have caused great losses and mental burdens to some consumers. The jadeite dyed by double salt in the early stage is red by Charcot filter (natural green calcium aluminum garnet jade is also red), and a batch of jadeite torus dyed by double salt was discovered by American Gemological Institute as early as 1956. At present, many dyed jadeites do not need double salt, and the characteristics under Charcot microscope are similar to those of natural jadeites with good stability. Charcot filter observation can only be used as a reference. In the past, colorants were deposited in the network cracks of dyed jadeites, but now some jadeites dyed green (including some B+C ornaments or pieces) can no longer see this phenomenon, so the colorants deposited in the cracks are not necessarily A goods. In recent years, a kind of jade bracelet and pendant with uneven light green dyeing is common in the market and sold as natural jade. This kind of jewelry has soft color, certain transparency (water), no glue injection, clear absorption line at 437nm under spectroscope, knocking sound and ultraviolet fluorescence characteristics, which are basically consistent with natural jadeite when observed by Charles filter. The retail price of this bracelet is generally 500- 1500 yuan, which is quite popular with the working class and tourists. According to the data of many tests, the pores are filled with a dye (non-polished powder), and the dyed jadeite is light green as a whole due to the reflection of light. Some dyes are whole, some are only partially dyed, and some are accompanied by purple (also known as "spring color"), which makes a bracelet show a special light green and lavender change. Soaking in detergent and other solvents (cleaning with ultrasonic wave if necessary) can wash off most of the dyes, but generally it will leave a light green after cleaning. The dark green filaments impregnated in the micropores can be seen with a magnifying glass with a magnification of 10 (obviously visible even with naked eyes). Dyed and washed, the color is lighter, but it is more like nature and more deceptive; Not only is it difficult for ordinary consumers to identify, but some bosses with certain business experience have not seen the doubts and entered this kind of jewelry in batches; Even if the professionals engaged in jewelry testing are slightly negligent, it is possible to issue a test report as natural jadeite.
3. The optical characteristics of jadeite are natural.
Natural emeralds are caused by a small amount of compounds. If the color of jadeite is natural or colored, a simple and reliable method is spectroscope, but some jadeite pieces have weak light transmission or light color, and the absorption line is not easy to observe. If there is fluorescence reflection, it can be checked by ultraviolet fluorescence instrument. Furthermore, the electron probe instrument can be used to detect the pigment in the color body, but the detection cost is high, and the pigment content of light color is often lower than the detection limit. Jadeite Jadeite generally has a strong absorption line of 437nm under the spectroscope. For chrome jadeite, it is difficult to see the absorption line of 437nm. Some literatures think that the absorption line of 437nm is caused by iron; But in the completely colorless glass jadeite, this line is also very strong; Therefore, the formation mechanism of 437nm spectral line needs further study. Emeralds with positive green color generally have complex absorption lines of 690 (strong), 660 (medium) and 630nm (weak). Usually, stepped absorption bands of -690, 690-660 and 660-630nm are formed, which are strong, medium and weak in turn; Light green, -630 band or line is too weak to see clearly. Dyed green with Luo salt, with a wide absorption band at 660nm; Some organic dyes are dyed green, purple, red and so on. There is no absorption in the region of 680-630nm. The ultraviolet fluorescence effect of jadeite is an important reference for identifying goods A, B and C;
(1) Natural jadeite generally has no fluorescence, and some "white cotton" has light yellow fluorescence.
(2) Jade B goods are mostly filled with organic glue and generally have blue-white fluorescence (filled wax and blue-white fluorescence); At present, many "Basanyu" bracelets and pendants (goods B) on the market have uniform blue and white fluorescence. Some B goods have no fluorescence, which may be filled with silica gel and other substances.
(3) At present, most dyed jadeites on the market have no fluorescence (the same as natural jadeites); But some have obvious fluorescence. Some fluorescence characteristics are important for identification, such as a jadeite dyed green with strong yellow-green fluorescence (dyed green after a short storage time, and turned yellow after fading), and a jadeite dyed red with strong orange fluorescence.
4. About "Emerald"
Some experts think that the important feature of natural jadeite is "emerald" (commonly known as "flying wing"), which is the flash of jadeite mineral (0 1 1). Crystal diopside (such as diopside in Qinghai jadeite) and amphibole (such as amphibole jade in part of "Black Wusha" in Myanmar) also have developmental cleavage (0 1 1), and may also have "emerald"; Microcrystalline jadeite is generally invisible, so it cannot be used as a characteristic symbol of natural jadeite.
5. Knocking sound
The knocking sound cannot be used as the basis for judging jadeite A and B goods. Some jade sellers often bump lightly with two bracelets, making a crisp "steel" sound, indicating that it is natural jade, and the obvious impact sound of jade B is slightly dull. However, it is not necessarily natural jadeite that sounds "steel", such as diopside (such as Qinghai jade) and sodium amphibole longer than jade (such as Myanmar "Shuimozi" jade). At present, some B goods appearing on the market can also make a crisp steel sound.
Step 6 mesh
Emerald rinsed with strong acid generally has obvious pores and network structure. Stress and weathering in natural jadeite can produce obvious pores and reticular structures, which are often difficult to distinguish from reticular cracks caused by acid corrosion. The view that "people who observe cracks, pits and pits must be B goods" may not be appropriate. The natural pores of jadeite can be filled with zeolite and clay minerals in the later stage; Mineral powder or polishing powder can also be filled in the process of cutting, grinding and polishing. These fillers are not B goods and are easy to identify.
7. Density
The density of natural jadeite is generally 3.25-3.45g/cm3. The density of jadeite B cargo is generally lower than 3.25g/cm3. The density of natural jadeite with obvious pores can be as low as 3. 15g/cm3. At present, a large number of glue-injected "Basanyu" ornaments on the market are made of jadeite primary ore. Due to natural crack pores and impurities, there are some primary pores after pickling and gluing during processing, but generally there is no obvious network structure. Similar to Emerald B, it has an emerald chicken heart (refractive index 1.66, density 3.3 13g/cm3). The infrared absorption spectra measured by Ouyang Qiumei and the author respectively show the same absorption peak of B goods as typical resin filling, but only a few pores are shown in the photos magnified by microscope and electron microscope by 500-2000 times, and no obvious filler is found in the pores. This type is called "invisible filling" (this is because the newly formed surface cracks of ornaments processed by injection molding materials are not filled). Therefore, it is not necessarily a commodity that is not obviously filled with resin under a magnifying glass or microscope.
8. Classification of jadeite grades
The jadeite jade pieces identified must be the premise of natural jadeite.
According to the composition (composition), color (clarity), cutting (weight), transparency (transparency) and structure (texture) of the 5C2T standard, the grades and price grades are classified (generally, there is no need to classify works for B and C commodities). In the jadeite industry, people think that the value of jadeite is largely determined by green, because most jadeite C products are green. In recent years, because purple jadeite is becoming more and more popular, there are not only jadeite dyed green, but also purple C products on the market!
There are several points to be identified!
(1) Visual observation
Color exaggeration, big contrast, incorrect and unnatural-artificial coloring.
(2) Observe with naked eyes or under a microscope.
Does color accumulate between gaps or particle structures? Is it deep outside and shallow inside? Is it a colored root? Are we even?
There are two typical cases of C goods with exaggerated colors. One is that the color is uneven, but it has the characteristics of accumulation in loose tissues such as cracks, and the outside is light. The other is that the color is very uniform, and its color is colorless silk and color root, which is essentially different from the genuine product in colorless head, color tail and even less light. This phenomenon is caused by injection of colored glue.
Color root is a phenomenon of color generation, which is strip, flake and block. Its depth has a gradual change, spreading from inside to outside or gradually penetrating into jadeite tissue. Color root is one of the identification criteria to judge whether jadeite is jadeite or whether jadeite has been artificially colored. However, Laokeng is a kind of high-grade jadeite. Because of its delicate structure and uniform color, it is difficult to see or see the color root.
(3) Magnification inspection
For the case that the color is uneven and looks like the real thing, we should pay attention to the phenomenon of adding color to the color, that is, the phenomenon of mixed color between true and false. The key of this situation is to find the hue difference between true color and false color at the edge of color overlap.
(4) Charcot filter observation
Observing under incandescent lamp, the color shows red, indicating that it is artificially colored; If the color does not change to red, there are two possibilities at the same time: natural color or dyeing, which need to be further identified by other methods.
(5) Identify the color change after irradiation.
Emerald is only on the surface, and it is distributed in a ring or patch. This kind of C jadeite is purple under the Xiake mirror. At first glance, the irradiated jadeite is mobile and transparent, but the jadeite is blue with bombardment marks on its surface. Compared with the unexposed part, the surface color of the bombarded part is darker.
(6) Distinguish between natural color and curium color
Curium color is a heat treatment method to make jadeite appear. Natural red jadeite has good transparency, and the red part has strong luster and aura. The red color caused by curium color is dim, thick and uniform. In the past, curium jadeite belonged to C goods, and the new national standard classified it as optimization treatment.
(7) Soak in boiling water
Unexpectedly, jadeite colored with inorganic raw materials and green polishing powder will turn green after being soaked in water at 80- 100 degrees for several hours. But high-tech dyed jadeite will not fade in hot water.
(8) Fading of chemical reagents
Drop dilute hydrochloric acid on the surface of some dyed jadeites, or scrub C-grade jadeites with cotton balls dipped in "Quziling". The green or purple has faded.
(9) Color identification of purple jadeite
The identification of purple is mainly through a magnifying glass, observing the relationship between color and jadeite particles, and judging according to the characteristics of color root and color shape.
The identification of purple jadeite should pay attention to: is it white or purple? White surrounds purple-natural purple; Purple is surrounded by white dye.
In addition, you can also observe with the help of ultraviolet fluorescent lamps. Natural purple jadeite generally has no fluorescence reaction under ultraviolet light, while purple dyed jadeite often has obvious fluorescence under ultraviolet light.
The common optimization treatment methods of jadeite jade are: heating treatment, bleaching, bleaching filling treatment, wax oil soaking and dyeing (coloring) treatment.
First, heat treatment
The purpose of heating treatment is to make the yellow, brown and brown jadeite of iron-containing minerals turn bright red. The basic principle is that yellow, tan or brown gambling stone shell materials after secondary oxidation are selected and heated to make limonite (Fe2O3? NH2O) is dehydrated and transformed into hematite, which is red, commonly known as "baked red". Just heat it in the air, and the temperature does not need to be too high. The method has simple manufacturing process and low equipment requirements.
The red color obtained by heating treatment is basically the same as that of natural jadeite, which is generally unnecessary or difficult to distinguish. From the identification characteristics, the natural red jade is slightly transparent, while the red jade obtained by heating has a "dry" feeling.
Second, bleaching
The purpose is to remove the "dirty color" and "black" produced by impurities to improve transparency and make it more beautiful. Generally, the main components of dirty color are oxides of iron and manganese; The main components of black are amphibole, chromite, pyrite and magnetite. In traditional jade processing, the oldest bleaching method is soaking sour plum soup, which has a history of one hundred years in China and is only used to remove iron, manganese and other oxides on the surface of jade. Modern bleaching treatment has made great progress in methods and achieved remarkable results. Its bulk method is to soak jadeite in bleaching solution to remove cracks or mottled substances such as black, brown and yellow in jadeite mineral particles. The most commonly used bleach is hydrochloric acid, followed by hydrofluoric acid or other acids, and even aqua regia. According to the characteristics of "dirty color" and "black color" contained in jadeite and the different bleaching solutions used, some jadeite only needs to be soaked for several hours, while others need to be soaked for several weeks.
Light bleaching treatment does not change the internal structure of jadeite, but only removes the variegated color on the surface of the sample, but it also slightly damages the surface structure of jadeite, and generally does not affect the durability of jadeite, while heavy bleaching treatment has obvious damage to the structure of jadeite. From the identification characteristics, photobleaching is not easy to be found, leaving only very fine cracks on the surface of polished samples. Deep bleaching will leave obvious cracks on the jade surface, criss-crossing, because there is no wax dipping and glue injection, so it looks pale and dry. If the structure of jadeite is damaged to a great extent, it needs to be filled.
Thirdly, bleaching and filling treatment
The jadeite treated by bleaching and filling is commonly known as "B" goods in the jadeite industry, and this treatment method has become quite popular. Bleaching is to remove yellow, black and other variegated colors, and the structure is generally not seriously damaged. Later, it was found that the transparency of jade could be improved by prolonging the time of removing yellow and black. However, judging from the degree of structural damage, some jadeite particles are dissolved while the mottled and dirty colors in jadeite are dissolved, which destroys the unique dense structure of jadeite and produces larger and more cracks, and some even appear loose crumbs. This severely bleached jadeite must be filled and consolidated before it can be used. There are many kinds of cement used for consolidation and filling, such as organic polymers (epoxy resin, Canadian gum, plastic and plexiglass, etc. ) or a mixture of polymer and jadeite powder. Recently, it is possible to use inorganic materials (glass) with refractive index similar to that of jadeite for filling and consolidation. It has been reported that some "B" goods were corroded by hydrofluoric acid or aqua regia, but the dirty colors such as yellow and black have not been completely removed, which is deceptive, and even the mottled colors such as yellow and black have not been removed, giving people the illusion that they should not be "B" goods.
There is also a kind of jadeite called "B C" in the market, and its treatment method is basically the same as that of "B C" jadeite. The fundamental difference is that the filler used in "B C" jadeite is a colored substance, that is, dyes or pigments are evenly mixed into colorless fillers, and then consolidated and filled. "B" jadeite is colorless.
The identification characteristics of jadeite improved by this method are as follows: no "emerald" or "emerald" is not obvious; The refractive index decreases and the luster darkens; Most of the specific gravity becomes smaller; The surface structure is characterized by "grid", "groove" cracks and "orange peel effect"; "B C" goods are unnatural in color, white, in a daze and floating on the surface; Most of these products made in the early days have fluorescence, but none in recent years; Infrared spectrometer is an effective method to detect products filled with organic matter (hydroxyl absorption peak). Due to the continuous development and change of this improved method, the identification of bleached and filled jadeite is still relatively shallow recently.
4. Soak in wax and oil
The purpose of soaking in wax and oil is to cover up the cracks in jadeite and increase transparency, commonly known as "hiding broken pieces". This method is often used for jadeite raw stones or finished products with many cracks and poor texture. The specific method is to put the jadeite raw stone or finished product to be treated into the liquid of oil or wax, and soak it with a little heating, so that the oil or wax permeates along the cracks and tiny cracks and fills them in the cracks, so that the cracks are not obvious. The jadeite treated by this method can not last long, but only temporarily covers the cracks, which increases the refraction and reflection ability of light and improves the transparency. This kind of sample will change when it meets acidic solution, and it will spill oil or wax when it meets high temperature. Wax dipping (or waxing) has a long history and is generally accepted. In the jade shop, it is called A goods. However, from the gemological point of view, because other substances are added to natural gemstones, they are also artificial beautification products, not completely natural products.
Verb (abbreviation of verb) dyeing treatment
The jadeite that has been dyed (colored) is commonly known as "C" goods. The purpose of the treatment is to make the light or colorless jadeite become the desired color, such as green, red or purple, or even multiple colors appear at the same time. At present, segmented dyeing and multiple dyeing often occur, and multiple dyeing is also called "additive color" in the industry. Jadeite dyed with chromium salt in the early days was red under Charles filter, and jadeite rings dyed with chromium salt in batches were discovered as early as 1950s. At present, many dyed jadeites are similar to natural jadeites under Charcot microscope, and their stability is good. In the jadeite dyed in the past, it can be seen that the dye is deposited in the network cracks. However, some light green jade bracelets and pendants are soft in color and have certain transparency. The absorption line is clear under the spectroscope, and the tapping sound, ultraviolet fluorescence reaction and Charles filter observation are basically consistent with natural jade. This kind of product is filled with organic dyes in tiny pores, and the dyed part is light green as a whole, resembling natural color.
Durability and identification: the durability of dyed (stained) jadeite is poor, and the color will change when exposed to light or acidic or alkaline liquids for a long time. Jadeite with rough dyeing work is easy to identify, but it is difficult to identify the dyed products with fine dyeing work recently. Professional appraisal depends on experience and instruments. Dyed jadeite is characterized by: the color floats on the surface, there is no color root, it is distributed in a silk network, with rich colors and big cracks; Using absorption spectrum characteristics and infrared spectrum characteristics; However, the colorful dyeing methods appear constantly, which makes its identification characteristics constantly change, so the comprehensive application of experience and methods in the identification process is very important. In addition, it is particularly noteworthy that "Tiancai" jadeite resembles "color root" and is extremely difficult to identify.
Six, other processing methods suitable for jade.
The coating or coating treatment of jadeite, commonly known as "coating", is to make the surface of jadeite appear "green" and "water" by mixing binder and green dye. This kind of processed product is difficult to identify, but experienced people in the industry can identify it by touching it. According to reports, irradiation treatment technology is also applied to the coloring of jadeite, which requires high intensity, long time and unsatisfactory overall effect, so it is rarely used. The splicing method is also applicable, for example, the jadeite with light water color and good color is stuck on the green low-grade jadeite or green glass with green glue and inlaid. In addition, the common method is to "coat gold" and "embed gold wire" at the crack. This is from the blog. You can also look for it.