Black pearls can generally be divided into the following three types:

1. Natural black pearl

Black pearl cultured by nuclear implantation (cultured in Hyriopsis cumingii, maybe in some kind of mother-of-pearl). This mother-shell lives in the coral reef waters of French Polynesia.

2. Rare brown to black seedless cultured pearls.

There are more and more colored pearls, including dyed black pearls, radiated pearls and the latest so-called "laser-treated" pearls.

3. Imitation pearls made of black shells.

Some rare imitations are coated with a layer of black essence de orient film on the surface of the ball core, or made into beads with black shells to polish the pearl luster.

Distinguish natural black pearls from cultured black pearls, colored black pearls and imitations. Careful observation of the luster of the coated pearls shows that the pearlescence of the coated pearls comes from the bottom of the polymer thin layer, while that of the untreated pearls comes from the top layer of the pearls. The abnormal reflection of the color on the top surface of the pearl can also be observed, which is also helpful for the detection of this kind of pearl. The color of this pearl is pink from the top and blue from the side; The black pearls treated in this way have purplish tops and green sides.

The characteristics of high-quality pure black pearls include:

1 Pearl surface is particularly smooth.

Pearls have a sticky feeling to the touch

3. The edge of nacre laminate is hard to see, and a sharp tool and a concave colorless cover can be seen.

This can be said to be the law of the market: as long as a commodity has a good market, it will inevitably be copied. Black pearls are no exception. It is not difficult for us to see so-called black pearls in jewelers, but some businessmen forget to add the word "dye" before black. When you ask whether these black pearls are real, profiteers can brazenly answer: they are really cultured pearls. Yes, they are dyed with real seawater or freshwater cultured pearls. But he wants to tell you that the beads have gone through the process of processing and dyeing, just like a jade seller wants to tell you whether the B and C products have been optimized. Of course it's not illegal. I'm telling you, it's not illegal in China. But in Tahiti, the main producing area of black pearls, if a businessman sells dyed pearls, his reward is imprisonment!

There are several common pearl dyeing methods:

Silver salt treatment-pearl is soaked in nitrate and dilute ammonia solution, and then reduced in strong light or hydrogen sulfide gas to make the color of pearl black.

X-ray irradiation-pearls turn black when exposed to gamma rays from cobalt sources.

Dye the nucellus-The nucellus is dyed black before being implanted into the pearl shell. When the pearl is formed, the black pearl core makes the translucent pearl look black.

Coating-coating a thin layer of black glue on the pearl surface.

It is not difficult to tell the difference between dyed pearls, and it is not difficult to say it easily. With the following common sense, you should know that your eyes are close to each other.

Color-black pearls have different shades of light gray to black, and its beauty lies in the color matching of look tones. Turn the black pearl slowly, and you can see the slight rainbow-like flash changing constantly. No two pearls are exactly the same. If you see a string (or even several strings) of black pearls with uniform black color and rich halo, it is almost certain to be dyed pearls. The dyed pearls are dull in color and gather in places where holes and defects are drilled.

Shape-Is the black pearl you see particularly round? Exquisite round black pearls are extremely rare and of high value. Typical black pearls are oblate, pear-shaped, oval and irregular, and many of them have flaws or rings, so if the super-value black pearls you see are smooth and round, they are probably dyed.

Size-The diameter of seawater pearls in China or Japan is usually less than 9 mm, while the diameter of black pearls is at least 8 to 9 mm, so round black pearls smaller than 8 mm are mostly dyed pearls.

Price-Are the black pearls you see surprisingly cheap? An 8mm round black pearl costs more than 1000 yuan, while a dyed pearl of the same size only costs 1200 yuan. If you are lucky enough to buy a black pearl at a reasonable price, Jinji requires the merchant to indicate on the receipt that the color of the pearl is natural.

If you want to buy expensive black pearls, the above appraisal method is still not at ease, so consider taking them to the jewelry appraisal unit for an exact appraisal with instruments:

Ultraviolet fluorescence test-Under ultraviolet irradiation, black pearls often fluoresce, ranging in color from bright red to coffee red, but most dyed pearls do not respond to ultraviolet rays or show dark green fluorescence.

X-ray examination-X-ray film can show the dyed pearls treated with silver salt, and a circle of pale white appears between the nacre and the nucleus of the dyed pearls, which proves its dyeing composition.

X-ray fluorescence test-pearls will emit radiation with a specific wavelength under X-ray irradiation, and the existence of chemical components and silver salts can be detected by measuring the degree of wavelength with a spectrometer.

Infrared photography test-shooting pearls with infrared film. The image of black pearl is light blue, while the image of dyed pearl treated with silver salt is yellow, or the color is blue-green to yellow-green. The main point of identifying black pearls is to identify a pearl or pearl chain. Traditional gem detection methods are rarely used. On the contrary, appraisers must combine the observation of appearance characteristics with some special detection methods as the identification basis, such as X-ray diffraction phase diagram, reaction under ultraviolet light, advanced spectroscopy, etc., in order to accurately judge which type of pearl belongs to. To identify a black pearl chain, you can follow the following steps.

Step 1: Check the overall appearance of the bead chain. When testing the bead chain, you should first hold the bead chain high with both hands and put it on a neutral background (light gray or milky white). Check whether the white light above the necklace comes from a double-tube fluorescent desk lamp. note:

1. Because natural pearls with the same shape and size are extremely rare, natural pearl strings are mostly classified according to size, and different beads usually have different shapes. Therefore, if a chain is composed of spherical beads with uniform size, it is likely to be a nucleated cultured pearl chain.

2. Compared with color uniformity, the color uniformity of cultured pearl necklaces is much better than that of natural pearl necklaces.

3. Roundness and crow's feet are the characteristics of cultured pearls.

Step 2: Observe and judge in detail. First of all, pearls and their internal drilling holes must be thoroughly cleaned. Dip a soft cloth and brush in warm soapy water to wash away those sticky organic residues and oil stains. Once cleaned and dried, it will be easier to identify. Under good optical fiber lamp illumination, you can use 10 magnification magnifying glass or low magnification microscope to check:

1. The pearl layer should pay attention to the following contents: The dentate appearance of female ring pattern can appear, because when the outer surface of natural pearls or cultured pearls is broken, the thin layer covering the pearl surface is actually aragonite flake mother beads. This appearance can be presented under a hand-held magnifying glass, which is quite different from the pearl-like structure of the coating essencedeorient. Its structure presents a smooth appearance with low water absorption. This structure is discontinuous and loose, covering the surface of the inner layer such as glass, plastic or shell beads. There is a thin layer of wax floating on the surface of mother-of-pearl, or it is difficult to observe the ring appearance of mother-of-pearl, so this kind of pearl is laser-treated black pearl or coated black pearl. Beads with smooth surface and often polished marks are polished shell beads, not imitation pearls. Pearls with dye aggregation in surface pits are dyed as seedless cultured pearls. ... class =' class1' > natural hemi-pearl and cultured hemi-pearl, with obvious combination surface.

2. It's best to use a small-diameter fiber lamp with adjustable brightness to illuminate the drilling hole of the pearl. Pay attention to observation: ... Those with thin concentric structures like onion layers are natural pearls. There is a gray-to-white central shell pearl in the middle, and a thin brown-to-black organic shell pearl between the shell pearl and the black parent material layer of the outer ball, so this is a black pearl cultivated by nuclear implantation. The drilling of black pearls needs special careful inspection, because it can determine which of the following pearls: natural colored black pearls, brown to black seedless (freshwater) cultured pearls. Nucleated black cultured pearls, dyed black nucleated cultured pearls, dyed black freshwater (seedless and freshwater nucleated) cultured pearls, irradiated nucleated cultured pearls and so-called laser-treated black pearls. For example, when a magnifying glass with a certain multiple and adjustable fiber lamp illumination is used to detect the black pearl borehole:

* Natural black pearls have onion-like layered structure, with a thin black layer superimposed. The seedless cultured black pearl is similar to the natural black pearl in structure, but there may be a central cavity with uncertain size and shape. * A nucleated cultured pearl has a white to gray central pearl core, which is first wrapped by a thin layer of black mother-of-pearl, and then the outer layer is wrapped by a layer of black mother-of-pearl with different thicknesses.

* The dyed nucleated cultured black pearl has a dyed black pearl core and a black pearl layer. * The nucleated pearl irradiated black is very distinctive, that is, it has a dark central pearl core and a slightly lighter, white to gray pearl layer.

* The laser-treated seedless pearl has a black hole covered with wax residue. ... without pearl layer, it presents a usually thin artificial flavor layer. Covering the surface of glass, plastic, shell beads or hollow glass balls is imitation pearls. There is a big hole in the center, and there is a pearl layer with pits on the surface around the hole of the string. This is a freshwater cultured pearl with active nucleus (seedless), which is usually considered as Pipa Pearl or China Pearl. There are two or more growth interruptions (possibly different colors). According to the recent disclosure, it is a kind of freshwater cultured pearl in China, which is dyed with full nacre or treated by laser. 3. Observe the pearl by transmission illumination. Place the pearl in the center of the adjustable diaphragm and let the strong white light pass through the pearl. In this way, you may see a striped (layered) structure, which is the core structure composed of shells. It is located in the center of cultured pearls with nuclei in the undrilled seawater, and similar layered structures can be seen in imitations of pearls such as shell beads. Step 3: Direct X-ray photography analysis Direct X-ray photography can provide the answers to the following questions: Is the black pearl natural, cultured or imitation? If pearls are farmed, what species are they? Direct X-ray photographic analysis has two main uses in pearl identification. Direct X-ray photography can provide a general measurement basis (general impression), which is aimed at pearls that have become part of the necklace, especially those pearls that have been strung on the rope. Because of the rope, it is impossible to observe the borehole. Secondly, in order to pursue the accuracy of each pearl identification, then this necklace must break the rope, take photos one by one under X-ray, and analyze and identify the structure shown in each picture. Similarly, separate X-ray photography can be used to identify any unperforated pearls that are set in forks or inlaid in jewelry. When testing pearls by X-ray photography, the obtained picture is a negative with opposite light and dark (the white part is developed by calcium layer and the black part is developed by soft part). The negative can leave a permanent record for identifying structural features:

* Natural pearls ... Onion-like opaque layers (thin aragonite layers) and transparent layers (alternating arc or ring-shaped shell protein layers) appear alternately, sometimes with a small transparent center.

Keshi pearl (the whole pearl accidentally formed during nuclear implantation) ... onion-like structure, usually with a radiopaque central cavity with uncertain shape and size. * Cultured pearls with nuclei ... The radiation penetration of the central nucleus is very poor, and the nucleus is surrounded by a thin layer of permeable shell protein. The outer layer is a relatively thin (akoya pearl) and a thick (Nanyang pearl) pearl layer, which has poor light transmittance. * Non-round cultured pearls with active nuclei (Biwahu or China), seedless cultured pearls ... usually have grotesque opaque shapes and sometimes contain a large, slender and permeable central cavity.

* Imitate pearls ... opaque or completely transparent spheres, which can't distinguish the bright and dark structures.

When summarizing this step of pearl identification, it must be emphasized that:

1. Direct X-ray photography is of little significance for the identification of some pearls. For example, black Nanyang pearls or natural pearls with thick nacre often cannot see the central arc structure or permeable shell protein layer during development.

2. Analysis of X-ray images requires in-depth theory and more practical skills.

3. Too much X-ray imaging will show some structural details of the pearl center, while insufficient imaging will show structural details of the pearl surface.

4. The subtle difference between the denser nacre and the denser nacre in the photos is often the only sign of nucleated cultured pearls.

Step 4: Optimize the detection of pearls. The fourth step to identify black pearls is to determine which method has been improved, whether it is dyed or irradiated, laser treated, coated or even polished shell beads. Dyeing and irradiation treatment: Except for nucleated cultured pearls dyed with silver nitrate (the identification basis can be found in X-ray photography: opaque dotted silver infiltrates around the shell protein layer on the outer layer of pearl nucleus) and dyed anglerfish or China active cultured pearls (the surface pits and defects are often attached with dyes), the outer layer of pearls with improved color is not easy to detect. If the pearl is not drilled, the laboratory will be required to identify any dyes used to improve the color by infrared spectrum analysis and Raman spectrum analysis. Relatively speaking, it is much easier to identify the improvement of color if it is a nucleated cultured pearl or a living nucleated freshwater pearl. For the pearls dyed by drilling holes, it can be found that the dye stuck in the holes is nucleated cultured pearls * pearl layer, and the shell protein layer and pearl core are dyed black nucleated cultured pearls, which is obviously compared with nucleated black pearls. The nucleated black pearl has a white pearl core and a black pearl layer, which can be seen from the borehole. The mother shell of nucleated black pearl is pearl oyster or black-lipped pearl oyster. * The color of nucleated cultured pearls with black core and white nacre is obtained by γ -ray irradiation. * Dyes from living nucleated pearls will attach to holes or drilled holes * The reaction of dyes on strings between natural black nacre and pearls to long-wave ultraviolet fluorescence is considered as a useful indicator of untreated. For example, the nacre of natural pearls and untreated cultured pearls is naturally black, and there is always a fluorescence with variable intensity but always dark reddish brown under ultraviolet fluorescence.

On the contrary, black mother-of-pearl after dyeing, irradiation and laser treatment is inert under long-wave ultraviolet light. Laser treatment of black pearls is not familiar with this technology, because this kind of pearl only appeared in the Australian market in the last 2 ~ 3 years. The application of this technology can at least give China freshwater seedless cultured pearls a beautiful black tone. It is doubtful that the improvement of color is entirely by laser irradiation. Because the heat generated by the laser will obviously carbonize the organic matter of the pearl, and it can also dehydrate the pearl and make it dry and scorch. In my opinion, if laser technology can be used to improve this black pearl with halo color, then to some extent, laser energy can also be used to improve the dyeing process with moderate color and the depth of dye penetration. Some unusual phenomena can be seen in the amplification detection of laser-treated pearls. Possible identification features include: l The pearls treated by laser have strong halo effect. The growth layers produced by the multi-stage growth process of pearls have been improved perfectly. Pearls are covered with a layer of wax, which is easy to scrape off and often covers up the concentric fingerprints of the pearl layer. The brown waxy layer fills the defects and spirals on the pearl surface. A layer of wax is attached to the drill hole of the pearl, which masks the growth layer structure of the onion-like concentric ring of the pearl. The treated mother-of-pearl is inert under long-wave ultraviolet lamp.

At present, we are introducing Raman spectroscopy into the research, trying to find the identification characteristics of this laser-treated pearl. Wax-injected pearls soak the casting beeswax in bamboo chips, which are often used to take cultured pearls just collected from fresh water out of shells and remove the active organic matter stuck on them. This wax-coated bamboo sheet will temporarily improve the luster of pearls. Wax attached to pearls can be easily found under a hand-held magnifying glass. Polymer coated pearls Some Tahiti black pearls (cultured) are covered with a colorless polymer (plastic) film to improve the luster of the pearls. We know that this treatment process was completed in Japan, and the pearls with poor luster were wrapped with a thick layer of polymer. This treatment method can be recognized by naked eyes: ... A careful observation of the luster of this coated pearl reveals that its pearlescence comes from under the polymer thin layer, while that of untreated pearl comes from the outermost layer of the pearl. The abnormal reflection of the color on the top surface of the pearl can also be observed, which is also helpful for the detection of this kind of pearl. The color of this pearl is pink from the top and blue from the side; The black pearls treated in this way have purplish tops and green sides. ... to test the residual bubbles in the colorless plastic layer on the pearl surface? As well as uneven surface morphology, evidence of finishing, scratches on the coating and evidence that the tax collector can press pits on the surface. Polishing pearls We know that we occasionally encounter some black Nanyang pearls that have been ground with soft abrasives. Such as sawdust, bamboo chips soaked in beeswax, burnt salt and polishing materials commonly used to remove biomass from the surface of pearls. This polishing material can also be used to polish rough and dull places on nacre.

Although the above treatment methods are acceptable, people do not accept such a process, that is, polishing pearls with a millstone with poor quality. Because this process will leave deep scratches on the surface of the pearl, which is also the identification basis of this pearl. The question is: how can this ordinary pearl be traded like a traditional pearl layer? Besides natural pearls, will people accept this kind of pearls? By coating a layer of polydisiloxane, the black nucleated cultured pearls with characteristic luster were coated with silicon. The characteristics that should be paid attention to when testing this improved pearl include: … the pearl surface is particularly smooth … the pearl has a certain degree of sticky feeling … the overlapping lamella edges of the pearl layers are difficult to see, and sharp instruments and concave colorless covering layers can be seen.