After dyeing, the color of black pearls is even, and the black color gathered in holes and cracks is darker. The surface color is pure black, while the natural black pearl is not pure black, but dark blue black with a slight rainbow flash, or black with bronze hue.

2. Powder method.

Dyed black pearls have black powder, and black pearls have white powder. However, taking pearl powder is a destructive experiment, so be very careful in operation, especially don't carve on black pearls without holes at will.

3. Particle size method.

Most of the black pearls are Pinctada maxima, and the Pinctada maxima produces large nucleus and big beads. Generally, the particle size is rarely less than 9 mm, so those less than 8 mm are round black pearls, mostly irradiated products.

4. Halo.

Black pearls discolored by radioactive radiation are rich in halo spectrum and accompanied by strong metallic luster.

5. Dilute acid method.

In some cases, cotton balls can also be dipped in dilute nitric acid (2%) to try to wipe pearls in inconspicuous places. Dyed black pearls will make cotton balls black. This method is destructive and should be used with caution. But experienced appraisers can often find the defects of colored pearls. Effective methods are instrument testing, such as infrared spectrum analysis and microscope.

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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 must be a fake. Black pearls are no exception. It is not difficult for us to see so-called "black pearls" in jewelers, but some merchants forget to add the word "dye" before "black".

When asked if these black pearls are real, profiteers can brazenly answer: These are real cultured pearls. Yes, they are dyed with real seawater or freshwater cultured pearls.

But he wants to tell the beads that they are processed and dyed, just as a jade seller wants to tell whether products B and C are optimized. Of course, if he doesn't tell them, 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 distinguish dyed pearls. If you have the following common sense, you should know that it is just around the corner.

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 is uniform,

Brightly colored black pearls are almost certainly dyed pearls. The color of dyed pearls is dim, and the black color gathered in holes and defects is dark. This is easy to observe under a magnifying glass of ten times.

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. Therefore, if the "super-value black pearl" you see is smooth and round, it is probably dyed.

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

Baidu Encyclopedia-Black Pearl