Introduction to the first author: Shen, the first vice-chairman of insurance institute of china Artifacts Professional Committee, the second and third executive vice-chairmen and secretary-general, and a senior engineer in the metallogenic simulation laboratory of Beijing Institute of Geology, nuclear industry.

Synthetic gems are produced in laboratories or factories. Therefore, in today's highly developed science and technology, the fidelity of the produced synthetic gemstones to natural gemstones has reached a level that is difficult to distinguish between true and false. Moreover, the color of synthetic gemstones is equivalent to the highest grade of corresponding natural gemstones, making synthetic gemstones an ideal material for imitation jewelry, but they are also used by some unscrupulous traders to make huge profits and harm consumers. Therefore, it is beneficial to learn some visual identification methods of synthetic gems.

First, the naked eye difference between colorless artificial cubic zirconia and diamond.

The macroscopic difference between diamond-like cubic zirconia and diamond can not be distinguished by their hardness and relative density, but can be distinguished by the following three methods.

1) is distinguished by the difference of refractive index and dispersion: the refractive index of synthesized cubic zirconia is 2. 18 and the dispersion is 0.060. Under the standard circular drilling and cutting, red, orange, yellow, green, cyan, blue and purple are flashing, and the light is dazzling, which is called "thief" light by people in the industry; The refractive index of diamond is 2.42 and the dispersion is 0.044. Under the round diamond cutting, the flashing light is mainly orange with blue light, which is soft and can be seen by experienced people at a glance.

2) Distinguish between the oleophilicity of diamond and the hydrophilicity of synthetic cubic zirconia: clean the desktop, press with your fingers, and leave clear fingerprints on the desktop if you see diamonds; Or use the stroke table, a line can appear, which is synthetic cubic zirconia; Or use atomic strokes on the table, and the diamond is displayed as a line.

3) The diamond selector (thermal conductivity meter) is the most reliable, because cubic zirconia has poor thermal conductivity, and the thermal conductivity meter does not change much, only one grid can be added; Diamonds have better thermal conductivity than gold. When measured with a thermal conductivity meter, the indicator light rises rapidly, a red light appears, and a chirp sounds.

Second, the visual distinction between purple synthetic cubic zirconia and amethyst.

Deep purple synthetic cubic zirconia is very similar to amethyst and can be distinguished by the following methods.

1) uses different refractive indexes: the refractive index of crystal is about 1.55, and the refractive index of synthetic cubic zirconia is 2. 18, so the synthetic cubic zirconia has a strong flash effect.

2) Polarizer inspection: The synthesized cubic zirconia is an equiaxed mineral, and the brightness does not change when the crystal rotates 360 under the polarizer, while the brightness and darkness of the crystal change when it rotates 360 under the polarizer.

Thirdly, the visual difference between hydrothermally synthesized emeralds and natural emeralds.

Emerald synthesized by hydrothermal method is very beautiful, which is difficult to distinguish from high-grade natural emerald. Identification can be made by the following methods:

1) Put the emerald on the black floor and illuminate the gem crystal with a spotlight flashlight. It can be seen that red to dark red emeralds are hydrothermally synthesized, while natural emeralds do not have this phenomenon.

2) Observe the characteristic inclusions of emerald crystal-three-phase nail inclusions with a magnifying glass of 10 times. Three-phase nail inclusions in emerald crystals grown by hydrothermal method appear on the same plane (Figure 1), sometimes three-phase nail inclusions can appear in groups on different planes, while three-phase nail inclusions in natural emeralds are scattered randomly.

Hydrothermal synthesis of figure 1 emerald three-phase nail-like inclusions

Fourth, the naked eye distinction between ruby synthesized by flame melting method and natural ruby.

The common synthetic ruby in the market is the ruby synthesized by flame melting method, with bright crystal, bright color and large volume. Pay attention to three points when identifying with the naked eye:

1) middle and low grade natural rubies are chapped, and sometimes two or three groups of growth lines or chapped at an angle of120 can be seen; Ruby synthesized by flame melting method is hardly seen, let alone 120. Intersection growth line. Individual counterfeiters artificially crack the synthetic ruby by heating and quenching, which is irregular and chaotic on the surface, that is, messy cracks.

2) The color of natural ruby is generally uneven, while the ruby synthesized by flame melting method is bright and uniform.

3) "Burst" traces of solid mineral inclusions or gas-liquid inclusions broken after heat treatment are often seen in natural rubies, that is, fingerprint inclusions; The ruby synthesized by flame melting method is very clean, and no solid mineral inclusions can be found. At most, gas inclusions or solid inclusions of clastic raw materials are accidentally found under the magnifying glass of 10 times.

4) Distinguish with a dichroic mirror: natural rubies are purplish red/orange red when viewed from the table; The dichroism of flame-melted ruby is opposite.

5) Look at the growth line: If natural rubies have obvious growth lines, they must be straight lines and form 120 with each other. Intersection angle; If the flame-fused ruby has a growth line, it must be curved (Figure 2).

Fig. 2 ruby growth line synthesized by flame melting method

5. Visual difference between sapphire synthesized by flame melting method and natural sapphire.

The common synthetic sapphires in the market are mainly those synthesized by flame melting. The difference between naked eyes and natural sapphires lies in the following points:

1) Most natural sapphires can see blue growth lines that are parallel to each other under the transmitted light (pay attention to shaking the gemstone when observing), and sometimes two or three groups can be seen to form 120. Blue growth line at the intersection (Figure 3); However, sapphire synthesized by flame melting method can hardly find growth lines, and if it can be found, it is also some curved growth lines.

Fig. 3 growth line of natural sapphire at120.

2) Dichroism identification: natural sapphire is blue when viewed from the vertical table and green when viewed from the parallel table. If the natural sapphire is cut and polished without a vertical C axis as a table top, it can be seen from the vertical table top that one side is blue and the other side is green. If it has this feature, it can be judged as a natural sapphire; The dichroism of sapphire synthesized by flame melting method is blue and blue-purple.

3) In China, when Fa Lan gemstones are fused by flame, the crystal edges are often blue, and the more colorless or even white they are toward the center. Therefore, if the pavilion is white, it is a sapphire synthesized by flame melting, which can be distinguished from natural sapphire.

Six, blue high refractive index rare earth imitation sapphire glass imitation sapphire and natural sapphire.

In imitation jewelry, blue high refractive index rare earth imitation sapphire glass imitation sapphire is widely used, and its naked eye difference from natural sapphire lies in the following points:

1) Tested by a polarizer: the blue rare-earth gem-like glass is amorphous, and the brightness does not change when rotated 360 by a polarizer, while the brightness and darkness of natural sapphire change when rotated 360 by a polarizer.

2) Dichroism detection: natural sapphire is blue when viewed from the vertical table and green when viewed from the parallel table; Rare earth gem glass with high refractive index has no dichroism.

3) Detecting with a thermal conductivity meter: adjust the thermal conductivity meter to four green squares, and if the indicator light of the thermal conductivity meter rises three to four squares rapidly when determining the gem, it is a natural sapphire; If it does not change or only increases 1 lattice, this is high refractive index rare earth gem glass.

4) According to hardness, the Mohs hardness of natural sapphire is 9, and the Mohs hardness of high refractive index rare earth imitation gem glass is 5.5. Therefore, the sample is used to scratch the glass, and the natural sapphire is marked, while the rare earth imitation gem glass with high refractive index has slippage.

Seven. Visual difference between blue spinel synthesized by flame melting method and natural sapphire.

Blue spinel synthesized by flame melting method is very similar to natural sapphire, which can be distinguished by naked eyes in the following ways:

1) Examined by a polarizer: Spinel belongs to an equiaxed mineral, and there is no change of four bright and four dark when rotated 360 under a polarizer, while natural sapphire has a change of four bright and four dark when rotated 360 under a polarizer.

2) Check with a dichroic mirror: natural sapphire has dichroism, that is, it is blue when viewed from a vertical table and green when viewed from a parallel table; The synthesized blue spinel has no dichroism.

3) Thermal conductivity meter detection: set the thermal conductivity meter to 4 green indicator lights, and then determine the gem. The blue spinel synthesized by flame melting method rises to 3-square yellow, and the natural sapphire appears 4-square yellow.

4) Check with Charles filter: blue spinel synthesized by flame melting method is red under Charles filter, while natural sapphire does not change color under Charles filter.

Eight, synthetic star ruby and starlight sapphire are distinguished from natural star ruby and starlight sapphire by naked eyes.

Synthetic star ruby and star sapphire are beautiful and bright, attracting many people to buy them. The naked eye can easily distinguish natural star ruby from star sapphire;

1) Use a spotlight flashlight to illuminate the ring face of the starlight gem. If there are six clear, bright and slender lines with thin intersections, they are synthetic star rubies and starlight sapphires (Figure 4); The six star lines of natural star ruby and starlight sapphire are short and thick, and the intersection point is unclear, and they are widened and brightened into a bright star cluster. Their star lines gradually taper outward from the intersection point, which shows that the length of the star line is much shorter than that of the synthetic star sapphire (Figure 5).

Fig. 4 Synthetic star ruby

Fig. 5 Natural star ruby

2) The matrix of synthetic star ruby and star sapphire is bright, bright and uniform; The matrix colors of natural star ruby and star sapphire are usually different shades and not bright. The starlight sapphire produced in Changle, Shandong Province, is mostly based on copper skin color.

3) Looking at the growth line from the reverse side of the gem, if you see the curved growth line, you can identify it as star ruby and star sapphire synthesized by flame melting.

Nine, glass imitation crystal (including amethyst) and rock crystal (including amethyst) to distinguish with the naked eye.

More common in the market are imitation crystal plus lead glass and amethyst high refractive index rare earth imitation gem glass, and their visual distinction methods are as follows:

1) Touch the gem with your palm or lips, and the stone crystal is cold; The glassy imitation crystal has a sense of temperature.

2) Inspection with a polarizer: the rock crystal rotates 360 degrees under the polarizer, with four bright and four dark changes, while the glassy imitation crystal does not change.

3) Check with a dichroic mirror: natural amethyst has dichroism, and dark natural amethyst has red violet/violet or blue violet/violet dichroism; Glass imitation crystal products have no dichroism.

4) Under the transmitted light, with a magnifying glass of 10 times, the bubbles that can be found can basically be classified as glassy imitation crystals.

5) Using feldspar with hardness of 6 as the test stone, the gemstone can be scratched on the feldspar, and the crystal can be scratched, while the glassy imitation crystal slips. If there is no feldspar, you can also draw directly on the glass. What can be scored is crystal, and what can't be scored is glassy imitation crystal.

6) Test with a thermal conductivity meter: adjust the thermal conductivity meter to 4 squares of green to test the gem, and the crystal can rise to 2 squares of yellow, while the glass imitation crystal product does not rise, and when the area is large, it rises to 1 square yellow.

Ten, glass imitation jade and natural jade to distinguish with the naked eye.

The glass imitation jadeite in the market has high transparency (good jargon) and deep green concentration, which is very beautiful, attractive and gullible. This kind of glass imitation jade is actually a kind of glass-ceramics containing chromium ions (also called synthetic mullite). The following methods can be used for visual identification:

1) Under the irradiation of transmitted light, observed with a magnifying glass of 10 times, there is no mosaic structure of jadeite (called emerald structure in the industry), but glass imitates jadeite.

2) If there are pits on the back (plane) of the steamed bread-shaped torus, it is glass imitation jade, which is caused by the shrinkage of the glass melt when it is cooled.

3) The color is dull green and transparent under the transmitted light. You can see many green spots formed by chromium ions, and sometimes you can see bubbles trapped in the glass body during cooling. These are the characteristics of glass imitation jade. Natural jadeite does not have these characteristics.

Eleven, artificial imitation pearls and natural pearls should be distinguished by the naked eye.

Artificial imitation pearls are made of clam shell powder, pearl semen (artificial) and glue. The appearance is round and bright, big and small. Pay attention to two points when distinguishing with the naked eye:

1) Two beads of natural pearls (including cultured pearls) do not slip when rubbed lightly, but have friction, as the saying goes, "astringent"; Two artificial pearls will slip when rubbed.

2) Synthetic imitation pearls have smooth surfaces, and natural pearls can always find "faults" such as growth lines, growth hills and pits under a magnifying glass.

Twelve, glass fiber imitation cat's eye gemstones and natural cat's eye gemstones.

There are more than 20 colors of glass imitation cat's eye gemstones produced by optical fiber and glass sleeve, and some varieties are very similar to natural cat's eye gemstones. Pay attention to the following two points when identifying:

1) The glass fiber imitation cat's eye gem must be opaque and ground into the shape of steamed bread (plain noodles in jargon). When we look at the joint of paraboloid and bottom plane from the side, we can see that the glass fiber imitating cat's eye is honeycomb structure. Natural cat-eye gems (golden green cat's eye, here also refers to the characteristics of quartz cat's eye, wood cat's eye, aquamarine cat's eye, sillimanite cat's eye and so on. ) You can only see the parallel structure from the back, but you can't find the honeycomb structure.

2) The hardness of all natural gemstone cat's eyes is greater than Mohs hardness 6, so feldspar can be scratched. The Mohs hardness of glass fiber imitation cat's eye is less than 6, so it can't carve feldspar and slide on it. If there is no feldspar, it can also be carved on glass. It is natural cat's eye gems that can draw "road marks", but it is glass fiber imitation cat's eye that can't draw "road marks" or slip.

Thirteen, the visual distinction between synthetic amber and natural amber.

Synthetic amber is generally made of organic matter (resin, plastic, etc.). ), and can be distinguished in two ways:

1) Rub it hard on clothes, and then quickly put it under your nose to smell. Natural amber has fragrance, and synthetic amber has odor, sulfur or perfume.

2) If conditions permit, you can use a red-hot needle to penetrate the sample, and the sample will smoke. If you smell scattered fragrance, it is natural amber, and the smell is synthetic amber.

refer to

He, Shen,. 1 196. Artificial synthesis and identification of gems. Beijing: Aviation Industry Press.

He, Shen. 2005. Gemstone synthesis technology. Beijing: Chemical Industry Press.

Shen, man. 1994. artificial gem. Beijing: China Geo University Press (internal).

Zhang Beili, Wang Manjun et al. 1997. Systematic gemmology. Beijing: Geological Publishing House.

People's Republic of China (PRC) national standard GB/T 16552-2003. Jewelry and jade appraisal.

People's Republic of China (PRC) national standard GB/T 16552—2003. Name of jewelry and jade.