The technology of synthesizing ruby has matured. At present, there are three main methods: flame melting method, flux method and hydrothermal method. Among them, the flame-melted ruby is easy to identify, and it is determined to be a synthetic ruby by observing the arc growth lines and bubbles inside. Ruby with bright red color and large particles sold in the market, especially in tourist shops, is actually this kind of ruby. Flux ruby needs professionals to observe its internal characteristics under a high-power microscope before it can be identified. The synthetic environment of hydrothermal ruby imitates the growth environment of natural ruby, and its internal characteristics are very similar to those of natural ruby. It is difficult to distinguish with general instruments, and other large instruments, such as X-ray instruments, are often needed.
Identification of synthetic rutile
The dispersion value of synthetic rutile is very high, which makes it emit colorful fire color. This feature makes it difficult to confuse it with any other materials. In addition, its extremely high birefringence makes its facet edge ghost extremely clear. These two characteristics are enough to confirm.
Identification of strontium acid
As a diamond-like material, strontium titanate is easy to identify. Strontium titanate is obviously different from diamond because of its strong fire color. Although the standard circular polyhedral strontium titanate is opaque in online testing, its obviously low hardness makes its surface show obvious wear marks, smooth facet edges and uneven facets. Although the same refractive index as diamond can be obtained on the reflector, there is no diamond reaction when it is detected by thermal conductivity meter. Caliper method or still water weighing can measure the specific gravity of non-inserted products, so as to confirm.
Identification of artificial ruby
1. Small curved growth lines and elongated bubbles can be seen in artificial rubies, and sometimes cloud-like bubbles can be seen.
2. Unmelted raw material powder can be seen occasionally in gems.
3. In dark and oblique light, you can occasionally see some fine white cloud inclusions.
4. Uneven crystal growth stripes can sometimes be seen under the microscope.
5. Gemstone crystals may have traces of seed crystals.
6. Iridium or molybdenum inclusions in gem crystals can be detected by electron probe and X-ray fluorescence analysis.
Identification of synthetic chrysoberyl
1. Curved growth lines and slender bubbles can be seen in artificial emeralds.
2. Unmelted raw material powder can be seen occasionally in gems.
3. In dark and oblique light, strip-shaped impurity inclusions and needle-shaped inclusions are occasionally seen.
4. The refractive index of synthetic chrysoberyl (1.740- 1.745) is slightly lower.
5. Iridium or molybdenum inclusions in gem crystals can be detected by electron probe and X-ray fluorescence analysis.
Identification of artificial yttrium aluminum garnet
Yttrium aluminum garnet is artificial gem, which can be distinguished from similar gems according to its physical and optical properties.
Identification of Gems Synthesized by Zone Melting Method
The crucible is not used in the process of regional melting to synthesize gems, so there is no pollution of crucible impurities. This technology can refine and purify the crystal, so there are few inclusions and growth lines in the crystal, and the crystal quality is high. The gemstone synthesized by this method has high purity and clean interior. Generally, the fluorescence is stronger than the corresponding natural gemstone; The absorption line under the spectroscope is simple and clear; The surface processing of gemstones is not fine enough, and "fire marks" often appear. For artificial yttrium aluminum garnet crystal, because there is no natural corresponding gem, it can be identified according to its physical and chemical properties. Due to the sudden change of process conditions in the crystal growth process, gem crystals with poor quality will also be synthesized. It is characterized by chaotic growth lines, uneven crystal color and even bubbles. Due to the high production cost of zone melting method, high-quality synthetic gems can rarely be produced in real commercial production. Therefore, there are few studies and reports on this kind of synthetic gems.
Identification of gemstones synthesized by cold crucible method
Cold crucible method is a method to produce and synthesize cubic zirconia crystals. This method was developed by scientists from the Lebedev Institute of Solid State Physics, Russian Academy of Sciences, and applied for a patent in 1976. Due to the good physical properties of synthetic cubic zirconia crystals, colorless synthetic cubic zirconia quickly and successfully replaced other diamond imitations and became a good substitute for natural diamonds. Synthetic cubic zirconia is easy to be doped and colored, and various brightly colored crystals can be obtained, so it is welcomed by jewelers and consumers.
Artificial cubic zirconia is often used as an imitation of diamonds. Therefore, the properties and characteristics of synthetic cubic zirconia crystals are the remarkable characteristics of synthetic cubic zirconia.
Identification of ruby synthesized by flux method
I. Residual entrainer
B, gas-solid two-phase inclusions:
C, platinum sheet
D, special color band or color gamut
Linear and angular growth bands can be seen in the gems synthesized by flux, which are consistent with the color bands in natural rubies and sapphires in appearance. However, in Lamla synthetic ruby, the phenomenon of stirred color and spindle-shaped color gamut can appear, and in Douros synthetic ruby, light red, colorless ribbon and blue triangular color blocks can appear.
F, seed crystal
Early products used large seeds. For example, Leichleitner Company only grows a thin layer of synthetic ruby on the seed crystal. At present, it is difficult to see seeds and their related characteristics in the process of synthesizing rubies and sapphires by most co-solvent methods.
G, luminescence
Ruby synthesized by cosolvent method shows moderate to strong red fluorescence under ultraviolet light, which can indicate the identification of ruby. However, some rare earth elements were added to Lamla ruby, which showed orange-red fluorescence under ultraviolet irradiation. A few samples may show blue-white fluorescence.
visible spectrum
The absorption spectrum of ruby synthesized by flux method is the same as that of natural ruby, but it is clearer and more obvious than natural ruby.
I. Trace elements
The chemical composition of cosolvent residues exposed on the surface of gemstones can be detected by electron probe analysis, and the trace chemical elements contained in gemstones can be analyzed by X-ray fluorescence spectrometer. The most commonly used cosolvents are oxides of some heavy metals, such as PbO, PbF2, BiO2, MoO2, B2O5, Li2O, and sometimes cryolite (Na3AlF6).
Synthetic colored crystals usually show a different color band from rock crystal. The color band of synthetic color crystal is always parallel to the seed crystal plate, while the seed crystal plate is usually parallel to the rhombic direction when synthesizing amethyst; The seed plate of synthetic topaz is parallel to the bottom axis. So using a polarizer can help determine.
The early products of emerald synthesis by hydrothermal method mainly contain type I water, but not type I I water. Later, by improving the process, the new product contains both type I water and type II water, but still contains more type I water, which proves that the general alkali content is low. While natural emeralds are higher. The relative intensity of absorption peaks of natural emeralds from different habitats and synthetic emeralds from different manufacturers are also obviously different. In recent years, the infrared spectra of emerald products synthesized by hydrothermal method generally show the absorption peaks of type I water and type II water, while there are both type I water and type II water in natural emerald, but there are more type II water.
The color and type of synthetic diamonds can also be controlled. Because the growth chamber is filled with air and the air contains nitrogen, most synthetic diamonds are Ib diamonds containing solitary nitrogen. Most of these diamonds are yellow to brown. If some nitrogen absorbent, such as zirconium or aluminum, is added into the reaction chamber, colorless and nitrogen-free IIA diamond can be obtained. If some boron is added at the same time, blue Ⅱ B diamond containing boron can be synthesized.
Synthetic diamonds can also be turned into colored diamonds by radiation.
Synthetic diamonds usually have no fluorescence under long-wave ultraviolet light, but often have yellow, green yellow and orange yellow fluorescence under short wave. However, natural diamonds usually have strong fluorescence under long-wave ultraviolet light, mostly blue and white, and are relatively weak or inert under short wave. Synthetic diamonds have a characteristic band phenomenon under short-wave ultraviolet light, that is, the fluorescence distribution characteristics in the growth direction of cubes and octahedrons, also known as "Marta cross band" phenomenon, as shown in the figure. Natural diamonds show annular fluorescence distribution. DIAMONDVIEW is an instrument specially developed by DTC, which is used to detect the fluorescence distribution characteristics of diamonds under ultraviolet light. Nearly colorless synthetic diamonds have obvious phosphorescence under short wave, while natural diamonds have no phosphorescence.
Synthetic opal is more transparent to ultraviolet rays than natural opal. The detection method of this property is: put the photographic paper into a dish filled with water, and put the detected gems and similar natural materials on the photographic paper. The exposure time is about 2-3 seconds. After development, a white edge can be seen around the image of synthetic gemstones, while the image of natural gemstones has no white edge.
Common glass imitations and their identification
A. Glass varieties imitating transparent gemstones
Glass is often used as an imitation of transparent gems, such as ruby, sapphire, emerald, aquamarine and olivine. It can have a color very similar to that of imitation gems, but the key to distinguish it is that its characteristic inclusions are different from imitation gems in refractive index, optical properties, relative density and spectrum.
(1) Surface and internal characteristics:
Molding marks, smooth facet edges and shrinkage cavities on the surface of molded glass. Bubbles and vortex lines often appear inside glass. In addition to natural glass, natural transparent gemstones rarely see single-phase inclusions. Natural gemstones often show mineral crystal inclusions, gas-liquid inclusions and so on, which are not found in glass. Some natural transparent gemstones have large birefringence, and after magnification, you can see the ghost at the edge of the facet, but you can't see it in the glass.
(2) Refractometer:
Usually, it is single refraction, which is different from the refractive index or optical properties of imitation gems. The refractive index of glass is generally 1.45- 1.70, and the common transparent natural inorganic gems in this range are birefringent.
(3) Abnormal birefringence:
Glass shows black cross extinction or abnormal extinction without interference ring under polarizer; Birefringent natural transparent gemstones can display uniaxial or biaxial interferograms.