The jewelry industry uses special terms to refer to artificial stones that look like precious stones: synthetic stones and imitation stones. The difference between them is minor, but very important.

Synthetic stones are made from an artificial material that has essentially the same chemical composition, crystalline structure, and optical and physical properties as natural stones. There are also materials that simply look like natural stones. They are called imitation stone and can be either natural or artificial.

Artificial imitation stone

• Synthetic spinel. Synthetic spinel is often used as an imitation because it can replicate the appearance of many natural precious and semi-precious stones (such as sapphire, zircon, aquamarine and peridot), depending on the color. The accurate reproduction of a wide range of colors is why this material is usually chosen to imitate birth month stones. Happens frequently.
• Synthetic rutile. Synthetic rutile appeared in the late 1940s and was used as an early imitation diamond. Made by flame crystallization, it is almost colorless, with a slight yellowish tint, but can be given different shades by adding chemicals as it grows. Rarely seen.

• Strontium titanate. This colorless man-made material became a popular diamond imitation in the 1950s. However, its dispersion (the optical property that creates the sparkle in a cut stone) is four times greater than that of a diamond. Strontium titanate is most often made by flame crystallization and can come in different colors, such as dark red and brown, due to the addition of certain chemicals during the growth process. Rarely seen.
• YAG and YGG are man-made materials that have been used for years as imitation diamonds. In the 1960s, yttrium aluminum garnet (YAG) and its cousin, gallium gadolinium garnet (GGG), joined the ranks of classic imitations such as glass, natural zircon, and colorless synthetic spinel. YAG and YGG also come in different colors. They are rare.

• Cubic zirconium dioxide (CC), or cubic zirconia. Early imitations of diamonds have been almost completely replaced by colorless CC over the past three decades. It is produced through a process called skull smelting. When the material melts, the outside remains cool and forms a solid surface that then holds the molten substance. Cubic zirconia can be made in almost any color, including darker shades, and is a convenient alternative to gemstones in purple, green and other dark tones, including black. Happens frequently.

• Synthetic diamond. The colorless synthetic diamond emerged in the late 1990s as an imitation diamond. It is closer in appearance to a diamond than any previous imitations, but today it is most often sold as a separate gemstone. Occurs occasionally.

• Glass. Industrial glass is an ancient imitation gemstone that is still used today. Because glass can be made in literally any color, this makes it a popular replacement for many natural stones. Although glass has less sparkle, it is used to imitate stones such as amethyst, aquamarine and peridot. Glass can be made to look like natural stones such as tiger's eye and opal, and layers of glass can be fused together to imitate agate, malachite or tortoiseshell. Happens frequently.

• Imitation of lapis lazuli. Highly prized in ancient civilizations, dark blue lapis lazuli has been mined in Afghanistan for over six thousand years. This stone is an aggregate of several different minerals. Sometimes it contains golden inclusions of pyrite, which make it even more attractive. The imitation lapis lazuli presented by Gilson has some ingredients and physical properties that differ from those of natural lapis lazuli. Rarely seen.

Composite stones

When a manufacturer glues or fuses two or more pieces of material to form a faceted stone, it is called a composite stone. Individual pieces can be natural or artificial. There are doublets (consisting of two segments) and triplets (consisting of three segments or two segments separated by a layer of colored bonding agent).

Composite stones are not always imitation. For example, natural opal sometimes comes in such thin layers that it must be hardened to be used in jewelry.

Imitation gemstones, namely synthetic stones are becoming more popular these days. Due to the fact that natural gemstones are expensive and very rare, there will always be imitation market and cheap fakes. In general, the purpose of imitations is to deceive people. They are made from natural and synthetic materials that look like real, expensive precious stones.

Imitations have been known for 6,000 years. Thus, the Egyptians used blue earthenware (glazed) to imitate turquoise. The Romans passed off colored glass as emeralds and rubies. During Queen Victoria's time, various materials were used to imitate mineral gemstones, as well as stones, including glass and resins.

Glass for imitation stones

Glass is the most suitable material because it can be painted in almost any color and cut, giving it the appearance of a real gemstone. However, there is a significant difference between glass and gemstones. As a rule, glass is much softer than the gemstone it is claimed to be, and therefore scratches much more easily.

There may be bubbles and funnels in the glass, which can be easily detected with a magnifying glass. A gemologist can easily distinguish glass by its single refractive index (1.5-1.7), because there are no gemstones with a single refractive index equal to this value.

Imitation diamonds

One natural gemstone can be used to imitate another, more expensive gemstone. For example, citrine can be used to imitate topaz, and colorless quartz or glass can be used to imitate the diamond itself. Colorless glass cannot be considered a good imitation of diamonds, because it is not hard enough and lacks glow and radiance.

Others imitation diamonds are cubic zirconium dioxide (fianite) and appeared relatively recently. It is about as hard as diamond, with a Mohs hardness rating greater than 9. The main difference is that diamond has one refractive index, whereas moissanite has two. In larger moissanite crystals this appears as doubling of the pavilion facets when viewed through the stone, but small moissanite stones set in jewelry are not easily distinguishable.

Other imitations of diamonds are also known, including yttrium aluminum garnet and strontium titanate, but all of them either do not sparkle (spinel, , topaz) or, on the contrary, sparkle too brightly (strontium titanate, rutile), or are very soft or too fragile. Imitations can be distinguished from diamonds due to the fact that they conduct heat much worse. Checking a stone with a device that measures thermal conductivity will immediately lead a gemologist to think about a fake.

Composite stones: doublets with a top layer of garnet and glued emeralds. As imitation stones so-called compound doublets also appear. This method began to be used several centuries ago and became widespread in the 19th century. A layer of precious stone is glued onto a dense base. However, most often the basis is ordinary glass, which is coated with quartz or other not very expensive mineral.

For example, a piece of green glass with a thin layer of red garnet on top can be used as a counterfeit emerald or green garnet. The doublet with a garnet top layer consists of two parts, which can be easily installed due to the difference in gloss. In addition, the glass may contain characteristic bubbles that are not present in the garnet.

If you look at this “stone” from the top platform, it appears green, but if you look at it from the side or immerse it in water, the red layer of garnet becomes noticeable. By changing the color of the bottom glass layer, you can make imitation precious stones all colors. Another composite is the bonded emerald, made from two layers of colorless quartz sandwiched between a thin layer of gelatin or green glass.

Composite stones: doublets and triplets of opal. A special category of composite stones includes opal doublets and triplets - thin “sandwiches” in which noble opal is present in the form of a thin layer. Opal doublets (they consist of two layers) are made by gluing a piece of noble opal, demonstrating the play of color, with a backing of base opal, quartz, chalcedony, glass or plastic. Opal triplets, in addition to the substrate, also have an upper, protective layer of.

Imitation opals

The play of color that distinguishes precious opals is the result of the interference of light on the internal spherical structure of the mineral. In 1974, the French scientist Pierre Gilson first demonstrated what was obtained in the laboratory. Gilson opals can be distinguished from natural stones by their mottled appearance and mosaic-like “links” between the colored grains. American scientist John Slocum synthesized glass opal, known as the "Slocum stone". Under a microscope, the color spots in Slocum stones appear somewhat wrinkled.

Chapter 6. Imitation of precious stones from glass

Glass is the cheapest and most common substitute for precious stones. At the end of the 18th century. Strase proposed a recipe for a special lead glass that successfully replaced precious stones: 38.2% silica, 53.0% lead oxide and 8.8% potash. In addition, borax, glycerin and arsenous acid were added to the mixture. This alloy is called rhinestone. It is characterized by high dispersion and lends itself well to cutting. This type of glass was used to imitate diamonds. Later they learned to make colored rhinestones. To obtain a ruby ​​color, 0.1% cassium porphyry was added to the glass mass, sapphire - 2.5% cobalt oxide, emerald - 0.8% copper oxide and 0.02% chromium oxide. Recipes have been developed for obtaining imitations of garnets, amethysts, and spinel.

Currently, glass imitating precious stones is widely used in jewelry.

So, the chemical composition and physical properties of synthetic and corresponding natural stones are the same. However, synthetic stones are a product of human labor, and they can be produced as much as you like.

Natural stones are creations of nature, their number is limited, and it is difficult to discover and obtain. This is why gemstones are tens and sometimes hundreds of times more expensive than their synthetic counterparts, despite the fact that synthetic stones are often significantly superior to natural stones in quality and color characteristics.

Jewelry stones are a beautiful creation of nature and man. Nature did not skimp, creating the deep tranquility of lush green emeralds, the tranquility of blue sapphires, the ardor of red rubies, the fabulous or passionate variability of white and black opals, the tenderness of pink and blue topazes, a boundless sea of ​​colors, shades, and designs. Man, having breathed his soul into them, carefully, lovingly processed them, gave them completeness, completeness, turned them into real works of art, designed to bring people joy, pleasure, inspiration, and not grief and tears, not to be an object of profit and enrichment, but evidence of the wealth and enormous spiritual power of the people.

Glass used as imitation can be of different transparency (transparent, translucent, translucent in thin chips, opaque) and color. Their physical properties depend on their composition, mainly on the lead content. Refractive indices of transparent glasses are 1.44 - 1.77; hardness 5 - 7 on the Mohs scale; density 2 - 4.5 g/cm 3 .

Glasses are isotropic, but over time they may develop optical anisotropy. The dispersion is 0.010, in glasses with a high lead content it may be higher.

Glasses can be distinguished by the presence of gas bubbles of various shapes, sometimes streaks, clots of dyes. In addition to purely glass imitations, double (doublet) and triple (triplet) stones are used, glued together from glass and natural stone, from lightly and densely colored stones, from natural and synthetic stone. Such counterfeits are clearly visible under a magnifying glass or microscope: bubbles located in the same plane are observed on the bonding surface.

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Synthetic gemstones

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Artificial or synthetic jewelry stones can be divided into four types:

• synthetic stones, i.e. artificial gems obtained by the synthesis of metal oxides;
• cultured pearls;
• natural imitations of precious and semi-precious stones;
• artificially colored and refined stones

Glass and plastic imitation jewelry stones are also widely used.

The most famous synthetic gemstone is diamond, which is a modification of carbon. Diamond was first synthesized by E. Lundblat's group in Sweden in 1953 (at a pressure of 8 GPa and a temperature of more than 2500°C). In 1954, G. Hall’s group in the USA, and in 1960, L.F.’s group. Vereshchagin in the USSR also carried out the synthesis of diamonds.

Synthetic quartz was first obtained (in the form of columnar crystals 0.5-0.8 mm in size) by W. Bruns in 1889 in England.

In 1900, G. Spezia (Italy) crystallized quartz up to 2 cm in size in an autoclave. Large quartz crystals weighing more than 2.5 kg were synthesized in 1955 in the USSR.

Currently, yttrium-aluminum garnets (YAG), spinels (ganite), and also (in 1976) artificial zirconium - cubic zirconia (jevalite, daimonsquay) (Zr 0.8 Ca 0.2 O 1.92) have been synthesized.

Synthetic stones are understood as artificially obtained crystalline or amorphous chemical compounds that are similar in composition and structure to natural ones or have an external similarity due to physical properties. Obtained by synthesis ruby, spinels, emeralds, quartz , as well as independent chemical compounds (garnet, cubic zirconia).

Synthetic, artificial gems, having the properties of natural stones, successfully replace them in jewelry made of precious metals, but they are cheap compared to natural ones, and glass imitations are just cheap fakes.

Synthetic corundums and spinels have a wide variety of colors, and the stones get their trade name from analogs available in nature - rubies, sapphires, tourmalines, alexandrites, aquamarines, etc. To obtain synthetic corundums, pure aluminum oxide is used, and to obtain spinel, a mixture of aluminum oxides and magnesium Depending on the given color, dyes are added: for ruby ​​- chromium oxide, blue sapphire - iron and titanium oxides, cornflower blue sapphire - oxides of iron, titanium, chromium, alexandrite - vanadium oxide, etc.

The prepared charge (seed) is poured in a continuous stream through a hydrogen-oxygen flame (flame of “explosive gas”), the temperature of which is above 2000°C, onto a refractory rod. A cone of melt is formed on the rod, which descends at a given speed. Thus, a single crystal grows in the form of a cylindrical rod (boule).

For getting synthetic star corundum (rubies and sapphires) Titanium oxide is added to the starting material. During the synthesis process, a mixed crystal is formed; upon its subsequent heating below the melting point of aluminum oxide, it disintegrates with the release of the finest needle-shaped crystals of rutile. The arrangement of rutile crystals in synthetic corundum is the same as in natural star corundum. When cut into a cabochon, a synthetic ruby ​​or sapphire produces the same star-shaped effect as a natural one.

Synthetic corundums and spinels have excellent physical and chemical properties; have zero porosity, high transparency, strength even at high temperatures, resistance to common acids and most alkalis. Their density is 3.98 - 3.99, hardness on the Mohs scale is 9.

Synthetic emerald obtained by flux and hydrothermal methods. In both cases, crystal growth occurs on a seed made of natural beryl. The crystal growth rate is 0.8 mm per day. In most cases, synthetic emeralds have a distinct color zonation.

Synthetic quartz It is grown hydrothermally, and the solvents of natural raw materials are solutions of hydroxides and carbonates of alkali metals - sodium or potassium. By means of dyes (metal oxides) or irradiation, quartz can be obtained from colorless to black, including the colors of all natural crystalline varieties.

Granatite (yttrium aluminum garnet) is an yttrium-aluminum oxide with a garnet structure. In its pure form, garnetite is colorless, density 4.54, hardness on the Mohs scale - 8.

Granatite is obtained in special apparatus at high temperatures in a deep vacuum by “pulling” the crystal from the melt. Due to its properties, colorless garnetite is used as an imitation of diamond, and with the help of additives, garnetite is colored in various colors.

Cultured pearls. Cultured pearls, like natural pearls, are grown in the body of a mollusk under natural conditions. The embryo is a pearlescent ball. It is enclosed in a piece of the mantle shell of a three-year-old mollusk that produces nacre, thus obtaining a “pearl bag.” This bag is placed in another shell, which is placed in a special reservoir. Enveloping the embryo can last from 2 to 7 years. As the pearls grow, their shells are checked several times a year. Grown pearls are indistinguishable from natural ones in appearance and have the correct specified shape. The shell of artificial pearls corresponds in chemical composition to natural ones and has the same physical properties. Artificial pearls can be grown in large quantities, take on given sizes and shapes and be no less beautiful than real ones.

TO natural imitations Precious and semi-precious stones include stones obtained from waste natural stones by gluing, pressing, alloying, as well as natural stones painted in a different color.

One of the types of imitation gems is doublets(duplicates), glued stones. Waste (thin plates) of natural gems that cannot be cut independently are glued with less expensive minerals, similar in transparency and color, and processed together. The most common are doublets of sapphires and emeralds. Rhinestone and colored glass can serve as backing materials. Doublets thus consist of an upper part, an expensive mineral, and a lower part, a cheap one. If you look at the stone from above, the gluing of the doublet is invisible, but if you view it, turning it sideways, at a certain angle to the light source, a reddish stripe along the perimeter of the gluing or weak reddish reflections of the glued edge are noticeable. Doublets have all the optical properties of a gem and, since the bottom of the stone does not wear out, are durable in use.

Amber imitated by pressing and fusion. Pressed amber is small grains and fragments of natural amber heated and pressed under pressure; they differ from natural amber in that they are more cloudy. The gloss is greasy, and the hardness and chemical properties are within natural limits.

Fused (fused) amber is a low-melting mass obtained as a result of the decomposition of amber during dry sublimation at a temperature of 420°C. Color from yellowish-brown to brown-black, melting point 180°C, soluble in benzene, carbon disulfide, hot linseed oil. Pressed and melted amber is inferior in quality and decorative properties to natural amber and is inexpensive.

To change the color of a number of stones, calcination is used for semi-precious stones and chemical coloring for colored ones. Taking advantage of the properties of a number of quartz group minerals to change color when heated, previously they were calcined in various ways: by baking them in bread, filling them with ash in a pot, coating them with clay, and after completely uniform cooling, the stones acquired pink or golden tones.

To change color agate and jasper they are kept for a long time (from several days to several months) in a sugar or honey solution, then treated with sulfuric acid and other reagents. Very often, agates are painted to imitate carnelian or sarder (red and brown), onyx (black or brown), chrysoprase (green), chalcedony (blue and light blue).

The red color is obtained by impregnation in iron nitrate and subsequent heating. The yellow color is obtained by etching agate impregnated with iron compounds in hydrochloric acid. The black and brown color of agate is achieved by boiling it in sugar syrup followed by etching with heated sulfuric acid. Green coloring is achieved by using chromium salts or nickel nitrate with further strong heating. Blue and blue coloring is obtained by impregnating agate in a solution of ferrocyanide (yellow blood salt) and then boiling it in copper sulfate.

As a result, chalcedony can take on the color of chrysoprase and carnelian, agate can take on brown and black color, and jasper can intensify the brightness of the color and change it. The color of turquoise can be enhanced by aniline dyes, but even in ancient times, to improve the color of turquoise (CuAl 6 (OH) 2 × 4H 2 O), it was placed in lamb fat or oil. Currently, artificial turquoise is obtained, among other things, by staining the mineral howlite, calcium borosilicate (Ca 2 [(BOOH) 5 SiO 4 ]) or chalcedony with copper salts or aniline dyes. In addition, synthetic turquoise (“neolithic”, “neo-turquoise”, “rese turquoise”) is obtained from turquoise crumbs sintered with an adhesive mass, glass, porcelain, and resins.

Glass and plastic imitation stones. Glass and plastic alloys are used as cheap imitation of gems and colored stones.
Glass alloys are low-melting transparent glass, into which oxides of lead, potassium and boron are added to enhance shine. Glass alloys are colored with oxides of copper, selenium, cobalt, uranium, manganese, etc. Stones are obtained by stamping and subsequent processing. To create the effect of the stone playing, a thin mirror layer of silver is applied to its reverse side, secured with varnish.

Opaque glass alloys can serve as an imitation of colored stones: turquoise, agate (black), lapis lazuli, etc.

Plastics serve as an imitation of stones of organic origin and some colored stones. The color of the plastic and transparency are set depending on what kind of stone is being imitated. To imitate pearls, milky-white plastic with slight transparency is used, followed by coating with pearl emulsion for a pearlescent sheen; for amber - unevenly colored, sometimes transparent, yellow tones; for coral - opaque, coral-colored; for turquoise - opaque, bluish-greenish, etc. etc., the shape is given by stamping.

Kazdym A.A.,
Candidate of Geological and Mineralogical Sciences,
member of MOIP

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Unlike synthetic gemstones, which have the same chemical composition, crystalline structure and physical properties as their natural counterparts, imitation gemstones bear only a superficial resemblance to the corresponding gemstone. As a result, the constants of imitation stones tend to be very different from those of natural stones.

A variety of materials are used to imitate more expensive natural gemstones, from natural minerals (sometimes colored) to a wide variety of man-made products.

The most common of the inexpensive imitations is glass (paste). It is recognized by its non-crystalline structure, the presence of stresses determined using a polariscope, low thermal conductivity (warm to the touch), relatively low hardness (expressed as rounded and abraded edges of the edges), the presence of conchoidal fracture, uneven color distribution (streaks) and gas bubbles.

As already mentioned, it is relatively easy to distinguish between glass and other imitation gemstones, since the physical parameters rarely coincide with the constants of the gemstones they imitate.

Diamond is the most commonly imitated gemstone due to its high price. Diamond imitations include natural stones such as colorless varieties of quartz, topaz, corundum and zircon. All these stones can be recognized by the presence of birefringence.

With the exception of zircon, all of these stones can be identified using a refractometer. The refractive index values ​​are also diagnostic for colorless synthetic spinel, synthetic corundum and paste (table).

Some physical constants of diamond and diamond imitations

Gemstone	Refractive index	Birefringence	Dispersion	Specific gravity	Mohs hardness
Flintglass
Synthetic spinel
Synthet. rutile
Strontium titanate
Lithium niobate
Synthetic moissanite

Diamond imitations set in metal settings are perhaps the most problematic stones due to their high refractive indices, which are usually outside the range of a standard refractometer.

Metals are generally good conductors of both heat and electricity, while most gemstones are poor conductors of heat and electricity. The most notable exception to this rule is diamond, which conducts heat many times better than copper and even silver, and, with the exception of natural blue diamonds, does not conduct electricity.

Thermal conductivity is a measure of a material's ability to conduct heat, and this ability may vary in different directions. Thermal conductivity is measured in watts per meter divided by degrees Celsius (W x m -1 x °C -1).

In table Some crystalline materials with anisotropy of thermal conductivity are indicated.

Thermal conductivity of some minerals

With the exception of the colorless synthetic corundum and spinel, which emerged as imitations more than 60 years ago, most artificial diamond imitations are by-products obtained from growing crystals for the electronics, laser and space industries.

Of these, YAG (yttrium aluminum garnet), GGG (gadolinium gallium garnet), CZ (cubic zirconia) and lithium niobate have no natural analogues and should be called artificial products rather than synthetic stones.

Until 1987, another diamond imitation, strontium titanate, was classified in the same category. However, in 1987, grains of this natural mineral, called tausonite, were discovered in the USSR. Therefore, strontium titanate should now be described as a synthetic stone and not as a man-made product.

CZ (cubic zirconium dioxide), known in Russia as cubic zirconia, in Switzerland - jevalit (Dzhevakhirjan company), in the USA - daimonesque (Ceres corporation), in Austria - Swarovski crystals, the most acceptable and widespread imitation of diamond .

In 1996, a new diamond imitation appeared - synthetic moissanite, produced in the USA by CZ Incorporated. It is yellow to colorless silicon carbide. This material has physical constants close to diamond, which does not always make it possible to distinguish it from diamond.

The type of test that determines whether a jewelry stone is a diamond is selected depending on the diagnostic feature used to identify the diamond. There are several tests for diagnosing diamonds.

Incident light method (or tilting the stone)

If you shine a light on a properly cut diamond cut stone and look at it from the platform at a right angle against a dark background, the stone will appear uniformly shiny.

This is because the edges of the pavilion act as mirrors and reflect incident light back through the site at an angle of total internal reflection.

If the stone is a diamond (and properly cut), you can tilt the top edge of the stone away from the viewing line and its shine will not deteriorate.

If the stone is a diamond imitation (and its refractive index is lower than that of a diamond), its brilliance will decrease due to the loss of some of the light. As a result, the edges of the pavilion farthest from the eye begin to appear black, since they no longer act as mirrors (light passes through them instead of being reflected back through the pad).

The lower the refractive index of the diamond imitation stone, the more pronounced this effect.

Exceptions to this test (stones with optical properties similar to diamond) are strontium titanate (also known as synthetic tausonite), synthetic moissanite, and synthetic rutile, which have refractive indices similar to or higher than diamond.

Strontium titanate and synthetic rutile can be identified by their very bright “game” (the dispersion of these stones is several times greater than the dispersion of diamond).

Synthetic moissanite has high birefringence and can be identified (like zircon) by the “bifurcation” of the edges at the pavilion faces when viewed through the main crown face.

This method also cannot detect imitations such as CZ, in which the pavilion is cut deeper than in an ideal brilliant cut in order to compensate for the low refractive index. In this case, the stone experiences total internal reflection, even if it is tilted.

Diamonds with a small table and a deep pavilion - the so-called "Old English" cut - will transmit light when tilted, so you need to make sure that the proportions of the stone correspond to the ideal brilliant cut before performing this test.

"Spot" test

This method is more applicable to loose stones than the previous one. However, like the previous test, it depends on the refractive index of the stone and its proportions and can also lead to erroneous results and has exceptions.

To perform the test, you first need to place a small black dot on white paper. If the stone is an imitation (with a lower refractive index than diamond), the dot will be visible as a ring around the culet. This effect is associated with the loss of light through the edges of the pavilion, which do not act as “internal” mirrors. As a result, the point becomes visible through each pavilion facet, which forms a ring (note that through diamonds with a shallow pavilion, the point will also be visible as a ring).

Light transmission test

This test is similar to the previous one, but the stone is placed not over the point, but with the platform facing down on any intensely colored surface. If the color of the backing is not visible through the pavilion of the stone, then it is diamond, strontium titanate, rutile, synthetic moissanite, or a deep pavilion imitation (however, a shallow pavilion diamond does not pass this test).

Test for the quality of finishing of edges

Diamond is the hardest of all known natural and artificial materials, and this allows for very high quality polishing of its edges. Due to the high hardness of diamond, the edges can be polished so that they are completely flat and have clear edges.

With softer stones it is impossible to achieve this quality of polishing, and the edges may be slightly rounded. If a diamond imitation product (even colorless sapphire) has been worn for several years, traces of abrasions or chips can be found on the edges.

Test for the ratio of stone mass and girdle diameter

Loose stones can be identified by checking the relationship between their mass and girdle diameter. This method is essentially based on determining the specific gravity of the stone. The relationships between the sizes of stones and their mass for a diamond and several of its imitations are given in Table.

The relationship between the mass of a stone and the diameter of its girdle

Girdle diameter, mm	Weight in carats (accurate to hundredths of a penny)
	Diamond				Strontium titanate

All stones are assumed to be cut to the correct brilliant cut. Permissible deviations in cut proportions can lead to weight changes of up to ±10%. Because of this, synthetic moissanite, which has a specific gravity of 3.22, may have the same mass values ​​as diamond and is therefore not listed in the table.

Reflectivity, thermal conductivity and electrical conductivity tests

Due to the high refractive index of diamond and some of its imitations, it is not possible to measure the refractive index using a refractometer. But since there is a direct relationship between reflectance and refractive index, diamond and its imitations can be identified using electronic reflectometers.

Diamond's thermal conductivity is also much higher than its imitations; the exception is synthetic moissanite, which can be identified by its very high birefringence. Therefore, one of the most widely used diamond recognition methods is based on thermal conductivity. Since the advantages and disadvantages of identification methods based on reflectance and thermal conductivity complement each other, testers have been released onto the market that combine both methods in one device.

A typical diamond thermal conductivity tester consists of a tip whose metal tip is electronically heated and a control unit consisting of an electrical circuit to detect the temperature drop as the tip touches the surface of the diamond.

None of the diamond imitations (natural or artificial) can have a similar drop in temperature, since they conduct or absorb heat worse than diamond (although synthetic moissanite is closer to diamond in thermal conductivity than other imitations, and therefore an error is possible when using testers with low sensitivity).

The loss of heat from the tip in contact with the diamond is recorded using a dial indicator, digital display or light signal. Sometimes the visual indication is enhanced by an audible signal.

The Klio Tester modification - KL-1202 is aimed at expanding the range of stones tested. Stones weighing more than 0.01 carats with a facet of at least 0.5 mm are identified.

For this purpose, this modification provides an additional removable probe for checking large stones for their belonging to moissanites. This probe is inserted into the Large Stone (L.S) socket if necessary.

The probe of the Klio Tester device has a number of features that distinguish it from analogues and which are aimed at increasing accuracy, reliability and ease of use.

The uniqueness of the device is based on the dual principle of measuring the thermal conductivity and electrical conductivity of the tested stone in one cycle.

When you touch the probe lightly (until it clicks), the thermal conductivity is measured. When pressing deeper (after the click), the electrical conductivity is measured. The device is equipped with a probe with a protruding copper tip, which heats up to a certain temperature during operation.

When testing, the tip is pressed against the test product, which is at room temperature. The speed of the heat distribution process depends on the thermal conductivity of the stone material. An electronic circuit converts the heat absorbed by the stone into a deflection of the meter needle. The instrument scale is divided into three colored sectors.

The red sector corresponds to imitation diamonds, the thermal conductivity of which is lower than the thermal conductivity of diamonds and is called “SIMULANT”.

The green sector is the diamond’s thermal conductivity zone and is called “DIAMOND.”

The yellow sector is the “MOISSANITA” zone.

Moissanite is a brand name for silicon carbide (SiC) that is very close to diamond in hardness and thermal conductivity and has a higher refractive index. Unlike diamond, moissanite is a semiconductor. Although this mineral exists naturally, widespread production of virtually colorless synthetic moissanites is now being developed.

When the tip touches the frame of the stone, the heat flow is redistributed between the stone and the metal of the frame, which leads to an error. Therefore, the device warns about touching metal with an audible signal.

The procedure for identifying diamonds is as follows. At the beginning of work, having carefully examined the products, it is necessary to conduct testing on the finishing of the stone, using a magnifying glass.

Then, using a micrometer (or at least a caliper), you need to determine the size of the stones based on the girdle and, in accordance with the table, presumably estimate their mass. By weighing each of the samples on an electronic scale, you can compare the results with the tabular ones and draw a conclusion about their authenticity.

The next stage may be testing samples using the incident light method (or tilting the stone), based on the phenomenon of total internal reflection of light in diamonds and its partial loss in imitations. True, such testing is difficult for people with poor vision.

Depending on which stones are given for identification (mounted or not), a "spot" test or a light "transmission" test can be performed. The results of this test can confirm or refute assumptions made about the insert stones.

The samples are most accurately tested for thermal conductivity and electrical conductivity using the Klio Tester - KL-1202. The following procedure for operating the device is recommended.

Before starting measurements, you need to carry out a control check of the device, which is advisable to carry out every time it is turned on, and also if you have doubts about the correctness of its operation.

First of all, you need to remove the protective cap from the probe and wipe the probe tip with a clean cloth or chamois leather to remove grease and dust.

Then install the plug of the network adapter into the socket of the electronic unit, and the adapter itself into a 220-240 V network. After this, you need to insert an additional removable probe into the “Large Stone” (L.S) socket.

Turn on the device by placing the switch in the “Open” position. With sufficient supply voltage, it takes about 30 seconds to warm up the device. The device will be ready for use as soon as the red light in the upper left corner of the scale lights up.

There are three plates on the instrument panel: “Test-simulant”, “Test-diamond” and “Test-moissanite”.

Press the tip of the probe for 1.5-2 s (sinking it halfway into the body) to the “Test-simulator” plate. The maximum deviation of the arrow should be at the top of the red sector.

Press the tip of the probe for 1.5-2 s (sinking it halfway into the body) to the “Test Diamond” plate. The maximum deviation of the arrow should be in the green sector.

Press the tip of the probe for 1.5-2 s (sinking it halfway into the body) against the “Test-moissanite” plate, and the arrow will deflect into the green field. After this, press the probe until it clicks; the arrow should deflect into the yellow field.

The control check of the additional removable probe is carried out only on the “Test-moissanite” plate.

The instrument needle should be in the yellow sector. When the probe hits metal, the arrow of the device should be in the yellow sector and at the same time a sound signal should be heard.

Touch the tip of the probe to the stone holder; a sound signal should sound. After this, you can test the products.

Before measuring, wipe the stone under study, and in the case of a mounted stone, the entire product, with a soft cloth or suede.

Place a special crocodile holder on the framed product and, without touching the frame, take it in one hand and the probe in the other. It is not allowed to touch the frame with your hand when measuring, as this leads to measurement error.

Select the largest size stone faces and take measurements as follows.

Orient the probe tip perpendicular to the surface of the product being tested, but do not touch it. Then lightly press the tip onto the surface of the product, pushing it only halfway (you should not hear a click). It is necessary to notice in which sector the arrow has deviated and push the tip in completely until it clicks.

If the stone being tested is a diamond, the arrow will deviate to the green sector, and after a click it will return to the red sector.

If the stone being tested is moissanite, the arrow will deflect into the green sector, and after clicking, into the yellow sector.

If the stone being tested is a simulator, then the arrow of the device will deviate into the red sector and, after a click, will remain there.

If, when pressing lightly or with the tip completely recessed, the arrow is in the yellow sector or a sound signal is heard, then you have touched the metal of the frame, and the measurement should be repeated. To avoid errors, it is necessary to remove the probe from the product and repeat the measurement after 10 s.

When measuring, do not allow the tip to slide on the surface, and also if there is no need to hold the probe on the product for more than 3 s.

Stones without rims should be placed in a holder located on the body of the device. The fixing location must be selected in accordance with the size of the stone. This will provide the necessary conditions for correct measurement.

If you are in doubt about the result, you should repeat the measurement.

If you have any doubts about the correct operation of the device, you must carry out a control check as described above.

If the measurement result is “Sham” or “Moissanite”, then testing is completed and there is no need to use an additional probe.

If the measurement result is “Diamond”, and the size of the stone is sufficient in size (diameter greater than 3 mm), then it is recommended to use an additional detachable probe.

When testing, using only a removable additional probe allows you to determine whether it is moissanite or not (the diamond and the simulant are not separated by this probe). Orient the probe tip perpendicular to the surface of the product being tested and touch it:

If the arrow deviates into the yellow sector, then you have moissanite;

If the arrow remains in the red sector, then (taking into account the previous measurement with a non-removable probe) you have a diamond in front of you;

If the arrow is in the yellow sector and a beep is heard, it means you have touched the metal of the frame and the measurement must be repeated.

Using an additional probe to check small stones may cause a beep on moissanite (the gauge needle is in the yellow sector of the moissanite and there is a beep even though you are not touching the metal of the setting).

When testing small stones in a setting, it is necessary to wipe the products more thoroughly, since when using an additional probe, a breakdown through contamination channels (on the surface of the stone) onto the metal setting is possible, which will lead to an incorrect measurement result.

When finished, turn off the device using the “off” button.

To avoid damage to the tip, immediately after measurements, be sure to put a protective cap on the probe, which should not be removed at all times when the device is not in use.

In the Gemological Dictionary of P. J. Reed, the following definition of artificial jewelry inserts is given: “Imitation (simulant) is a term for designating materials that correspond to a gem in external characteristics. Despite the external similarity, imitation differs from natural stone either in composition, or structure, or physical constants.” Most often, there are differences in all three listed characteristics. Imitation should not be confused with refinement. Treated stones completely retain the composition and structure of the natural material, but have higher quality indicators of appearance, improved with the help of certain physical and chemical influences. Artificial inserts are similar to the natural analogues that they imitate, only in appearance, and their physical, chemical and morphological characteristics can be quite different from the natural analogue.

People have been trying to find ways to create imitations of precious stones since ancient times. The desire to copy an object implies that it has some attractive qualities and, therefore, is valuable for copying. Imitation in some way serves as a form of recognition of the merits of the copied gem, therefore, as a rule, the more valuable the natural stone, the more varieties of its artificial imitations exist.

Artificial inserts should be distinguished from synthetic ones (that is, artificially grown by humans). Most synthetic analogues have the same chemical composition (with the exception of slight differences in the content of impurities) and the same physical characteristics as their natural analogues. Artificial inserts are an imitation using materials with completely different properties.

There are several methods of imitation:

Reconstructed jewelry inserts;

Manufacturing of composite jewelry stones;

Production of imitations of precious stones from glass (rhinestones);

Production of imitation precious stones from plastic materials;

Passing off less valuable gems for more precious ones.

Cultured pearls, grown as a result of the artificial introduction of a foreign object into the body of a pearl oyster, can be conditionally classified as a group of artificial inserts or separated into a separate group.

Reconstructed jewelry inserts

The starting materials for the manufacture of reconstructed inserts are waste from jewelry production, crystal fragments, and stones of low or non-jewelry quality. The raw materials are crushed, dyes, fillers and binders can be added to the mineral crumbs; the mixture is then sintered. The method allows you to obtain stones of almost any size.

An example is the reconstructed turquoise inserts. Turquoise is ground into a fine powder, copper phosphate is added as a dye, synthetic resin is added as a binder, and the finished insert or bead is immediately pressed. When making reconstructed aventurine, a filler (copper chips) is added to the mixture to imitate the aventurine effect. Currently, reconstructed inserts are made to imitate almost any stones that are opaque and translucent in thin layers: lapis lazuli, malachite, rhodonite, jasper, etc.

A new variety in the range of reconstructed inserts are the so-called “matrix stones”. For example, “matrix opal” - thin plates of noble opal several millimeters in size are placed in synthetic resin, and then a cabochon-shaped jewelry insert is formed.

Diagnosis is carried out using a microscope. Under high magnification, you can see that the internal structure of the reconstructed stone is completely different from that of the natural one.

Composite jewelry stones

The most common form of compound stones is doublets, stones made of two parts. In this case, the crown is made from an expensive gem, and the pavilion, as a rule, is made from some cheap material (quartz, painted glass, etc.). The difficulty of making a doublet lies in the gluing of parts, invisible to the naked eye, in order to create the effect of a “single mineral”. Most often, gluing is carried out at the girdle level. Subsequent fastening of the doublet using blind or prong fastening completely hides the gluing area. The technology for creating doublets is now so advanced that sometimes even professionals have difficulty distinguishing a doublet from a real gem by appearance.

In history, the most famous are the “pomegranate-topped doublets,” which were produced in large quantities at the court of Queen Victoria (late 19th century). These stones consisted of a thin plate of almandine (crown) welded to red-tinted glass (pavilion) and imitated garnets. Around the same time, the first doublets appeared - imitations of alexandrite, in which the crown was also made of a thin almandine plate, and the pavilion was made of green glass.

In doublets imitating emerald, the crown is usually made of colorless transparent beryl, and the pavilion is made of glass painted emerald green.

In opal doublets (cabochon processing), the upper part is represented by a thin plate of noble opal, and the lower part, usually masked in a frame in products, consists of ordinary base opal or even plastic.

Composite stones can be made from three elements, then they are called triplets. In this case, a variety of combinations of materials used are possible. For example, when making a classic opal triplet, the main element is made of noble opal, the base is made of ordinary ignoble opal, and a thin plate of rock crystal is glued on top to increase the shine and play of the stone. Sometimes glass, synthetic corundum or spinel may be used as a coating material.

In addition to the classic opal triplet, there is a triplet on the market with the trade name “mosaic opal”. In this case, not even a single plate of noble opal is glued onto the substrate, but small flat pieces that are filled with polyacrylic.

In such a triplet as the “soldered emerald” (also known in the market under the trade names “Sude emerald” or “Smarill”), the crown and pavilion are made of lightly colored or colorless beryl, and a thin plate of emerald colored beryl is placed between the crown and pavilion the color of glass or a special synthetic adhesive. Quartz and synthetic topazes and spinels can also be used to make the crown and pavilion.

In the case of “soldered” alexandrite, a special colored filter made of synthetic material is placed between the crown and the pavilion at the girdle level, which creates the alexandrite effect of changing color under different lighting conditions.

Imitation glass gemstones

Glass is a common and cheap substitute for precious stones. It most successfully imitates their external properties. Glass inserts have a bright shine, transparency, and good uniform coloring.

The composition of glass used to imitate gemstones varies. Thus, the composition may contain:

Silicon oxide (38 to 65%);

Oxides of sodium and potassium (from 10 to 20%);

Calcium oxide (no more than 5%);

Barium oxide (3 to 8%);

Lead oxide (14 to 40%).

The most dispersed is the imitation of glass gems, called “stras” or “rhinestone” after the German jeweler Georges Strass, who at the end of the 19th century. proposed the following recipe: 38.2% silicon oxide, 53.0% lead oxide and 8.8% potash. In addition, a small amount of borax, glycerin and arsenic acid is added to this mixture. Stras's recipe is used to make imitations of diamonds, in which lead glass is shaped into a full-cut diamond.

To obtain an imitation ruby, 0.1% cassium purple is added to the rhinestone mixture, which provides a red color.

To obtain a blue color that imitates sapphire, 2.5% cobalt oxide is added. Emerald (green) color is imitated by adding 0.8% copper oxide and 0.02% chromium oxide to the rhinestone. You can get amethyst using the same method. To do this, add 2.5% cobalt oxide and a small amount (to the required tone) of manganese oxide to the mixture. Currently, glass coloring technology allows you to imitate almost any colors, tones and shades by selecting the appropriate dyes.

By adding insoluble substances (bone meal, cryolite, tin oxide), you can get opaque white, milky glass, which serves as an imitation of base opal. It is possible to obtain black rhinestone - marblit by introducing 3-5% manganese compounds with iron oxides. This rhinestone is an excellent imitation of black tourmaline (sherla).

Giving rhinestones the required shape is carried out in several ways. In some cases this is casting followed by grinding and polishing, in others it is stamping. Hollow glass beads are made by blowing.

Large rhinestones can undergo a special artistic treatment called faceting on a copper wheel. In this case, you can apply various designs and even bas-relief and high-relief images to the rhinestones. Blown beads can be decorated by iridescence, that is, by applying the thinnest layers of metal oxides, giving a rainbow effect of the same type that is obtained from oil or oil stains on water. To enhance the optical properties, silver amalgam is often applied to the lower part of the rhinestone and then secured by bronzing.

Rhinestones are easy to distinguish from natural gemstones, since they do not have a crystalline structure, are fragile, and their hardness on the Mohs scale does not exceed 6. For diagnosis, it is enough to run a file along the girdle: in this case, if the insert is made of rhinestone, it crumbles, if it is made of natural or synthetic stone, it remains intact. Rhinestones differ from natural stones in their lower thermal conductivity, so traces of breath disappear from glass more slowly than natural crystals. Natural stones feel cooler to the touch than glass imitations.

Currently, rhinestones are used mainly in the manufacture of costume jewelry of various levels of performance and cost.

In addition to rhinestones, there are other glass imitations. For example, the most attractive imitation pearls are considered to be the so-called “Roman pearls,” which are hollow glass beads coated on the inside with pearl essence and filled with wax to give them an external impression of hardness. To imitate turquoise, tinted frosted barium glass can be used, as well as ceramic materials such as porcelain and earthenware. There are quite a large number of glass imitations of opal on the market.

Sometimes glass imitations may have incorrect trade names. For example, glass imitation tanzanite is known in the market as “synthetic tanzanite.”

Imitation of precious stones from plastic materials

To imitate precious and semi-precious stones from plastic materials, aminoplasts and acrylates are most often used. These types of plastics are transparent, have high mechanical strength, shine, take color well, and are quite resistant to chemicals and light.

Aminoplastics are carbide resins, heat-resistant (up to 1200 °C), characterized by high ductility, and can be painted in various colors. Acrylates are esters of acrylic and methacrylic acids. The most common is polymerized methacrylic acid methyl ester. Plastic inserts are produced by pressing.

The most commonly imitated plastic materials are pearls, turquoise, opal, amber, and coral. Some plastic imitations are quite common and have their own trade names. For example, “Hamburg turquoise” (also known under the trade name “Neolith”), which appeared on the market in the late 50s of the 20th century. This product consists of a mixture of aluminum hydroxide, copper phosphates and synthetic mol as binders. Currently, a number of products with a similar chemical composition are produced, imitating turquoise and united under the name “neo-turquoise”.

Various substances can be used to finish plastic imitations. For example, to obtain a rainbow “pearl” effect, an emulsion containing 25 g of transparent celluloid and 5 g of pearl essence per 100 ml of acetone is applied to the surface of pressed beads.

However, imitations made from plastic materials are quite monotonous, and they are easy to recognize by their appearance: they are much lighter and softer than stones, and often have too “correct” coloring.

Imitation of valuable types of jewelry stones using less valuable gems

Precious stones in jewelry can be replaced with others of less value. However, if an imitation is passed off as a natural gem when making purchase and sale transactions, this is a type of falsification, i.e. fakes. Since the most valuable of jewelry stones is diamond, it is most often counterfeited.

The most popular diamond substitutes are zircons and colorless sapphires. The advantages of sapphire include its hardness, which is close to that of diamond, but its brilliance and color play are much worse, which can be seen even with the naked eye. Diamond is the most brilliant and highly reflective mineral (refractive index 2.42), while colorless sapphire is relatively dull (refractive index 1.77). The color play of zircon is close to that of diamond, the brilliance is slightly higher than that of sapphire, but much worse than that of diamond; In addition, zircon has a lower hardness.

Other colorless stones (spinel, tourmaline, topaz, beryl, rock crystal) can also be used as diamond imitation. However, all of them are inferior to diamond in their characteristics: hardness, density, refractive index (table).

Properties of diamond and colorless imitation minerals

Name mineral	Chemical composition	Hardness (Mohs)	Coefficient refraction
Diamond	Crystalline carbon	10,0	2,41-2,42
Zircon	Zirconium silicate	7,0 - 7,5	1,99-1,93
Corundum (colorless	Aluminium oxide	9,0	1,77-1,76
Spinel	Magnesium aluminate	8,0	1,72
Tourmaline	Complex borosilicate of aluminum, lithium, sodium	7,0-7,5	1,64-1,62
Topaz	Fluorinated aluminum silicate	8,0	1,62-1,61
Beryl	Beryllium aluminum silicate	7,5	1,57-1,58
Quartz (rock crystal)	Silicon oxide	7,0	1,55-1,54

To imitate emerald, peridot, demantoid, and tourmaline are used. Ural craftsmen were very clever in forging emeralds before the October Revolution of 1917: they hollowed out a void in any transparent stone and filled it with a green solution of chromium salts, and carefully sealed the hole.

Turquoise can be replaced with lapis lazuli, howlite, magnesite, chalcedony, dolomite and even bone, tinting the imitations with copper salts or ultramarine. The so-called “Viennese turquoise” is known, which is a mixture of malachite powder with aluminum hydroxides and phosphoric acid, which is compacted under pressure. “Viennese turquoise” refers to reconstructed inserts. In appearance, it is more matte than natural, and does not have its characteristic shine (the refractive index of “Viennese turquoise” is 1.45, while natural turquoise is on average 1.62).

Pearls are imitated in many ways. In some cases, balls of various sizes are cut out of mother-of-pearl shells, and they are often coated with a special pearl essence from a special substance - guanine, obtained from the scales of bleak fish (to make one kilogram of pearl essence, scales from 35,000 fish are needed), which gives them an even more natural look. pearl shine. In other cases, hematite and polished anthracite are used to imitate black pearls, but such fakes are easy to recognize. Firstly, hematite is almost twice as heavy as natural pearls (the density of hematite is about 5, and natural pearls are 1.6-1.7), and secondly, this imitation has a metallic sheen that is uncharacteristic of black pearls. But anthracite beads can easily be mistaken for natural black pearls, since these stones are similar in brilliance and weight.