Synthetic analogs of precious and semi-precious stones. FAQ

Artificial or synthetic gemstones 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 of jewelry stones are also widely used.

The most famous synthetic gemstone is diamond, which is a modification of carbon. For the first time, diamond was 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. Vereshchagin, 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.

At present, yttrium-aluminum garnets (YAG), spinels (ganite), and also (in 1976) artificial zirconium - cubic zirconia (dzhevalite, daimonsquai) (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 their physical properties. By synthesis, obtained ruby, spinels, emeralds, quartz , as well as independent chemical compounds (garnet, cubic zirconia).

Synthetic, artificial gems, possessing 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 the existing analogues in nature - rubies, sapphires, tourmalines, alexandrites, aquamarines, etc. magnesium. Depending on the specified 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 ("detonating gas" flame), the temperature of which is higher than 2000 ° C, onto a refractory rod. A melt cone is formed on the rod, which descends at a predetermined speed. Thus, a single crystal grows in the form of a cylindrical rod (boule).

To receive synthetic star corundum (rubies and sapphires) titanium oxide is added to the starting material. In the process of synthesis, a mixed crystal is formed; upon its subsequent heating below the melting point of aluminum oxide, it decomposes with the release of the finest needle-like rutile crystals. The arrangement of the rutile crystals in synthetic corundum is the same as in natural star corundum. When cut in cabochon, a synthetic ruby ​​or sapphire has the same star-like 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, the hardness on the Mohs scale is 9.

Synthetic emerald are obtained by flux and hydrothermal methods. The growth of crystals in both cases 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 zoning.

Synthetic quartz 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 its natural crystalline varieties.

Garnet (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.

Garnetite is obtained in special apparatus at high temperatures in a deep vacuum by the method of "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 painted in various colors.

Cultured pearls... Cultured pearls, like natural pearls, are grown in the body of a mollusc under natural conditions. A mother-of-pearl ball serves as an embryo. It is enclosed in a piece of the mantle shell of a three-year-old mollusk that produces mother-of-pearl, thus obtaining a "pearl sack". This bag is placed in another sink, which is placed in a special reservoir. The embryo enveloping can last from 2 to 7 years. As the pearls grow, the shells are checked several times a year. Grown pearls are outwardly indistinguishable from natural ones, they have the correct given shape. The shell of artificial pearls corresponds to the natural chemical composition and has the same physical properties. Cultured pearls can be grown in large quantities, take on specific sizes and shapes, and be as beautiful as real pearls.

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

One of the types of imitation gems - doublets(doubles), glued stones. Waste (thin plates) - natural gems that cannot be cut on their own, are glued with less expensive minerals, similar in transparency and color, and processed together. More often than others, there are doublets of sapphires and emeralds. Rhinestone and colored glasses can be used as adhesives. The doublets, therefore, 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 look at it, turning it sideways, at a certain angle to the light source, you can see a reddish strip along the perimeter of the gluing or weak reddish reflections of the glued edge. Doublets have all the optical properties of a gem and, since the bottom of the stone does not wear out, they are durable in use.

Amber imitate pressing and fusion. Pressed amber - small grains and fragments of natural amber heated and pressed under pressure; they differ from natural amber by a large turbidity. The gloss is oily, 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 fused amber is inferior to natural amber in quality and decorative properties and is inexpensively valued.

To change the color of a number of stones, calcination is used for gems and chemical coloring for colored ones. Using the properties of a number of minerals of the quartz group to change color when heated, they were previously calcined in various ways: by baking in bread, covered with ash in a pot, coated with clay, and after complete uniform cooling, the stones acquire pink or gold tones.

To change the 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 dyed, imitating carnelian or sarder (red and brown), onyx (black or brown), chrysoprase (green), chalcedony (blue and 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. Black and brown color of agate is achieved by boiling in sugar syrup followed by etching with heated sulfuric acid. The green color is achieved by using chromium salts or nickel nitrate with further strong heating. Blue and blue color is obtained by impregnating agate in a solution of ferrocyanide (yellow blood salt) and subsequent boiling in copper sulfate.

As a result, chalcedony can take on the color of chrysoprase and carnelian, agates - brown and black, and jaspers - enhance the brightness of the color and change it. The color of turquoise can be enhanced with 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 butter. Currently, artificial turquoise is obtained, among other things, by staining the mineral of howlite, calcium borosilicate (Ca 2 [(BOOH) 5 SiO 4]) or chalcedony with copper salts or aniline dyes. In addition, synthetic turquoise ("neolithic", "non-turquoise", "reze 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 a cheap imitation of gems and colored stones.
Glass alloys are low-melting transparent glass, in which lead, potassium and boron oxides are introduced to enhance the gloss. Glass alloys are stained with oxides of copper, selenium, cobalt, uranium, manganese, etc. Stones are obtained by stamping with subsequent processing. To create the effect of playing a stone, a thin mirror layer of silver, fixed with varnish, is applied to the reverse side of it.

Opaque glass alloys can imitate 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 the transparency are set depending on which stone is imitated. To imitate pearls, milky white plastic with insignificant transparency is used, followed by coating with a pearl emulsion for a pearlescent shine, amber - unevenly colored, sometimes transparent, yellow tones, coral - opaque, coral in color, for turquoise - opaque, bluish-greenish, etc. are formed by stamping.

Kazdym A.A.,
candidate of geological and mineralogical sciences,
member of MOIP

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Imitation gems, 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 imitations. In general, the purpose of imitations is to deceive people. They are made from natural and synthetic materials that look like real, expensive gemstones.

Imitations have been around for 6,000 years. Thus, the Egyptians used blue faience (glazed) to imitate turquoise. The Romans passed off colored glasses for emeralds and rubies. During Queen Victoria's time, various materials were used to simulate mineral gemstones, 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 for which it is issued, and therefore, it is much easier to scratch.

There may be bubbles and funnels in the glass, which are easy to spot with a magnifying glass. A gemologist can easily distinguish glass by its single refractive index (1.5-1.7), because precious stones with a single refractive index equal to this value do not exist.

Imitation diamonds

One natural gem can be used to mimic another, more expensive gem. So, for example, citrine can be used to imitate topaz, and non-colored 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 shine.

Others imitation diamonds are cubic zirconia (cubic zirconia) and appeared relatively recently. It is about the same hard as diamond, on the Mohs scale its hardness is more than 9. The main difference is that diamond has one refractive index, while moissanite has two. In the larger crystals of moissanite, this appears as a doubling of the pavilion facets when viewed through the stone, but small moissanite stones embedded in jewelry are difficult to distinguish.

Other imitations of diamonds are also known, including yttrium aluminum garnet and strontium titanate, but all of them either do not have 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 the gemologist to the idea of ​​a fake.

Composite stones: doublets with garnet top layer and glued emeralds. As imitation stones so-called composite doublets also appear. This method began to be used several centuries ago and became widespread in the 19th century. The gemstone layer is glued onto a solid base. However, most often, ordinary glass is taken as a basis, which is coated with quartz or another 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 fake emerald or green garnet. The garnet top doublet is in two parts, which can be easily installed due to the difference in gloss. In addition, the glass may contain bubbles characteristic of it, which are not present in the garnet.

If you look at this "stone" from the upper platform, it appears green, but if you look at it from the side or submerge it in water, a red layer of garnet becomes noticeable. By changing the color of the lower, glass, layer, you can make imitation gems all colors. Another composite is a glued emerald made of two layers of colorless quartz, between which a thin layer of gelatin or green glass is enclosed.

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

Imitation opals

The play of color, which distinguishes noble opals, is the result of the interference of light on the inner spherical structure of the mineral. In 1974, the French scientist Pierre Gilson first demonstrated the obtained in the laboratory. Gilson's opals can be distinguished from natural stones by their mottling and mosaic-like “bundles” between the colored grains. American scientist John Slocum synthesized a glass opal known as the "Slocum stone". Under a microscope, the color spots in the Slocum stones look somewhat wrinkled.

Imitation(lat. imitatio) is an imitation of someone or something; fake. Like everything rare, expensive and beautiful, precious stones have caused numerous attempts to reproduce them artificially since ancient times. Already Pliny wrote about glass imitations of various precious stones, as well as about the manufacture of triplets. In 1758, the Austrian inventor, chemist Josef Strass, mixing and fusing green flint, iron oxide, alumina, lime and soda, obtained a colorless mass, which it turned out to be possible to cut and grind, after which it began to sparkle like real diamonds. The basis of many fake stones today is a pure, unpainted glass alloy, named after Joseph Strass - rhinestone. It is widely used for imitation of precious stones and bottle and window glass, optical crown glass (alkaline lime glass), optical flint glass, and borosilicate glass. Manganese, nickel, copper, iron, chromium, etc. are used as dyes. Another imitation method is duplication, resulting in doublets and triplets. There are other types of fakes or imitations as well. For example, you can imitate natural opal by heating the glass and then quickly cooling it (Pliny wrote about this), as a result of which it becomes covered with cracks. Imitate natural gemstones, synthetic stones and various artificial products.

Fake stones- artificial production of stones imitating natural minerals - precious, semi-precious and semi-precious stones. These are synthetic stones, imitation stones. Many gemstones are based on a beautiful, clean, unpainted glass alloy (see rhinestone). They can be cut and polished, after which they acquire the ability to sparkle, like natural minerals. Another way to counterfeit is duplication. It consists in the fact that the upper (front) part, made of a real gemstone, is glued onto the lower (back) part, consisting of glass, rock crystal or synthetic material.

Here are the main ways to simulate:

Doublets- imitation of precious stones, obtained from two components. They were known even in ancient Rome. Today, doublets are made using opal: a thin layer of opal is glued to the opal uterus. Sapphire, ruby ​​and garnet doublets are also used, when a thin plate of the corresponding stone is glued on top of glass or synthetic spinel. They are called: doublet sapphire-glass or sapphire-synthetic spinel, etc. The emerald is imitated by making from colorless beryl: faceted beryl is cut in half and glued to a green intermediate spacer. A pale emerald with an intensely colored glue is also used.

Artificial resins- materials used as imitation amber, as well as in jewelry for clothes (buckles, buttons, etc. are made from them)

Ceramic masses- a material such as porcelain or pottery, with the help of which jewelers successfully imitate opaque precious stones, especially turquoise. In addition, nowadays fashionable jewelry is made from faience, majolica, porcelain: brooches, pendants, bracelets, rings, as well as various sets and headsets.

Optical crown glass- alkaline lime glass used to imitate precious stones.

Optical flint glass- English crystal, glass containing lead; used to imitate precious stones.

Semi-doublets- imitation of large gemstones, glued together from two of the same smaller stones. Since the value of precious stones increases in proportion to the square of their mass, such an imitation, issued for one large stone, will cost much more than both of its smaller stones.

Resol- a synthetic thermosetting polymer, which is a viscous liquid or a solid, soluble and low-melting product from light yellow to black. It is used to imitate amber.

Reinkisel(Rhine flint) - glass containing multicolored inclusions (schlieren) in a white or colorless glass mass. Currently used as imitation material in costume jewelry.

Ruby doublets- imitation of natural ruby ​​by gluing a thin strip of ruby ​​stone on glass or synthetic spinel.

Sapphire doublets- imitation of natural sapphires by gluing a thin sapphire plate onto glass or synthetic spinel. They are called sapphire-glass or sapphire-synthetic spinel, respectively.

Resins- chemically complex substances produced by resin-producing trees and synthetically. A distinction is made between soft and hard resins. Hard resins have the same hardness as gypsum, some are slightly harder, others are slightly softer, but most of them are scratched with a knife. There are transparent and opaque. One type of hard resin - amber - is widely used for the production of various types of jewelry. Some resins are used to imitate amber. In the manufacture of bracelets and some other decorative items, Indian craftsmen use shellac, painting the resin in yellow and other colors.

Titanium glass(flint glass) - glass in which lead oxide is replaced by titanium oxide. Used to simulate natural minerals.

Triplet- imitation of precious stones, consisting of thin layers of natural stone, which is glued between two pieces of rock crystal. For example, a quartz-opal-quartz triplet. Counterfeits for precious stones were already known in Ancient Egypt and Rome during the time of Pliny. Pliny wrote about the manufacture of triplets: “It is very difficult to distinguish real from counterfeit ones, since a method has been invented to falsify gems of a certain kind, using genuine stones for this. So, they learned to glue sardonyx from three different gems so skillfully that it is impossible to detect it, although its black, white and red lead colors in fact all belong to different stones. "

Faience(French faience, from the name of the Italian city Faenza - Faenza, where the faience was produced) - ceramics made of white-burning clay, covered with a colorless glaze with a white dense fine-grained shard that is not translucent in a thin layer. Brooches, pendants, earrings, bracelets, headsets are made of faience, most often painted with paints and covered with glaze, or decorated with moldings (molding). Faience is an excellent material to imitate natural turquoise.

Phenoplasts- plastics based on phenol-formaldehyde resins. Easily processed and painted in any color. In appearance, they can imitate (see Imitation) natural stones, including pearls, coral, prelamutr, glass and other materials. They are used for making beads, earrings, rings, brooches, bracelets and other inexpensive jewelry.

Flintglass(lead glass) is a material used to imitate precious stones. Consists of oxides of potassium or sodium, lead oxide. Lead glass of the following composition is sometimes used to imitate a diamond: 38.2% silica, 53.3% lead oxide, 7.8% potassium carbonate and a small amount of other substances. This composition gives very high refractive indices of light. Previously, this material was called rhinestone. Flint glass is used to make cheap glass jewelry. Flint glass stones are beautiful when skillfully cut. The addition of lead increases light refraction and dispersion. But these imitations are soft, and therefore, in the process of wearing, during friction, they quickly lose their polish, scratch, and suffer from sulfur oxides present in the atmosphere. Over time, jewelry takes on a brownish tint.

Phosphor glass- glass, which contains the same components as in crown glass, but part of the silica is replaced by phosphorus oxide. Used to simulate precious stones.

Unlike synthetic gemstones, which have the same chemical composition, crystal structure and physical properties as their natural counterparts, imitations have only an external resemblance to the corresponding gemstones. As a result, the constants of the imitation are usually very different from those of natural stones.

A variety of materials are used to mimic the more expensive natural gemstones, from natural minerals (sometimes colored) to a wide variety of artificial products.

The most common inexpensive imitation 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 in roundness and scuffing of the edges of the edges), the presence of a concave fracture, uneven color distribution (filaments) and gas bubbles.

As mentioned, it is relatively easy to distinguish between glass and other imitations of 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 tag. Imitations of diamonds include natural stones such as colorless varieties of quartz, topaz, corundum and zircon. All these stones can be recognized by their birefringence.

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

Some physical constants of diamond and diamond imitations

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

Metal-mounted diamond imitations are arguably the most problematic stones due to their high refractive indices, which are usually off the scale 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 striking 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 can vary in different directions. Specific thermal conductivity is measured in watts divided by meter and degree Celsius (W x m -1 x ° C -1).

Table some crystalline materials with thermal conductivity anisotropy are indicated.

Specific thermal conductivity of some minerals

With the exception of colorless synthetic corundum and spinel, which emerged as imitations more than 60 years ago, most artificial diamond imitations are byproducts of growing crystals for the electronics, lasers and space industries.

Of these, YAG (yttrium-aluminum garnet), GGG (gadolinium-gallium garnet), CZ (cubic zirconium dioxide) and lithium niobate have no natural analogues and should be called artificial products and not synthetic stones.

Until 1987, another imitation of diamond, 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 an artificial product.

CZ (cubic zirconium dioxide), known in Russia as cubic zirconia, in Switzerland - djevalite (Jevahirjan company), in the USA - daimonesk (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 United States 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 gemstone belongs to diamonds is selected depending on the diagnostic criterion by which the diamond is identified. There are several tests available to diagnose diamonds.

Incident light (or stone tilt) method

When a properly cut brilliant-cut stone is illuminated and viewed from the deck at right angles against a dark background, the stone will appear uniformly shiny.

This is because the edges of the pavilion act like mirrors and reflect the incident light back through the platform 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 brilliance 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 look black, since they no longer act like mirrors (light passes through them instead of being reflected back through the platform).

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

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

Strontium titanate and synthetic rutile can be identified by their very bright "play" (the dispersion of these stones is several times higher than that of a diamond).

Synthetic moissanite has a high birefringence and can be diagnosed (like zircon) by “bifurcation” of the ribs at the sides of the pavilion when viewed through the main facet of the crown.

It is also impossible to identify imitations such as CZ with this method, in which the pavilion is cut deeper than the ideal brilliant cut in order to compensate for the low refractive index. In this case, the stone has a complete internal reflection, even if it is tilted.

Diamonds with a small area and deep pavilion - the so-called "Old English" cut - will transmit light in an oblique position, so before doing this test, you need to make sure that the proportions of the stone match the ideal brilliant cut.

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 put a small black dot on the white paper. If the stone is an imitation (with a refractive index lower than that of a diamond), the dot will appear 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 face of the pavilion, which forms a ring (note that through the 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 not placed over a point, but a platform down on any intensely colored surface. If the color of the substrate is not visible through the stone pavilion, then it is diamond, strontium titanate, rutile, synthetic moissanite, or imitation with a deep pavilion (however, a diamond with a shallow pavilion does not pass this test).

Edge Finishing Test

Diamond is the hardest of all known natural and artificial materials, and this allows you to achieve a very high quality of polishing of its edges. Due to the high hardness of the diamond, it is possible to polish the edges so that they are completely flat and have sharp edges.

It is not possible to achieve this quality of polish on softer stones, and the edges may be slightly rounded. If a diamond imitation product (even a colorless sapphire) has been worn for several years, traces of scuffs 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 ratio between their mass and girdle diameter. This method is essentially based on determining the specific gravity of the stone. The relationship between the size of stones and their mass for a diamond and several of its imitations are given in table.

The ratio of the mass of the stone and the diameter of its girdle

Girdle diameter, mm	Carat weight (to the nearest hundredths of a second)
	Diamond				Strontium titanate

All stones are assumed to be cut with the correct brilliant cut. Tolerances in cut proportions can lead to weight changes of up to ± 10%. In this regard, synthetic moissanite, the specific gravity of which is 3.22, can have the same mass values ​​as diamond, and therefore is not shown in the table.

Tests for reflectivity, thermal conductivity and electrical conductivity

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

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

A typical diamond thermal conductivity tester consists of a tip, the metal tip of which is electronically heated, and a control block, which consists of an electrical circuit to determine the temperature drop when the tip touches the surface of the diamond.

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

The loss of heat by the tip on contact with the diamond is recorded using a dial gauge, digital display or light signal. Sometimes the visual indication is amplified by an audible signal.

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

For this, this modification provides an additional removable probe for checking large stones for their belonging to moissanite. This probe can be inserted into the Large Stone jack (L.S) if required.

The probe of the Klio Tester has a number of features that distinguish it from analogs and are aimed at improving 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.

By lightly touching the probe (until it clicks), the thermal conductivity is measured. With deeper pressure (after clicking), the conductivity is measured. The device is equipped with a probe with a protruding copper tip, which heats up to a certain temperature during operation.

During testing, the tip is pressed against the test item 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 gauge needle. The scale of the device is divided into three colored sectors.

Red sector - corresponds to imitations of diamonds, the thermal conductivity of which is lower than the thermal conductivity of diamonds and is called "SIMULANT".

The green sector is the zone of thermal conductivity of a diamond and is called "BRILLIANT".

Yellow sector - "MUASSANITA" zone.

Moissanite is a brand name for silicon carbide (SiC), which 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 in nature, widespread production of practically colorless synthetic moissanites is currently developing.

When the tip of the rim touches the stone, the heat flux is redistributed between the stone and the metal of the rim, which leads to an error. Therefore, the device warns of touching metal with a sound signal.

The procedure for identifying diamonds is as follows. At the beginning of work, having carefully examined the products, it is necessary to test 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 by the girdle and, in accordance with the table, presumably estimate their mass. Having weighed each of the samples on an electronic balance, one can compare the results with the tabulated ones and draw a conclusion about their authenticity.

The next step can be testing samples by the method of incident light (or stone tilt), based on the phenomenon of total internal reflection of light in diamonds and its partial loss in imitations. True, people with poor eyesight find such testing with difficulty.

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 deny the assumptions made about the stones-inserts.

The samples are most accurately tested for thermal conductivity and electrical conductivity using the Klio Tester - KL-1202. The following order of work with 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 its correct operation.

First, 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 insert the plug of the mains adapter into the socket of the electronic unit, and the adapter itself into the 220-240 V network. After that, you need to insert an additional removable probe into the "Large Stone" (L.S) socket.

Switch on the device by placing the switch in the "op" position. With sufficient supply voltage, it takes about 30 seconds to warm up the device. The device is ready for operation as soon as the red light in the upper left corner of the scale comes on.

There are three plates on the panel of the device: "Test-simulant", "Test-diamond" and "Test-moissanite".

Press the tip of the probe for 1.5-2 s (half-drowning it in the housing) 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 (half-drowning it in 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 (half-drowning it in the housing) to the Test-Moissanite plate, while the arrow will deflect to the green field. After that, drown the probe until it clicks, the arrow should deviate into the yellow field.

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

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

Touch the tip of the probe to the stone holder; an audible signal should be heard. After that, you can test the products.

Before measurement, wipe the examined stone, and in the case of a rimmed stone, the entire product, with a soft cloth or suede.

Put a special crocodile holder on the item in the frame and, without touching the frame, take it in one hand, and the probe in the other. Do not touch the frame with your hand when measuring, as this will lead to a measurement error.

Select the largest facets of the stone and measure as follows.

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

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

If the tested stone is moissanite, then the arrow will deviate to the green sector, and after clicking - to the yellow sector.

If the tested stone is a simulator, then the arrow of the device will deviate to the red sector and, after clicking, will remain in it.

If, with a light pressure or with a fully recessed tip, the arrow is in the yellow sector or a sound signal is heard, it means that you have touched the metal of the frame, and the measurement should be repeated. To avoid an error, it is necessary to move the probe away from the product and repeat the measurement after 10 s.

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

Rimless stones should be placed in the holder located on the body of the device. The place of attachment must be selected in accordance with the size of the stone. This will provide the necessary conditions for correct measurement.

If you have any doubts about the result, you should repeat the measurement.

If you have any doubts about the correct operation of the instrument, you should carry out a proof test as described above.

If the measurement result is "Simulant" or "Moissanite", then the 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 (with a diameter greater than 3 mm), then it is recommended to use an additional split probe.

Using only a removable additional probe during testing allows you to determine whether or not moissanite is in front of you (the diamond and the simulant are not separated by this probe). Orient the probe tip perpendicular to the surface of the item to be tested and touch it:

If the arrow has deviated to the yellow sector, then you have moissanite in front of you;

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

If the arrow is in the yellow sector and a sound signal is heard, then you have touched the metal of the frame, and the measurement must be repeated.

Using an optional probe to check small stones can trigger a beep on moissanite (the needle is in the yellow sector of the moissanite and there is a beep even though you are not touching the metal of the rim).

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

At the end of the work, turn off the device with the "off" button.

To avoid damage to the tip, immediately after measurements, be sure to put on a protective cap on the probe, which must not be removed all the time 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 any gem in terms of their external characteristics. Despite the external similarity, imitation differs from natural stone either in composition, or structure, or in physical constants. " Most often, there are differences in all three of the listed characteristics. Imitation should not be confused with refinement. Refined stones completely retain the composition and structure of natural material, but have higher indicators of the quality of appearance, improved with the help of certain physical and chemical effects. Artificial inserts are similar to their natural counterparts, which they imitate, only externally, and their physical, chemical and morphological characteristics can be quite different from their natural counterpart.

People have tried to look for ways to create imitations of precious stones for a long time. The desire to copy an item implies that it possesses 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 a natural stone, the more varieties of its artificial imitations exist.

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

There are several ways to simulate:

Reconstructed jewelry inserts;

Manufacturing of composite jewelry stones;

Making imitations of precious stones from glass (rhinestones);

Making imitations of precious stones from plastics;

Issuing less valuable gems for more precious ones.

Cultured pearls grown as a result of artificial insertion of a foreign object into the body of a pearl oyster can be conditionally assigned to the group of artificial inserts or isolated into a separate group.

Reconstructed jewelry inserts

The initial raw material for the manufacture of reconstructed inserts is jewelry production waste, crystal fragments, stones of low or non-jewelry quality. The raw material is crushed, colorants, fillers and binders can be added to the mineral chips; then the mixture is sintered. The method allows you to get 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 as a binder, and the finished insert or bead is pressed immediately. In the manufacture of reconstructed aventurine, a filler (copper chips) is added to the mixture in order to imitate the aventurine effect. Currently, reconstructed inserts are made to imitate almost any opaque and translucent stones in thin layers: lapis lazuli, malachite, rhodonite, jasper, etc.

A new type of assortment of reconstructed inserts is the so-called "matrix stones". For example, "matrix-opal" - thin plates of noble opal a few millimeters in size are placed in synthetic resin, and then a cabochon-shaped jewelry insert is formed.

Diagnostics is carried out using a microscope. Under high magnification, it can be seen that the internal structure of the reconstructed stone is completely different from that of the natural one.

Composite gemstones

The most common form of compound stones are doublets, two-piece stones. In this case, the crown is made from an expensive gem, and the pavilion, as a rule, is made of 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 level of the girdle. Subsequent fastening of the doublet with a deaf or prong setting completely hides the place of gluing. The technology for creating doublets is now so advanced that sometimes even professionals can hardly distinguish a doublet from a real gem in appearance.

In history, the most famous are "pomegranate-top doublets", which were made in large quantities at the court of Queen Victoria (late 19th century). These stones consisted of a thin plate of almandine (crown) welded to a red-colored 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 plate of almandine, and the pavilion was made of green glass.

In doublets imitating emerald, the crown, as a rule, is made of colorless transparent beryl, and the pavilion is made of emerald green colored glass.

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

Composite stones can be made of three elements, then they are called triplets. In this case, the most varied combinations of materials used are possible. For example, when making a classic triplet of opal, the main element is made of noble opal, the base is made of ordinary ignoble, and a thin plate of rock crystal is glued on top to increase the shine and play of the stone. Sometimes glass, corundum or spinel can be used as the 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 whole plate of noble opal is glued onto the substrate, but flat small pieces, which are poured with polyacrylic.

In such a triplet as the "welded emerald" (also known on 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 dyed is placed between the crown and the pavilion. color of glass or special synthetic adhesive. Quartz and synthetic topaz and spinels can also be used to make the crown and pavilion.

In the case of "welded" alexandrite, between the crown and the pavilion, at the girdle level, there is a special colored filter made of synthetic material, which creates an alexandrite color change effect under different lighting conditions.

Imitation Glass Gemstones

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

The composition of the glass used for imitation gems varies. So, a composition can contain:

Silicon oxide (38 to 65%);

Sodium and potassium oxides (10 to 20%);

Calcium oxide (no more than 5%);

Barium oxide (3 to 8%);

Lead oxide (14 to 40%).

The greatest dispersion is possessed by imitation of gems made of glass, called "stras" or "rhinestones" after the name of the German jeweler Georges Strass, who at the end of the 19th century. proposed the following formulation: 38.2% silicon oxide, 53.0% lead oxide and 8.8% potash. In addition, small amounts of borax, glycerin and arsenic acid are added to this mixture. Strass's recipe is used to make imitation diamonds, with lead glass being shaped like a full-cut diamond.

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

To obtain a blue color that mimics a sapphire, add 2.5% cobalt oxide. The emerald (green) color is imitated by the addition of 0.8% copper oxide and 0.02% chromium oxide to the rhinestone. Amethyst can be obtained in the same way. For this, 2.5% of cobalt oxide and a small amount (to the required tone) of manganese oxide are added to the charge. Currently, glass coloring technology allows you to simulate almost any color, tone and shade by selecting the appropriate dyes.

By adding insoluble substances (bone meal, cryolite, tin oxide), an opaque white, milky glass can be obtained, which serves as an imitation of base opal. It is possible to obtain a black rhinestone - marblite by introducing 3-5% manganese compounds with iron oxides. This rhinestone is a perfect 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 - stamping. Hollow glass beads are blown.

Large rhinestones can undergo a special artistic treatment called copper wheel faceting. In this case, you can apply a variety of patterns and even bas-relief and high-relief images to rhinestones. Blown beads can be decorated by irisation, that is, by applying the thinnest layers of metal oxides, which give the rainbow effect of the same kind that is obtained from stains of oil or oil on water. To enhance the optical properties, silver amalgam is often applied to the lower part of the rhinestone, followed by its fixing by bronzing.

Rhinestones are easy to distinguish from natural gems, since they do not have a crystalline structure, are fragile, and their hardness on the Mohs scale does not exceed 6. or synthetic stone, it remains intact. Rhinestones differ from natural stones in less thermal conductivity, so the traces of breath disappear from glass more slowly than natural crystals. Natural stones feel colder to the touch than glass imitations.

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

In addition to rhinestones, there are other glass imitations. For example, the most attractive imitation of pearls is considered to be the so-called "Roman pearls", which are hollow glass beads, covered from the inside with pearl essence and filled with wax to give them an external impression of hardness. To imitate turquoise, they can use tinted frosted barium glass, as well as ceramic materials such as porcelain and earthenware. A fairly large number of glass opal imitations are known 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 plastics

To imitate precious and semi-precious stones from plastics, aminoplasts and acrylates are most often used. These types of plastics are transparent, have high mechanical strength, gloss, perceive color well, and are sufficiently resistant to chemicals and light.

Aminoplastics - carbide resins, heat-resistant (up to 1200 ° C), are highly plastic, 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 common plastics imitate pearls, turquoise, opal, amber, coral. Some plastic imitations are quite common and have their own trade names. For example, the "Hamburg Turquoise" (also known under the trade name "Neolith"), which appeared on the market in the late 50s of the XX century. This product consists of a mixture of aluminum hydroxide, copper phosphates and synthetic c mol as binders. A number of products are currently being produced with similar chemical composition, imitating turquoise and collectively known as non-turquoise.

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

However, imitations made of plastics are rather monotonous, and they are easy to recognize by their appearance: they are much lighter and softer than stones, and often have too "correct" color.

Imitation of valuable types of gemstones with less valuable gems

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

The most popular substitutes for diamond are zircons and colorless sapphires. The advantages of sapphire include hardness close to diamond, but its brilliance and play of color is 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). Zircon color play is close to diamond, 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 imitations of diamond. 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 refractions
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 (rhinestone)	Silicon oxide	7,0	1,55-1,54

Chrysolite, demantoid, tourmaline are used to imitate emeralds. Ural craftsmen very cleverly forged emeralds before the October Revolution of 1917: a void was hollowed out in any transparent stone and filled with a green solution of chromium salts, and the hole was carefully sealed.

Turquoise can be replaced with lapis lazuli, howlite, magnesite, chalcedony, dolomite and even bone, tint 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. "Vienna Turquoise" refers to the reconstructed inserts. In appearance, it is more matte than natural, and does not have its characteristic luster (the refractive index of "Viennese turquoise" is 1.45, while natural - on average 1.62).

They imitate pearls in many ways. In some cases, balls of various sizes are cut out of mother-of-pearl shells, while often they are covered with a special pearl essence from a special substance - guanine, obtained from the scales of the bleak fish (to make one kilogram of pearl essence, scales from 35,000 fish are needed), which makes them even more natural pearl shine. In other cases, hematite and polished anthracite are used to imitate black pearls, but such a fake is 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, such an imitation has a metallic luster uncharacteristic of black pearls. But anthracite beads can easily be mistaken for natural black pearls, since these stones are similar in luster and weight.

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

Currently, glasses imitating precious stones are 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 you can make them as much as you like.

Natural stones are the creations of nature, their number is limited, it is difficult to find and get it. That is why a gem is tens, and sometimes hundreds of times more expensive than its synthetic counterparts, despite the fact that synthetic stones are often significantly superior in quality and color characteristics to natural stones.

Jewelry stones are a wonderful creation of nature and man. Nature did not stint, creating a deep tranquility of luscious green emeralds, the serenity of blue sapphires, the ardor of red rubies, the fabulous or passionate variability of white and black opals, the tenderness of pink and blue topaz, an endless sea of ​​flowers, shades, patterns. A person, 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 a testament to the wealth and tremendous spiritual power of the people.

Glass used as imitation can be of different transparency (transparent, translucent, translucent in thin chips, opaque) and colors. Their physical properties depend on the composition, mainly on the lead content. Refractive indices of transparent glasses 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 can develop optical anisotropy. Dispersion 0.010, in glasses with a high lead content can be higher.

Glasses can be distinguished by the presence of gas bubbles of various shapes, sometimes streaks, blobs of dyes. In addition to purely glass imitations, double (doublets) and triplets (triplets) stones are used, glued from glass and natural stone, from weak and densely colored stones, from natural and synthetic stone. Such fakes are perfectly visible under a magnifying glass or a microscope: bubbles located in the same plane are observed on the gluing surface.

Glasses (and plastics) are used to imitate translucent and opaque stones: turquoise, chrysoprase, carnelian, etc. Their density and hardness are low.

Aventurine glass differs from aventurine in physical properties, as well as in the presence of a regular three- or hexagonal shape of inclusions of copper shavings.