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Russian Gemstones Encyclopedia

Vladimir Bukanov. Russian Gemstones Encyclopedia

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

GLASS


GLASSES (Gläser—Verres——тЄкла), from Germ. Glas. Amorphous. Hardness 5-6. Density 2.2-4.2. Glass luster to diamond one. Fragile. Glass is one of non-expensive artificial materials, which are used for the imitation of gemstones. It is produced through melting under high temperature. According their composition and origin, glasses can be classified as natural (See tektites) and artificial ones. Artificial glasses of different composition are widely used in jewelry; they can be divided into transparent, translucent (opaque) and non-transparent ones as well as glasses with various optical effects – opacified glass, enamel, smalto and technogenic scoria. Glasses vary widely in their composition and properties. Necessary color can be got with admixture of oxides of metals, rare earth elements and different fine-dispersed components. So, yellow canary glass contains uranium and displays fluorescence in ultraviolet rays. There is a small admixture of lead in lead glass and in composite glass its content is high. Rare-earth silicate glass with the effect of cat’s-eye is called catseyte. Flint glass, because originally they added ground flint into it. Selenium glass, red because of the admixture of selenium, is used for the imitation of ruby. Thallic glass is made with the admixture of thallium; it has the density up to 5.4. Usually, they use following kinds of glasses for the imitation of gemstones: crown glass, flint glass, borosilicate glass, opal glass and other ornamental glasses. In Austria, the Swarowskiy Firm produces significant volumes of faceted green glass with high level of refraction – swarogreen with the density of 2.9.

Calcium glass, or crown glass is an alkali-calcareous glass, it includes common window pane or bottle glass received from the mixture of silica, calc, potash or sodium with admixture of coloring agents. It has the hardness of 5.5 and the density of 2.6. It is often obtained with the method of pressing – pressed glass, it is used in bijouterie as an imitation of gemstones. Bohemian crystal is also a common kind of glass enriched with calcium. When faceted in the diamond pattern, it is called baccara.

Lead glass, or flint glass contains significant admixture of lead oxide, which increases its dispersion, density and improves optical properties. It is usually faceted for ornamental purposes, including the imitation of brilliants. Such glass – called strass, with a content of lead oxide up to 53%, was invented in 1758. Later, they found the method of producing of colored strasses, including rose glass with the admixture of neodymium and ruby glass with the admixture of gold. To strengthen the luster of such glass imitation, they put metallic foil under it or covered it with amalgam or film of silver, aluminum or others.

Borosilicate glass can be made from calcium glass through adding of boron oxide to it. They are the hardest glasses with the hardness up to 7, which are used for the imitation of aquamarine under the trade name mass-aqua. From such glass the Japanese firm Kyoto Ceramics Co. has made an imitation of opal, in which the effect of play of color is produced with tiny microspheres of silica. On the analogy of borosilicate glass it is possible to produce phosphoric or fluoric glass. A variety of fluoric glass is opal glass, or milk glass, which has a decreased level of density and hardness because of the content of fluorine, the admixture of fluorite or other fluorine-containing components.

Decorative glasses. In Japan, they made a glass imitation with the effect of cat’s-eye, produced with inclusions of very fine fibers of actinolite. This mineral gives golden-brown color to the glass; such imitation is called Victoria stone; it has the hardness of 6 and the density of 3. When the color is emerald-green, such glass is known under the trade name imori jade. In the U.S.A., a similar imitation consists of silicate glass with the admixture of fine-fibrous rare-earth silicate producing the effect of cat’s-eye. The trade name of this imitation is catseyte. From orange-red fluoric glass they made the first imitations of fire opal with iridescence producing with metallic flakes or with the diffraction of rays on the surface of this glass. Later, they made other imitations. fire agate and Lake Superior fire agate. From white glass they made such imitation as topaz opal with inclusions of very fine metallic flakes. In the U.S.A., there is also a beautiful imitation from silicate glass enriched with sodium and very fine foil flakes. The texture of this glass is fine-lamellar, that’s why it displays iridescence because of the interference. This imitation of noble opal is known under the trade name Slocum stone, or essence opal with the hardness of about 6 and the density of 2.4-2.5. Another one example of similar imitation is polychromatic glass with opalescenceatonyx. Star glass is classified as compound stone and has a substrate with carved star pattern. To imitate pearls, they use alabaster glass with opalescence. They made also an imitation of such popular gemstone as agate – glassy agate, which is produced with fusion of pieces of polychrome glass.

Paste is a common term for different imitations of gemstones from lead glass colored with enamels and used for making of gem imprints. Such blue paste frit was known in Ancient Egypt as Egyptian cyanus.In China, glass rice paste was used as an imitation of nephrite or jadeite. Enamel is a glass compound received through melting of powder put on a jewelry item. Usually enamels are non-transparent or half-transparent; they differ with technique of their producing. In the ancient times, they used enamels for imitation of gemstones. They are not the same as enamel glaze – transparent glass covering. Among non-transparent opacified glass one of the most popular is copper glass, as well as blue cobalt glass with white spots of cristobalite, which is used for imitation of lazurite.

Glass-ceramic is cryptocrystalline material formed with small (0.1-10 mm.) irregular oriented crystals in glassy mass. This material of different level of transparency is made through melting of silicate glass with adding of oxides of lithium, manganous, calcium, aluminum and phosphorus and also small volumes of oxides of manganous, chromium, cadmium, titanium, vanadium and others. Color: ruby-red, yellow, green, light blue of various intensity and tones. Glass-ceramic is also used for imitation of colored stones.

Technogenic scoria and glass. Among them, they classify scoriae, which are used as cheap imitations of gemstones, for example, black ferrous scoria – ferrolite, quartz scoria – opalescite and others. To this class they also classify tengizit – a kind of glass formed under the long burning of oil fountains, when rocks around a well are melted. As a result of partial decrystallization, olive-green and brownish diopside-wollastonite veins and sphaerolites are formed in them. Because of its ornamental properties, tengizit is used for jewelry-artistic produce. Color: light blue, deep blue to black. Texture is massive, veined-spherical, porphyry-like or pleated structure. Hardness 5.5. In the water content tengizit is close to obsidian, in its composition – to basaltic glass. It is easy cut and processed, ideal in polishing. One more version of decorative glasses is formed as a result of fusion of rocks at start of space vehicles. It has received in name the of NASA obsidian, on the cosmodrome in the U.S.A. Feature of this rock is iridescence caused thin metallic inclusions.

Mineral glass is received through artificial melting of natural materials: quartz glass, beryl glass, diopside glass and others. Among them the widespread are quartz and beryl glass. Usually they are colored. Beryl glass has the hardness 7 and density 2.5. For imitation of spinel and aquamarine it colored blue with the admixture of cobalt. For imitation of emerald, so called scientific emerald, or smaragdolin, green color is received with the admixture of chromium. Diopside glass is usually faceted to imitate natural chrome-diopside.

Synonyms. Electric emerald, after its color | Indura emerald | Plique-a-jour enamel, Fr. | Paste, from Ital. “paste” – pastry | Purpurin, syn. hematinon, royalite | Copper ruby, with the admixture of Cu, syn. scientific ruby | Slocum stone, after the producer J. Slocum from Michigan, the U.S.A. | Strass, after the Austrian chemist J. Strass; according the other sources, after the French chemist G.F. Strass (1700-1773) from Strasburg.

Glass, colorless – Amause | Falun brilliant | Baroda gem | Lead crystal | Diamante | Simili diamond | Jena glass | Litik, Old Russ. faceted glass | Simili | Rhine stone | Simple stone.

Color glass: ~ emerald: Brighton ~, electric ~, ferrous ~, Medina ~, Spanish ~. |~ glass: color ~, crystal ~, Germ., for faceting; emerald ~, ruby-gold ~, golden ~, hessonite ~, lazurite ~, fire opal ~, orange ~, with the admixture of cadmium; polychromatic ~, ruby ~, with the content of colloid gold; sapphire ~, solar ~, golden-yellow, syn. desert amethyst; topaz ~, uranium ~, yellow, with the content of uranium Haematinon, red. | Helenite | Hyalite | Imori jade | Scientific sapphire, blue | French stone | Glassy stone | Vienna turquoise.

Decorative glass – victoria stone; syn. imori stone, imori jade, meta-jade | Murava, Old Russ. | Poliva Old Russ. | ~ glass: agate ~, resembling agate in texture; aventurine ~, rose ~, syn. ruby ~; muslin ~, patterned; star ~, syn. astrolite; starlyte ~| ~ enamel (after the technique of its production): granulouse ~, guilloché ~, limoges ~, painted ~, partitionic ~, relief ~, retuse ~, window ~| Shaton stone, from Fr. “chaton” .

Technogenic glass – Iron scoria | Tengizit.

Treatment. The first finding of glass beads in Mesopotamia is dated to 3000 B.C. In Ancient Egypt, the method of glass production has been known since 1500 B.C. Beside the invention of enamel and decorative beads, glass was used for imitation of pearls.In the tomb of Tutankhamen (1350 B.C.), they discovered light blue glass beads made as an imitation of turquoise. Another imitation of those times was aventurine glass (See aventurine). Agate glass was made even in Ancient Rome in the first century A.D. Then, the technology of its producing became familiar in Venice among glass-blowers of the island of Murano. In the 15th cent., they made here polychromatic millefiory glass used in mosaics and also transparent filigree glass with threads of milk glass forming a lattice pattern. In India, in Baroda, near Akhamadabad, they faceted glass for adornments. They put metallic foil under glass; such strass had the trade name Baroda. Glass imitations were widely used for adornments of icons together with gemstones. The most ancient example is an icon from Trir, Germany, dated to 1266. In its frame there are 328 gemstones and 24 glass imitations. A richly decorated with gemstones belt of Elisabeth, the wife of Karl IV, made in the second half of the 14th cent., also has insets of glass of different colors. In a bowl from gilded silver in the Museum at Prazském Hradè, Prague, Czech Rep., made in 1716, from 200 gemstones 13 are pieces of colored glass.

In the 17th cent., the center of manufacturing of art glass became Czech and Silesia. In Czech, they opened the production of Bohemian glass used in bijouterie. With the beginning of industrial production of lead glass in Europe and wide manufacturing of strass, glass became a concurrent to natural quartz in applied art. A large collection of gems and intaglios of Philippe, Duke of Orleans, the regent of France in 1715-1723, was copied in glass and enamel by chemist Homberg using the Orleans paste around 1700. Also antique cameos were copied by the Scotch chemist D. Tassie (1735-1799), who worked out Tassie paste. For imitation of brilliants, they used glasses with high level of refraction – strass, invented by the French chemist J.F. Strass (1700-1773). In the 18th cent., they began to engrave different compositions on the glass surface with diamond tools. In Venice, they invented purpurin – a glass compound of purple color with silver sparkles. In 1874, there, blue glass for imitation of sapphire was invented; it was known under the trade name sapphirine. In the 19th cent. popular in Europe jet, because of lack of this material, was sometimes replaced with black jetty glass, or French jet, manufacturing of which was opened in France. Because it was easy in formation and very highly decorative, it was widely used for non-expensive adornments in mass scale. In Britain, such glass was usually a bit reddish or pink in the light because of the admixture of manganous; its trade name was Vox-Hall glass. Victorian traditions of Great Britain supposed long mourning procedures. Awidow had to wear a mourning dress up to 2.5 years; her adornments couldn’t be glistening. That’s why jet came into fashion. When it was replaced with black glass, they had to make it duller. Beads from black matte glass were called crepe stones. For imitation of black opal, glass was put on an under-laying from onyx or obsidian. Faceted glass in gemstones imitations with faces covered with mercury amalgam was called shaton stone.

In Russia, the technique of plique-à-jour enamel was used even in the second half of the 11th cent.; and since the early of the 12th cent., enamel has become the main type of decoration of gold adornments in Kievan Russia. The peak of its prosperity was in the 17th cent. Various objects were decorated with enamel – armaments, harness, dishes, earrings, signets and buttons. At the same time, painting on enamel was developing. Miniature portraits of tsars on enamel in frames with brilliants became the most honorable awards in Russia. They are represented in the collection of the State. Hist. Museum, Moscow. The flourishing of fashion on glass adornments was in the middle of the 19th cent. Especially popular were glass fruits, bracelets from glass threads, beads and bugles. The latest ones, opposite to round beads, were represented with tiny glass tubes up to 1.5 cm. long. In the Chinese Palace in Oranienbaum, by St Petersburg, the walls of the Bugles chamber were embroidered with white bugles. Bugles were also used in decoration of clothes. In jewelry non-transparent red glass was widely used – purpurin consisting from dendrite-like red crystallites, perhaps, cristobalite. The secret of admixtures necessary to produce this glass has been lost. In the jubilee Easter Egg by the firm of K. Fabergé, made to the 300th anniversary of the House of the Romanovs, a shield with the state emblem was made from purpurin.

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