Russian Gemstones Encyclopedia

Vladimir Bukanov. Russian Gemstones Encyclopedia



NACRE (Perlmutter—Nacre—ѕерламутр), from Germ. Perlamutter – mother of pearls (1554), because it is formed in pearl-shells.

Composition & Properties. CaCO3 – 85%, H2O– up to 3% and bioorganic substance conchialine – 12%. Hardness 2.5-3.5. Density 2.7-2.8. Nacre and shells described here are classified as bio-mineral bodies of the group of hydrogenous jewelry-ornamental materials. Nacre is a bio-mineral substance of the inner layer of mollusk shells, composed with thinnest flakes of aragonite or calcite and organic adhesive conchialine. Nacre is formed on the surface of shells of pearl-bearing sea and freshwater mollusks. After its structure, it is identical to pearls and it is being produced by a mollusk during all its life-time. Thin-layer texture of nacre covering and stepped character of growing of the flakes of aragonite lead to silver shining, luster and iridescent chatoyancy typical for nacre. As well as in pearls, it is connected with diffraction and interference of light. Color of nacre in different kinds of shell can be different: silver-white, rose, greenish-yellow, green. Outside shells are usually covered with bioorganic substance – conchialine. Between it and nacre surface of shells there is a porcelain layer composed with fine-fibrous crystals of calcite oriented perpendicular to the surface of shells. Evidently, this is the reason of high durability of shell and pearls composed with material, which is nor very hard.

Nacre shells. They are extracted usually together with pearls in its traditional regions (See pearls). Shells of freshwater pearl-oysters have been being extracted since antiquity, mainly for manufacturing of nacre buttons and as material for incrustations. In the early 20th cent., in Russia, their extraction existed not only on the northern rivers, where shells can be found till nowadays, but also in the southern regions, in the basins of the rivers Don, Dnepr and Dnestr. In 1930s, this extraction was organized in the Primorskiy Region only, in the basin of the Amur River. In the U.S.A., during the “pearl fever”, the extraction of shells in the basin of the Mississippi River was about 35,000 tons. As a result of such high-grading and pollution of rivers, colonies of pearl-oysters got degenerated; and nowadays, they are registered in the Red Book through all over the world. Some species of lake shells of spiral shape of the central volute, known under the trade name oil pearls, or Antilles pearls, are used for imitation of pearls.

In comparison with freshwater mollusks, shells of sea mollusks are more variable in size, shape and color. It is one of the natural wonders. The best in ornamental properties are Haliotis shells, from the genus of Gastropod. Bright colored outside, they possess a thick layer of multi-colored nacre inside. Because of their yellow-blue-green chatoyancy and bright iridescence, they are used in jewelry under the trade name abalone and others, and in China under the name fuh’yu. The most widespread sea pearl-oysters shells are mollusks from the genus of Pinctada. The size of their shells varies from 7 to 30 cm. in cross-section; color is uneven, usually more intensive at the edges. According the color, they classify black-lipped and golden-lipped Pinctada and others. They are found along the coast of Australia, Central America, islands of Oceania and Philippines. Green-lipped Pinctada is also called Manila shell, silver-lipped and golden-lipped ones – Sydney shells or Darvin shells. Pinctades from the Persian Gulf display reddish tone – there is Egyptian or Alexandria shell, and rose one is called Bombay shell, they were called after the trade-centers of nacre: Alexandria in the Mediterranean Sea and Mumbai (form. Bombay), on the coast of the Indian Ocean.

Spiral-twisted Nautilus shells are found in the Pacific and Indian Oceans. They were popular among jewelers in the 16-17th cent., because of the fashion of “naturalia”. These beautiful shells, up to 25 cm. in cross-section, are colored reddish-brown transversal stripes outside, and black near the mouth. Inside they are covered with a fine layer of nacre. The central volute with nacre substrate is used as an imitation of pearls under the trade name Nautilus pearls, blistered pearls, cock comb or cock de pearls. Inner partitions of these shells are used as material for encrustation in the Florentine mosaics. By the coast of South-East Asia, there is a plentitude of pearl-oyster Placuna, which is also called glass oyster, or Chinese glass. Its thin nacre shell is up to 16 cm. long; it is transparent in the first year of its life. It is used as spangles and for encrustations in jewelry.

Synonyms. Nautilus shell – Pearly shipbuilding. Haliotis shell – Sea opal | Paua | Sea ear shell.

Fossil nacre. Nacre, as well as pearls, has not long life-span, because of drying and destruction of conchialine. However, there are known facts when nacre was discovered in the fossil state with preservation of its typical iridescence in green and red tones. In Canada, near Letbridge, in the south of the Alberta Prov., in chalk sediments, they discovered Ammonite shells and Baculita shell with partly preserved nacre layers. But because of fragility of these shells, they can extract not more than 5% of ornamental material, which received the trade names ammolite, calcentite or korite. Similar material – fire ammonite – was found in Kazakhstan. In Russia its findings are known among well preserved fossil ammonites in the Yaroslavl’ and Ul’yanovsk Regions.

Synonyms. Fossil nacre – ammolite, a composed word from ammonite and “litos” – Gk. a stone | Korite, after a businessman Kormos, who send this material into trade | Calcentine, after the composition.

Legends. Astrologers believe that nacre strengthens abilities of a person in matrimonial relations. It is good for those, who were born under the sign of Aquarius, and bad for Gemini. Others shouldn’t wear it constantly.

Porcelain shells. Beside nacre shells, more hard porcelain shells without nacre covering are of interest. They are typical for large sea mollusks. Among them, there is Tridacna up to 1.5 m. in cross-section and 300 kg. in mass; Strombus, and also well known Pecten. Thick Strombus shells, which are called Giant’s ear shell, up to 30 cm. in cross-section and up to 5 kg. in weight of their shucks, are good materials for carving. For glyptic such property is useful as alternation of color from a layer to a layers, which gives a chance to make rose pattern on white background. Because of its large size, Strombus shell is called Giant shell, or King shell. Similar usage is described for large shells of mollusks Turbo shell and snails Cassis shell and some others.

As ornamental material, shells of some sea snails are of interest; they live on the northern coast of Australia and Indochina. More precisely, they use their oval or round parts of shells – operculum, 1-2.5 cm. in cross-section with spiral lines of growing on the outer surface. They are characterized with iridescent color from yellowish to white, reddish to dark brown and green. Because of this, operculum is used in adornments and in the Eastern markets it has the trade name Chinese cat’s-eye. There is nothing of the real effect of cat’s-eye, but their green concentric circles are rather beautiful. Shells of the freshwater mollusks Unio, because of their comparatively large size and flattened shape, are rough material for nacre. Development of the industry of cultured pearls made it necessary to grow shells artificially as inoculums. It was put into a production line at first in Japan, then in other countries of southern seas. On the Tuamotu Is., Melanesia, and no other islands of the Pacific Ocean shells are growing to the size of a soup-plate during three years.

Describing shells we can’t miss an exotic material, connected with them, – visson, or sea gold silk. It is the name for a tissue, which was made from byssus threads of some bivalve mollusks. These threads attach shells to substratum. In the composition this thread is close to such bioorganic material as conchialine. Color of byssus threads is fair golden to dark brown, and old ones are black. Depending on the size of mollusks, the length of these threads can be 3-10 cm., sometimes up to 20 cm.; the thickness is 10-70 mc. After the complicated processing they make very expensive tissue from these threads; it was evaluated on the weight of gold. It was popular in the Mediterranean states in the antique and medieval times. In the 18th cent., they made luxury produce from it, laces and richly decorated ladies-bags. Nowadays, it is produced in the only place in Italy for souvenirs.

Another exotic product of the life-process of Murex shell is its purple secretion, from which red-violet purple was made. Because of small proportion of the purple secretion in shells, it was extremely expensive. Purple was known in Ancient Egypt, because pharaoh’s mummies were swaddled in tissues colored Purple. It was widespread in Ancient Greece; that’s why on the Phoenician coin they depicted a Murex shell. Purple togas were available for reigning persons only. In antique times, purple pigment was used for painting of marble, purple was added into glass to produce purpurin.

Synonyms. Operculum, from Lat. brachial cover – Chinese cat’s-eye | Guadakanal cat’s-eye | New Guinea cat’s-eye | Pacific cat’s-eye | Shell cat’s-eye | Maonaperle, Germ. | Chinese stone.

Treatment. According archaeological findings in ancient tombs, different peoples have used nacre shells as the first adornments since the times of the Cro-Magnon man. A necklace from shells, which was found during the excavations in Iraq (5,000 B.C.), is one of the most ancient adornments at all. Brown-golden, glossy Caury shell was discovered in tombs of Germany and in Scythian barrows of the 8-3ss cent. B.C. In China, they were used as money even 1,500 years ago. In India, they were in exchange in the 4-6ss cent. In Ancient Egypt shells were evaluated so high that they were imitated from gold, gemstones and ivory. In some regions of East and Central Africa, shells served as money till recent time. Coins were made from shucks of big mollusks in the shape of discs, up to 10 cm. in diameter with a hole to string them on a cord.

Since antiquity, nacre has been used in glyptic, as well as for incrustation of weapon and jewelries. Soft and tender play of color in nacre suits to the luster of precious metals and gemstones. Material of shells was found an application for manufacturing of beads, bracelets, pectorals, carved work of art and so on. Among the most ancient products from nacre there is a signet “Dioscures” in the collection of the State Hermitage, SPb., it was made on Peloponess in the 8th cent. B.C. In the Armory Museum Kreml., Moscow, a nacre cup of a Kazan’ voevoda (governor) and a powder-flask from Nautilus shells made by Russian masters of the 17th cent. are exhibited. There is also a jug from Antwerp, which was made from three such shells mounted in silver. In the 16-17ss cent., nacre was especially in fashion. Works by European masters of that period are collected the best in the Grün. Gew., Dresden, Germany. There are many goblets from Nautilus shells and jugs incrusted with nacre, as well as decorative vessels in the shape of birds and animals. In the 17-19ss cent., when fans were in fashion, some of them were made from nacre. The beauty of nacre induced the Russian painter M.A. Vrubel’ (1856-1910) to create a pastel panel “Pearl”, where at the background of polychromatic Abalone shell two girls were depicted, symbolized pearls. A depiction of Pecten shell, or sea cock is a favorite motive in painting and architecture. In the end of the 17th – in the beginning of the 18th cent., the style of Rococo received its name after it. The term Rococo was based on the Fr. word “rocaille” – an ornament of shells. Shells are popular among modern jewelers, too. In the end of 1940s, the American master S. Shepps made a wonderful set – clips and a brooch from shells decorated with sapphires. Jewelers from Hog Kong made an elegant brooch of shell, about 5 cm. in diameter, decorated with pink topazes and brilliants, to one of gemstone and jewelry shows. In Russia, among modern carving on shells, we should mention works by the St Petersburg artist Petr Sal’zman (born 1952), who creates unique cameos with portraits of literature personages, artists and architectural sightseeing’s of St Petersburg.

Imitations. For imitation of nacre they use Peruvian bone palm tree fruits, and recently – plastic with the effect of nacre (See pearls).