Silver

 Silver usually occurs in massive form as muggets or grains, although it may also be found in wiry, dendritic (tree-like) aggregates. When newly mined or recently polished, it has a characteristic bright, silver-white colour and metallic lustre. However, on exposure to oxygen in the air a black layer of silver oxide readily forms, tarnishing the surface. Because of this, and the fact that it is too soft to be used in most jewellery in its pure form, silver is often alloyed with other metals, or given a covering layer of gold. Electrum, an alloy of gold and silver in use since the time of the Ancient Greeks. contains 20-25 per cent silver. Sterling silver contains 92% per cent or more pure silver (and usually some copper), and Britannia silver has a silver content of 95 per cent or more. Both alloys are used as standards to define silver content

.  OCCURRENCE -  Most silver is a by- product of lead mining, and is often associated with copper. The main silver mining areas of the world are South America, the USA, Australia, and the former USSR. The greatest single producer of silver is probably Mexico, where silver has been mined from about AD1500 to the present day. The finest native silver, which occurs naturally in the shape of twisted wire, is from Kongsberg, Norway. 

-Silver wine cup-

This part gilt silver cup was fashioned in 1493,when the silver was valued as height as gold.

Gold

 Gold

The color of gold depends upon the amount and type of impurities it contains. Native gold is typically golden yellow, but in order to vary its color and increase its hardness for use in jewellery, gold may be alloyed to other metals. Silver, platinum, nickel, or zinc may be added to give a pale or white gold. Copper is added for red or pink gold; iron for a tinge of blue. Gold purity is defined by the proportion of pure gold metal present, and this is expressed as its carat (ct) value. The purity of gold used in jewellery varies from 9 carat (37% per cent or more pure gold), through 14, 18, and 22 carat, to 24 carat, which is pure gold. In many countries, gold is "hallmarked" to indicate its degree of purity.

 • OCCURRENCE Gold is found in igneous rocks and in associated quartz veins, often in small quantities invisible to the naked eye. It is also concentrated in secondary "placer" deposits - as nuggets or grains in river sands and gravels. Gold may still be extracted from placer deposits by the traditional panning method, but modern commercial mining involves large earth-moving machinery and concentrated acids for processing the ore. The main gold-bearing rocks occur in Africa, California and Alaska (USA), Canada, the former USSR, South America, and Australia.

 • REMARK Gold has been used for coins, decoration, and jewellery for thousands of years. It is attractive, easily worked, and wears well.

 

gold grains

                                  

IMITATION AND ENHANCEMENT

                           

  IMITATION gems have the appearance Lot their natural counterparts, but their physical properties are different. They are made to deceive. Man-made materials, such as glass and synthetic spinel, have been used to imitate many different also be modified to resemble more valuable gems. It is possible to enhance authentic gemstones by hiding cracks and flaws, or by heat-treating or irradiating to improve their color. 

GLASS IMITATIONS 

Glass has been used for centuries to imitate gemstones. It can be made either transparent or opaque, in almost any color, and, like many gems, has a vitreous lustre. At first sight, therefore, it may easily be mistaken for the real thing. However, it can usually be detected by its warmer feel, and by the evidence of wear and tear that results from its greater softness. Chipped facets and internal swirls and bubbles are common. In addition, unlike most of the gems it imitates, glass is singly refractive.

Opal Imitations

Gemmologists call the flashes of color in opal its "play of color", or iridescence. It is caused by the interference of light from the minute spheres of silica gel that make up the gem. This structure is imitated to great effect in opals made by the French manufacturer, Gilson, although the difference can be seen in the mosaic-like margins of the patches of color. There are various other opal imitations, including stones made of polystyrene latex, or of different pieces assembled as one. In an opal “doublet" (two pieces) the top is natural precious opal, but the base is common (potch) opal, glass, or chalcedony. A "triplet" (three pieces) has an additional protective dome of rock crystal.

SLOCUM STONES 

The American John Slocum developed imitation opals with a convincing play of color, but they lack the silky, flat color patches of genuine opal, and the structure looks crumpled when magnified.

GARNET-TOPPED DOUBLET

 One of the most common "composite" stones (stones made of more than one piece) is the garnet-topped doublet, or GTD. A thin section of natural garnet is cemented to a colored glass base, which gives the GTD its apparent color. The deception is most easily seen at the junction of the two layers, which may be obvious. 

DIAMOND IMITATIONS

 Many natural materials have been used to imitate diamond, but zircon is the most convincing. Synthetic imitations are popular, but each has its faults (right). Imitations can usually be detected by testing the heat conductivity of the stone.

HEAT TREATMENT 

Heating may enhance or change the color or clarity of some gems. Techniques range from throwing gems in a fire to "cook", to use of sophisticated equipment. The outcome is certain for some gems (like aquamarine, changing from green to blue), but less so for others.

STAINING 

Stains, dyes, or chemicals can alter the appearance of a gem, coating just the surface, or changing the whole specimen. For staining to be effective, a stone must be porous or contain cracks and flaws through which the color can enter. Porous white how lite, for ex- ample, can be stained to imitate turquoise.

OILING

 Oils may enhance a gem's color and disguise fissures and blemishes. It is common to oil emeralds in order to fill their natural cracks and flaws.

Synthetic Gemstone

                                                          SYNTHETIC GEMSTONES 

SYNTHETIC GEMSTONES are made in laboratories or factories, not in rocks. They have virtually the same chemical composition and crystal structure as natural gemstones, so their optical and physical properties are very similar. However, they can usually be identified by the differences in their inclusions. Many gems have been synthesized in the laboratory, but only a few are produced commercially-generally for industrial and scientific purposes.

MAKING A SYNTHETIC

 Man has tried to replicate gemstones for thousands of years, but it was not until the late 1800s that any substantial success was achieved. In 1877 French chemist Edmond Frémy grew the first gem-quality crystals of reasonable size (see bottom right), and then around 1900 August Verneuil devised his technique to manufacture ruby. With a few modifications, the Verneuil "flame- fusion" method is still in use today. The powdered ingredients are dropped into a furnace and melt as they fall through a flame hotter than 2,000°C (3,630°F), fusing into liquid drops. These drip on to a pedestal and crystallize. As the pedestal is withdrawn, a long, cylindrical crystal, which is known as a boule, forms.

FLU MELT TENIQUE 

Pionred by the French chemise Edmond Frémy, the flux-melt technique is still used to make emeralds. The powdered ingredients are melted and fused in a solvent (flux) in a crucible. The material must be kept at a very high temperature for months, before being left to cool very slowly.

FLAME-FUSION CORUNDUM

Synthetic corundum manufactured by flame-fusion grows as a single mass called a "boule". It has the same inner structure as a natural crystal and can be cut to shape.

SHAPES AND COLORS 

Because of the way they are made, synthetic gems may show subtle differences in shape and colour that help to distinguish them from their natural counterparts. For instance, corundum produced by flame-fusion has curved growth lines, rather than straight ones, because the ingredients have not mixed together fully. Some synthetic gems may also suffer from uneven colour distribution. Flame-fusion spinel is manufactured to imitate gems such as ruby, sapphire, aquamarine, blue zircon, tourmaline, peridot, and chrysoberyl.

DISTINCTIVE INCLUSIONS 

Synthetic gems have different inclusions from natural gems, so often the best way to tell them apart is to examine them with a loupe (below) or a micro- scope. Synthetic inclusions may be typical of a process, or of a synthetic gem species. For instance, in Verneuil rubies, gas bubbles have well-defined outlines; in flux-melt emeralds (right), characteristic "veil" and "feather" patterns form. 

GILSON GEMS

 Lapis lazuli, turquoise, and coral produced by the French manufacturer, Gilson, are similar to their natural counterparts, but are not true synthetics because their optical and physical properties differ from the natural gems. Gilson lapis lazuli, for example, is more porous and has a lower specific gravity.

GILSON EMERALD INCLUSIONS 

Synthetic emeralds from the French manu- facturer, Gilson, have characteristic veil-like inclusions. The gems are made from poor- quality material by a flux-melt method.

HISTORY AND FOLKLORE

 

             HISTORY AND FOLKLORE

THERE ARE NUMEROUS myths and legends associated with gems. Some tell of cursed stones; others of stones with special powers of: healing, or that protect or give good luck to the wearer. Some of the largest known diamonds have legends associated with them that have been told and re-told over centuries, and many now lost are surrounded by tales of intrigue and murder. Some mines are thought to be cursed - probably a rumour spread by the mine-owners to keep unwanted prospectors away. In Burma, for instance, where all gemstones belonged to the monarch, the belief that anyone who took a stone from a mine would be cursed may have been deliberately cultivated to curb losses of a valuable national asset.

                                     

crystal gazing

Since Greek and Roman times, balls of polished rock crystal have been used to see into the future. The difficulty of finding a flawless piece large enough to be polished adds to the mystique. The mystic gazes at the ball, lets the eyes go out of focus, and then interprets the misty.

 DEATH MASK This Aztec funeral mask adorned with turquoise may have speeded entry to the next world.

 PERUVIAN GOD

 

 This 12th-century ceremonial knife from Peru is made from gold adorned with turquoise. The handle has been formed into the image of a divinity.

THUMB GUARD 

This 17th-century ring. mounted with rubies and emeralds, was protect archers' thumbs when releasing arrows.

BIRTHSTONES 

 Certain gems have traditionally been associated with different months of the year, and are thought lucky or important for people born under their "influence". This probably stems from the ancient belief that gems came from the heavens. Many eultures associate gems with the signs of the zodiac, and others with the months of the year, but the selection varies from country to country, perhaps influenced by availability of gems, local traditions, or fashions. The custom of wearing birthstone jewellery started in 18th-century Poland, and has since spread throughout the world. The most popular selection today is shown right.

CRYSTAL HEALING

 a very long history, as the rituals of medicine men in ancient tribes attest. Crystal healers today believe that each gem has the power to influence the health and well-being of a specific part of the body. The light| reflected off stones placed on vital nerve points is thought to be absorbed by the body, supplying it with healing energy.

ROCK CRYSTAL

 Prized for their beauty and clarity, rock crystals are often chosen for use in crystal healing. 

 

CRYSTAL PENDANT

 Gems worn close to the skin are believed to heal or protect.

GEMS THROUGH THE AGES

GEMS THROUGH THE AGES

PEOPLE EVERYWHERE, throughout history, have followed a natural instinct to collect things of beauty and value, and have used whatever gems they found locally - from shells to sapphires to adorn themselves. Today, the whole range of the world's gems is available to those who can afford them There are more gem-producing areas than ever before, new stones are on the market, and jewellery designs continue to evolve. But the inherent attraction of gems their beauty, durability, and rarity - remains the same.


First Uses

Gem materials were probably first used as much for their durability as their beauty. But beauty was not ignored, even then. For example, the Stone Age obsidian axe below has been wrought to be attractive as well as practical, and ancient civilizations did fashion gems purely for adornment. Although most were primitive in design, some were highly intricate, with painted surfaces. Down the ages, gems have also been offered as prestigious gifts, and their portability and intrinsic value gave them a natural use as currency.

EARLY COLLECTORS 

The earliest collectors found gems with no more equipment than a stick or shovel, a basket, and a sharp eye. Similar Stone Age tools found in the Mogok area of Burma show that rubies have been mined there for thousands of years - and the same methods of panning the stream with wicker baskets are used today. Evidence of more organized early mining - for example, abandoned mines and waste dumps is found in the Urals of Russia, on the shores of the Mediterranean, in Cornwall, England, and in many other places worldwide.

ANCIENT JEWELLERY 

Very little jewellery made before the 18th century services. The best examples are probably those of Ancient Egypt, much of it gold set with gems such as turquoise, lapis lazuli, and carnelian. It shows the great skill of the Egyptian goldsmiths: the gold refined, annealed, and soldered; the probably using silica sand, a technique also known to the Ancient Chinese. The Romans fashioned - went on to develop the polished stone rather than the setting. The art of the goldsmith and lapidary survived in the Dark Ages, though in medieval times gothic style was functional - mainly buckles, clasps, and rings.

UP TO THE PRESENT With the discovery of the Americas in the 15th century, European trade in gemstones expanded, and 16th- ahd 17th-century jewellers could use gems from all over the world. With the rise of an affluent merchant class, jewellery became more widely owned, · and diamonds first became fashionable. In the 20th century, an increase in demand for affordable gems, and the scarcity of the most valuable, will doubtless continue the trend to use more varied gem species in jewellery.

GEM-ENCRUSTED MODERN BROOCH 

Jewellery has passed through many styles, from baroque in the 16th century and floral themes in the 17 th, to art deco and beyond in the 20th.

POLISHING CARVING AND ENGRAVING

PRECIOUS METALS AND GEMS usually I massive, microcrystalline stones and organics-can be worked by polishing, carving, or engraving. Polishing is the oldest form of fashioning. Carving produces three-dimensional objects by cutting them from a larger mass of material. Engraved images are made by scratching out lines or holes, or by cutting away to leave a raised image. Carving and engraving require tools harder than the material being worked.




Polishing

The shine given to the surface of a stone - either by rubbing it with grit or powder, or against another stone - is its polish. Dark- colored gemstones and those that are translucent or opaque, for instance opal and turquoise, are often polished rather than faceted, as are organic gems. They may be polished as beads or as flat pieces to be used in inlay work, or cut en cabochon with a smooth, rounded surface and usually a highly polished domed top and flat base.

Carving

Carving usually refers to the cutting of decorative objects from a larger mass. Stones as hard as 7 on the Mohs' scale were carved in Ancient Egypt, Babylonia, and China. Impure corundum (emery) was used for carving and engraving in India; nowadays a hand-held chisel or turning machine is used. Popular stones for carving include serpentine, Blue John, malachite, azurite, rhodonite, and rhodochrosite

 CHINESE CARVING Carving of gemstones in China dates back to the Neolithic period. The most prized material was imported nephrite jade, and decoratice objects like this model pagoda are still made.

Engraving

 Engraving usually refers to the decoration of the surface of a gemstone by the excavation (scratching out) of lines, holes, or trenches with a sharp instrument, known as a graver or turin. Of all engraved objects, cameos and intaglios are perhaps the most popular. A cameo is a design (often a human profile) in flat relief, around which the background has been cut away. In an intaglio it is the subject, not the background, that is cut away, creating a negative image that may be used as a seal in clay or wax. Intaglios were particuiarly popular with the Ancient Greeks and Romans, and are still prized by collectors.

GOLD ENGRAVING

The surface of gold and other precious metals used in jewellery may be decorated with intricate patterns, using a hand-held chisel called a graver. Engraved gemstones gained prominence in Europe in the Renaissance period. During the Elizabethan period in Britain cameo portraits were often given as gifts, particulariy among the nobility. All through the ages, layered stones have been used for cameos or intaglios, with onyx and sardonyx particulariy popular. Other gems suitable for engraving include rock crystal, amethyst, citrine, beryl, peridot, garnet, lapis lazuli, and hematite, as well as organic materials such as ivory and jet.

MODERN DESIGNS 

This citrine prism, with its clean, architectural lines and exquisite engraving, demonstrates the flair and craftmanship of modern designers. Its maker, Bernd Munsteiner, uses conventional cuts to create classic modern jewels akin to pieces of sculpture. Bernd Munsteiner is one of many artists working in Idar-Oberstein in Germany. Together with Hong Kong, Idar- Oberstein is considered to be one of the most important centres for gemstones today.