Sunday, 30 June 2013

Introduction to Andalusite (Al2sio5)

AndalusiteANDALUSITE (Al2sio5)

Silicate of aluminium.

Crystal system

Orthorhombic

Appearance

It occurs as squat prismatic crystals with poor luster, or aggregates of elongated crystals arranged in "sheaves.' The color varies from light yellowish brown to green-brown, light brownish pink, grayish green or definite green with pronounced pleochroism making it hard to identify the main color. Some crystals have dense dancer inclusions in the center which in cross section, exhibit a cruciform pattern. These stones are known as chiastolite

Physical properties

It has a hardness of 7-7.5 and a density of about 3.13-3.20 9icrn3. The refractive indices are about no 1.632, fly 1.643. It has distinct prismatic cleavage.

Genesis

Andalusite groupAndalusite is a characteristic mineral of areas of contact metamorphism between granites and argillaceous rocks.

Occurrence

It is not a rare mineral. Fine crystals are found in Spain (Andalusia), whence the name. Other sources are Brazil, the United States (California, Maine, Massachusetts), Australia, Sri Lanka, Burma, Austria, and occasionally Italy.

Andalusite

This gem is named after Andalusia, where fine maul occurs.

Appearance

It is a dull yellowish green with faint pinta brown reflections, or it may be yellowish brown-greens even violet brown-green or, rarely, a definite green lie difficulty in describing the color of this gem is because its strong pleochroism, which is heightened by the facets/ Cut stones, to the point of being almost iridescent; bulls colors are never very lively. It has unexceptional, vitro luster. It is regularly given a faceted, mixed oval square or rectangular step cuts are also used, but there are less suited to its modest luster and cannot justice its exceptional pleochroism.

Distinctive features

Its peculiar color range, unusual pleochroism, and modest luster make it quite easy to distinguish from all other gems. Some say it can be conk with alexandrite, but the pleochroism of andalusite is very different from the true color change of the other. It she that when alexandrite is a yellowish green with a fantods change, it may look vaguely similar; but checking thirsty would immediately distinguish between the two stones. The chiastolite variety with its black cross-shape is unmistakable.

Occurrence

The gem variety comes mainly from Brad (state of Minas Gerais), but also Sri Lanka, Burma, the Soviet Union, the United States and, of course. Andalusia

Value

Chiastolite
Quite low, probably because of the rather drab color and poor luster, It is anything but a rare stone, yet it is not plentiful on the market and is mainly in demand with collectors. The most valuable stones are those with the most pronounced greenish to reddish pleochrotsm chiastolite variety has a longer history of gem use thanes transparent type, having been worn as an amulet, but Is value is equally low and similar to that of opaque ornamental materials.

Simulants and synthetics

Not being valuable or wet known, it is not imitated. Nor has it been produced synthetically, at any rate on a commercial scale.

Writer – Curzio Cipriani and Alessandro Borelli

Friday, 21 June 2013

Wonderful Gold Smith

HIP FLASK
These include gold liligree boxes for bezoars and jewellery in gold, rock crystal, and gemstones."The number of jewellers and dealers were many, catering to a never-slackening demand. According to the Madras Census Report, 1881 in Madras, an exceedingly poor country, there is one male goldsmith to every 408 of the total population; in England, a very rich country, there is only one goldsmith to every 1,200 inhabitants."

Or the most part, jewellers executed pieces only when they received specific commissions. They were well versed in the vast terminology of ornaments and designs. Clients provided the craftsman with gold and gems; ornaments had only to be mentioned by name to be reproduced faithfully. Large items were not stocked for ready purchase. But the late 19th century witnessed a change.

Perhaps due to declining royal patronage and growing western influence, more and more jewellery houses were set up in the major cities. None maintained records, and few can recall the names of their great designers and setters. They functioned as workshops, executing orders from printed catalogues or fulfilling commissions for individual clients. But the services of the home jeweller continued till recent times. The many jewellers catalogues that were printed at about this time featuring a large variety of designs, with details of weight and price, are valuable documents of design (429, 430). An illustrated catalogue, namuna-i-zewara t,' published in Bombay in 1898, contains almost S00 designs of ornaments popular in different parts of the country. Customers could select and order items depending on their budget. By the middle of the 20th century, 'mail-order' jewellery was a flourishing business.

Legacy of Craftsmanship

Closed set, but simulating kundala velai, with diamonds, rubies and emeralds, the gently curved form of the pendants adds a lifelike quality to the peacock and floral motifs.An idea of the precise nature of early craftsmanship methods is based on a few surviving examples and evidence manifest in workshops found in the course of excavation of ancient sites. Each region developed its own specialization and evolved new methods by absorbing and combining from different sources. The earliest jewellers were undoubtedly the bead-makers, whose skills date to the pre-Harappan period. Beads were made from semi-precious stones, steatite, faience, terracotta and other materials, and even exported to distant destinations. Steatite beads, glazed and polished, carved with trefoil motifs, were abundant in the Harappan sites. Gold imported from south India into the Indus cities was beaten into thin sheets and worked in a variety of techniques. Though John Marshall believed that the practice of filling hollow pieces with a Inc core was of Greek origin, there is evidence to suggest that inc occurs even in the jewellery of the Indus valley. Few Indian gem-set jewels were made without a Inc centre. (Lac, a natural resin secreted by an insect, is produced exclusively in India.)

By the 1st century A.D., the entire jewellery manufacturing industry was in an advanced stage of excellence. Craftsmen were adept at extricating impurities and melting gold, beating it into sheets, forming it into shapes by soldering component pieces, casting from moulds, and decorating the finished product by engraving, repousse, granulation, filigree and inlay. The influx of Greek craftsmen to India in the post-Alexander era introduced new techniques. 

Stamped gold units with applied filigree and faceted granules are linked together. The term for the ornament derives from the cups (kuzhi) that shine (minna).These influences combined with the jewellers' indigenous skills to produce some of the most spectacular surviving items of ancient Indian craftsmanship. To the local skill of incrustation, Greek craftsmen introduced granulation and filigree, whose origins can be traced to the Sumerians. Dating to the 1st century A.D., the Taxila gold hoard provides comprehensive evidence that the craftsman's knowledge of goldsmithing and metallurgy was in an advanced state.

The Taxila jewellery employed moulds and dies to form the structure of the jewel. Stone moulds of two types were used. Solid pieces were cast by pouring molten metal into hollow moulds and sheet gold was worked by taking impressions off one-piece moulds (434). Copper and bronze dies were employed for the heavier pieces. Once complete, entire surfaces were covered with minute granules of gold in what is known as "field grain work";" or filigree, whereby fine wires, plain, twisted or plaited, were soldered on to the surface of the finished jewel in decorative patterns. In addition to these techniques, two types of incrustation were used to decorate and embellish jewellery surfaces. Precious and semi-precious stones were enclosed in cloisons formed by thin metal strips, the edges turned in to hold the stone securely in place, the compartments positioned close to each other covering the entire surface, or alternatively randomly scattered in cloisons.

The legacy of ancient craftsmanship is exemplified in this finely-worked sheet gold bracelet in the form of fishes.Designs and manufacturing techniques travelled the trade routes from one region to the other. With a vast and ancient repertoire at his fingertips, the jeweller continued to produce beautiful pieces of jewellery. Since fashions were fairly constant over several centuries, with only subtle variations, the Indian craftsman grew imaginative. While flora and fauna remained the core of his inspiration, he ceased to be merely imitative. Fantastic forms emerged, decorative details grew even more complex, and ornaments became veritable icons. He sometimes borrowed from other disciplines and even combined more than one technique to achieve the best possible result. Even the cire perdue or lost wax process was used in some parts of India, such as Rajasthan, to fashion anklets and bracelets.

Writer – Usha R Bala Krishnan & Meera Sushil Kumar

Thursday, 20 June 2013

Grossular Garnet (Ca3Al2Si3O12)

Andradite garnet
Silicate of calcium and aluminium, belonging to the garnet group. The name grossular is due to the fact that some of these crystals resemble gooseberries, the Latin name for which is grossularia.

Crystal system

Cubic

Appearance

Grossular also has the typical crystal form of garnets, occurring in isolated crystals which are often complete, in the shape of a rhombic dodecahedron, sometimes combined with a trapezohedron. They vary in transparent to serniopaque. The typical color is light (gooseberry) yellowish green; but they can be a strong to bluish green, honey yellow or pinkish yellow, or even perfectly colorless. When transparent, the crystals have god luster. Like other garnets, they have no cleavage. The greenish to yellowish varieties are used as gems.

Physical properties

HessoniteThe hardness is 6.5-7.5 or a little more. The density is somewhat variable: from 3.58 to 3.69 g/cm3. The refractive index is about 1.74. Occurrence Grossular is not a rare mineral. The type; used as gems mainly come from the gem gravels of Sr. Lanka (honey yellow variety); and the United States. Canada, Mexico, Madagascar, Kenya, and Tanzania (green variety).

Hessonite 

The yellow-brown variety of grossular is called hessonite (or essonite). Its name comes from the Greek meaning "inferior," gems of this color being regarded the least valuable.

Appearance

Tsavolite
It is a honey-yellow or yellow-brown sometimes tending to a pinkish orange similar to tiding spessartine. It has good luster and seemingly good parency, but when viewed with a lens or other magnification, the interior always looks "treacly," dulating, contorted areas of lesser transparency, highly concentrated sugar solution with frequent, transparent crystalline inclusions. The gems are norm given a mixed, oval, or round cut.

Distinctive features
Seen through a lens, the treacly appearances combined with the color are sure memo identification. Nothing comparable is found in other of similar color, such as citrine quartz, topaz, and sapphire. Its luster, in any case, is superior to that of quartz. It is distinguished from zircon of a similar cold its lack of obvious birefringence. Occurrence It mainly comes from Sri Lanka, but it found in the United States, Canada, and Brazil.

Value

The value of hessonite is rather low, like that mandine and pyrope, despite its very attractive ance.

Simulants and synthetics

It has neither been nor produced synthetically.

Green Grossular

The green variety of grossular garnet, discovered a le decades ago and found mainly in Kenya, near the Tsavo National Park, is also known as Tsavorite (or Tsavolde)

Appearance

It is a light, verdant, or dark green, shit to the color of the better green tourmalines and sometinn it is said, even comparable to African emeraid. It hasps luster. These gems, which are usually given a round o. pear-shaped mixed cut, or occasionally a brilliant cut generally small, rarely exceeding one carat and new more than a few carats.

Distinctive features

Green grossular
Being singly refractive, green grossular is distinguished from green tourmaline, by the letters strong birefringence and pleochroism, and from melt green zircons, which are obviously birefringent, whets measurement of the physical properties is necessary  distinguish it from green sapphire when the latter doesrd display clear pleochroism. It is very similar in all respectst a recent artificial product of comparable structure, namely green YAG (Yttrium Aluminium Garnet), from which it distinguished by its physical properties.

Occurrence

It is very rare; being found mainly in Kenya and Tanzania, but also in Pakistan.

Value

If a good color (a lively, strong green), it can to the top price bracket for secondary gems; this is especially true of the very rare examples weighing a few carals. Little known by the general public, it is in demand by collector, and connoisseurs.

Simulants and synthetics

Green grossular has only been known for a few decades. Green YAG fan (an artificial product with the structure of garnet, but not containing'''. silicon) closely resembles it and can be a good imitation. It is not produced synthetically.

Writer – Curzio Cipriani and Alessandro Borelli

Wednesday, 19 June 2013

Introduction to New Goldsmith

Kundan-set white sapphires with embossed sheet gold work on the reverse. Individual units are strung together to render flexibility to the ornament.The technical expertise available and the manner in which such details were inscribed in stone for posterity are truly remarkable.

In the 16th century, Duarte Barbosa refers to the Malabar region as the centre of the gem trade. The best craftsmen, skilled in handling gold and gems, gathered here to cater to the trade. Rubies were imported from Pegu (Burma), where "they know how to clean but not how to polish them, and they therefore convey them to other countries, especially to Paleacate, Narsinga, Calicut and the whole of Malabar, where there are excellent craftsmen who cut and mount them." They had devised their own methods for distinguishing between rubies from different mines. The ones from Pegu were the finest, called numpuclo, the ones from Ceilao (Ceylon) were called mancca and spinels were referred to as carapuch. To test the quality of the rubies, "the Indians put them on the tongue; those which are finest and hardest are held to be the best. To test their transparency they fix them with wax on a very sharp point and looking towards the sun they can find any blemish however slight.

Jewel merchants were organized into guilds. In the city of Vijayanagar in the 12th century, for example, tradesmen of the various guilds were located in the market. They enjoyed such complete freedom in their trade, that all manner of precious stones were brought and sold openly in the markets. "The Ainnurruvar, often styled the Five Hundred Svamis of Ayyavolepura (Aihole), were the most celebrated of the medieval south Indian merchant guilds... Among the countries they visited were Chera, Chola, Pandya, Maleya, Magadha, Kausala, Saurashtra, Dhanushtra, Kurumba, Kambhoja, Gaulla, Lata, Barvvara, Parasa ( Persia), and Nepala. They traversed land-routes and water-routes, penetrating all the countries of the six continents. They traded in elephants, bloodstock, sapphires, moonstones, pearls, rubies, diamonds, lapiz lazuli, onyx, topaz, carbuncles, emeralds and other precious articles; 'they paid the Sunka regularly and filled the royal treasury with gold and jewels."

Kundan-set foiled diamonds on the front, the reverse in embossed sheet gold.The crafting of jewellery was a product of teamwork, involving a variety of specialist skills. The designer (naqash, chitera); the goldsmith (sonar); the engraver (gharailvala, khodnaker); the enameller (minakar); the gem-setter (kundansaz); and the stringer (patua). All these skills were nurtured within the caste. This combination of skills necessitated a degree of aesthetic convent ionalism. Working with familiar stereotypes, each specialist was able to execute his task and pass the unit on for the next process in a well-orchestrated sequence of teamwork. Individualism in this scenario would have only bred aesthetic chaos. The whole emphasis on the solo act was, in fact, foreign to Indian aesthetics, particularly in the plastic and decorative arts.

Traditionally, since craftsmen worked within a guild system, each specialist contributed his particular skills towards creating a thing of beauty. That is what mattered and personal identity was effaced to the objective, though not personal commitment. If anything, the latter intensified in inverse proportion to the former in the quasi-religious atmosphere of the Indian crafts, where the craftsmen worshiped their tools, as many of them still do, before the day's work. Being a family-based profession, areas of specialization were nurtured within the family. When they moved from one atelier to the other, or migrated to other parts of the country, the entire family moved, ensuring minimum disruption in the workforce.

As members of the lowest strata of society, craftsmen and people directly or indirectly connected with handling precious gems remained anonymous; but there were rare exceptions. Jewellers were permanently employed by temple administrations during the Chola period, to execute commissions of jewels for the temple deities. The Mughal emperors established workshops or karkhanas within the precincts of the court, each supervised by a master craftsman of repute. In Jahangir's court, mention is made of goldsmiths and in aycrs. The names of Puran, Kalyan and Hunarmand are credited with manufacturing ornaments, jewellery and thrones of exceptional quality. The design and manufacture of the Peacock Throne is attributed to one Austin Bordeaux who was given the title of Hunarmand or skilftml, in recognition of his skills. Hortensio Borgio was credited with the first cleaving of the Koh-i-Nur diamond; "Bebadal Khan, the Darogha of Goldsmiths' workshop in Shah Jahan's time was a celebrated lapidary, a great calligraphist and also an author of some respectable verse."17 Ram Singh Malam, who worked for Rao Lakhpatji, the ruler of Kutch (1741-60), was a multi-dimensional craftsman. He lived in Europe for 18 years and on his return extended his skill in areas ranging from architecture to glass-making, jewellery and enamelling. Many members of the goldsmith caste were also painters of repute. 

Moonstones, tourmalines, sapphires and aventurines are inlaid with diamonds, rubies and emeralds, and strung with emerald and sapphire beads on two strands of small pearls.Jewellery designers were versatile, crossing boundaries and extending their proficiency to other areas. As early as in the 8th century,an inscription in the Virnpaksha temple at Pattadakal near Bijapur "records that the royal architect who planned that edifice, used to design the palace jewellery"; earlier, an inscription on the hand of a Yaksha figure of the Satavahana period dating to the early 1st century B.C. records that the sculptor of the image was the goldsmith Kanhadasa.

In the 16th century, when Portugal controlled the gem trade in India, Goa was home to goldsmiths and jewellers from different parts of the country and world. They gathered on the km Direita to work with the best stones that came out of the mines of India and to meet the demand for exceptional quality jewels in the country and abroad. Indian goldsmiths travelled to Lisbon, and "Raul Li Xatim, the son of a Goan goldsmith, actually stayed on in Lisbon between 1518 and I 520,21 perhaps to undergo training and gain knowledge of the kind of items sought after in Portugal. Business flourished, fuelled by high demand within the country and overseas. Together with foreign dealers, goldsmiths from Portugal also settled in the city, executing commissions for the governors and viceroys. Between 1622 and 1628, Domingo Nunes, a Portuguese jeweller living in Goa, "carried out several commissions for Dom Francisco da Gama, the viceroy.

Writer – Usha R Bala Krishnan & Meera Sushil Kumar

Tuesday, 18 June 2013

The Uses of Gold

Gold in Industry

Gold Teeth
International statistics indicate that three industries absorb most of that part of the world's gold production which is neither hoarded nor used for the manufacture of currency. In 1974, the jewelry industry used about 214.1 tons of pure gold, the electronics industry used 98.9 tons, and dentistry used 65.6 tons. The 74.2 tons remaining for industrial use was largely employed in surface-coating various products.

Thus, in 1974, a total of 452.8 tons sixty one percent of total gold production for that year was used in manufacturing. Almost without exception, industry and commerce used one form of gold alloy or another. These were produced in a wide range of combinations. In every major industrial country, highly specialized enterprises have sprung up to meet the need for gold alloys. In some cases, such plants are state-owned but usually acquire their supplies of "raw" gold and old gold through the agency of private firms. Where necessary, the old gold is separated metallurgically into its constituent elements for recycling. Enterprises processing precious metals are, incidentally, among the few businesses that have always practiced almost total recycling procedures. They tend to make almost complete use of waste and scrap. This is not for ecological reasons but because of the value of the precious metals involved.

Facial of Gold for beauty
Metallurgy has now reached so advanced a state of development that alloys can virtually be "made to measure" for almost every requirement. They can be produced according to an enormous variety of specifications: color, chemical and physical characteristics, malleability and temperability. When necessary, combinations of qualities can be achieved.

Gold content is of special significance in the manufacture of jewelry. It is measured in carats. Pure gold is said to be twenty-four carats fine. A gold alloy only seventy-five percent pure is said to be eighteen carat gold. Measurement is also made in parts of pure gold per thousand. If ten percent of a gold alloy is other metals, it is said to be 900 gold. Fourteen carat gold is 585 pure, and so on.

The various kinds of gold solder used in the jewelry and dental industries make very specific demands on the metallurgist. The solder has to be of the same color and gold content as the surrounding substances, particularly in jewelry. But in order to guarantee an effective connection, the solder must have a lower melting point than the pieces it connects. Solder with a particular gold content is sometimes known as control solder. It is defined according to a regulated color scale and a scale of melting points and is divided by name and quality into various categories. It makes multiple soldering possible without damaging existing joints.

Fine, Finer, Finest

Gold use in space
In the past, goldsmiths working by hand produced their own alloys for sheet, wire and casting purposes. An intricate series of closely guarded secrets and techniques were involved. But the quality of the finished product and its gold content had to be taken on trust by the customer who had no choice but to rely on the craftsman whose work he commissioned a Nowadays standards of quality are so high that it is necessary to have modern smelting and heating equipment, a well-furnished laboratory and a highly qualified all team of specialists to produce the finished product.

The raw material of all gold alloys should be the purest possible gold. Financial institutions, which are C very much concerned with material value, find so-called "Good Delivery" gold with its fineness of 995. A perfectly acceptable. This gold is in fact further refined T before it is processed metallurgically. Methods include crefinement by electrolysis. This is based on the principle that metal ions, under the influence of an electric current in a conducting solution, change their polarity from plus to minus.

"Good Delivery" gold is poured around thick anode plates suspended in a gold chloride bath. The cathodes consist of refined sheets of pure gold. With the correct electrolytic stirring and current, the gold moves to the cathode from the anode and separates there into dark yellow crystals. Silver, combined with insoluble silver chloride, sinks to the bottom of the bath while platinum metals iridium, osmium, palladium, rhodium and ruthenium remain suspended in the solution and may be extracted chemically. The gold which forms around the cathode is more than 999.9 percent pure.

Nail polish of Gold
In the past, the purity of gold could only be determined approximately with the use of a touchstone. Later, the Archimedean principle which Archimedes allegedly discovered in 250 BC while bathing was also used. Archimedes had been commissioned to determine the gold content of a crown without damaging it. While in the bathtub, he established that the amount of water displaced by a body corresponds to the volume of that body, and perceived that the specific gravity of a body could be deduced from its weight and volume.

These days the gold content of a test piece is usually analyzed. Another method employs calorimetric measurement the light absorption of a test specimen is compared with the standard reaction of known gold alloys.

Gold Alloys -The Supreme Metallurgical Skill

Gold Coin
Alloys can also be described as solid state mixtures. They are small crystalline agglomerates, not chemical compounds. That is why they have no clearly defined melting point at which the substance liquefies. Alloys melt in temperature band liquid islands of crystals with a lower melting point form first to be followed by those with higher melting points. The crystalline structure alters during the heating process before the melting point is reached. Quenching makes for stabilization of changes in many alloys in a process known as tempering.

Color, Hardness, Chemical Stability

Alloys used in jewelry making must meet specific color and gold content requirements. Colors tend to range from red to yellowish-green. They generally consist of gold-copper-silver alloys in which the copper and silver components vary in proportion. Other characteristics are also varied. The amount of silver in the alloy does not affect its hardness, but copper does. The hardest alloys are twelve and fourteen carat in which copper and silver are dominant.

Brick of Gold
White gold alloys tend to be very popular. It is possible to produce soft white gold, with palladium content, or hard gold-nickel alloys. Platinum gold alloys are much in demand in dental technology because they are capable of withstanding the chemically aggressive environment of dental cavities remarkably well. They also have the hardness required in dental work, in view of intense pressure often produced in the chewing process.

Gold alloys are melted in small quantities. Fine gold and alloy metals are usually provided in granular form because they can thus be mixed with greater accuracy. During the melting process, impurities including oxygen in the air must be carefully avoided. Smelting only works successfully in a vacuum or with a protective gas.

Before alloy bars are processed into such semi-finished products as sheet metal and wire, mechanical means are employed to remove burrs and porous surfaces. The bars arc then placed in a roughing mill through which they pass several times. This alters their crystalline structure to the extent that they must be homogenized with a first interim heat treatment. Through various stages of the milling process, constantly interspersed with additional heat treatment, sheets and rods gradually attain their finished appearance. The final stage for sheets involves passing them through rollers which produce a high surface finish. Wire goes through a drawing bank where polished diamond and hard metal draw stones produce the desired affect.

Jewellery
Seamless tubes are produced by means of punched-out metal discs. They are formed in the course of several deep draw stages on great presses and shaped into tubes. The final stage takes place on special drawing banks which create correct lengths and cross-sections.

Modern Casting and Traditional Technology

One of the oldest of all techniques is used for casting gold alloys for making jewelry and for dental technology the so-called cire perdue (lost wax) process. While in jewelry manufacture the rough casting is only an approximation of .the form and dimensions of thing final products, dental casting, however, requires also lute precision for surfaces which cannot be furtha ,Id worked. Tolerances in dental casting consist of tenths of millimeters.

Browne
In jewelry-making, models often made of tin are putting through an intermediary stage to produce equivalents rig in wax. For this purpose, they are bedded down in silicon. After the silicon hardens, the models are re-moved, leaving an outline, a negative form, which is then filled with wax to produce a precise facsimile of the entire model. If several identical pieces of jewelry are is required, it is a simple matter to cast the appropriate number of wax models; the negative can be used time I and time again. To cast the series in a single operation, individual models are laid out in a cluster. This is sometimes called a "wax tree".

A hollow form is needed for casting the metal. The wax tree is placed in a steel casting cylinder with the crown pointing downward. It is surrounded with a plaster-like fire-resistant substance which is packed! tightly. Only the stem of the tree appears above the casting. The cylinder is heated in a furnace to about 250 degrees centigrade; the wax melts and can be poured or centrifuged out, while the cast bakes to  become a "muffle".

shaving razor of Gold
During preliminary heating, the appropriate proportions of alloy have been brought to melting point. The liquid alloy is now poured into the cavity left by the stem of the tree. It flows through its branches to the appropriate molds. When the cast is full, there is a momentary pause before the centrifuge is started. The delay is needed to permit air and gas holes to be swallowed in the still molten metal.

Centrifugal force gradually presses the setting metal into all corners and angles of the form, producing complete and accurate castings. To free them, the muffle in which they were formed must be destroyed, a hence the name "lost form." The final stages include r carving, lapping and polishing.

The process employed in dental technology is similar, except that dental work is always "made to measure" and each item is individually produced to size. Since only one piece is cast each time, the casting cylinders arc notably smaller. The molds, which often are very complex, require particular attention because only a casting that fits properly is of any use. As metal sets, it loses volume.

As it cools, it shrinks. When a casting has very varied cross-sections, as is often the case in dentistry, intense stress can be produced in the broader areas so that cavities are formed in the metal. This may be prevented by casting channels set above the broad areas, provided with spherical bulges known as "lost heads". When cooling, the metal sets in these lost heads after setting in the casting, because of its greater volume. This has the effect of drawing metal out of the lost heads so that cavities form there with no resulting damage.

Writer – Micbael Globig

Introduction to Green tourmaline

Green tourmalineThis color variety of tourmaline has no separate name; it is as well-known as rubellite and indicolite. 

Appearance

Green-colored tourmaline comes in a mire range of different shades, so, at first sight, many greet tourmalines may look very similar to other gems. Shaw may include the yellowish-green of some olivine, or the stronger, deeper green of others; a lights paint box grey, like some zircons, is also possible as is a stronger vets& of this color, like some African emeralds. Tourmaline cr be a brilliant green, a touch colder than the color Omer aid (this is typical of tourmaline); or leaf green, tending h deep olive green (also very typical and known, in fact, a tourmaline green). If they are large, green tourmalines are given either a step cut (not always with truncated cornet) or a pear-shaped or oval mixed cut. If the stones are small they are most often given a round or roundish oval. Mid to light-colored specimens have good luster. Clarke stones often look a bit opaque. Many are virtually heel inclusions.

Distinctive features

RubelliteThe more definite or darker shade is characteristic. Loss of transparency along the stone particularly in gems that are cut rectangular is peculiar to tourmaline. Mid-green stones that are given a rectangular cut often show alternate longitudinal lines of lighter are darker color because of the way in which light is reflecti4 from the pavilion facets. This optical effect is unique and. therefore distinctive. But when the color is similar to that at other gems, the identity of the stones can only be distil-gushed by measurement of physical characteristics suth as density and refractive indices.

Occurrence

Green Tourmaline
Green tourmaline is found in Brazil, Its United States (Maine), Tanzania, Mozambique, and Namibia It is also extracted in the Soviet Union and from the gem gravels of Sri Lanka, where the lighter stones, some-what like olivine, are the most common. It is quite plentihr and widespread.

Value

As with rubellite and indicolite; only the lively mid-colored stones are valuable When the color is min) characteristic pale green, or the most typical dark or olive green they are worth much less.

Simulants and synthetics

It is neither imitated nor produced synthetically.

Writer – Curzio Cipriani and Alessandro Borelli

Monday, 17 June 2013

The Unknown Goldsmith


The pommel is carved from rock crystal in the form of a ram's head, inlaid with gold and square-cut rubies, to resemble a bridle; the eyes are of cat's eye. The scabbard is possibly European. Rock crystal has been described by Pliny as: "While a stone to the touch, it seems like water to the eye." The technique of working in this material was mastered by the Indian goldsmith. The atelier a single small worn, hot, humid and poorly ventilated. Here, men sit amidst burning furnaces and heating crucibles,   surrounded by the gentle tap-tap-tap of stones being set, gold being cut, wires being drawn and pipes being blown. This is the workshop and the humble abode of the Indian jeweller. Handmade and painstakingly crafted, each ornament is the culmination of a creative process combining artistic genius, technical prowess and manual dexterity, made with an attention to detail that could only be the product of love and dedication.

The Indian jewel was created by an unknown craftsman, who was also a master of metallurgy. What he crafted was not valued merely for its size or the quality of the gems he used. He seemed to possess supernatural powers in his deft handling of the medium, imparting a sense of illusion, maya, to the object. This quality is expressed in the Shilappadikaram: "In one of the rooms of Mashattuvan's stately house stood a large couch. Its legs, studded with precious stones, were made with such art that they were thought to be the work of Maya, the craftsman of the genii."

The goldsmith, or sonar as he is popularly known in the north, and thattan, achary or tattasari, as he is known in the south, belongs to a separate caste, whose position in the social hierarchy is relatively low. Traditionally, he worshipped his own idols, married within his community and passed his technical expertise as well as his trade down to his sons. By virtue of his extraordinary skill, he had the privilege, perhaps more than any other section of the lower castes, of interacting with men and women from the upper castes, had access to the zenana, and was trusted with handling incalculable amounts of wealth.

Seven rows of faceted gold beads form this classical ornament for the neck. The kantha-tuda and kanthika mentioned in ancient inscriptions were most likely the predecessors of this elegantly simple necklace. References to goldsmiths and their functions and duties abound in texts through the ages. The Yajurveda refers to bead-makers as manikara, and the goldsmith as hiranyakara. Asvaghosha calls them s-parna kara, sparna karmara and ratna karmatya. "Perhaps the first indicated an ordinary goldsmith and the second a specialist,"4 while the third was probably the gem-setter. But the name suparanakara, meaning 'one who worked in gold', was most common.

With the large supply of gold and gems at their disposal, kings established ateliers (kharkbane), their sole purpose being to create jewels for the ruler. The Arthashastra pronounces that workshops for gold (akhsashala) were to be established by the state and supervised by the goldsmith (sauvarnikah), who was also an employee of the state. Private goldsmiths worked under the supervision of the sauvarnikahs State-run workshops produced items for the general public, but in the imperial set-up, goldsmiths were part of the court organization.


Hara Necklace
While workshops in the court and market-place were common, the tradition of the family jeweller is perhaps unique to India. Until recently, the jeweller would come to the house of the client, carrying his work-table and all his tools, and execute his commission under supervision. Since women were not (lee to go out often, this arrangement allowed ladies of the household to gather and spend time together; furthermore, an eagle-eye was kept on the jeweller, ensuring that there was no theft of gold and that gemstones were not switched with those of inferior quality. The jeweller built up generations of trust working with one family, and as the craft passed from father to son, so did his clientele.

Since so much of Indian jewellery was worn for superstitious reasons and for its apotropaic powers, craftsmen always paid the closest attention to detail and workmanship. This was based on a belief that the wrath of the unknown, which the jewel was meant to deflect, could also befall the maker if due attention and care were not accorded to technical details. Since gold was a prized commodity, every effort was made to minimize loss. The gold workshop was well-organized and meticulously supervised. The entry and exit of unauthorized people was strictly regulated. Tools and unfinished articles could not be carried out of the workshop. 

Large foiled emeralds and spinels are embellished with birds and flowers outlined with gold wire, enamelled and set with gems. The Arthashastra even stipulates that "artisans doing the work of setting in gold, bead-making, plating and gilding and ornamental gold, and blowers, servants and dust-washers, shall enter and leave after their garments, hands and private parts are searched." The superintendent of the workshop closely monitored the workers to prevent pilferage. He was advised to watch out for strategies such as a "sudden movement of the hand, the weights, the fire, the wooden anvil, the tool-box, the receptacle, the peacock's feather, the thread, garment, talk, the head, the lap, the fly, attention to one's person, the bellows-skin, the water-platter, and the fire-pan, these he should know as the means of pilfering." Gold dust was meticulously collected and weighed to reduce the amount from the total weight of the finished ornament. A caste of gold-separators, called Jalagadugu in the south and Niyariya in the north, collected the sweepings, ashes and refuses from outside goldsmiths shops and painstakingly sifted the gold.


The absence of a system of hallmarks coupled with the practice of alloying gold with other metals to render it stronger led to cheating. Hence it became standard practice for jewellers to test the purity of gold on a touchstone before accepting old ornaments to be recycled into new pieces. The metal or ornament to be melted is rubbed on a soft black touchstone called kasanti. The purity is established by comparing the streak thus produced with a streak of standard gold.

The magnificent kali-tiru worn by Chattier women on their wedding day is substituted by these simpler, but no less exquisitely crafted, pieces for everyday wear.
Goldsmiths were conversant with the various properties of gold and the method of mixing various metals to obtain different hues, colours and strengths. They could classify gems and were adept at cutting and piercing stones. This is borne out in various ancient texts, including those by Kautiiya and Patanjali. In the 2nd century literary work, the Shilappadikaram, there is a reference to the categorization of diamonds into four 'castes' on the basis of the colour of the stone, and a listing of the different kinds of flaws in a stone, namely "kakapada, kalanka, bindu and rekha."1" Indian texts on gemmology recognize many categories of diamonds, based on their characteristic properties. "Good diamonds were supposed to be ujjala or bright, adosa or flawless, amala varitara or free from impurities and transparent like water. Rainbow like colour, ambudendradhanuh was a desirable property."

The beginnings of such technical expertise were most likely gained in the flourishing markets of the gem-trading centres of south India, where special streets were inhabited by dealers selling gold and varieties of gems, and jewellers crafting items of adornment. The first references to the qualifications of a gem specialist arc in the 6th century text, the Agastimata, where he is called a mandalika. The Rayanaparikkha, dating to 1315, reiterates the credentials of the gem appraiser, an expert who determines the value of the gem and functions as an intermediary between the seller and buyer.

Worn on elongated ear lobes, this light thoda or thodu, measuring no less than 9 cm in diameter, is made from sheet gold worked in repousse with geometric and floral designs. The 11th century inscriptions in the Rajarajeshvaram temple at Thanjavur detail the classifications adopted by gem experts. Pearls were graded on the basis of quality and shape, to include round pearls (vattam), polished pearls (oppu muttu), small pearls (pala muttu), pearls of red water (sivanda neer), pearls of brilliant water ( kuhrnda neer), pearls with lines (varai), pearls with red dots (kurn), pearls with wrinkles (tirangal) and twin pearls (irrattai muttu). Diamonds and rubies are similarly classified; with smooth edges (matta tarai vayiram), flat and smooth edged diamonds ( matta tarai sappatti vayiram), spotted diamonds (porivu), red-spotted diamonds (rakta-bindu), pure diamonds ( tooya ayiram) and round diamonds (urulai vayiram); a smooth ruby (komalam), bluish ruby (neela-gandhi), unpolished ruby (talam), ruby with flaws (trasam), and so on.

Writer – Usha R Bala Krishnan & Meera Sushil Kumar