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Black Spinel

Written by Modern Jeweler On May 2, 2013.

It is custom in India for a child to wear “baby bracelets” on both its right and left hands for the first year of its life. Composed of gold and black gems, this color combination is widely believed to ward off evil.

Kuntal Shah, president of Oscargems in New York, remembered this cultural fact of life in her native country when she chanced upon an enormous surplus of black spinel rough in 2005. “I decided to start making baby necklaces of alternating 14k or 18k gold and micro-faceted black spinel beads,” she says. “The response was spectacular. I sold thousands of gold and spinel baby bracelets at $50 to $60 retail.”

As luck would have it, black gems became a global fashion fixture and Shah began showing black spinel at gem and jewelry shows in this country-where she took the opportunity to talk it up with designer clients such as Alison Osborne, Hastings, Nebraska. “The moment she showed me some faceted black spinels, I knew this was the black gem I was looking for,” Osborne says.

That’s high praise from Osborne, a black gem aficionado who uses dark gems frequently in her designs. “I have a deep fondness for black gems and I am always on the lookout for new ones,” she continues. “Among my favorites are black labradorite and black tourmaline. But I am making widest use of black spinel at the moment.”

With enthusiastic customers like Osborne, it is hardly surprising that black spinel is Shah’s number one seller this season. Whether it will continue to be her top-seeded stone remains to be seen. But the fact that Osborne plans to stay with the gem whether or not the fashion dress code remains black and white suggests this gem has enough staying power to soon earn staple status.

And fashion is only one of the factors working on its behalf.

Blazing Black
When one thinks of black gems, two choices usually come to mind: black onyx and black diamond. Of the two, black onyx is by far the most popular and affordable. Over the last decade, however, black diamond has carved a deep niche that it has never had before, especially in irradiated jet-black form.

Nevertheless, if supply is great enough (and Sri Lanka, Tasmania, and Burma are current producers), black spinel could leap-frog over both of them to assume new leadership in this color category. The main reason: It is a best of both worlds choice that guarantees it future importance to jewelers.

In smaller sizes, black spinel offers the luster of diamond for a price just slightly to the north of onyx. Shah micro-facets her beads and smaller calibrated stones to emphasize their diamond-like appearance.

In larger sizes, the similarity to diamond is not so strong. But stones still have “high facet definition and sharpness they never have with onyx,” says Osborne.

The end result is the best bargain in blackness the gem world has ever known. And, unlike onyx and diamond, black spinel is not treated. “The color is a gift from nature,” says Shah. So is its ability to shine like diamond.

One of black spinel’s biggest beauty secrets is its hardness-eight on the Mohs scale, enough to give it “superior luster when polished,” says Eric Braunwart of Columbia Gem House, Vancouver, Washington. “Because black onyx is less dense and hard, it can’t take as good a polish. Black spinel gives you an absolutely smooth black surface.”

These virtues encourage dealers like Braunwart and Shah to facet stones with everything from conventional to checkerboard arrangements. Yet most stones cost under $5 per carat, often under $2 per carat in small sizes.

True, black onyx is readily available for $2 to $5 per stone, depending on size, but Braunwart is convinced many jewelers will resist the temptation to be onyx-wise and spinel-foolish. “The large difference in quality should outweigh the small difference in price,” he says.

If Braunwart and Shah are right about black spinel’s future, this variety of spinel could do wonders for the breed as a whole.

Black Onyx

Written by Modern Jeweler On May 2, 2013.

Now that the term “semiprecious” has become politically incorrect in gem dealer circles, it is being replaced by a more subtly derogatory term, “ornamental.” While the term means “decorative,” its prevailing connotation is of something bauble-like that is both showy and valueless. No wonder the adjective is heard mostly in conjunction with chalcedony quartzes such as carnelian and, above all, black onyx.

Unless used for sculptural purposes, black onyx never costs more than a few dollars per carat. That’s why it rarely inspires rapture or scholarship. So while jewelers are aware that it was a mainstay gem of the art deco period and is widely used today in men’s jewelry, few know that black onyx was more celebrated before our century or that it boasts a millennial history with long stretches of veneration.

The earliest and possibly grandest highlight of that history dates from around 250 B.C. when a large onyx (probably banded rather than uniformly colored) was chosen as the sixth stone in the 12-stone breastplate of Aaron, unquestionably the most famous gem vestment in Judeo-Christian history.

In addition, black onyx merits attention as one of the first known and most popular treated gems, its color the result of a staining process recorded by Roman soldier-scientist Pliny the Elder in the gem section of his vast treatise, “Natural History.” Indeed, it is onyx’s status as a treated stone that poses one of the quartz world’s nagging mysteries; the exact period when “onyx” shifted meaning to refer exclusively to solid-color rather than patterned agates.

In our time, certainly, the word “onyx” conjures up gems with lacquer-like single colors, whether black, green, blue or red. But that’s not what the word originally evoked when the ancient Greeks coined onychion, from their word for “fingernail,” as “a generic term for onyx, sardonyx and agate,” explains quartz expert Sy Frazier. Shortened nearer our age to onyx, but still referring, in essence, to banded agates, the original association with fingernail makes good philological sense, but only if you think of non-treated agate. Look at a fingernail and you’ll see three alternating bands of light and dark curving across the cuticle, similar to the curved light-and-dark banding of agate.

But did the Greeks even know of dyed onyx? Or did, as many suspect, the process begin with the Romans? If so, did the Romans practice staining widely enough for it to be considered as much of a norm for this gem as it is today? Or, more likely, was the word associated equally with natural banded and treated solid-color gems?

One thing is for sure: During the Victorian era, the name began to stand almost entirely for solid-color gems. And it was then, notes period jewelry specialist Jeanenne Bell, that black onyx wrote the oddest chapter in its history by playing the role of a black-gem stand-in: similar to that of red spinel in the ruby market.

The Jet Set

In the mid-nineteeth century, when onyx was in final transition from a banded to a monochrome gem, demand for the black variety became the greatest ever known. Ironically, much of the demand was based on the popularity of a look-alike: jet, a fossil coal also known as “black amber.”

The boom in onyx was part of a larger boom in black gem and jewelry materials including jet, glass, vulcanite (an early plastic), gutta-percha (a rubber resin) and a host of other substances. This boom was due to the sustained popularity of mourning jewelry during most of the nineteenth century, especially the reign of England’s Queen Victoria from 1837 to 1901. When Victoria’s husband, Prince Albert, died in 1861 and the queen vowed to wear black for the rest of her life, the already expansive market for mourning jewelry exploded, so much so, writes Diana Scarisbrick in The Jewelry Design Source Book, “its manufacture assumed the proportions of an industry.”

In America, where the Civil War further fuelled demand for mourning articles, jewelry manufacturers began to substitute onyx for jet, the age’s black gem of preference, on a massive scale because the stained agate had better color, luster, hardness, and durability. However, its most endearing advantages were greater availability and far lower price relative to jet, the result of a surging supply of treatment-friendly material from Brazil that started in 1821. Although onyx is plentiful throughout Europe (Idar-Oberstein is founded in an agate-rich region), the South American variety took to staining more readily.

Of course, few in the jewelry world knew that black onyx was artificially colored at all. The process, kept a trade secret in Germany’s Idar-Oberstein until a small booklet was published on the process in 1913, allowed this cutting center to control the black onyx market after staining was introduced there in 1819.

The stories of how the recipe got into German hands is as fascinating as the recipe itself. According to Frazier, Johan Jakob Hahn, a German cutter, learned the technique from his cellmate, an Italian, in a Paris debtor’s prison. Another legend has it that a man from regularly brought agate to Idar-Oberstein for cutting taught the method to a cutter there. In light of the fact that Pliny’s writings are the oldest ones known on the process, it is no coincidence that both stories credit an Italian as the source of the technique.

Carbon Coloring

Starting in 1813 and continuing through the mid-century, German cutters discovered a series of coloring techniques that allowed them to turn agates various colors: first red (carnelian) using heat alone, then, in 1819, black using what is called the sugar-acid process. Kurt Nassau summarizes the latter process in his indispensable book, “Gemstone Enhancement”: “Two liquids are…used for black agate, the first consisting of 375 grams sugar in 1 liter of warm water, having the consistency of thinned honey. After being soaked in this for 2-3 weeks, the agates are transferred without drying into concentrated sulfuric acid (very dangerous). After being heated for 1 hour and boiled for 15 minutes to 2 hours and then cooled, the agates are removed, washed well, and then dried very well at medium temperatures. The concentrated sulfuric acid extracts water out of the sugar, leaving behind pure black carbon.”

More recently, a quicker, supposedly less permanent dyeing technique involving immersion and heating of stones in a cobalt solution has been used. But purists stick with the sugar-acid method first described by Pliny nearly 2,000 years ago.

Black Crystal Opal

Written by Modern Jeweler On May 2, 2013.

Ask a gem collector which variety of opal is the most prized in the world and chances are pretty good you’ll get the right answer: Australian black opal. But don’t ask which kind is the next best. The answers you’ll usually hear-Australian semi-black or boulder opal-are wrong.

Collectors can be excused for not knowing the runner up in value terms to black opal. Unless they’re connoisseurs, they may never have heard of the world’s second most valued opal. Called black crystal opal, it’s also from Australia. But unlike, say, boulder opal, which is a distinct variety of this gem, black crystal opal is more akin to a sub-species. Indeed, most opal guidebooks classify black crystal opal between well-known black and semi-black when it comes to both value and regard. So how come few people know about it when it’s so highly esteemed?

That’s a tricky question, one whose answer sounds like a Zen riddle. Collectors do know about crystal opal, only they don’t know that they know.

Unless explained by an expert, black crystal opal is very likely to be mistaken for black, semi-black or even gray opal. That’s because most people who have seen black crystal opal probably weren’t told what they were looking at.

The same goes for light crystal opal-even more so. Since crystal opal occurs in both light and dark forms, and since light (or white) opal is a jewelry store staple, the odds are great that jewelers may have sold light crystal opal without labelling it as such.

But now that black crystal beauties from Lightning Ridge, Australia’s most famous opal mining area, are more available, consumers should take note of this stunning opal.

Great Balls of Fire

The name opal is a shortened version of opalus, a Roman coinage that sums up this gem’s chief aesthetic attribute: color play. Perhaps the best description of opal ever penned is found in Pliny the Elder’s treatise from 79 AD, Natural History, which devotes a volume to gems: “For in them you shall see the living fire of ruby, the glorious purple of amethyst, the sea-green of the emerald, all glittering together in an incredible mixture of light.”

Although the world marveled at opal for centuries, the precise cause of its color play, also known as iridescence, was not known until the1960s. Then electron microscope studies revealed that the richness and brilliance of opal colors were the result of light diffraction (the breakup of light rays into spectral colors) within the stone. Here’s how opal works its color magic:

Light enters a stone, passes through lattices of silica spheres into a surrounding silica solution where it is diffracted and reflected out of the stone.

Gemologists found that both the size of these spheres and the orderliness with which they are arranged influences the number, strength and pattern of colors an opal exhibits. “For instance,” writes Andrew Cody in his photo guide, “Australian Precious Opal,” “blue colors are evident where the spheres are smaller, and at the other end of the spectrum orange and red will be evident where the spheres are larger.”

In short, sphere size correlates with specific wavelengths of light transmitted from stones. Depending on the range of sphere sizes, many or just a few colors are emitted. Moreover, spheres have to be grouped together with sufficient regularity to ensure broad, vivid colors.

Color vividness in opal is a function of body color, a term that refers to the tonal background in which opal’s spectral colors swim. Basically, there are two classifications of body color: light and dark. The former includes those backgrounds from milky white to medium gray and the latter backgrounds from strong gray to jet black. Black opal’s appeal over and above its greater rarity relative to white opal, is that its dark background acts as a color intensifier.

Whether light or dark, most opals have a colorless base, known as “potch,” that renders them opaque or slightly translucent. No matter how crisp and brilliant the color play of such opals, it will seem confined to the surface of the stone. However, when stones are highly translucent or transparent, their color is as visible inside the stone as on its surface.

There are two kinds of transparent opal. The first, and more common, is called jelly opal and features colors that are hazy, intermittent, and rarely effulgent. While sometimes magnificent, jelly opals have colors that seem to be suspended like flies in amber within the stone rather than to emanate from it. What’s more, jelly opals occur only in light opal form.

Bicolor Tourmaline

Written by Modern Jeweler On May 2, 2013.

At last count, gemologists had logged in more than 100 tints for tourmaline, making it the gem world’s king of color. Centuries ago, however, when its broad palette meant constant confusion with other stones, tourmaline was one of the gem world’s masters of disguise. Indeed, the gem’s root-name, is turmali, a Sinhalese term used by Ceylonese dealers and means “mixed gemstones of unproven identities.” Today the original name is still apt because it reflects a gemological diversity so great that the gem is classified as a group rather than a family.

Yet, strangely enough, the gem that comes in more colors than any other begins life as colorless, or nearly so. During formation, its crystal structure hungrily absorbs trace elements from its host solution. Some of these chemical impurities — most notably, manganese for pink and iron for green — act as coloring agents when they replace atoms normally present.

This susceptibility to color change through chemical substitution makes tourmaline what is called an “allochromatic” gem. Of course, tourmaline is far from alone in this trait. In fact, without such color-susceptibility, many revered gems would be missing from jewelry stores. If, for instance, chromium didn’t replace aluminum in beryl, there would be no emerald.

Nevertheless, tourmaline takes to a wider variety of tinting than any other gem. And because it does, explanations of color causes in tourmaline are still largely theoretical and often conflict with one another. When it comes to color, tourmaline seems to play by lots of rules. “In Brazil, the color chemistry for tourmaline changes from pocket to pocket within an occurrence,” gemologist Joel Arem notes, “while in California it remains fairly uniform throughout the whole San Diego gem belt.”

Many tourmalines provide a visual record of changes in their chemistry by displaying two, sometimes three, areas of different color along their crystals. When cut, these multicolor gems become what Arem calls “history books of tourmaline growth.” Most frequently seen with two large zones of adjoining color, the gem is best known as bicolor tourmaline and usually features combinations of pink and green. Both the pinks and greens run wide gamuts from magenta-purple to brownish-pink and aloe to granny-smith apple green, with numerous intermediate shades.

Occasionally, bicolors depart from pink-green pairings and couple spruce-greens with aqua-blues, aqua-blues with cherry-pinks, and grass-greens with pumpkin-oranges, to name a few of the most beautiful combinations. “No doubt, new finds will give us new color combinations,” Arem adds.

Local Colors

At present, bicolor tourmalines are mined principally in Brazil, Zambia, Madagascar, Nigeria, Afghanistan and California.

It would be nice to lay down some hard-and-fast rules for buyers of bicolor tourmaline. But taste with this gem is as wide as its color palette. And that’s how it should be. However, if you insist that stones be eye-clean, this will pretty much restrict you to California, whose Himalaya Mine in tourmaline-rich San Diego County is famous for flawless bicolors. This doesn’t mean San Diego is the one source of flawless stones. Most localities produce some, but nothing proportionate to California. No matter what the origin, flawless bicolor tourmaline will nearly always have lighter hues.

As for color composition, California’s tends to have soft yellow-greens reminiscent of spring grass and pastel purples, often with a touch of brown.

It is hard to generalize about Brazilian color. In addition to green and salmon-pink, some stones show a combination of green with a dusky brownish-purple. Occasionally, stones possess a lovely indicolite-blue that commands an extra premium for rarity.

Zambia is noted for striking grass-green/pumpkin-orange combinations and, once in a while, unique aloe-green/terra cotta pairings. Madagascar’s stones have duskier greens and pinks. Afghanistan’s stones tend toward mint green and pastel pink. Be on the lookout for rare periwinkle-blue/magenta team-ups. Finally, there’s Nigeria, a source known for pairings of the same color, usually light to dark green.

When selecting bicolor tourmaline, expect the ratio of the two colors to be at least 60/40- with 50/50 the ideal. Breaks between colors should be straight up and down with minimal transitions.

Singular Sensation

Bicolored tourmaline has always been a gem for custom jewelry only. The very things about the gem that turn on makers of one-of-a-kind jewelry turn off manufacturers of mass-production jewelry.

Strike one for manufacturers is the unusual shape.While other tourmalines come in cushion, oval and even round shapes, bicolored ones are typically cut only as emerald shapes, many of them extremely thin.

Benitoite

Written by Modern Jeweler On May 2, 2013.

If mining company owner Rod Dallas hadn’t sent two prospectors up into the southern Mt. Diablo range to look for copper and mercury late in 1906, California might not have its state gem today.

The gem is benitoite, named after the stone’s sole source of facetable material in San Benito County, California, near the Fresno County line. Due in part to the fact that it has only one meaningful occurrence, benitoite became California’s state gem in 1985.

It is highly doubtful, however, that the gem would have been awarded such status just because of its rarity. Beauty and gemological uniqueness (it’s the only gem known in its crystal class) played equally decisive roles. In fact, it can be said California’s lawmakers were acknowledging benitoite’s remarkable and swiftly attained stature among gem collectors. Right after it was identified as a new species, benitoite became a paragon among collector gems.

Shiny Blue Pebbles

Like its brethren state gems, Main tourmaline and Montana sapphire, benitoite was found purely by chance. As so often happens, its discoverers were distracted from the pursuit of metals by the chance glimpse of a mineral-in this case, highly reflective blue pebbles lying on the bank of a small mountain stream at a spot some 4,000 feet above sea level. “It would have been hard not to notice these gems,” explains author Peter Bancroft, who devoted an entire chapter of his 1984 book, “Gem and Crystal Treasures,” to benitoite and who explored for the gem in the 1930s. “Benitoite is found in dry, scrub-infested country where serpentine [a very soft, flaky mineral with a dull green color] is the predominant base rock. Given this terrain, anything bright and shiny would stand out.”

Benitoite is certainly bright and shiny. But even among the ranks of the radiant, few colored stones exhibited brilliance as great as those from the new deposit in California’s Coast Range. So while its denim- to violet-blue colors at first led many jewelers to mistake it for sapphire, some who were intrigued by its unusually high dispersion suspected it was something else altogether.

One skeptic at Shreve & Co., the San Francisco jewelry store that was to be the mystery gem’s earliest marketer, persuaded his superiors to send samples to George Davis Louderback, a geologist at the University of California, Berkeley, for study. In July 1907, he published the first of two papers on the stones, identifying them as a new species that he named “benitoite” for its geographic origin. The name has proven apt since no other deposit-let alone source-of facetable benitoite has ever been found.

For Collectors Only

What is now known simply as the Benitoite Mine is very small. Bill Forrest and Buss Gray, who have owned the mine since 1987, are convinced that if it had been worked all year round once discovered, it would have run dry decades ago. They ought to know, since they’ve worked the mine longer than anyone else-leasing it for 20 years before buying it. For them, a mining season lasts five or six weeks, usually in March and April. “Lack of water becomes so severe a problem by May that we must shut down operations,” Gray says.

Six weeks isn’t time enough to find much benitoite. Maybe that’s why, excepting its brief association with Shreve & Co. between 1907 and 1912, this gem has no other history as a jewelry stone-although Tiffany is said to have tried for an exclusive on the mine’s output once the news broke of benitoite’s existence. This lack of jeweler interest is probably for the best, since benitoite’s one major drawback is a hardness of 6.5, the same as tanzanite, that makes it risky for ring use.

In any case, retailer neglect hasn’t hurt benitoite’s status. To the contrary, immediately after it was announced as a new gem, benitoite ignited an ardor in collector circles which is as strong now as ever. Today, estimates Gray, at least 90 percent of all benitoite is sold to collectors-most, until recently, in Europe. Now, however, a fast-growing audience for the gem is found in America.

From an aesthetic standpoint, it’s easy to see why benitoite has endeared itself to collectors. Fine specimens typically feature flattened, triangular gem crystals, rarely more than one inch wide, that are translucent with white centers and blue edges. These crystals either protrude from or are embedded in granular snowy-white masses of natrolite that serve as matrix. The contrast between these distinctive and well-formed benitoite crystals and their host rock is dramatic and impressive.

Further aesthetic delights are revealed once these crystals are extracted (using hydrochloric acid) from the natrolite for faceting. In color, faceted stones most often resemble sapphire and tanzanite, with darker stones more like the later, lighter ones the former. On rare occasion, cut stones are either pink or colorless. Unless stones are overly dark, something rare for this breed, benitoite looks stunningly brilliant-the result of dispersion only a tad less than that of diamond.

Small is All

For those who like their gems to possess girth, benitoite may be a disappointment. Since crystals are usually highly included, only small areas can be cut that are eye-clean. What’s more, the flatness of most benitoite crystals restricts the cutter’s maneuverability and chances for good recovery. Last, best color is attained by cutting along a crystal direction that requires considerable rough to be sacrificed.

Consequently, stones most often finish to sizes between 10 points and slightly over 1 carat-regardless of the size of the crystal from which they originate.

“On average, we cut five stones a year that weigh 2 carats or more,” says Gray. “We’re lucky if we find one crystal every five years that yields a stone over 5 carats.”

To date, the largest faceted benitoite known weighs 7.80 carats and is on display at the Smithsonian Institution in Washington D.C.


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