California
IT WAS formed when the Earth鈥檚 first continent was still unbroken, and is
probably older than anything you see around you. It has survived the demise of
dinosaurs and the rise and fall of empires. It adorns royalty and movie stars.
And it is, apparently, still a girl鈥檚 best friend.
Few things are as magical or mysterious as a glittering diamond. 鈥淓ach gem is
a piece of history,鈥� says George Harlow, curator of the diamond exhibition at
the American Museum of Natural History in New York. Something that may have
survived for three billion years has got to be special.
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But what if the sparkling diamond on your finger wasn鈥檛 formed in the intense
pressures and ferocious heat that pevail miles beneath the Earth? Supposing it
came instead from a vat of chemicals in an industrial estate on the outskirts of
San Francisco? Could such a fake ever feel as special?
Advances in chemistry have not only made the creation of synthetic gems a
reality, but these little fakes are now so good that it is almost impossible to
tell the real thing from a crafty copy. That鈥檚 fine when synthetic gems are
clearly labelled, but who do you turn to if you think an unscrupulous dealer has
sold you a dud? Enter the Gemological Institute of America (GIA), based in
California. Although it has no regulatory role, the GIA helps to monitor the
industry and keeps jewellers and gemologists up to date about counterfeiters鈥�
latest tricks and techniques. James Shigley, director of research at the GIA,
says that most jewellers can usually spot a synthetic gem. And when they are
unsure, jewellers often send their hard-to-identify gems his way. But as the gem
makers get more skilful, it has become ever harder to be sure what you鈥檙e
looking at. 鈥淚t is a challenge to recognise some of these things,鈥� admits
Shigley.
Faking gems has a long history. The first attempts were pretty clumsy, but
this changed with the arrival of two revolutionary techniques for cooking up
gems. The first was devised at the turn of the century by the French chemist
Auguste Victor Louis Verneuil, who created impressive synthetic rubies using a
method now called Verneuil flame-fusion (鈥淭he fake in the crown鈥�,New
Scientist, 21 December 1991, p 25).
Verneuil knew that real rubies and sapphires were crystals of aluminium
oxide, Al2O3, and that they gained their colour from
contaminants鈥攃hromium ions in rubies, and iron and titanium ions in
sapphires. His idea was to trickle aluminium oxide powder and the right
colour-giving contaminant through a torch-heated chute kept at more than 2000 掳C.
When the resulting molten liquid hits a pedestal at the bottom, it
crystallises. As the crystal builds up, the pedestal is slowly lowered so that
the mound, called a boule, is never directly in the flame. When the crystal is
several centimetres high, it can be cut into individual stones.
Warts and all
Verneuil gems are easy to identify because they contain bubbles and curved
growth lines that are visible under a low power microscope. The lines result
from layers of melted aluminium oxide dripping onto the growing boule and
trickling down the sides before crystallising. Each drop adds an additional
curved cap to the boule.
There are two problems with this technique. First, while the Verneuil process
could turn out sapphires or rubies, emeralds proved impossible to grow.
Secondly, Verneuil gems have none of the tiny imperfections of natural gems.
These have irregularities in the crystal structure that can form unique
feather-like patterns, or contain particles of the rock in which the gem
formed.
However, improvements in technology have made it possible to produce gems,
warts and all. Not only do these synthetic gems have the same chemical
composition and crystal structure as natural gems but, most importantly, they
mimic the flaws in a natural stone.
The pioneer who made these fakes look almost real was Carroll Chatham. In
1926, the teenaged Chatham decided to grow some diamonds. He dissolved graphite
in molten iron and dropped the fiery solution into a vat of liquid nitrogen that
he鈥檇 placed outside his parents鈥� basement window. He expected that, as the
red-hot solution cooled rapidly, the dissolved carbon would crystallise into
pure diamond. Instead, the resulting explosion blew out the windows around his
San Francisco home.
Urged by his father to find another hobby, Chatham turned his attention to
emeralds. When he was 21, Chatham had his first success and by 1938, he had
introduced the first lab-grown emeralds to the market.
The key to his process was a special solvent called a flux, a combination of
chemicals such as lithium oxide, molybdenum oxide and vanadium oxide that remain
liquid at high temperatures. Emeralds are crystals of beryl,
Be3Al2Si6O18,
with some chromium mixed in for colour.
Verneuil鈥檚 technique did not work for emeralds because there is no way to melt
all the components together: some of them evaporate before others have even
melted. But Chatham鈥檚 unique and highly secret flux recipe got round this
problem. He suspended tiny seed crystals in the hot flux so new crystals had
something to grow from, much like providing the first row of a complicated brick
pattern to help place the subsequent rows. After a long wait鈥攊t can take
over a year to grow marketable stones鈥攐ut came emeralds.
Chatham鈥檚 son Tom has carried on his father鈥檚 business, distributing
lab-grown rubies, sapphires and emeralds from his San Francisco office.
With his back to a well-lit case of colourful synthetic gems, Chatham says,
without a hint of irony, 鈥渓uckily, our product is not perfect.鈥�
Spot the fake
Although the imperfections he鈥檚 referring to lower the quality of the stones,
they make the jewels more realistic and therefore more expensive than Verneuil
gems. They also make flux-grown gems hard to spot by visual inspection alone. It
takes a trained eye and a lot of equipment to tell if an eye-catching gem is
what it pretends to be. Chatham says that even trained jewellers or gemologists
occasionally get it wrong. Crooked dealers can buy synthetic gems and try to
sell them overseas as the real thing.
This is where the GIA comes in. Suspect gems might have been labelled
correctly when they were first sold, but such information gets lost as gems
change hands, says Shigley. 鈥淏y and large, people who sell treated and synthetic
gems attempt to disclose the information.鈥� Jewellers are keen to sell honestly
because if they make one mistake, their reputation is gone forever. It is partly
this fear that makes them send stones to the GIA for analysis.
No single technique can determine a gem鈥檚 origins. When a suspicious jewel
turns up, Shigley first examines its colour, which depends on the light absorbed
by tiny amounts of metal ions trapped inside the stone. The differences can be
subtle, impossible to distinguish by eye alone. A red stone could be a
ruby鈥攕ynthetic or otherwise鈥攐r a similar-looking gem called red
spinel. Checking more closely under a microscope, Shigley looks for the curved
lines of Verneuil gems or for the dark-coloured platinum inclusions of flux
grown jewels. These tell-tale impurities come from the platinum growth chamber
where they are grown.
If Shigley is still unsure, he turns to fluorescence for clues. When
electrons in a crystal are excited, they fluoresce with a characteristic colour.
Although synthetic gems may have the same crystal structure as natural ones,
subtle differences in the atomic arrangements create differences in the energy
levels that the electrons can occupy. This causes them to fluoresce at slightly
different wavelengths. For example, red spinel and ruby fluoresce at different
wavelengths when ultraviolet light is shone on them, and a natural emerald gives
off a reddish light slightly different from that of its synthetic
equivalent.
If such tests are inconclusive, he can also look at the strain patterns in
the crystal鈥檚 structure. Putting a transparent material such as Perspex between
a pair of polarising filters reveals the patterns of strain inside the material.
In the same way, natural gems show unique strain patterns that are
characteristic of the way they grow.
Shigley can also replace the ultraviolet light with high energy X-rays and
examine the fluorescence again, this time inside an X-ray spectrometer. Or he
can use X-ray crystallography to reveal a gem鈥檚 exact crystal structure.
Taken together, this battery of tests will usually reveal the synthetic, says
Shigley. But sometimes things aren鈥檛 so tidy and the occasional mystery still
pops up.
One such puzzle was a star ruby that had stumped other jewellers. Natural
star rubies are highly valued. They contain thin filaments of titanium oxide
that reflect light in a beautiful, star-like pattern. But the top of the mystery
gem had the gas bubbles and curved lines typical of a Verneuil gem while its
middle layer was slightly opaque and seemed to be where the star originated. It
turned out that the gem was built from several bits. The synthetic top and
unidentifiable bottom gem were fused together and at the join, someone had
scored fine lines in three directions, reflecting light in a too-perfect
star.
Facet lift
According to Shigley, this sort of assemblage appears regularly at the GIA.
Manufacturers often glue an expensive gem on top of a less expensive one. When
done honestly, it reduces the cost of a natural-looking gem. However, Shigley
has seen a few less than honest versions. And although it鈥檚 relatively easy to
spot a synthetic stone, once it鈥檚 been fused to a real stone and the whole
conglomeration treated in some way, things become far more complicated. One
purplish-red stone was being sold as natural spinel. When Shigley examined it,
however, he found that the bottom half of the stone was synthetic spinel. Since
the synthetic was similar in colour to a natural stone, it is possible that the
manufacturers made an honest mistake. Then again, maybe they didn鈥檛.
The most difficult fakes to spot are natural gems that have undergone the
mineralogical equivalent of a face-lift. These gems look real, but are doctored
to make them more expensive. Many gems on the market today fall somewhere
between natural and synthetic. They may have originated underground, but it took
a little laboratory magic to put them in a jeweller鈥檚 display case. For
instance, emeralds, which are prone to cracking, often have a plastic or oil
filler to disguise faults. Diamonds can have dark inclusions removed with a
laser knife, or be irradiated to improve colour.
Heat treatment often works wonders. Cook a ruby in the presence of chromium
ions and the colour of the gem will improve鈥攁t least in the outer few
millimetres. Many sapphires are also heated to enhance their natural blue. Such
treatment dissolves titanium oxide contaminants, which can make the gem cloudy,
and removes an electron from the colour-giving iron contaminant. Iron without
the extra electron will steal an electron from a neighbouring titanium ion,
changing the stone鈥檚 colour in the process. This trickery can turn a valueless,
murky-grey sapphire into a highly prized deep-blue gem. It can also make its
distributors some extra money.
What of the most prized gems, diamonds? General Electric and De Beers have
been growing diamonds for industrial use since 1955, but these tend to be
yellowish-brown or blue in colour. Officially sold only for industrial use,
gemologists have seen a few synthetic diamonds masquerading as real gems.
Brown-yellow diamonds have been spotted in Antwerp and London. 鈥淒espite the
limited numbers of synthetic diamonds seen, the fear that they will enter the
marketplace and will not be readily identifiable continues to haunt the trade,鈥�
says Shigley.
Gems with attraction
Such fears came a step nearer reality when Chatham turned his attention to
the diamonds that gave his father such explosive problems. It began when he got
a call from some Russian scientists claiming that they could grow 鈥渨hite鈥�
diamonds. 鈥淚 told them that if they could grow them, I could sell them,鈥� Chatham
recalls. And so he has become the first gem manufacturer to grow white diamonds
for jewellery.
The new gems are dismissed by Cheryl Pellegrino of the Diamond Information
Center, the marketing arm of diamond giant De Beers. 鈥淒iamonds are a gift of
love,鈥� she says. 鈥淲e don鈥檛 think synthetics will ever compete.鈥� But not everyone
shares her lack of concern. 鈥淪omeone very high up in the GIA came to me and
said: `You just can鈥檛 do this. It isn鈥檛 right鈥�,鈥� says Chatham.
Though Chatham鈥檚 white diamonds look like the real thing and are being
marketed as jewellery, the GIA says it is easy to spot them. Synthetic white
diamonds fluoresce a yellowish-green colour under ultraviolet light while
natural diamonds emit either blue or a weak yellow light. The synthetics also
contain iron impurities from the growth chamber. The clue is a dark reflective
inclusion, which hints at the presence of iron.
And there鈥檚 a simple test to confirm it, says Shigley. You just dangle the
diamond on a string and hold a magnet next to it. If it moves, you鈥檝e been
had.