What
makes pink diamonds pink?
By
Jane O’Brien
BBC
News, Washington
They’re
one of the world’s rarest jewels – but nobody knows for certain why
pink diamonds are pink.
That
hasn’t stopped investors from snapping them up at auction and sending
prices skyrocketing. In October a new world record was set at a
Sotheby’s sale in Hong Kong when an 8.41-carat pink diamond sold for
$17,768,041 (?11,438,714) – more than $2.1m (?1.8m) a carat.
“Everybody’s
talking about them, and everybody loves them,” says Jeffrey
Post, curator of the National Gem and Mineral Collection at the
Smithsonian’s National Museum of Natural History in Washington, DC.
“Yet you can’t tell people why they’re pink.”
Other
diamonds get their colour from chemical impurities that absorb light.
Yellow diamonds contain traces of nitrogen, and blue diamonds contain
boron. But no similar impurities have been found in pink diamonds,
leading scientists to speculate that the colour may be the result of
some kind of seismic shock that altered the stone’s molecular
structure.
It’s
now hoped that a cache of brown and pink diamonds from the Argyle
mine in Western Australia may solve the mystery. The mine, owned by
Rio Tinto, is the world’s largest source of pink diamonds, even
though they’re so rare that only a few are produced each year.
As
well as revealing what makes them pink, scientists hope that studying
the diamonds will tell them more about the history of the planet.
Diamonds
are the Earth’s messengers, says Post. “They come from a hundred
miles below the surface and tell us about a part of the Earth that we
can’t visit. They’re also giving us a peek back in time because most
diamonds formed about two to three billion years ago.
“Each
one is a time capsule, and the pink diamonds, because they’re
different from all the other diamonds, have a different part of the
story to tell.”
Scientists
have already examined the Argyle diamonds using a mass spectrometer
to try to find any trace of impurities that may be causing the pink
colour. The machine agitates the diamonds and analyses the chemical
structure of the atoms that are released.
“There
is no impurity that we’ve been able to associate so far with the pink
colour in diamonds,” says Post. “Spectroscopic measurements
don’t show you any additional features that you can ascribe to a
particular colouring agent.”
They’ve
also used a focused ion beam to cut a tiny trench in the surface of
the diamonds and remove a slither than can be measured under a
powerful electron microscope. They’ve discovered that most pink
diamonds are not uniformly pink but have pink zones that alternate
with clear areas.
The
zones, known as twin planes, were formed by some kind of shock –
possibly the result of volcanic activity that propelled the diamonds
to the surface or from something that happened to them as they were
being formed deep underground.
“The
twin plane itself should not give rise to colour,” says Post.
“But we think when those twin planes form, and slide back and
forth, one against the other like a fault plane, that certain kinds
of defects formed. The defects give us the pink colour. But what
we’ve not been able to do yet is find the specific kind of defect.”
Although
pink diamonds are among the most valuable jewels today, 20 years ago
they were little more than a geological curiosity. Sales have been
driven by savvy marketing and a growing appreciation of their
uniqueness.
“It
really comes down to the rarity,” says Richard Revez, a gem
expert at Florida-based Kravit Estate Department. “When you talk
about coloured diamonds, they’re already in the elite 1% produced in
the world. Pink diamonds are the 1% of the 1%.”
He
says the most sought-after diamonds are actually red, but orange,
green, blue and yellow are highly desirable. An orange diamond
attracted the highest price paid per carat for any diamond at auction
last year, selling for $35m, or $2.4m a carat.
“We’ve
craved diamonds for millennia,” says Revez. The first gems were
probably discovered on river banks in India, but their existence is
recorded in Greek and Roman history. “It was believed there was
a vein that ran directly from the heart to the ring finger – that’s
why we wear (diamonds) on our ring fingers. And Cupid’s arrows were
tipped with diamonds to pierce the heart easier,” he says.
Archduke
Maximilian of Austria is believed to have started the tradition of
diamond engagement rings among the upper classes when he presented
one to Mary of Burgundy in 1477.   But
it wasn’t until the 1950s that international standards to grade
diamonds were set by the Gemological Institute of America (GIA), a
classification system that is still used today.   But
only science can reveal why pink diamonds are pink.
Pink
diamonds can be artificially created, says the Smithsonian’s Post.
And the only way to tell if it’s a synthetic stone is to understand
what causes the colour to occur naturally.    “Then
I can tell you for sure that that is a diamond that came out of the
earth as opposed to one that came out of somebody’s laboratory. It
can make the difference of millions of dollars in the value of a
single diamond, knowing whether it is a natural pink or not.”

BBC
? 2014

24
December 2014

Extra note by Mike : Although we cannot (yet?) make Pink Diamonds from ashes or hair, we have experimented snd have made 20x  0.5ct ‘pinks’ brilliant cut (just to see if we can do it from pure carbon). So if anyone is interested, we are willing to sell them at ?2500 per 1/2 carat – just call us………