Gem
World Jewellers
Facts and figures about Opals.
Nature's
Fireworks:
Mysterious opals
contain the wonders of the skies - sparking rainbows,
fireworks, and lightning - shifting and moving in their
depths. Opal has been treasured throughout history around the
world. Archaeologist Louis Leakey found six-thousand year old
opal artefacts in a cave in Kenya!
Roman historian Pliny described the beauty of opal as the
combination of the beauty of all other gems: "There is in them
a softer fire than the ruby, there is the brilliant purple of
the amethyst, and the sea green of the emerald - all shining
together in incredible union. Some by their splendour rival
the colours of the painters, others the flame of burning
sulphur or of fire quickened by oil." Opal was much loved and
valued highly by the Romans, who called it opalus.
At the same time, opal was also sought in what would become
the Americas. The Aztecs mined opal in South and Central
America.
Opal was also treasured in the Middle Ages and was called
ophthalmios, or eye stone, due to a widespread belief that it
was beneficial to eyesight. Blonde women wore opal necklaces
to protect their hair from losing its colour. Some thought the
opal's effect on sight could render the wearer invisible. They
were recommended for thieves!
Opal as Muse:
A beautiful opal called the
orphanus was set in the crown of the Holy Roman Emperor. It
was described as follows: "as though pure white snow flashed
and sparkled with the colour of bright ruddy wine, and was
overcome by this radiance." This opal was said to guard the
regal honour.
Opals are also set in the crown jewels of France. Napoleon
gave Josephine a beautiful opal with brilliant red flashes
called "The burning of Troy," making her his Helen.
Shakespeare found in the opal a symbol of shifting
inconstancy, likening play of colour to play of mind in one of
the most apt uses of gemstone symbolism in literature. In
Twelfth Night, he writes: "Now the melancholy God protect
thee, and the tailor make thy garments of changeable taffeta,
for thy mind is opal."
In the nineteenth century, opal was considered unlucky due to
the plot of a popular Sir Walter Scott novel of the time. The
heroine of the novel has her life force caught in the
beautiful opal she wears in her hair and she dies when the
fire in the opal is extinguished.
Queen Victoria loved opals and often gave them as wedding
presents. She and her daughters created a fashion for wearing
opal. Queen Victoria was one of the first to appreciate opals
from an exciting new source: Australia.
Ancient opal came from the mines near Cervenica, Hungary, in
what is now Eastern Slovakia, where hundreds of men mined the
stone. Ancient opal fanciers never had the chance to see the
opal of Australia, where the opal of today was born, which far
surpasses the beauty of Hungarian opal in fire and brilliance.
A Gem of Water, Born in the Desert:
The story of opal in Australia
begins more than 100 million years ago when the deserts of
central Australia were a great inland sea, with silica-laden
sediment deposited around its shoreline. After the sea receded
and disappeared to become the great Artesian basin, weathering
30 million years ago released a lot of the silica into a
solution which filled cracks in the rocks, layers in clay, and
even some fossils. Some of this silica became precious opal.
Opal is one of the few gemstones that is sedimentary in
origin. Opal still contains 6 to 10 percent water, a remnant
of that ancient sea.
Gold panners in Australia found the first few pieces of
precious opal in 1863. Mines at White Cliffs began producing
in 1890.
Only opal with a perfectly aligned grid of silica spheres will
show play of colour, which is created through diffraction. The
size of the spheres determine the wavelengths and therefore
the colours seen. The brilliance of the colours are determined
by the regularity of the grid.
The strength of the colours seen in opal also depend on the
background body colour and the transparency of the stone. The
body colour determines the variety of opal and has a large
impact on the value.
Black opal, opal with a black to dark grey body colour, has the
most brilliant colours and is the most valuable. Crystal opal,
the next most costly type of opal, is transparent with flashes
and is highly valued due to the brilliance of its colours and
the fact that many layers of colour within the stone can also
be seen. White and milky opals tend to have more diffused
colours due to the light background colour. This is the most
affordable type of opal.
Another more unusual type of opal is boulder opal, which has
opal with an ironstone host rock matrix which creates a
natural dark background to view its fire. These sometimes
occur in "splits" a matched pair of opals created when a piece
of boulder opal is split along the opal vein. These are
particularly favoured for earrings, since they are mirror
images of each other.
Choosing an Opal:
Within each opal variety, the
brilliance of the play of colour is the most important value
factor. After this consideration, the colours seen and the
pattern of the colours will also influence value. Generally,
opal with red fire is the most valued because opal that shows
red will also show other colours when rolled back and forth: it
contains the whole spectrum. The pattern of the play of colour
also influences value. Generally large flashes and broad
patterns are more rare and valuable than small pinfire
patterns.
Black opal is found only in Australia in Lightning Ridge, the
most famous opal deposit in the world since it was discovered
in 1903, and in Mintabie, which also produces large quantities
of light opal.
Another large opal producing area in Australia is Coober Pedy,
which produces light opal. The name Coober Pedy is an
Aboriginal name meaning "white man in a hole." If you visit
Coober Pedy, you will understand how it got its name: many
houses - and even a church! - are burrows dug into the ground
called dugouts. This type of dwelling is quite practical and
cool as temperatures soar in the daytime.
Andamooka is known for producing crystal opal and light opal.
Boulder opal is produced in several areas in western
Queensland.
In addition to Australia, a small quantity of precious opal is
produced in Brazil. Mexico and the state of Oregon in the
United States produce a volcanic opal called fire opal. Fire
opal is transparent opal ranging in colour from colourless to
yellow, orange, and red. Sometimes it also shows play of
colour
in addition to its bright orange body colour. Low quality opal
was recently discovered in Ethiopia.
Opal is cut in Australia, Hong Kong, Mexico, Germany, and
other places. Calibrated sizes are widely available in light
opal, which is very popular with jewellery manufacturers around
the world due to the beauty even of inexpensive pieces. Black
opal is cut in free sizes due to its rarity and high value.
Boulder opal is often available in the natural shape of the
rough. Fire opal can be found in both faceted and cabochon
cuts, including many interesting fancy shapes.
A green translucent opal that resembles chrysoprase or jade,
which is called prase opal, is found in Tanzania. A beautiful
blue-green opal is found in Peru in the Andes Mountains. These
types of opal do not display play of colour.
The hardness of opal ranges from 5.5 to 6.5 on the Mohs scale.
It should be protected from heat and strong light, which can
dry it out, causing cracks. Ultrasonic cleaners, metal polish,
acids, and any strong solvents should be avoided. Exposed
corners or points on pear or marquise shape opals may chip if
hit while they are being worn. Opal is best set in a protected
mounting.
Opal Grading Opal Lore Opal Jewellery
The factors to consider in grading opals are: Size of Colours, Number of Colours, Brightness/Life, Inclusions, Size, and Cut.
An opal with large patches of colour is worth more than an opal with small patches of colour. Several colours are worth more than one colour. The brightness of the colours is very important. Bright, vivid colours are more valuable than muted, dull colours. Look for extinction. That is what happens when you turn an opal different ways and the colours can only be seen in some directions and not others. The more life and less extinction an opal has, the more valuable it is.
Inclusions (unless they are interesting, such as one that is in the shape of Australia or something) detract from the value.
A large opal (all things being equal) is worth more than a small one up to a point. If an opal is too large to be useful for anything, it is hard to sell, and thus less valuable.
A well cut opal will be symmetrical, well polished, and not lumpy.
Many opals that used to be bright and lively, seem to lose their colour. People say that they "dried out" and that's why they lost their colour. Take a closer look. Is the surface "frosty" looking? Opals are not hard to scratch and frequent wearing will put a lot of tiny scratches on the surface. Then it is like trying to see a rainbow through frosted glass. The colours are there, but very dull. Polishing the opal will bring the colours back to their vivid best.
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