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About Opal
Including information on caring for opals
at the bottom of the page.
BE SURE AND LOOK AT THE Doc's Corner PAGE FOR MORE OPAL INFORMATION
VISIT THE Doc's Opal Bench PAGE TO SEE AN OPAL BEING CUT.
Opal is a wondrous gemstone with a chemical composition of SiO2nH20, a hydrous
silicon dioxide. Similar to quartz, but containing water trapped between
spheres of silica in an orderly arrangement. If you think of packing round objects
like tennis balls into a big box in an orderly manner, row upon row, layer after layer,
you will get some idea of what an electron microscope would show you about how precious
opal is formed. Precious opal contains approximately 6% to 10% water. In
stable opal, the water is locked in microscopic "chambers" formed by the
arrangement of the spheres of silica.
The fantastic colors produced by opal are a direct result of the size of the spheres of
silica and the spaces between them. The light rays are split by the voids developed
by the lattice arrangement of spheres and spaces. Think of a prism that splits
white light into the spectral colors. In opals, a specific color is produced by a
specific size of sphere and the resulting size of the void between spheres. The size
of the voids is determined by the size of the spheres. The colors perceived are
dependent on the size and arrangement of the spheres/voids. The smallest spheres/voids
yield violets, blues, greens and the larger spheres/voids yield oranges and reds.
The different arrangements can cause the colors to be visible from certain angles and not
from other angles. The visible colors can change or disappear as the stone is
rotated. See the Directional Play of Color page
for a greater understanding of this phenomena.
The opal potch, or opalized material base without play of color, also contains
silica spheres, but they are not in an orderly arrangement and therefore, do not produce
the even voids that would produce a regular diffraction of the light waves as they are
reflected back to the eye. Opal material without play of color is also is known as
common opal. There are many beautiful varieties of common opal in the world, but
they do not contain the play of color that transforms opal into precious opal.
Opal occurrences in Australian are found in deposits formed from around 1.8 to 70 million
years ago as a function of geological occurrences specific to certain areas of
Australia. There is a great deal of literature available on this subject.
Since 96% of the world's opal production comes from Australia, the unique set of
conditions required to produce opal there seem to have been the best in the world.
Each and every piece of opal is unique. No two stones are exactly alike. There are,
however, some similarities that allow opal material to be categorized and valued. These
are, of necessity, rather loose guidelines as opal is a "stone of exceptions."
Opal lovers can learn the basics and use them as a guideline in their opal purchases. We
will attempt here to give you an indication of the basics.
Opal has a variety of base, or background, colors from black through all variations all
the way to pure white and crystal clear. The most valued opals are the blacks followed by
the crystal clears. The problems immediately start to develop when you try to determine
exactly what constitutes black opal. The characteristics effecting opal value are so
subjective that even the experts do not always agree. In Australia there are four
shades of "black" opal encompassing every thing from pure black through dark
gray opal. Additional categories cover the ranges between black and light opal under the
semi-black categories and then the light categories. All of these labels simply cover the
base or background colors that are feasible in opal material.
The next "color" area to consider is the color of the fire or "play of
color." Red is the rarest and therefore the most valuable color. Blue is the most
common and least valuable color, but the occurrence of red and blue fire is rare and
valuable. In general the multi-colored opals are the most valued with an
emphasis on the multi-colors with a dominance of red. There are many exceptions, of
course.
The next area of concentration in valuation is the pattern that the fire colors take on
the stone. Harlequin patterns are the most valued as they are the rarest. The flash or
broad spread of color is the next most valuable of the larger categories and the pin fire,
which is the little dots of fire, is the least valuable of the fire patterns as it is the
most common. There are numerous other patterns, but these are the main three.
This makes valuing opal sound pretty simple, but as previously stated, opal is a
"stone of exceptions." After reading the guidelines above, you are likely to
pick up a stone next week with a large amount of black background that eventually gives
way to a translucent honey color. The colors may be zoned into some red pin fire at one
end in the honey opal with some broad flash blue that rolls to green over the black with a
solid black area in between. The end result of your study will be that even if you know
what a black opal with blue fire is worth or a translucent honey opal with red pin fire is
worth, you still do not know exactly what your stone is worth. This is the rule rather
than the exception. There are many good sources of information on valuing opal available
to anyone who is interested in learning the guidelines.
If you are cutting opal as a hobby for your own
enjoyment, or for the jewelry that you make, we like to recommend, that you work with what
you like or what you know that your customers will like, or what will look good in an
individual piece of jewelry. If blue is your favorite color and you are not at all
fond of red, then I would seek out the blues unless you have a customer who specifically
asks you for red opal. You will find that there are plenty of customers out there who feel
that same way. Do what you love and do not worry about what the experts say! Let us know
what you are looking for, do not hesitate to call us or email us and ask for our
recommendations based on your wants. We are very familiar with our stock and will have a
good idea of what we have that will work for you.
An additional area that effects the value of an opal cabochon is whether the cabochon is a
solid, a doublet, a triplet or a mosaic. A solid opal is exactly what it sounds like it
is, a solid piece of natural opal. This is the most valuable type of cabochon. A doublet
is a thin slice of opal mounted with epoxy onto a usually black piece of opal potch. The
advantage of the doublet is that it allows you to utilize a good piece of opal that is too
thin to be used as a solid cabochon. A triplet is like an opal sandwich with the middle
piece being a thin slice of opal epoxied between a clear quartz covering and a black
usually potch base. A triplet allows even thinner pieces to be used in creating a
cabochon. A mosaic is like a triplet except that the opal color is provided by little
pieces of opal material set between the other two layers. The mosaic concept allows for
tiny pieces of very colorful opal material to be assembled into a single very colorful
stone. The advantages to the purchaser are that a very colorful doublet is less expensive
that a solid opal showing the same coloration. The same is true for the triplets with the
added advantage of the quartz top which protects the relatively soft opal material
eliminating one of the considerations in setting the stones. Mosaics can be quite colorful
by utilizing tiny colorful bits of opal material from several different sources. Good ones
can be quite attractive.
Now that you are totally confused on the subject of
valuation we will refer you to one of the authorities in this area. One of the
recognized experts in the area of opal evaluation is Paul B. Downing.
Mr. Downing in his book, Opal
Cutting Made Easy, says,
"Here are the
characteristics you should consider:
(Photos are by Liz McKay and added here to
help illustrate Mr. Downing's text.)
BRIGHTNESS
OF THE STONE: The brighter, the better!
 
BASE COLOR
– While what you like is a matter of personal preference, generally black base color
is most valued, followed by crystal, semi-crystal, gray, and white.
White base
 *
Gray base
 *
Cut crystal base
Gem Crystal
base
Gem Black Base
Black - Excellent Rough
Gem crystal over a black core, very
unusual
FIRE PATTERN – Again, a matter of
preference, but harlequin is very rare and most valued with flashfire and pinfire less
preferred, in that order.
* *
 *
 *
COLOR OF FIRE
– Also a matter of preference, but in the United States red is usually preferred. Multicolor is more preferred than single color
stones.
 * * *
 * * *
SIZE AND SHAPE
– Larger stones are more valuable as are stones which will cut high dome solid gems.
ORIENTATION OF
COLOR – Stones that show their best color in an orientation which allows you to cut
larger stones are most preferred.
CRACKS –
They should be avoided if possible and should never be included in a finished stone."
There are many sources of theories on
valuing opal but Mr. Downing will certainly get you pointed in the right direction in this
book. We sell copies of this great little book in our section labeled "Other
Neat Stuff ." We are frequently asked to
recommend books for beginners and this one is the best ones that we know about. Paul has also written other books and has tapes
available on opal cutting. All are available
on his web site at http://www.paulbdowning.com.
If you contact Mr. Downing to purchase a book, he
would like to know that you heard about him from this sight, so use our name and get us
some brownie points.
If you are cutting opal as a hobby for
your own enjoyment, or for the jewelry that you make, we like to recommend, that you work
with what you like or what you know that your customers will like, or what will look good
in an individual piece of jewelry. If blue is your favorite color and you are not at
all fond of red, then I would seek out the blues unless you have a customer who
specifically asks you for red opal. You will find that there are plenty of customers out
there who feel that same way. Do what you love and do not worry about what the experts
say! Let us know what you are looking for, do not hesitate to call us or email us and ask
for our recommendations based on your wants. We are very familiar with our stock and will
have a good idea of what we have that will work for you.
One of the most frequently asked questions that we hear is,
"How do I care for my opal?"
The
answer is relatively simple. Just remember that opal is a relatively soft stone and
you should not "expose" your opal to things that could scratch the surface of
the stone or crack it. i.e. do not wear your opal ring while cleaning out the garage
or digging in your garden. An accumulation of tiny scratches on the surface of an
opal over time will dull the appearance of the stone. Look on the Doc's Corner Page to see one of these abused opals that we
recently worked on successfully. We show the before and the after photos.
The
second area of concern is that opals do not like chemicals. So, do not expose your
stone to them. i.e. do not wear your opal ring while washing dishes. An
exposure of this type will over time cause the surface of the stone to appear cloudy and
less brilliant.
A
third consideration with your opal is extremes of heat, cold and dryness. Do not
subject the stone to extremes of any of these. i.e. do not lie in the sun with your
opal on and expose it to extreme heat of the sun over a prolonged period.
Particularly, do not heat your opal ring in the sun and then dip your hand into the ice
chest with the ring on. Where dryness is concerned, the extreme dryness in safety
deposit boxes has been know to cause problems. More than one person has gone to
retrieve their opal to find it had cracked while being stored under these
circumstances. If you find that you must store your opal for some period of time
somewhere then pick a place with a very moderate temperature and you might put the opal in
a plastic bag with a little bit of distilled water. We do not recommend
that put oil on your opal. If you do have hair line cracks, scratches or crazing on
your stone, the oil will fill them and then start to attack dirt. It is possible
that the stone itself over time could absorb some of the oil with the same result.
Not a pretty thought. If you are just starting out, remember that opals are
more fragile than some stones and an opal in a ring should be in a protected
setting. You might even want to consider a triplet for your ring and put that really
good one into a pendant or pin. You are welcome to contact us for design
ideas. We do custom jewelry work and work with a number of very talented jewelers as
well.
Opal
is a life long learning experience. We will continue to add information about opal
to this page as time permits.
We
also have information about opal on the Doc's Corner Page
including a glossary with photos.
Photos
marked with an asterisk (*) are used courtesy of Our Australian Connection
with permission. All of them are, or have been, on sale there in the past. The
presence of the photo on this page is for information only and does not insure that that
particular opal is still available at this time.
Gold Rush Jewelry, Bead and Art Company
P.O. Box 635 Fairplay, CO 80440
719-836-2143
You are welcome to call us. This number rings at our home and studio which are located in
the same place. Just place your call at some reasonable hour for our time zone which is
Mountain Time in the United States. You may also contact us by email at any of the
addresses below.
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