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 Boulder
opal has a special place in my mind. Most of the times I've seen
precious opal in jewelry, it is absolutely beautiful and obviously
exceedingly special. Yet, boulder opal, which is a type of precious
opal, has a striking ying/yang quality of extraordinary beauty in a
matrix that is as ordinary-looking as dirt.
When
this piece was broken, it cleaved along a plane of opal leaving a lot
of it exposed, but very difficult to use. The opal itself is exceedingly
thin and the surface is uneven, so it can't be cabbed. Boulder opal is
mostly cabbed by cutting across the thin lines of opal to emphasize the
difference between the opal and the matrix.
But,
when it comes to capturing every bit of the incredible color, hope
springs eternal! I found a bit a little over one inch long that had opal
showing along the
top edge. There wasn't enough on any side to do a
proper cabochon, but there was a little bit. I made it into this
free-form cab that looks like it is flowing through the matrix. I
didn't grind it down to make a smooth surface the whole way; partly
because I didn't want to waste any of the gorgeous opal and partly
because it gave more of a look like it was active and moving.
OPAL FOR CRAFTSPERSONS
The
natural irregularities of opal make it unsuitable for most commercial
jewelry making. Much of the material you see, especially if it is
reasonably priced, is likely to be laboratory-created. From the
craftsperson's point of view, it is a beautiful, predictable product to
work with.This pendant I received as a gift shows two varieties of fire
opal and I love it and I'm pretty sure it was made with lab-created
stone.
WHERE IN THE WORLD?
You
won't find this very cab-worthy stone nearby unless you are in
Queensland, Australia although small amounts have been reportedly found
in Brazil and Canada. It's a lot easier to get it the way I did--I
purchased two chunks at the show in Tucson earlier this year. One of
them is pictured at the top of this blog post.
ORIGINS
Back when dinosaurs were alive (the Cretaceous
period - approximately 50-65 million years ago), silica from
decomposing rocks mixed with water creating a gel. This settled into the
cracks in the ironstone or sandstone boulders or puddled on the top and
solidified over time become boulder opal.
Notice
I called this "precious" opal; there is also an opal material called
"common". The difference is both how it formed and more importantly, how
it looks. Precious opal is formed when the gel opal sets down in a
series of rows. When seen in the light, it flashes iridescent colors
that can include red, yellow, blue, green, often
called "fire" because of the dramatic play of color, sometimes called
"flash". The value of the stone depends on the drama in the flash.
 Common
opal, on the hand, is well, common; but not without its charms. A
friend once gave me a hunk of common opal. I took one look at it and
decided it looked like halibut to me, so I tidied it up a bit and liked
it so much I ended up making a meal display for the "Rock Hard Cafe"
display I take to shows. My halibut is shown here with a sandstone
baking potato and some jade peas.
CARING FOR YOUR BOULDER OPAL
You've
probably learned that opal dries out and has to be stabilized in water,
with oil, or chemical preservatives like Opticon.
According to Opals Down Under boulder
opals are very stable, can not absorb water, and are unlikely to crack.
They are about the same harness as glass (about 6.5 on the Mohs scale).
Soaking a boulder opal in water may hide small flaws (be sure to see it
dry if you're thinking about purchasing it), and rubbing it with oil
will only make your boulder opal oily, but neither will do anything to
enhance your stone.
In
terms of preventing damage, Opals Down Under states, "The only major
things that can damage your opal are impact, extreme fluctuations in
heat (e.g. placing your opal over a flame) or exceedingly low humidity
for long periods. Extreme variations in heat cause the opal to expand
and contract, causing cracks or crazing." One thing that can definitely
damage opals over time is having it touch other surfaces and acquire
tiny scratches that affect the shine. If that happens, a professional
jeweler can polish the stone and remove the scratches. The possibility
of scratching these beautiful stones is why many people choose to wear
their opals as pendants or earrings to protect them from contact with
other surfaces. It's also a good idea to store them in a jewelry box or
bag.
If you're
thinking about working on some boulder opal, I say go for it! The
material is soft enough that it won't take forever to cut, shape, and
polish it, and you'll love the results!
Have you worked with boulder opal? I'd love to see a picture of the cabs you made!
Until next time,
Your Lapidary Whisperer,
Donna
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