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What does a crazed opal look like?


#1

What does a crazed opal look like? How do I know what to look out
for?

Tracy Munn


#2

Crazed opal appears to have many tiny fissures or cracks running
through it, almost always randomly. I actually see it fairly rarely
and usually only in very old pieces, although occasionally I have even
been offered it for sale by dealers.

Daniel R. Spirer, G.G.
Spirer Somes Jewelers
@spirersomes
www.spirersomes.com


#3
    What does a crazed opal look like?  How do I know what to look
out for? 

Do you know what an old china plate that has spider web cracks, well
that is what a moderate progression of crazing looks like in an opal.
It will start with a single small shallow crack on the surface and
as time progresses, it gets worse. As has been stated here, once the
process starts, there is no reversal or solution. Crazing should not
be confused with cracks though. Some cracks are the result of damage
to the stone. You can grind out a crack and salvage a stone. You can
not grind out crazing or salvage a stone experiencing it.

I have heard it said that there are two types of opal, that which is
cracked and that the is going to crack. I don’t follow this school
of thought. I have seen some very old opals that were in fine shape.
I have seen opal that would start to craze and crack within minutes
of removing it from water. Some areas produce opal that is know to
be unstable, IE Nevada and some Mexican locations. Some produce opal
that is known to be very stable, IE Andamooka crystal has the
reputation of never crazing.

Don


#4

Tracy, Unfortunately it is impossible to miss a crazed opal. It is a
heart rending situation, especially if it is a nice bright opal. What
you will generally see is a spider web of small, usually short,
surface like lines similar to the crackle on a piece of fine
porcelain. On some opals they will appear a bit lighter than the
material around them. On others they may retain the color of the opal
but they will look like scratches. But they are cracks, albiet very
small. They usually will start out as surface cracks but, in time,
will go the whole way through. You can tell this if you hold the
stone up to a strong light and see the surface crack on the top and
the shadow of the crack on the bottom. I’ve had a few stones over the
years that crazed so badly that they simply fell apart into hundreds
of little pieces. In my experience, once a stone shows crazing, it is
not worth recutting it as it will simply re-craze. Best to break it
into little pieces, put it into a tiny plastic bottle with mineral oil
and make earrings out of it or make it into inlay with resin. Breaks
my heart to see one!

Cheers from Don at The Charles Belle Studio in SOFL where simple
elegance IS fine jewelry and it is wet, wet, wet!


#5

Look for one or more cracks in the stone. Sometimes so many that the
stone looks reticulated with a network of cracks, somewhat like the
pattern of tortoisehell although less regular.

Opals contain water in their structure; more or less water depending
on the source and the type of opal. Crazing occurs when the opal is
stressed; losing its water stresses the stone. Picture the cracks
which form as mud dries; the process is somewhat similar. The
conventional wisdom is that those opals which contain the most water
are the most susceptible to crazing. In opal like Honduras crystal for
example if you cut to grind away a crack usually a new one (or more)
will form more or less promptly as soon as the stone dries out again
after grinding.

Also, opals from volcanic matrix (eg basalt and rhyolite, such as
Honduras and Mexican) are held to be more susceptible to crazing than
opals from sedimentary formations (Australian). Opal diggers will
often keep the rough stones in a dry room, or out in the hot sun, for
a period of several months to a year; stones which have not crazed
under that stress are assumed to be safe for cutting & wear.

Some cracks may be may be shallow, others deeper. They can be
difficult to spot, particularly when you buy rough that’s been kept in
a jar of water or a water bath. Water hides cracks which are already
there and retards the formation of new ones. Oil is even worse. Never
buy opal that’s been kept in oil, unless you soak it in acetone first
to dissolve the oil out and then let it dry & check for cracks.

Cracks in a finished stone should be evident. When checking rough, a
good technique is to hold the (dry!) stone at the very edge of the
shade of one of those common “draftstman’s arm” type desk lamps. Let
the light fall into the stone but not into your eyes, in other words
look slightly down into the stone, at the same time turning the stone
to check from all directions. This helps show cracks clearly.

Cheers,
Hans Durstling
Moncton. Canada


#6

tracy munn - if you see a large brightly sparkling, iridescent chunk
of matter with wildly tangled hair flowing in the breeze, foam around
its snarling mouth, & unfocused bloodshot eyes heading toward you -
run! you now know what a crazed opal looks like. and, if you see an
opal that has faint lines in a crackle pattern either on or below the
surface of the stone that is also a crazed opal. joke, people - ive