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Crazed opal II


#1

Anyone, I am not attempting to be extremely repetitve in my opal
comments, but I just had a few more things to add.

Other reasons for my interest in crazed opal involve black opal. If
you have a stone that is black (or actually just opaque) where you
cannot easily see cracks on the surface or especially internally, how
can you fairly value a stone? It seems as though it would be very
easy to write off alot of nice crystal material out there that is
really just the same quality as the opaque as far as crazing or
cracking because you see all imperfections easily. Also, people say
that feathers usually don’t reflect orange light, but some do. The
feathers often divide lines of color, so they should not cut across
patterns. What if you have feathers on two lines of color, where
underneath, the lower feather casts a shadow across the pattern
above? The reasons why I keep asking these questions is just because
these criteria are so critical, and it seems like there is a wide
door open for the dishonest to intervene: “Yeah, that opal looks
real nice and bright, but those aren’t feathers, it’
s crazing. I’ll give you 50 bucks for it”.


#2

If you have a microscope you can see crazing in black opal. I have
looked at and sold thousands of opals in my life and can’t say I have
ever seen naturally occurring feathers that look the same as
crazing. They may look similar but they don’t look the same.

Daniel R. Spirer, G.G.
Spirer Somes Jewelers
1794 Massachusetts Ave
Cambridge, MA 02140
617-491-6000
@spirersomes
www.spirersomes.com


#3

If an opal is going to craze, it will crack on the outer surfaces
first… because that’s where the stress is the least, or where it
will lose water first. That’s why a piece can look good in water,
then craze when you start working it. I was so excited once about a
16 gram (80 carat) piece of blue opalized clamshell, I came home from
a show and roughed out the shape. The next day, when I went to finish
the stone, it was a maze of spider-webby crazing, top and bottom.
Now, I always ask the dealer to take the rough out of a bottle of
water for me to examine first if it’s something I’m seriously
interested in. Had I done that, I should have noticed the little
orange flashes already present.

Feathers (tiny cracks) in black crystal material often reflect little
rainbow colors as fractures in other transparent materials do. If you
see a lot of ‘feathers’ scattered over the surface of black crystal
opal, you’re probably looking at crazing beginning to happen. Virgin
Valley can do this. I have some low grade VV that will form a crackle
surface within minutes of being taken out of water as all those
little feathers grow and connect! And I’ve seen stable material that
has been cut into incredible gems with not a feather in sight. You
just have to look carefully and know the material, or work with
someone you trust to know the material.

I can’t speak for black crystal, because I don’t work with it, but in
transparent fire opal, if you see a single ‘feather’ or a larger
isolated crack, don’t try to grind it away. Sometimes, that will
work, but more often, it causes the crack to spread. Instead, saw
through the crack or trim off the affected area. If the stone is
otherwise stable, you can then cut and polish in the usual way with
no problems.

Carol
www.eclecticlapidary.com


#4
and can't say I have ever seen naturally  occurring feathers that
look the same as crazing. They may look similar but they don't look
the same. 

Another thing that is sometimes confused with cracks in black opal is
a strong definition between color patches. I have seen some that
look very much like a crack face up but when examined closely, you
can see that it is the junction of the two color patches.

Don


#5

I’ve been reading all these emails about crazed opal. I have two
suggestions, comments: Buy from a reputable dealer, preferrably from
someone from whom you’ve purchased before and who guarantees his or
her product. Do not buy opal in water. After or while you are
examining the material you may choose to wet it to get a better look
at the color, but check it out dry first. If there is a problem
you’re more likely to see it while the material is dry.

Kevin Kelly


#6
if you see a single 'feather' or a larger isolated crack, don't try
to grind it away. Sometimes, that will work, but more often, it
causes the crack to spread 

Sometimes, the cracks you see in opal are the result of the grinding
process. They will be short cracks and aligned in groups of cracks
all parallel. I discovered this some six years ago when I got in a
hurry revolving the matrix from a very nice piece of Coober Pedy blue
crystal. I used the 180 grit hard wheel on my Genie to remove it.
When I got the matrix off the stone, I noticed the cracks. My first
though was bad opal and I had another piece. Upon closer inspection
though, the cracks were in parallel groups. I pitched the stone in
my junk opal pile and it has kicked around for over six years now and
there has been zero growth in the cracks. The matching piece has
been dry for the same time and shows no indication of cracking.

What happens with the corse wheels is a diamond on the wheel scribes
the opal like a glass cutter then on the next rev of the wheel it
whacks it a bit to start the crack opening. As the diamond is very
small, the cracks are usually not very deep or long. Most are in
the 1 to 2 MM range in length. In my case, it didn’t hurt the
stability of the stone, just it marketability.

Don


#7

Charles, There is a difference between crazed opals and opals with
inclusions. A crazed opal will have lost the fire or be in a state
of losing its fire. Once an opal looses the water it looses most of
the fire. Crazing allows the water to escape from the opal. There
is no method to replace the water and seal the opal. There also is
no method to stop the crazing once it starts. Crystal opals starting
to craze appear to be hazy internally. Jelly opals often show the
first signs of crazing with an opaque spot inside the stone. Opaque
opals start showing crazing with small cracks and a dull look. While
badly crazed opals can crumble with only slight hand pressure. That
is why you should never buy opals in liquid. Buy them dry and out of
direct sunlight. The worst place to buy opal is at an outdoor show
with the opals in bottles of water. Inclusions in opals are quite
different from crazing. But, you can have both in the same stone.
This becomes a very difficult subject. Especially with crystal
opals. Cutting crystal opals should be done on glass wheels or laps
or anything but metal or silicon carbide. Cutting them on metal
wheels induces stress fractures into the surface of the stone. These
tiny fractures open up after a period of time and look like crazing,
but they are not. Careful recutting of these stones can yield a
stable gemstone. Internal inclusions in crystal opals are in two
categories. Fractures and included minerals. Internal fractures
weaken the stone and drastically decrease the value of the stone.
Internal fractures also can spread and lead to a broken stone. In
crystal opals included minerals detract from the value of the stone.
So what I am saying is that an opal with feathers in it is not
valuable and is prone to further destruction.

Gerry Galarneau


#8

All, I had an interesting conversation with a major opal dealer at a
recent show I was a dealer in. He was a dealer there also and was
asking me a lot of questions about my fold down, interior lighting,
glass show cases. He wanted the security of the locking cases, but
was very concerned about the heat generated from the interior
lighting. Being an opalholic I asked him if his opal was stable.
Most stable opal will withstand the heat of lighting. He told me in
no uncertain terms that no opal is guaranteed to be stable. His
opals are all sold in a condition “as is” when they are purchased.
He sells black Australian opals up to $100,000, or maybe more. I
told him about the recent guidelines in the USA about disclosure.
Especially about “special care instructions.” He was very upset and
said that he would change his invoices to say that the items were
purchased “as is” at the time they were purchased. No guarantees.
This comes from one of the two largest opal dealers from Australia
that shows in the USA. I thought “as is” was a used car salesman
tactic.

Gerry Galarneau