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Disputing all opal cracks theory


#1

Hi all,

I would like to dispute the claims made that all opal cracks
eventually, this is simply not true, Some unstable opal will crack
and craze but this is a very small percentage considering the
amount of opal in the market place. Claims like this is not good for
any industry just like some people will slam opal from certain
counties, this is an unfair and uneducated claim as there is
unstable and risky material in any gemstone category and the only
way to avoid this risk is education, education and more education
on the particular gemstone you wish to purchase. I have cut and
carved black opal here on the field in Lightning Ridge for 13yrs
now and have spoken at length to long term opal buyers and their
percentage of stones cracking over some 30 and 40 years in the
trade was less than 1%, yes less than 1%, Keep in mind that these
buyers deal mostly in Black opal and Queensland boulder opal.

I am only responding to this as it’s the 2nd time in the last 3mths
that these suggestions have been made.

Just a quick comment on all the orchid posting contributors, you
people are just wonderful and so sharing with your hard won
experiences, this is probably the most valuble thing in the
jewellery trade today. WELL DONE TO YOU ALL.

Christine


#2

totaly agree with Christine I carve and freeform lightening ridge,
mexican opals all the time and I must say that if kept properly most
opal crystal or otherwise lasts just as well as any other stone.

Teri D
America’s only Cameo Artist
www.cameoartist.com


#3

Dear Christine,

I certainly agree with of most of what you say, but will have to
take great exception to your inference that most opal sources
produce crack free opal. There are some opal localities that rarely
produce crack free opal ( i.e. Virgin Valley, Nevada ), some that
have a high rate of cracking, ( Queretaro, Mex. ) and some that
almost never crack ( your own Lightning Ridge )

While you may perceive that spreading rumours about opal instability
is a threat to your industry I would suggest that your greatest
threat is the pervasive spread of jewelry made with man made opal.
Oddly enough one of your most illustrious residents there at the
"Ridge" has done much of the pioneering work in opal synthesis.

Yes…education is the best antidote to ignorance. We all have to
keep an open mind and explore every aspect of a problem before we
can form an enlightened perception.

Ron Mills ,
Mills Gem Co. Los Osos, Ca.


#4

Christine,

What I said about opal was not a slam and in no way meant to
denigrate the industry! Goodness knows I have cut enough opal over
the past 30 years and still do cut it. I also teach opal cutting.
What I said was a statement of reality based on my experience and
what I have seen with my own eyes. I have had many many opals come
in to me that were from one Grandma or another and a percentage of
them were crazed…not cracked…but crazed. Many were chipped
many scratched, etc, etc. That was, after all, what the original
point of this discussion was - how to repolish an opal. I doubt the
statement was unfair either but I totally agree with you that
education is the way to preclude ‘old wives tales’. That is why
many people talk about opal being ‘unlucky’ which is pure nonesense.
On the other hand, there are certain aspects of nature that we
cannot ignore and the delicate nature of opals is one of them. But
then the same is true with Tanzanite which has its own problems of
acceptance as well as other stones.

By the way, I have a nice piece of LR black that …guess
what…its crazed! Guess its just part of that 1%!! Would I make a
general statement about LR black crazing because of this one stone?
No way…I have cut too much of it to say that. But, its crazed.
Bolder opal? Well, I haven’t seen it but woudn’t bet it won’t
craze! Mexican opal? It crazes. Baltic Opal? It crazes. Two opal
materials I don’t think crazes is Louisianna opal and Hondoran
black. Nonetheless, opal is one of the most beautiful stones on
earth and nothing I would or could say from my little studio will
have much effect on the world opal market!

Cheers from Don at The Charles Belle Studio in SOFL where simple
elegance IS fine jewelry! @coralnut2


#5
    I would like to dispute the claims made that all opal cracks
eventually Christine 

I’m not a gemologist or lapidary artist, but I would tend to agree
with you and the others who’ve disputed this claim that all opals
eventually crack. I base my opinion on my experience with repairing
estate jewelry. I have seen many, many opals, some very old, with
abraision, chips, etc., all probably from wear. But on rare
occaissions, I’ve seen opals with multiple fractures that appear to
be the result of internal stresses rather than external impact. I
have strong suspicions that the primary cause of this condition is
that the opal has been subject to extreme or abrupt temperature
changes, such as putting an opal in the jewelry case, under the hot
lights, or in a store window with the sun blazing in on, then back
into the nice, cold safe for the night. Or wearing an opal ring to
do dishes in hot water, then rinsing one’s hands in the cold water.

David L. Huffman


#6

The reason I say that opal can crack when it’s old and being
repolished is that I’ve had it happen completely without
explanation, even under sufficient water to keep it flushing.

Upon father reflection I realized a couple of things. First that
since opal that needs repolishing is more than likely a ring or
bracelet stone that’s been abraded through wear. It has by
definition had a bit of a tough time of life or it wouldn’t be
scratched to begin with. That’s the exact reason it needs
repolishing. Had it not received rough wear, it wouldn’t need
repolishing. The other part of that is that when it needs
repolishing, obviously it’s because it’s cloudy and you can’t see
through that cloudiness. It seems very possible that there are
problems underneath that cloudiness that a person polishing wouldn’t
know about because you can’t see through it until it’s somewhat
better polished or unless you wet it. Of course then the water gets
into and fills the crack temporarily which is why you can see
through the clouds. Then when it dries again, the crack might
reappear but you can’t see though it again. Even a tiny crack could
cause a big problem. As all of us who have cut opal know, once a
crack begins somewhere, it will sooner rather than later extend
across the stone unless that part of the stone where the crack is is
removed. Actually one question has always kind of struck me and is a
little difficult to explain. Why is it when a small crack is removed
from a stone the rest of the stone tends to stay stable but when the
crack is left it seems to inevitably want to extend? The part of the
stone that remains uncracked, or uncrazed if you will, should not
seem to be affected by a crack that’s not reached there whether you
remove the crack of leave it. It’s possible that a weakness or
instability actually remains whether you’ve removed the crack or
not.

Incidentally, I believe it was Charles who made a distinction
between cracking and crazing. To me that’s a distinction without a
difference. I know it is semantically the same, dictionary-wise. At
least according to the Oxford English dictionary. I wonder what the
difference in stone speak would be.

Derek


#7

Hi all,

I am so glad that Christine has defended our good old opals. My
brother regularly mines on the Ridge, my husband-to- be cuts them
and I have set a few of them in silver.

I dont seem to have any problems setting them, even though im just a
beginer However, black opal is very different from other kinds of
opal. having spent a bit of time on the Ridge myself and having a few
miners as friends, I know a few tricks that they do just to sale bad
quality opals to the novice, hence the misconception regarding opal
quality.

But please dont underestimate the fire of Lightning Ridge, it is one
of the most beautiful stones I have seen. And seeing my brother in
the mines, I can honestly say that I have a much greater
appreciation for them.

Ps, wet pumice powder on a polishing disc can do wonders for the
scratches on the stone.

Take care


#8

Would like to ask your opinion… Regarding the opal thread -

I received a ring as a gift about 10 years ago. It was made by a
local artisan. I was told that the center stone is a triplet - a
round opal sandwiched between a lower layer of black onyx, and the
top layer being clear quartz.

My question is, will the quartz layer prevent fissures or cracks
from occurring inside the opal, or will it merely provide some
protection against abrasion?

I also admit that although the quartz layer has become abraded, I am
hesitant to have it polished, as I am not sure if this might heat up
the opal or damage it.

Any opinions shared would be welcome.
Sincerely,
Mary Beth


#9

Mary Beth,

An Opal Triplet is created because the Opal is generally to thin and
delicate to be used as a gemstone on its own.

The Onyx back and clear Quartz top are glued to the Opal to give it
strength and durability. This does not mean it makes the Gemstones
indestructible.

An Opal triplet should be taken care of the way a solid Opal would
be. Avoid harsh household cleaners, extreme heat and cold as well as
sharp blows.

If the Opal doesn’t have cracks or crazing now it most likely will
not develop them unless the stone is subjected to the harsh
treatments I mentioned above.

As for repolishing the Quartz top of a Triplet, yes it can be done
but you should have a professional lapidary do this job. If the stone
is not kept cool the Opal can craze or crack and the glue can become
compromised.

Greg DeMark
greg@demarkjewelry.com
http://www.demarkjewelry.com
http://www.outdrs.net/~demark


#10
    My question is, will the quartz layer prevent fissures or
cracks from occurring inside the opal, or will it merely provide
some protection against abrasion? 

Hi Mary. You probably know this but, for the most part, opal
triplets are constructed for precious opal that is too thin to be a
durable solid opal, usually the type where there is a thin seam of
color that wouldn’t be thick and durable enough by itself. That
being said, yes, the quartz layer, along with the backing (be it
onyx/chalcedony, jade, etc.) AND the glue/epoxy/binding agent can
all act together to help protect the thin opal layer inside from
cracking/crazing/chipping/breaking and, as you mentioned, abrasion.

I’m not saying it will prevent any of the above, only that it can
help prevent them. Also, please note in the second sentence, I said
"for the most part." There are other reasons to make triplets from
opal. And I’ll never take a position as to whether "all opals crack"
or not. Every opal on the planet (except for the lab-createds) is
millennia in the making; I don’t think I’ll be around long enough to
really know. I feel much more like a curator or custodian than an
owner.

James in SoFl, President of the local chapter of Opalholics
Unanimous.


#11

Hi All,

There is no 100% accurate answer to your question Mary Beth but I
will have a bash at it anyway.

The crystal is there first and foremost to create the illusion of a
cabbed stone and to magnify the colour and pattern of the very thin
sliver of opal in the triplet.

If it is a well made triplet it should not crack or craze, most
problems happen with triplets when they are worn in water doing the
dishes ect. This causes the glues to let go and then the colour of
the opal has a clouded effect as it has lost total contact with the
quartz dome. Most triplets are calibrated and are not very expensive
so I would tend to get my jeweller to replace the triplet if it
gets too scratched. If you know a lapidary person that makes triplets
who will do the repolishing of the triplet you may be able to get
the job done without damage to the triplet.

An inexperienced person may cause heat while repolishing and this
will also cause the glue to let go and this may not be noticeable
until some time has passed.

Here once again as with everything please get recommendations as to
who has the experience to do the job.

In the States you guys have some of the best lapidary people in the
business so please use your countrymen’s talents and buy local, it
may be a tad more expensive but the quality will surpass most
imported goods.

Your local lapidary clubs are a huge well of and most
are only too happy to help out with advice and recommendations for
these sorts of jobs.

Christine


#12

Sorry to be late getting to this, my wife has been in the hospital
and my mind has been there rather than on things like this.

Let me offer a different view on the hows and whys cracks in opal. I
do want to emphases this is speculation on my part, I don’t have the
equipment to verify it.

There has been some interesting work done on the effect of moisture
on cracks in glass. A limited review was published in “The Eclectic
Lapidary”

http://www.bovagems.com/eclectic/HTML/19980101_9801GEMPOL.html

I believe the original article was:

B. C. Bunker and T. A. Michalske, “Effect of surface corrosion on
glass fracture,” in Fracture Mechanics of Ceramics, edited by R. C.
Bradt, A. G. Evans, D. P. H. Hasselman et al. (Plenum Press, New
York, 1986), Vol. 8, pp. 391-411 If anyone has access to the original
I would like to read it.

The proposed fracture mechanism is that when a crack occurs in glass
and moisture is present, a chemical reaction takes place at the
bottom of the crack causing the crack to grow. If you want a better
explanation, read the references, I am trying to put a long article
into one sentence.

The effect appears to take place in obsidian (a natural glass), but
as far as I can find, no work has been done on whether quartz is
affected by the reaction.

Now for the speculation, if opal is susceptible to the reaction,
then any opal that has been scratched or has had its surface polish
abraded (or wasn’t well polished to begin with) could have cracks or
crazing occur over an extended period of time. Opal’s molecules are
more tightly bonded than glass so if the reaction does take place, I
would expect it to be slower and sometimes taking years to occur
doesn’t seem unreasonable to me. I would also expect that opals from
different locations could give faster, slower, or no reaction. I
would also expect that this would be a different mechanism and
independent of the traditional moisture related cracking normally
associated with opal.

If anyone has had unexpected crazing of finished stones it would be
interesting to know if they could have had surface problems prior to
the occurrence. It would also be a good argument for getting the best
polish possible on your stones.

Dick Friesen
@friesenr


#13
    I would also expect that opals from different locations could
give faster, slower, or no reaction. 

Quite true, and possibly the main factor that will keep this notion
more theory than fact. Opal contains water to a largely varying
degree, due in large part to where and when it formed.

James in SoFl


#14
    I would also expect that opals from different locations could
give faster, slower, or no reaction.
    Quite true, and possibly the main factor that will keep this
 notion more theory than fact. Opal contains water to a largely
 varying degree, due in large part to where and when it formed. 

The moisture cracking is a chemical reaction and could be
identified by the same techniques used to identify the reaction in
glass but I don’t think anyone will spend the money and time to do
it.

The water in opal is not free to enter into the reaction and should
have little or no effect on it. It creates it’s own cracking
problem.

I am just spectating that if the reaction existed in opal, it is a
possible explanation for cracking that takes place in what should be
stable opal long after it is cut.

Dick Friesen
@friesenr


#15

G’day Christine

Thanks for your comments on the cracking/crazing theory, obviously
coming from a not quite unexperienced hand in the middle of Opalland.
I’ve used opals - mainly black Lightening Ridge and Qld. Boulder for
more than 10 years and have had hundreds of them through my hands. I
yet have to experience one cracking og crazing. Well, I’m an
opalholic, - and perhaps also a little lucky.

Niels from windy Bornholm, where the autumn leaves show almost
opallike colours