I have read a fair amount of opal reference material, and have tried
polishing by hand as well some small stones. One thing I am very
curious about is cracked or crazed opal. All the sources say that
cracked or crazed opal is highly discounted, or even of no value as
jewelry. However, I see no specific process to perform to examine
for cracks except shining a light through the underside of the stone
and looking for orange reflected light. What magnification is
considered to be the maximum? Is 5X or 10X magnification too high,
or are we supposed to use the naked eye alone? I for one would not
be suprised to find that almost every opal has cracks if one were
using a scanning electron microscope to look. I mean, the grits we
use to polish the opal have a finite size, and can inflict damage,
even if only on the micrometer scale. What appears to be polish
could in actuality be countless numbers of tiny indentions, and even
cracks on the microscopic level. If the cracks incr ease a million
times in size from sub-optical microscopic size to barely visible
with the convenient pocket loupes, and stop growing for some reason,
are they a problem? So, I ask, how much looking is too much for
something that obviously can drastically affect the value of the
stone?
Blaine: I think you are confusing scratches with cracks. Any visible
crack through or partially through the stone is said by the opal
appraisers to destroy it’s value. I would assume a crack that
actually has width and length is going to be eye visible. Usually
they go through or a good ways through the stone once the cracking
process starts. If the “crack” is small enough to be polished or
easily cut out, you have your solution. I would value such a stone
based on the value without the “crack” less the repair cost, as that
would be consistent with good appraisal practice.
All, This is not a disagreement with Roy. It is a disagreement with
appraisers. I have seen other appraisers do the same with opals. As
a gemstone cutter once an opal shows crazing I deem the opal unusable
and the opal has no value. I know that if I recut the stone to
remove the surface crazing it will only be a matter of time before
the stone will show crazing again. This process cannot be stopped.
If you recut the stone and sell it you will have an unhappy customer.
I have seen pounds of crazed opals offered for sale at really cheap
prices. The seller always says that all the stones need to be recut
to regain their value. If that is so then why did not the seller
recut the stones? Why do appraisers assign value to crazed stones?
It makes no sense to me.
Gerry, I have to agree with you.An opal may not show crazing for some
time after it is cut either so you may buy it and it may not appear to
have crazing going on but if it is going to craze nothing will stop
it.It’s crazey! (Sorry) Buyer be ware only buy opals from dealers that
stand behind their pieces…J Morley Coyote Ridge
I have a very nice rock opal that has started to craze ( crack and
fall of the stone back )…I have had this stone for 10 yrs and it
has always been very stable…my question is there any kind of epoxy
or coating that will prevent the stone from falling apart.
I remember reading somewhere that an important collection of opal was
saved from condition you describing by pressure cooking opals for
several hours. I do not have clear recollection of the process, but I
believe that glycerin was added to water as well. If you want to do
your own research, I am referring to Czechoslovakia opal collection
restoration.
Ron -I have used Opticon with great results on opals. You MUST
disclose that it has been used if you are selling the item. If you
want details on how to use it contact me off list and I’ll give you
more info.
I believe that glycerin was added to water as well.
Please never use glycerin with opals! It is hygroscopic, which means
it attracts water to itself. This is fine for hand creams where
glycerin pulls water from the air and helps hold it in skin, but
when an opal is immersed in glycerin, it pulls water out of the opal
structure and will make crazing worse or cause it.
I was unable to find the reference to restoration of a damaged
Czechoslovakian opal collection, and it is possible a process was
used involving an epoxy and a vacuum, but such a treatment would
have been done by skilled conservators.
Crazing is cracking. It’s like safety glass breaking but not coming
apart.
Filling the cracks with an epoxy material to hold it together may be
possible, but it usually requires repolishing afterwards. Years ago,
Opticon used to be recommended for this purpose, but it yellowed
over time. I haven’t seen any treated this way in many years so this
may no longer be true. Opticon may have been changed since then, and
it may need a vacuum system to get it deep into the cracked areas. I
believe it also needs heat which can worsen your original situation,
so you risk losing your opal altogether. There may be other products
on the market now that work in a similar way.
If it’s a valuable or treasured stone, it might be worth exploring a
professional restoration. The only person I know who can restore
some broken opals is Stan McCall, but I do not know if his process
works on crazing. And since I’ve been out of the loop concerning
opals for some time, again, there may be others now.
Please never use glycerin with opals! It is hygroscopic, which
means it attracts water to itself. This is fine for hand creams
where glycerin pulls water from the air and helps hold it in skin,
but when an opal is immersed in glycerin, it pulls water out of the
opal structure and will make crazing worse or cause it.
Glycerin is added to water precisely for the reason you indicated. It
helps opal to retain water. Besides, if you read carefully, opals
were not submerged in glycerin. They were pressure-cooked in water to
which some glycerin was added. However, there could be some other
ingredients. Further research is required before using this method in
practice.
If it looks crazing, then it is already cracked, and you need to seal
it. Yes, a resin like Opticon is the standard but if you want to
avoid the yellowing over time, you should use something that is “UV”
curable or a photopolymer resin. From what I’ve seen and read, you
might be best off to talk to Jamey Swisher… He runs the gemaddicts
forum ( Index of /forums ) and is also on the opal
forum ( http://www.ganoksin.com/gnkurl/o6 ) as “Gemaddicts”. I think
Jamey would be best to give you the lowdown on the PhotoPolymers and
any application to opals. Anything I would pass along would be third
party from his postings anyway, so track him down and give him and
email and hopefully he’ll be able to help you fixing your opal.
Yes, obviously if this opal is passed on or sold, then any
treatments should be disclosed… But if it saves a great opal from
turning into fish tank gravel, it will be worth the time.
Hxtal is mostly used as an adhesive with glass. Some of us
lapidaries, have been using it as a fracture, or pit filler for
cabachons. As of late, I have used it mostly when replacing a knifes’
wooden scales (handles) with a high quality agate or jasper. It wil
penetrate through a slab, in every nook and cranny, and takes about a
week to reach full strength, and then you can grind and polish.
I have used Loctite cyanoacrylate (SuperGlue) successfully with
crazed opal on 5 or 6 occasions. I place the opal in a small
polyethylene prescription bottle lid, cover with Loctite and leave
it with a 100W bulb directed at it from about 8 inches for 24 hours.
Then I remove the opal, wipe carefully with an old T-shirt and spray
it with a SuperGlue accelerator, allow to sit for another 24 hours,
and re-polish. I’ve also pulled a vacuum on them with a bell jar
while the opal is in the superglue, but I see no differences.
All my customers have been happy.
I’ll add that many years ago Opticon was used (the 220 version) but
it yellows over time. The 330 does not yellow, but 2 part epoxies do
not do as thorough a job as the cyanoacrylate, and they may yellow
slightly as well. With repeated exposure to moisture, the epoxies
will SWELL and can make the situation worse. Also, be aware that the
new formulations of both Loctite and Devcon 2 part epoxies do swell
upon curing. This won’t be a problem in and of itself, but will
demand that the stone be re-polished. You should wait a minimum of 48
hours for the cure to be nearly complete.