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 Post subject: Oiling Opals
PostPosted: Fri Oct 21, 2005 4:20 pm 
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Please tell me what's best to use on opals. I've heard oil, but they didn't say what type, and I've also heard you should use glycerin. And does what you use depend on whether or not it's set in metal? Can anyone shed some light on this for me? I appreciate the assist. Thanks! :?

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PostPosted: Fri Oct 21, 2005 11:05 pm 
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The best thing for opal is to be keep in a place where the atmosphere is humid as water is a natural component of opals. If the opal become dry then it will crack. So my advise instead of oil will be some kind of moisturing solution or just keep a glass of water near you gem, you can also keep your opal I think in water...
But well I'm not an opal expert so all this should be confirmed by an expert in the opal field.

All the best

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The views expressed here are V. Pardieu’s opinions and do not necessarily reflect those of GIA Laboratory Bangkok (http://www.giathai.net)where he is an employee since Dec 2008.


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PostPosted: Sat Oct 22, 2005 2:49 am 
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Hi Crystal Star,
Here are a few links on opal care
http://www.swissgemshop.ch/index.html?l ... unset.html

http://www.opalmine.com/opals-encyclopedia-8.php

Golecha

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PostPosted: Sat Oct 22, 2005 8:19 am 
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Opals contain between 5-15% water. Without the water, opal would not show play of color. I recently examined a collection of opal jewelry put together by a jeweler in the 30-40's and left to his daughter. The collection contained some extraordinary stones that would probably cost close to a million dollars today. Unfortunately every opal was crazed which reduces the value of the stones by 80%. The collection had been kept in a bank vault. Most vaults are dehumidfied to keep the money from rotting. Unfortunately they also suck the water out of the opal causing them to craze. Avoid bank vaults!!!

Oddly enough, at auction set opals are often purchased with little or no regard for crazing.

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PostPosted: Sat Oct 22, 2005 8:45 am 
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Would keeping them in a humidor be a solution?


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PostPosted: Sat Oct 22, 2005 9:48 am 
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I have also heard that since opal is an amorphous substance, devitrification is as important a factor with crazing as water loss.

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PostPosted: Sat Oct 22, 2005 10:39 am 
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Yes particularly if you had a few good Havana cigars to keep them company.

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PostPosted: Sat Oct 22, 2005 12:50 pm 
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I do actually, or rather my Mr. Right does.


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PostPosted: Sat Oct 22, 2005 3:54 pm 
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Just a little add on... Opal has a different tendency to craze or loose its own water content, depending on its origin. The ones that come from sedimentary deposits (such as a great portion of Australian opals, and others from minor deposits throughout the world) usually are more resistant then the ones that come from igneous deposits (most of Mexican opal, some from Brazil, and so on). Many lapidaries used to cutting opal develop a habit of keeping a piece of rough in the open (some will even leave it in the sun for days) as a "test drive" for spontaneous crazing, since most of the opal rough that is going to craze will do so in the weeks or months that follow its extraction from the environment it was formed in, and exposed to surface conditions. Some deposits are known to deliver stones that are so prone to crazing that they are simply not considered suitable for cutting. Of course, under extreme conditions (such as very low to no humidity environments, as bank vaults mentioned earlier), any opal could craze.

As for opal care, opal shouldn't be considered a porous material. It is not. Lots of discussion here, many still have that idea going around, but it isn't true. It won't absorb water whatsoever. You should keep opal in normal conditions of humidity, so it won't craze. If the weather where you live is quite hot and dry (desert, or around the tropics in summer time and no rain), you should have extra care, such as keeping it immersed in water once in a while or sitting on humidified cotton or cloth, for example. But if the opal crazes, there's no watter bath that's going to place those H2O molecules back. It's a one way trip. The water got in there as the opal was formed. Period. Either it stays for good or, if it leaves, it's gone. No fixing.

Oh! And oil won't make a difference. Some say it turns the opal impermeable, so it keeps the water better. The truth is, it only helps disguise any crazing that is already there.

Any comments are welcome on this!
V


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PostPosted: Mon Oct 24, 2005 9:38 pm 
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Many thanks to all for your replies. I got a gorgeous 10.5ct Australian opal set in 18kt yg, about 7 years ago, from House of Onyx, and nothing was said about caring for it. Over the last year 2 or 3 people mentioned using either oil or glycerin on it was necessary, so I'm glad to hear it isn't since I've never done so. Thanks! :)

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PostPosted: Tue Oct 25, 2005 1:06 am 
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Great information OpenMind. It is common practice here in Australia to keep opals in water up until they are cut. This not only keeps them from drying out in the arid Australian conditions, but also keeps them looking their best. I keep all mine in small jars of water. I have a friend who mines in Coober Pedy, and they keep all there finds in water jars. If they dry out and craze, they don't want it to be their problem. They are usally passed on within a few days anyway, as money is always tight for these fellas. Your observation regarding the water can’t be put back is correct - once crazed always crazed. It is however possible to have them recut, however with opal cutting, you never know if you will end up with a worse or better stone with the play of colour. That is why you see many quality opals that are free form cut.

Richard, most opals in the market place do indeed have 5-6% water, although this can vary significantly on locality and specimen. Some dealers here South Australia quote the water content between 4% to 30%, although 5-6% is usually referred to as precious opal. Most south Australian opal (mainly from Mintabi, Coober Pedy and Andamooka) has less than 10%.

Less than the magic 5% decreases the play of colour, and more than the 6% decreases the stability of the opal. I have seen some large precious black opal at a local dealer that is sitting in a jar of water, and they say is not suitable for jewellery as it is too unstable. They won’t even take it out to let you look at it, as they are worried about its stability.

Solid opal should be cleaned gently with mild detergent in warm water and a soft toothbrush or cloth. There should be not need for oiling, and I would certainly not recommend this. Doublets & triplets may be wiped with a damp soft cloth and mild detergent, but should never be soaked or immersed, as they can come unstuck as it were. Always avoid chemicals and ultrasonic cleaners.

For bank vault storage, you should cover them in cotton wool, drop a few drops of water onto the wool, and place it in a small zip lock, or sealed plastic bag. This is only necessary for long terms storage in low humidity. For short period soft cloth bag is usually fine. In the 1980s, many Japanese businessmen were caught out by cracked and crazed opals that had been stored in low humidity storage vaults. Most high end opal dealers, certainly here in Australia, usually give you advice regarding care of your opals.

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Last edited by Martin on Tue Nov 01, 2005 2:17 am, edited 2 times in total.

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PostPosted: Mon Oct 31, 2005 9:09 am 
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Opal crazing would occur according to conditions.

Certain mines (across the globe) produce opal that will craze almost instantly and have to be transferred into a jar of water. You can enjoy them looking through a jar.

Others remain very stable unless subjected to severe heat and dryness. These types of opal remain stable with normal use and never, I repeat never, have to be stored in water or with a humidifier. The only caution would be not to stick it in a front display window with hot lights on it for weeks on end.

Because of the size of the molecules, oil will not go into an opal and protect it. Eventually, you will need to wipe the nasty stuff off and then it is exposed to the air again.

The main point is, if you want to enjoy an opal looking at it in a jar of oil or water then buy the kind that can only exist in such. Otherwise buy stable material from a reputable dealer who can guarantee stable material. By guarantee it would mean someone that you can go back to that would give you an exchange or a refund.

Bear Williams


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PostPosted: Mon Oct 31, 2005 6:30 pm 
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Thanks Bear! That's good to know, and after these many years with no problems I'm thinking my opal is the very stable kind, which is very likely why Renee at HOO didn't give me formal care and feeding instructions. I do have one I got some years ago that was called a sea opal and came in water, that's an aqua blue faceted gem. I've kept it in water for years, but now that I've got equipment I'm going to take it out and do some testing on it to see what it really is. I really appreciate all this good info everyone has shared. Thanks to all! :D

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PostPosted: Mon Oct 31, 2005 8:06 pm 
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Bear,

Here in Adelaide, South Australia, there are dozens or opal retail outlets, and it is fairly common for them to have a very small dish of water in the corner of the cases to keep them humidified under the strong lighting. Some say it is not necessary, however some of those opals have been in the same cases since I first came to Australia almost 8 years ago. It would be quite understandable why you would add a little “insurance” just in case….

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PostPosted: Tue Nov 01, 2005 12:36 am 
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Opal that is crazed is like a piece of broken glass. You can glue it back together but it will always be broken.
I have a number of opals that crazed after being stored for a long period of time in a hot, dry storage area. Since that time I have been using a large zip-lock bag with a couple of damp (water) cotton balls placed with the opals.
Its best to have the opals polished on all surfaces. The polishing compound halps to seal the stone.


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