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 Post subject: Ethiopian black opals
PostPosted: Fri Nov 22, 2019 3:19 pm 
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I have juste been shown a series of big beautiful black ethiopian opal for sale, complete with many multicolor fires.
My first thought was that they were artificially smoked or dyed opals, but the seller assured that they were natural.
To convince me, the seller showed me this article from the GIA - dating back from 2014 :

https://www.gia.edu/gems-gemology/winte ... m-ethiopia

I am still skeptical - maybe I am wrong - because the lot I have been shown was really numerous and the stones were spectacular.
Are the natural black from Ethiopia common on the market ?
Would they be easy to separate from treated opals ? Actually, I didn't take time to examine them thoroughly.
The seller was supposed to come back from Jaipur where he did his shopping...


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 Post subject: Re: Ethiopian black opals
PostPosted: Fri Nov 22, 2019 4:17 pm 
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I have one, purchased in Tucson a couple years ago. It's very small.
Would you feel comfortable asking the seller for a lab report?


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 Post subject: Re: Ethiopian black opals
PostPosted: Fri Nov 22, 2019 4:23 pm 
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I wouldn't mind, if ever I see him again, but I didn't have the impression he had any...
I was just surprised at the number he had - with many other middle end stones of all kinds, nothing ugly but nothing extraordinary either.
I was so sure that his black opals were treated, and he was so sure that they weren't (of course !), I only wondered if something had changed on the market of opals these last months, that might have escaped my vigilancy !


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 Post subject: Re: Ethiopian black opals
PostPosted: Fri Nov 22, 2019 6:46 pm 
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I purchased some rough at Tucson also the last couple years. They aren't terribly expensive since they often shatter when you try to cab them. Maybe a fifth withstand cutting and they can be spectacular.


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 Post subject: Re: Ethiopian black opals
PostPosted: Sat Nov 23, 2019 2:53 am 
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In my office in Kenya I'm offered often opals from Ethiopia. But heard that the dark opals often dry out and cracks after some years. So I never been taking them. The lighter ones I think are more ok and looks very beautiful. It's very regulated in Ethiopia, still a lot being smuggling out of the country. So easy to get hold of in or out of the country.


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 Post subject: Re: Ethiopian black opals
PostPosted: Sat Nov 23, 2019 9:00 am 
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The ones in the linked GIA article were abundant for a while, and rather inexpensive, but have a pervasive problem of cracks--not crazing, I don't think, but they are already cracked. As you cut them they sometimes just fall apart, presumably as you remove the small bits of still-connected opal. It is a weird feeling. But what percentage don't have this issue can come out spectacular. Black stones also cometimes come out of the normal deposit in Welo. They don't resemble the dyed/smoked blacks in the hand much, as the treated material is usually totally jet black and also usually transparent or translucent when backlit.
Note Shewa also produced/produces black stones which might also contribute to a bad reputation on stability.

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 Post subject: Re: Ethiopian black opals
PostPosted: Sun Nov 24, 2019 4:36 pm 
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OK, I'll have to check that if I ever see that stuff again.
I found the material beautiful but I was too diffident to pay much attention.
It was an afterthought to want to see it again - bu too late for this time.
I guess I'll see some again, if they come in abundancy on the market.
Thanks to all !


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 Post subject: Re: Ethiopian black opals
PostPosted: Mon Nov 25, 2019 1:23 am 
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Okay, I'm apologising in advance for the beginner question (I'm not familiar with opals at all), but when you're talking about them cracking, do they do so under stress, while being worked on for example, or can they crack out of the blue, or due to environmental issues like sudden temperature changes?


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 Post subject: Re: Ethiopian black opals
PostPosted: Sun Dec 22, 2019 11:03 pm 
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In 2013, there was a find which included many black Opal from Ethiopia that were untreated. This was not far from the 2008 find that produced Welo (Wollo) Opal that is abundant today. These Opal from the 2013 were non-hydrophane. They look very much like smoked black Welo Opal.

The Opals that were prone to craze & crack were the Ethiopian Opals of the early 1990's find.

Here is an article from Jeffrey Bergman on all the Ethiopian Opals. It is in my opinion the finest article on them.

http://www.gem.org.au/ckfinder/userfile ... 2010_1.pdf

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 Post subject: Re: Ethiopian black opals
PostPosted: Mon Dec 23, 2019 10:37 pm 
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OliVDB5590 wrote:
Okay, I'm apologising in advance for the beginner question (I'm not familiar with opals at all), but when you're talking about them cracking, do they do so under stress, while being worked on for example, or can they crack out of the blue, or due to environmental issues like sudden temperature changes?


GIA wrote:
Stability
Opal is generally stable, but heat from intense light can cause fracture lines called “crazing.” High heat or sudden temperature changes can also cause opal to fracture. Opal is attacked by hydrofluoric acid and caustic alkaline solutions.
Hardness and toughness
Opal hardness is variable depending on its exact composition and formation conditions, and ranges from 5 to 6.5 on the Mohs scale. Its toughness is very poor to fair, making opal a gem that is suitable for jewelry but requires care when wearing so as to not scratch or break the stone.


From personal experience, when I was young, I used to cab Mexican opals. The ones I have left are ALL crazed now. I have some pieces of Victorian opal jewelry, made with Australian opal, that are perfect after 150 years. None of the Ethiopian hydrophane opals I have purchased over the years have crazed. so far.


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 Post subject: Re: Ethiopian black opals
PostPosted: Tue Dec 24, 2019 1:00 am 
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Yeah, I'm not sure crazing is an issue with the black opals from near the main find in welo, but they start out pretty cracked as I mentioned. It also seems that every time I look at the stock available there are less pieces without visible cracks, since all the clean ones have been picked out. It's really spectacular stuff when you get a solid piece though!

We had several opals from Welo cut back when it was a new find, and a few did crack during the initial drying period, though it was like one or two if I remember right. That's about what I'd expect--if it survives wet cutting and drying it's probably fairly stable.

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 Post subject: Re: Ethiopian black opals
PostPosted: Tue Dec 24, 2019 2:28 am 
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I have a pretty large piece of Australian opal (white background) that I bought many years ago. Upon inspection a couple of years ago I found that it was crazed throughout. I may be able to salvage a few small, crack free stones, but wow, what a disappointment. ps, I live in a very humid part of the country (PNW).

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 Post subject: Re: Ethiopian black opals
PostPosted: Tue Dec 24, 2019 3:17 am 
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Some aussie opals do have problems. There are quite a few opal mines with different characteristics. I know I'm preaching to the choir here.

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 Post subject: Re: Ethiopian black opals
PostPosted: Sat Dec 28, 2019 9:55 pm 
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I've sold hundreds of Welo Opals. Just sold a 20.36 ct stone. Spectacular stone. Link is below to video. Not a single complaint. The early 1990's find, which was not Welo Opal was prone to cracking & crazing. It is still producing as far as I know, but you don' see much on the market since the 2008 & 2013 find.

https://www.youtube.com/watch?v=oVJuV3P5bXg&t=37s

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 Post subject: Re: Ethiopian black opals
PostPosted: Sat Dec 28, 2019 10:23 pm 
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Fortunately Shewa opal roigh is very easy to spot, and tenda to be unstable in a quick and spectacular way (at least the clear based stones). But some Welo can certainly craze during or immediately after cutting. Fortunately this is not very likely to be an issue if you're sourcing them already cut, though buying rough can be a bit risky (then again buying any rough is risky in some way or other).

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