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 Post subject: Variety in Ethiopian (Welo) Opal
PostPosted: Thu Mar 31, 2011 8:30 am 
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Haven't posted in a while so I thought I'd share some of my collection of Ethiopian opal rough. I just got a sampler parcel and I was amazed at the variety. To the best of my knowledge, all of these are from the Welo/Wollo region, which is 'white' opal, distinct from the chocolate nuggets found in Mezezo.

This is what I've seen the most of, these are white base with a range of transparency from very clear to totally opaque and a range of color play but with strong play not uncommon. This material is usually very hydrophane in my experience, and the stone I gave my Dad in Florida looks a lot different there (I live in Virginia). I have cut about a half dozen of these within the last year and have not had any problems with stability. I have heard mixed reports about this material's stability.

The stone on the right is water clear, the left one is a little cloudy.
Image

This is the same material, but with an 'egg' in it. This is a great specimen that I have been hesitant to cut, I've heard that exposing the center can cause cracking.

Image

Backlit to show the egg:
Image


Also fairly common is the yellow/orange jelly material. This looks kind of like mexican fire opal but with a range of color play. I haven't cut any of this, although I hear it is very unstable. Also hydrophane, but seems less 'thirsty'. I have hydrated and dried this material several times without any cracking.

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 Post subject: Re: Variety in Ethiopian (Welo) Opal
PostPosted: Thu Mar 31, 2011 8:40 am 
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Less common is this material, I was told it is obtained by breaking away the surrounding material from the 'egg' type opal above. I haven't cut any of this and don't know much about it, although I have been told it tends to be fairly stable. The pieces I have all seem to be contra-luz.

Lit from the front:
Image

And from the side (this piece is spectacular and almost 20 cts!):
Image

I also have a clear piece, although this one seems to be cracking:
Image

Finally, there is this material with a clear blue base. No experience with this, and I only have the one piece. It is supposedly very rare, but stable. The pictures don't do it justice, it has amazing clarity and color play.

Image

Image

I'm afraid to cut most of this, but if I work up the nerve I'll try to post some shots on 'Off the Dop'. I'd love to hear from some of the cutters who have experience with any of this material.

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 Post subject: Re: Variety in Ethiopian (Welo) Opal
PostPosted: Thu Mar 31, 2011 12:49 pm 
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It's the alien eggs again! :shock:

We are goners . . .

Joking aside, that blue is stunning =D>


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 Post subject: Re: Variety in Ethiopian (Welo) Opal
PostPosted: Fri Apr 01, 2011 12:36 am 
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I especially like that blue one!

I recently cut 17 Welo opals, mostly whitish or clear, except for a coffee colored one and one yellow. None was very large, the size ranging from about .5 carat to about 5 or 6 ct. All were hydrophane to some extent.

As for cutting the stuff: My early experiences a couple of years ago suggested that Welo opal tends to be extremely heat sensitive, so to take no chances, I dopped most of them with Elmer's glue. One I tried CA on, but it pulled a flake out of the top of the finished stone, so I had to sand it out and re-polish, using cerium oxide. Also, final shaping and sanding was all done by hand- no machinery of any kind. (Just being cautious.) I used a succession of wet or dry silicon carbide papers, from 325 grit through 1,000 or even 2,000 grit, which yielded a fine pre-polish. Wet sanding with a worn paper seemed to give the finest surface.

Dick Davies
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 Post subject: Re: Variety in Ethiopian (Welo) Opal
PostPosted: Fri Apr 01, 2011 9:49 pm 
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Wow, wow, wow.

I love the contra luz and the blue.
:-D

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 Post subject: Re: Variety in Ethiopian (Welo) Opal
PostPosted: Fri Apr 01, 2011 11:37 pm 
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Your white and clear bases are the most stable. The colored bases are mostly unstable. Especially the yellows. Oranges next in line. And blues last. If you hydrated them and dried them out and no cracks appeared then you may be ok. The best way for the unstable colored bases is to cut them dry, using something like extender fluid instead of water, but not much. Go very slow and do NOT allow ANY heat to build up. By hand is the best, but can be done on a machine at lower speeds.

The Contra Luz inner eggs are almost identical to the Mexican material that used to come out of Magdalena a few decades ago. It should be fairly stable, but still heat sensitive. Quite a bit of it is being flooded on the market in yellow and the whitish clear bases as "Old Stock" Mexican Contra Luz opal as it carries a premium to collectors and such way over that of Welo, probably due to the rarity of the material from Mexico.

The thing that I found that gives the ultimate polish on Welo, and most other opals I've tried so far, is the M-5 Polish on a soft leather wheel, just spray the pad with a spritz or two from a plant mister sprayer and start polishing and once the pad goes dry is when the super "wet" polish will come in, it happens fairly quickly. Of course you need a great pre-polish, but that is the main key to ANY good polish. I typically just use the 6" flex wheel on the end of my Genie, except on the colored base material, which I just put the pad on a rubber backing pad and do by hand, as the higher speed of the Genie will typically create enough heat to crack up most of the colored bases. For cutting and pre-polish I simply use the Genie but I start at the 600grit wheel instead of the others, then hit 1200, and then 3000, then the M-5. I used to use Optical grade cerium oxide(without the pigments and a finer screened grade) or the French Cerium, but I am now sold on the M-5.

I really wish the colored bases were far more stable. One of Jen's sources actually refuses to buy and sell the colored base material any longer due to so many complaints and unhappy buyers. :/

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 Post subject: Re: Variety in Ethiopian (Welo) Opal
PostPosted: Sat Apr 02, 2011 4:42 pm 
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Great info, thanks for the tips. Too bad about the colored base material, the orange base did seem really brittle when I was cleaning out the potch. Cutting with no water and no heat sounds like a chore but I'll give it a try on some of the orange stuff. I may just leave the blue one alone as a specimen.

Richard, I've heard of using Elmer's for dopping but haven't tried it yet. I've used CA in the past but the acetone makes me nervous. Do you do anything to waterproof the Elmer's?

I'm actually going to be faceting this material, I don't have any cabbing equipment and most of it is clear and deep enough for it. May try a few rosettes. I've gotten pretty good results from cerium on a greenwing, but have had a hard time avoiding scratches. Any little bit of contamination on the polishing lap can really wreak havoc. Swishman, where can I find the M-5 polish?

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 Post subject: Re: Variety in Ethiopian (Welo) Opal
PostPosted: Mon Apr 04, 2011 12:00 am 
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bobsiv said:

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Richard, I've heard of using Elmer's for dopping but haven't tried it yet. I've used CA in the past but the acetone makes me nervous. Do you do anything to waterproof the Elmer's?


I haven't bothered with waterproofing. I do try to keep it dry, or if it gets wet I set it aside to dry out before continuing. I used CA once, but it pulled a flake out of the top of the stone, so I had to re-sand and polish. Luckily the opal was fairly thick so the slight removal of material did no harm.

DD


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 Post subject: Re: Variety in Ethiopian (Welo) Opal
PostPosted: Mon Apr 04, 2011 10:55 pm 
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Acetone does NOT hurt the opals. Just soaked a triplet to pull it apart due to a fricken air bubble, lol. Welo slice looked very strange when pulled it out and no color play but then a few minutes later right back to normal, lol.

M-5 can be gotten all around the internet. Got mine here:
http://www.coloradoprospector.com/Miner ... olish.html

Also can get in smaller and alrger amounts from here:
2oz http://cgi.ebay.com/ROCK-Lapidary-Polis ... 4cf4590096

8oz http://cgi.ebay.com/ROCK-Lapidary-Polis ... 3f0654e725

4oz http://cgi.ebay.com/ROCK-Lapidary-Polis ... 4cf44fc107

1/2oz http://cgi.ebay.com/ROCK-Lapidary-Polis ... 4cf4673e26

Colorado Prospector is the best price place at only $10 shipped for a 4oz jar. Ships quickly too!

Cutting without water is typically just done by hand, lol. But can do on a machine if keep things slow and go little by little. Most just prefer to stabilize them using Opticon or Water Glass(sodium silicate) in a simple vacuum and a little heat in a canning jar.

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 Post subject: Re: Variety in Ethiopian (Welo) Opal
PostPosted: Thu Apr 21, 2011 1:15 pm 
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It is good to get some insight into your experiences, because these 2 sources seem in conflict in their opinions so had me a bit confused.

agta source

Update 9-1-2011:
"In The Loupe" source

Previously I was unable to find the Loupe source, but just now checked again and it was available. Page 2.


Last edited by cat-foster on Thu Sep 01, 2011 4:42 pm, edited 1 time in total.

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 Post subject: Re: Variety in Ethiopian (Welo) Opal
PostPosted: Tue Apr 26, 2011 3:01 am 
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The eithiopian welo opal is very good opal in the world, i have manufacturing from 4, years, i am very happy to making the welo opal
Now my labours are understand how to make eithiopian opal, so you will check the attachment of eithiopian opal cut stones


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 Post subject: Re: Variety in Ethiopian (Welo) Opal
PostPosted: Sun May 08, 2011 5:18 pm 
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well i have no personal experience with this eithiopian opal,but cutters/faceters here in india says it breaks when they try to cut it.

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 Post subject: Re: Variety in Ethiopian (Welo) Opal
PostPosted: Sun May 08, 2011 7:15 pm 
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Beautiful pieces!

How wearable is it? What happens when you try to set a piece? How should it be cared for.

Pure curiosity here, but is there a source for getting the little bits of broken opal from depressed and irate cutters etc or the pretty but uncuttable material - I'm thinking it would make superb and exotic fish-tank gravel!


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 Post subject: Re: Variety in Ethiopian (Welo) Opal
PostPosted: Mon May 09, 2011 2:00 am 
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pandora wrote:
Beautiful pieces!

How wearable is it? What happens when you try to set a piece? How should it be cared for.

Pure curiosity here, but is there a source for getting the little bits of broken opal from depressed and irate cutters etc or the pretty but uncuttable material - I'm thinking it would make superb and exotic fish-tank gravel!

what an idea,fish tank gravel.......but who will spend so much money for the fish tank gravel? u can indeed find chips or material which is un cuttable,may be most of the cutters throw them in garbage,but they are gems,when somebody like u need them,they command a price :wink:

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 Post subject: Re: Variety in Ethiopian (Welo) Opal
PostPosted: Tue May 10, 2011 9:26 am 
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Interesting idea, unfortunately all of this material that I have seen is hydrophane, which means it absorbs water and becomes clear. Especially when submerged, it wouldn't show any play of color. I have used some of it as potting gravel though, which is pretty striking.

As for fragility, I can only give my own anecdotal experience, but it seems to agree with what I've heard. The orange base material pretty much exploded when it got wet and then dried. The very clear material is a little iffy, I've had about a third of the pieces I've cut develop some small cracks. The more opaque material seems very stable, I've only had one stone develop a crack and it was very small.

I haven't had any problems working with the finished stones, I was worried about it at first but I worry less and less about damaging the finished stones the more I work with it. Of course, only time will tell how well these will hold up to repeated changes in hydration.

As a cutting note, it has been hard for me to get the pavilion angles shallow enough to maintain the color play, especially in round cuts. Even 34 degrees can be too steep and can kill the color with reflected light. With the very clear stones I am now cutting mostly rosettes. I hate to admit it (because I don't know how to do it) but I think cabbing is probably best for a lot of the material I have.

These stones looked spectacular on the dop, but as soon as I took them off most of the color play went dead due to reflected light.

Image

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