64 carat ETHIOPIAN Contra-Luz Opal

[Chrysoz]

Just to irritate you guys more, I have got a question I can''t really get an answer for somewhere else... I recently (just a couple of days ago) bought a 64 carat crystal opal rough from ethiopia, with a pretty nice play of colors. I am 100% sure it''s the real thing, even if I think I got it quite cheap.
What do you think, how much can it be worth after a proffesionall cutting? (it''s the same stone shown on the pic)
Now, I am just beeing anoying, but sometime in the close future I hope I can answer some questions too....

I will be most grateful for answers!

 

[naderon]

Hello,

Ethiopian opal is VERY risky when purchased in rough. The vast majority is unstable and breaks during or 6 months after cutting.
That being said, there is some "stable" Ethiopian opal out there but it''s hard to find. Apparently it is growing in popularity and Japan in particular is falling in love. Nowadays to get the quality stuff you have to go through the Ethiopian government...

Also, it''s pretty much impossible to tell what it''s going to be worth after cutting just by looking at the rough. Wish I could help you more, but there''s probably a reason they sold it for a good price in rough form (i.e., they were most likely afraid to cut it or knew not to)

Glad to see a young one with such passion for gemology! I myself am only 22 (still considered young I guess).

 

[Chrysoz]

Thanks!
I party agree with you that they wouln''t have sold that opal it is would make "crown jewels", and in fact, I bought in on ebay
(I know what you are thinking: It is probably a fake, and that little boy doesn''t know a shit about gemstones) but, from one of ebay''s three best sellers. I will put a link here and see if you agree. Even if it was a 0.99$ auction, i think i got it cheap, i bought it for 61 dollar and even similar rough on 15-20 carats has been up over 100$. A cut stone on 1,28ct was sold the same day as I bought my rough, that wnt out for a price of over 300$, so there must be some quality...

At the same time i bought this, i lost the bidding for a 10 carat wonderfully cut PINK danburite on 160$, that is high prices for ebay.

http://search.ebay.com/_W0QQsassZravenstein-investment-gems

And here is the link to the gem rough I am talking about:

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&rd=1&item=160141894980&ssPageName=STRK:MEWN:IT&ih=006

I have heard about that they can crack a couple og times before, but just lets hope thus won''t

And besides, it''s so large that you can still cut the peices left if the whole rough brakes into, lets say 10 peices. But you are probably right, I will take it to a good cutter here in sweden and see if it will work.

Thanks again!

 

[colormyworld]

Hi Chrysoz. Welcome to the forum.

The opal in your picture looks to show a nice play of color. Here in the states they find some very beautiful opal also but it is not stable. By which I mean the water in the stone will diffuse out of it. When this happens the stone will " craze" or start getting what looks like little cracks all through the stone. After a time the stone will lose its color and fall apart. I hope this is not the case with your stone.

 

[Chrysoz]

Date: 8/12/2007 7:57:24 AM
Author: colormyworld
Hi Chrysoz. Welcome to the forum.

The opal in your picture looks to show a nice play of color. Here in the states they find some very beautiful opal also but it is not stable. By which I mean the water in the stone will diffuse out of it. When this happens the stone will '' craze'' or start getting what looks like little cracks all through the stone. After a time the stone will lose its color and fall apart. I hope this is not the case with your stone.

Thanks for the welcome, this forum already feels like home

Thanks for the information also, but I already know that opals is a kind of hard Silica-gel with with varying percentages of Water( Often called "crystal water" in opals) in it. From what I know the thing you mentioned do not only appear in US opal (I guess you mean from oregon crystal opal?), but also in all kinds of opal, even in the australian ones. I have heard you can prevent the opals (both white, black and "crystal") from drying through put some oil on them regulary. The sources do not agree with each other what kind of oil you should use, many say synthetic mineral-oil, others say usual cooking-oil...
But I think I will be able to figure that out before I get the stone

Have some of you heard this too, or is it just bullshit? Even if it sounds quite logical to me...

 

[colormyworld]

Wow Chrosoz You are well versed in the subject. I think given time all opal will craze. I think opals that form in sedimentary rock are more stable than those that form in volcanic rock. As for coating with oil I am not sure, I have heard this will not stop the process.

 

[Richard M.]

First, do you have crystal opal or contra-luz? They''re not the same thing. Crystal displays an intense play of color against a transparent base at all times (regardless of the potch color -- orange, clear, yellow, brownish, etc.) Contra-luz means "against the light" and shows play of color only by transmitted light. It''s a separate opal category.

Ethiopian opal mostly forms inside lithophysae, commonly known as "thundereggs." This type of volcanic opal usually contains excess water and is notoriously unstable due to shrinkage from evaporation. That said, a certain percentage appears stable but only time will tell for how long. (As in most opal deposits there are several modes of Ethiopian opal formation and the country produces some sedimentary precious opal, which can be stable and very nice).

Opal valuation is a very difficult task, requiring lots of experience and "hands-on" exposure to a wide range of opal types, qualities and markets. As a general rule, the sale price of rough is a fairly reliable indication of market value. You can expect a reasonable "added" value from fashioning the rough into a usable gem -- if it proves to be stable.

Richard M.

 

[Chrysoz]

Date: 8/12/2007 2:29:44 PM
Author: Richard M.
First, do you have crystal opal or contra-luz? They''re not the same thing. Crystal displays an intense play of color against a transparent base at all times (regardless of the potch color -- orange, clear, yellow, brownish, etc.) Contra-luz means ''against the light'' and shows play of color only by transmitted light. It''s a separate opal category.

Ethiopian opal mostly forms inside lithophysae, commonly known as ''thundereggs.'' This type of volcanic opal usually contains excess water and is notoriously unstable due to shrinkage from evaporation. That said, a certain percentage appears stable but only time will tell for how long. (As in most opal deposits there are several modes of Ethiopian opal formation and the country produces some sedimentary precious opal, which can be stable and very nice).

Opal valuation is a very difficult task, requiring lots of experience and ''hands-on'' exposure to a wide range of opal types, qualities and markets. As a general rule, the sale price of rough is a fairly reliable indication of market value. You can expect a reasonable ''added'' value from fashioning the rough into a usable gem -- if it proves to be stable.

Richard M.

Even more wow!

I did think contra-luz and "crystal" was the same thing, then I have learned something here already

In that case, this stone qualifies under Crystal opal, not Contra-luz, as I said, I thought it was different namnes for the same thing.
I understand it''s very hard to tell the calue of a opal, especially one you haven''t seen, but thanks so much anyway.

Isn''t it pure logic that the stone can''t evaporate if you put on a solid layer of, for example, oil, over the whole stone? (maybe I am making a fool of myself now, and perhaps oil isn''t solid at all?)
Thanks all!

 

[Richard M.]

Isn''t it pure logic that the stone can''t evaporate if you put on a solid layer of, for example, oil, over the whole stone? (maybe I am making a fool of myself now, and perhaps oil isn''t solid at all?)

That''s a widely held belief but I strongly disagree with it after many years of cutting opal from lots of different locations, as do numerous opal experts. I won''t buy oil-treated opal rough because oil discolors the opal and doesn''t prevent crazing anyhow. Opals that are destined to crack will do so, and I''d rather know sooner than later.

When I buy opal for cutting I dry it if it''s stored in water for display, and lay it on a shelf near my cutting machine. If it remains uncrazed for a few months I cut it, then store the cut stones dry for at least a year before mounting or selling them. Opal from certain locations is much more likely to craze -- Nevada, Ethiopia, Mexico, Idaho, etc. The world''s most stable opals come from Brazil and Australia, and certain mining locations in those countries can produce cracky opal from time to time. But dealers who sell it don''t stay in business long.

Richard M.

 

[Chrysoz]

Thanks you very much, I will ask the seller if they have stored it dry, if they haven''t, I will do as you say.
Nice with someone with this great knowledge about opal. If it is stable, can you it with facets in the same way as ordinary fire opal, or du I need to take extra precautions? I won''t cut it myself, but
I will probably let one of sweden''s best cutters make an as large fancy as possible and then some smaller stones.

 

[Richard M.]

Yes, transparent opal can be faceted. I know of several cutters who have done it. But I don''t understand the reasoning behind it. Facet cuts are designed to create brilliance in transparent gems by optically controlling the pathways/reflections of light to return it to the eye through the stone''s crown facets. Precious opals, in contrast, display the unique property called "play of color," created by light diffraction through its internal structure that breaks white light into spectral colors. That effect is displayed much more effectively in cabochons, in my opinion.

Richard M.

 

[Chrysoz]

Date: 8/13/2007 1:19:30 PM
Author: Richard M.
Yes, transparent opal can be faceted. I know of several cutters who have done it. But I don''t understand the reasoning behind it. Facet cuts are designed to create brilliance in transparent gems by optically controlling the pathways/reflections of light to return it to the eye through the stone''s crown facets. Precious opals, in contrast, display the unique property called ''play of color,'' created by light diffraction through its internal structure that breaks white light into spectral colors. That effect is displayed much more effectively in cabochons, in my opinion.

Richard M.

I like facted stones more, but it is possible that I will cut a abochon of it.
I have now talked to a friend of mine, one of the best expert on Ethiopian Crystal opal, and he tell me there is no need to worry. This kind of opal does crack sometimes, but that is very rare.