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 Post subject: Buying your first Rough...
PostPosted: Mon Aug 27, 2012 2:12 pm 
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Greetings,

I realize I'm still learning, but each area of this topic intrigues me. I recently decided to buy a piece of rough topaz online and was curious to get some insight about it, and what I can potentially do with it. It was sold as a 104.9 carat Topaz with VVS clarity, which makes me wonder why the clarity was listed. Can you tell clarity before a gem is cut (my logic says: no, but correct me if I'm wrong)?
Image Image
Image Image


It isn't obvious from the pictures I've taken, but it appears to have a very slight pinkish hue at the extreme ends. Can it be told at this time what color the stone would have if cut? (i.e. Golden, Imperial, Brown, or whatever colors there are associated to this stone type.)

From the pictures is it possible to tell whether it is gem grade rough or would a lapidary be the best to decide such a fate? Given its relative size, would it be cost effective to get the gem cut or is it best to leave it as a shelf piece? I was thinking of having it cut for a pendant.

There's a lot of surface inclusions, a arc-shaped inclusion in the upper center and a fairly decent sized area that appears to be free of inclusions (judgement made on being able to read through portion of stone.) If there are smaller inclusions that affect the stone's structural integrity, would they be visible as a whole, or is that a risk you take when getting it cut?

I have a lot of questions each time I post, it just shows me how much I have to learn. I can't determinate rough quality at this phase, though I figure the only way to learn is to ... try. I realize that a lot of the information I need to determine a stone's kind is present on the forums here; however, at this time, I do not have sufficient resources (space) to obtain my own tools for running the appropriate tests (apartment is 600sqft.)


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 Post subject: Re: Buying your first Rough...
PostPosted: Mon Aug 27, 2012 6:23 pm 
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Based on pictures without studying the rough, picture upper right is the most telling when compared to the rest. The left half of the stone appears to be fractured. Upper right shows what appears to be a split that diagonally bisects the rough yielding maybe 60% of the orginal size in faceting material. So to start, only half the stone is workable "from pictures". That split appears to be on a cleavage plane. I would probably try an emerald cut with the lower right corners of the stone being near the culet. You might get a 20+ct stone out of it, but that is a guess based on insufficient information.

That section of stone does pass the white paper test (it was correct to include it). It could be pretty. BUT.... that is based on pictures without anyone looking at it with magnification. I have some lovely bluish topaz crystals, but under much closer inspection, they look like an aquarium bubbler is somewhere in them.

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 Post subject: Re: Buying your first Rough...
PostPosted: Tue Aug 28, 2012 12:55 am 
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I'll post a reply in a few hours with a video of the rough. I'm not sure what diagonal bisection you're talking about, from rotating the stone it appears as though the inclusions are mostly surface inclusions, short of the arc-ish inclusion in the center; though I will admit that I am not qualified to make such an assertation.

Edit:

Here's a link to a youtube video of the rough.

If anyone can identify what color the topaz would be called, please do so. I wonder if at this point it can even be determined? The pink band that I mentioned only seems visible under certain lighting conditions, which is odd. It's times like this when I wish I could identify the thing myself, so I could give facts other than subjective viewpoints based upon lighting conditions and other factors.


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 Post subject: Re: Buying your first Rough...
PostPosted: Tue Aug 28, 2012 7:31 am 
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It's difficult to manually focus a camera, hold a stone, and hold the camera at the same time, so I tried to get an example of the 'pink'ish view I was referring to and noticed that in certain lighting conditions one orientation of the stone was champagne color, and rotating it 90 degrees made a reddish hue propagate the stone:
Image Image


The images are crap because of my lack of experience, I don't know what specific conditions need met to make the hue visible, so low light was the only way I could get it to appear. It doesn't seem to be incandescent vs fluorescent? The back light in these images is my monitor.

I remember reading something about a polarizer which lets certain wavelengths through at one angle and nothing through at another. Could a similar case be what's occurring here?


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 Post subject: Re: Buying your first Rough...
PostPosted: Tue Aug 28, 2012 12:17 pm 
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Experts in rough often know not only the clarity but the shape and the approximate carat weight before the cut.

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 Post subject: Re: Buying your first Rough...
PostPosted: Tue Aug 28, 2012 1:46 pm 
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Do you know where the stone is from? To me, it looks kind of like the material coming out of Gilgit, Pakistan (or labelled as such), based on the shape, color and (possible) color zoning. There is quite a bit of this available on Ebay. If that is indeed what it is, I don't think it's precisely imperial topaz (which is also found in Pakistan, but from the Katlang mine), but rather something in the brown/champagne range. I have read that these colors are sometimes produced by irradiation, and that there are also sometimes problems with fading in sunlight.

My experience with Gilgit material has covered a few of those bases. I left a cola-colored crystal in the sun, and in a few hours it was champagne. I have another that has a brown-orange core from one angle, which turns golden when rotated 90 degrees, though I'm not sure if this is a product of true pleochroism or just really odd color zoning, because I have yet another which, when sliced parallel to the C axis, revealed an x-shaped zone of brown color in a clear base. (As you might guess, despite these things I rather enjoy this material).

But that's all really a cardhouse of speculation based on incomplete data. Because of various monitor settings, etc., you will have much more luck showing it to someone in person.


Last edited by Stephen Challener on Tue Aug 28, 2012 8:56 pm, edited 1 time in total.

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 Post subject: Re: Buying your first Rough...
PostPosted: Tue Aug 28, 2012 7:23 pm 
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I always had trouble with picturing the finished stone shape, inside the the rough that was cuttable

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 Post subject: Re: Buying your first Rough...
PostPosted: Tue Aug 28, 2012 9:48 pm 
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Barrett wrote:
I always had trouble with picturing the finished stone shape, inside the the rough that was cuttable


I cannot do it well either so I do not usually buy rough as I cannot compete with them. Some of the best are the guys that only do the preforming but don't usually facet anything as they have lots of practice looking and planning. Others are the big buyers but most of them likely were preforming and/or faceting before they became buyers. Best regards, Lee

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 Post subject: Re: Buying your first Rough...
PostPosted: Tue Aug 28, 2012 10:15 pm 
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Well,

The website said it was from Brazil. The color it gave was 'golden', but I don't know if it's accurate. There's likely things I don't know about gem optics that coukd skew the perceived color of the rough.

I recently read that a light coating of oil could allow you to see inside the stone. I tried it and the clarity shot up a lot. Is the clarity you perceive by coating the surface what you can expect of a cut stone, or would it be greater? Further, why does this work in the first place?


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