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 Post subject: Re: Topaz blues
PostPosted: Tue Jan 15, 2013 7:09 pm 
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AlexanderMorou wrote:
Is there a tried and true way to discern the resultant color of a cut stone? If you're choosing large rough, does the method change, since there's more material to block the light, thus darkening the appearance of the stone...?

Well...I wouldn't say there's a "tried and true" method, but there is a new and surprisingly effective method pioneered by Marco Voltolini.

Are you familiar with the white paper test? Well, replace it with the "small mirror" test.

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maialetto wrote:
I'd like to add something about predicting a cut stone outcome. In fact I've not been using the "white paper test" for years. I've never posted it because I always forget to take the pictures... The white paper test is good to get "if a stone will cut too dark or not", but I find it very inaccurate for predicting the real color of the finished gem. The system I use is as easy as the white paper test: wet your stone (or cover it with clear varnish, etc.) if the surfaces are frosted, and place it on a little mirror: the color you see it's ~ the color the pavilion facets will reflect. Instead of using the angles of the pavilion facets to reflect the light, here you are cheating and using a mirror. :)
But a picture is worth a thousand words:
Image
Here I'm using exactly the same lighting conditions...


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 Post subject: Re: Topaz blues
PostPosted: Tue Jan 15, 2013 8:27 pm 
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Arya Akhavan wrote:
AlexanderMorou wrote:
Is there a tried and true way to discern the resultant color of a cut stone? If you're choosing large rough, does the method change, since there's more material to block the light, thus darkening the appearance of the stone...?

Well...I wouldn't say there's a "tried and true" method, but there is a new and surprisingly effective method pioneered by Marco Voltolini.

Are you familiar with the white paper test? Well, replace it with the "small mirror" test.

---------------------------------------------------
maialetto wrote:
I'd like to add something about predicting a cut stone outcome. In fact I've not been using the "white paper test" for years. I've never posted it because I always forget to take the pictures... The white paper test is good to get "if a stone will cut too dark or not", but I find it very inaccurate for predicting the real color of the finished gem. The system I use is as easy as the white paper test: wet your stone (or cover it with clear varnish, etc.) if the surfaces are frosted, and place it on a little mirror: the color you see it's ~ the color the pavilion facets will reflect. Instead of using the angles of the pavilion facets to reflect the light, here you are cheating and using a mirror. :)
But a picture is worth a thousand words:
Image
Here I'm using exactly the same lighting conditions...


Okay, here's a try:
Image


Using olive oil on the outside, and as close to a small mirror I could find.


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 Post subject: Re: Topaz blues
PostPosted: Tue Jan 15, 2013 8:47 pm 
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That's shaping up to be a nice color! Keep it in the light, though, just to see how much more it fades (if at all).


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 Post subject: Re: Topaz blues
PostPosted: Wed Jan 16, 2013 10:44 am 
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Arya Akhavan wrote:
That's shaping up to be a nice color! Keep it in the light, though, just to see how much more it fades (if at all).

Previous post was done in haste, I had to take a picture, adjust it for thumbnail and regular size, and post the message here in five minutes.

Here's a few of it in incandescent light. I think it's the angle of the light entering the stone that's causing the color, rather than the incandescence of the light.
Image Image


There's a blurred part of the image because the 'mirror' I'm using as a steel notepad cover with my name on it. I can't recall if I've posted my real name here or not, so I blurred it out just in case. It also helps if I post it elsewhere.

I'm starting to understand what people mean by 'fire' in a gemstone. While I don't expect such a color to result from it being cut, if one were to flash that red around it'd be extremely pretty when cut. My annual income is too far away from the prices such topaz variety stones fetch (or in the second stone's case, nearly three times my annual income). Depressing to know such a fact. :-)


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 Post subject: Re: Topaz blues
PostPosted: Wed Jan 16, 2013 1:51 pm 
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Yeah, I know that feel. It's possible to find topaz that will show that type of color for affordable prices (irradiated katlang--I guess the traces of chromium lend it the brilliant orange/red-orange hues?), but it fades to rather uninspiring pastel hues, which is so frustrating. I mean, look at this one: http://www.ebay.com/itm/28-50cts-RIGHT- ... 589aee1bca The color in the photo is just about accurate--if it would only be stable! And they come in redder hues as well, and look fantastic when faceted. [That said, the article on this material in G&G says that a subset is photostable, which would be neat).
Re: color zoning. I don't necessarily see a phantom in the photos you posted, but it's not always apparent since you need to be looking at it essentially from the side. The most common zoning I've seen in smaller stones is one edge being strongly colored and the rest less so, but you have to view it from exactly the right angle to really see it.

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 Post subject: Re: Topaz blues
PostPosted: Sat Jan 19, 2013 3:52 am 
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Well,

If this thing is getting lighter, it's doing so slowly. I can't tell if there's any change, so either it's stabilized, or reached the limit of the lights I'm using:
Image


One's the previously mentioned 4000K light, the other is an OttLight. If it's a waste of time, I'll just buy one of those sun lamps on eBay.


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 Post subject: Re: Topaz blues
PostPosted: Sat Jan 19, 2013 12:34 pm 
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If you have a hardware store nearby, buy a black light and use that. It puts out a lot of UV, so it should speed the process along.


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 Post subject: Re: Topaz blues
PostPosted: Sat Jan 19, 2013 1:26 pm 
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I tried briefly (two hours) a cfl blacklight until I read they're usually cheaply made by dipping a regular cfl in a coat of dark paint that blocks most visible light. Looked like a black light but didn't do the usual look beyond making whites look vibrajt in a dark room.


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 Post subject: Re: Topaz blues
PostPosted: Sat Jan 19, 2013 4:22 pm 
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Hmm...I just checked up on good black lights, and I haven't been able to find a good product. This might be a good time to ask one of our resident scientists, like Jon Rolfe (Gearloose). Or you could just wait for the 2-4 weeks and see if daylight is strong enough to fade the stone. :)


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 Post subject: Re: Topaz blues
PostPosted: Thu Mar 21, 2013 5:49 pm 
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I'd suggest that a couple of hundred bucks isn't a bad price to pay for that, assuming that it's a clear and clean as it appears to be.

Try selling it as is, or have it cut into gems, can't go wrong. Could produce something very big, even if it fades to colorless, no big deal.

Any decent local rockshop will have modestly priced UV lights, but it seems a waste of money when you could just leave it on a windowsill for a while.

Personally... I'd hate to let go of it. Gem crystals are wonderful things.


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 Post subject: Re: Topaz blues
PostPosted: Fri Mar 22, 2013 12:10 am 
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By the way, one thing I've noticed with topaz like this is that using an LCD monitor to view the stone's pleochroism (brown-red to pure yellow on my pieces) also seems to make zoning more obvious. Not necessarily very useful, but kind of fun anyway.

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 Post subject: Re: Topaz blues
PostPosted: Fri Mar 22, 2013 12:32 am 
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Scarodactyl wrote:
By the way, one thing I've noticed with topaz like this is that using an LCD monitor to view the stone's pleochroism (brown-red to pure yellow on my pieces) also seems to make zoning more obvious. Not necessarily very useful, but kind of fun anyway.

Wait, how do you do that with a computer monitor? Don't you need a polarizing filter?


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 Post subject: Re: Topaz blues
PostPosted: Fri Mar 22, 2013 12:34 am 
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Same effect I've noticed on topaz, I tried asking what was causing it but no one responded in kind.

I think the screen itself is the filter, but I'm not sure.


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 Post subject: Re: Topaz blues
PostPosted: Fri Mar 22, 2013 3:05 am 
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Arya Akhavan wrote:
Scarodactyl wrote:
By the way, one thing I've noticed with topaz like this is that using an LCD monitor to view the stone's pleochroism (brown-red to pure yellow on my pieces) also seems to make zoning more obvious. Not necessarily very useful, but kind of fun anyway.

Wait, how do you do that with a computer monitor? Don't you need a polarizing filter?

LCD monitors put off polarized light. It's part of how they work. It's a very neat trick, which I learned here-lots of fun, and a good way to play with a collection of stones.

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 Post subject: Re: Topaz blues
PostPosted: Sun Mar 24, 2013 10:17 pm 
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Quote; I was thinking I was bidding a digit or two less than what I did, so instead of the reasonable, for a pretty rock, $22.42 price tag, it had an extra digit thrown in.

For future reference it is OK to back out of an ebay auction when you make a mistaken bid. Just ask to cancel the transaction and they will do it.

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