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 Post subject: Color Change Gahnite???
PostPosted: Wed May 31, 2006 1:53 pm 
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Hi, people,

I have found a very interesting phenomenon on eBay recently, the appearance of a stone I had never heard about: color change gahnite. I knew gahnite already, as a rare stone, usually dark green, found mostly in Brazil. But these stones have no apparent similarity to the kind of gahnite I know. And they are usually from Africa. Could they be a new variety if gahnite, or is it another stone, maybe color change spinel, or even gahnospinel?

Please take a search on eBay for gahnite, or look at

http://cgi.ebay.com/ws/eBayISAPI.dll?Vi ... RK:MEWA:IT or

http://cgi.ebay.com/ws/eBayISAPI.dll?Vi ... %3AIT&rd=1

for instance.

What do you think about it?

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PostPosted: Wed May 31, 2006 2:37 pm 
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Image Image
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The Ebay pics appear to have been altered. The incandescent colors a far more intense and red than I generally find. If you can get any stuff with this intensity and degree of change, I would really like to get some samples.

The above pics (all spinels ) show some CC's. The bottom two pics within the left pic, and the top and bottom right pics within pic on the right. I do have others that change to reddish without nearly the intensity of the Ebay stuff.

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PostPosted: Wed May 31, 2006 3:03 pm 
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UX4,

Hi, What makes you think the photo's have been messed with? I'm not doubting your assesment I'm just wondering what you are basing your statement on. Usually I look for 'coloured' tongs or a different coloured background when trying to spot enhanced photo's but the tongs in this case remain silver and the background isn't changed all that much (no more than a different incident light might cause)...

...please explain what makes you suspicious as I'd like to understand more fully the techniques used to trick us mere mortals

Be well

Frank

PS ... nice spinels I never knew they could change quite so radically


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PostPosted: Wed May 31, 2006 3:14 pm 
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Hi Frank...

...4 things make me suspicious:

1. An Ebay seller that I do not know

2. The intensity of the color change to red in incandescent, which I have observed in none of my stones, unfortunately.

3. Artifacts in the reddish pics that often appear when colors are altered. I'll try to point them out in a following post. Note: I have no problems with processing to show accurate colors and saturations. But, it does raise a flag as it is so often employed to mislead.

4. my suspicious nature!

I really like the PICS and, if the pics are accurate, would like to get samples the stuff.

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PostPosted: Wed May 31, 2006 3:26 pm 
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Frank wrote:
I look for 'coloured' tongs or a different coloured background when trying to spot enhanced photo's but the tongs in this case remain silver and the background isn't changed all that much (no more than a different incident light might cause)...



...Frank, I forgot to note that the above technique is not reliable, although it may be true in many cases. Sometimes, a different color background is a strong indicator that at least one powerful IP technique was NOT employed! In the digital protography era, nothing is impossible, and many techiniques are toooooooooo easy.

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PostPosted: Wed May 31, 2006 4:21 pm 
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IP indicia

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I do NOT consider the above conclusive. Simply flags. It is enough to alert me of the possibility. Deeper analysis may be done.

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PostPosted: Fri Jun 02, 2006 6:29 pm 
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Thanks, ux4, I think they might be spinels, that was my first guess too, but what impresses me is that among the stones they offer there are many different types of color change, red to purple, purple to green, orange to green, green to gray, orange to red, etc and the only type of color change spinel I have seen in from blue to (bluish) purple. Anyway, they should not sell those stones as gahnites, because they are not gahnites. And there is more than one seller selling those stones, generally in lots.

Andre Philippe

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PostPosted: Fri Jun 02, 2006 8:03 pm 
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I'm just guessing but "garnet" might sound a lot like "gahnite" to a non-English speaker.

The stones pictured remind me a lot of the colors and color-changes in a parcel of small Tanzanian CC pyrope-spessartite garnets I recently had cut. The color changes in my stones are easily as dramatic and varied as those shown.

As for whether the images have been altered, who can really say without actually inspecting the stones? I've struggled to capture honest daylight/incandescent images of alexandrites and CC garnets and can only say: "It ain't easy, folks!" Try it and if you succeed without having to resort to at least a little Photoshopping to create "eyeball-accurate" colors, please share your secrets.

ROM


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 Post subject: Re: Color Change Gahnite???
PostPosted: Wed Jul 26, 2006 12:20 pm 
MIR-A-GEM wrote:
Hi, people,

I have found a very interesting phenomenon on eBay recently, the appearance of a stone I had never heard about: color change gahnite. I knew gahnite already, as a rare stone, usually dark green, found mostly in Brazil. But these stones have no apparent similarity to the kind of gahnite I know. And they are usually from Africa. Could they be a new variety if gahnite, or is it another stone, maybe color change spinel, or even gahnospinel?

Please take a search on eBay for gahnite, or look at

http://cgi.ebay.com/ws/eBayISAPI.dll?Vi ... RK:MEWA:IT or

http://cgi.ebay.com/ws/eBayISAPI.dll?Vi ... %3AIT&rd=1

for instance.

What do you think about it?


Hi,

I did visit this seller this May during my visit to Thailand. They are in Chanthaburi and really jovial and good guys.

Regarding gahnite, the answer is very simple indeed. Among color change spinels there are some color change garnets !!!! Spinels are those changing from violet/purple to red/pink, while garnets - from green to purple. However, both stones are quite lovely and look nice.

Hope it helps.

Cheers

Vitalii


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PostPosted: Wed Jul 26, 2006 3:37 pm 
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Well, the guys from Thailand may be good and jovial, but selling garnet as gahnite is misrepresentation anyway, even if the stones are nice...

What ROM said about pronunciation makes sense, but looking at their eBay store, one can see they sell garnets (spelt garnets) so they know there is a difference between gahnites and garnets.

About color change spinels, I have seen one (and I have it in my collection) that changes from purple (incandescent) to blue (natural ou fluorescent), but I have never seen one that changes from purple/violet to red/pink.

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PostPosted: Wed Jul 26, 2006 4:04 pm 
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Gahnite is a member of the spinel family, where the magnesium has been replaced with zinc.
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And I have some cc garnets that change from violet/purple to red/pink and others that go bluish green to purple.


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PostPosted: Wed Jul 26, 2006 4:20 pm 
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Oh, sure, Barbra, I have seen garnets that change from purple/violet (fluorescent) to red/pink (incandescent), and in fact I guess it is quite common; I might say most almandines do that color change.

I was referring to color change spinels, where I have never seen that specific color change.

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PostPosted: Thu Jul 27, 2006 2:24 am 
MIR-A-GEM wrote:
Well, the guys from Thailand may be good and jovial, but selling garnet as gahnite is misrepresentation anyway, even if the stones are nice...

What ROM said about pronunciation makes sense, but looking at their eBay store, one can see they sell garnets (spelt garnets) so they know there is a difference between gahnites and garnets.

About color change spinels, I have seen one (and I have it in my collection) that changes from purple (incandescent) to blue (natural ou fluorescent), but I have never seen one that changes from purple/violet to red/pink.


Actually, the stone sizes you refer to are quite small (sell in parcel), that's why Thai dealers do not test every stone separately (but might to do so). You are absolutely right this leads to misrepresentation. But, buying small stones in lots is always MIXED fortune. I used to buy parcels of rough small spinels in Vietnam - some stones appeared to be ruby, some sapphires and some spinels. I made some more than expect.


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