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9 color change garnets

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zeolite

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Here''s my first (failed) attempt to show all 9 CC garnets. In this first picture, I used a daylight fluorescent and a full spectrum fluorescent, because I didn''t have two daylight fluorescents. These mixed fluorescents actually make the color change weaker, since the full spectrum fluorescent has strong oranges and reds, which brings the color closer to incandescent bulbs. Look at the shield cut on the right. The big side of the shield is showing the cooler color of the daylight fluorescent. The point side of the shield is showing much more orange due to the enhanced red phosphors of the full spectrum tube. The round front center stone is not showing its pastel green well in this picture, because the fluorescents are too far to the side, in order to illuminate the center two rectangular cuts.

4828ccfluores.jpg
 

zeolite

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Here is the exposure using G.E. Reveal bulbs. I''ll try both pictures again when I can get a second daylight fluorescent bulb of the right length for my fixture.

48291ccincand.jpg
 

zeolite

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Bekily, Madagascar (southern tip of Madagascar).
 

T L

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I love that blue/teal one. Thanks for the amazing photo. You have such a great collection!
 

MonkeyPie

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That curious pear-ish cut one on the right is calling my name. Lovely stones!
 

chrono

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Cool! I love the blue/red colour changer the best.
 

arjunajane

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I love the colour of the one to the furthest left, but they''re all gorgeous!
What type is that one may I ask?
 

zeolite

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All are a mixture of pyrope and spessatite. The left round is 2.12 cts. Here is an explanation of the cause of color change in gems:

The color change occurs only with gemstones that have an absorption band in the yellow region. This is usually caused by trace metals such as vanadium. The color change is visible when the gem is viewed in daylight (or fluorescent light) and then under incandescent (light bulb) light.

Daylight has little red, the yellow is blocked by the absorption band, so the gem shows cool colors such as green or blue. When you take this same gem under incandescent light, there is little blue, the yellow is blocked by the absorption band, and the gem shows only warm colors such as orange, pink or red. The critical factor in color change gems is that they must block nearly all light in the yellow region of the visible spectrum.

Slightly differences in the exact centering and in the width of the absorption band, explain the different warm or cool colors you see when you examine multiple color change gems side by side, as in the picture above.
 

LaurenThePartier

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Zeolite - you always post the BEST gemstone pics! What are you shooting with, if you don''t mind me asking?
 

zeolite

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Date: 4/20/2009 11:42:15 PM
Author: LaurenThePartier
Zeolite - you always post the BEST gemstone pics! What are you shooting with, if you don''t mind me asking?
Thank you, Lauren,

Let me answer ths in another thread. This question has broad appeal, and might be missed if buried in a CC garnet discussion. The answer is more complex and cheaper than just using expensive cameras.
 

Catmom

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Oooooo, so cool! I love color change stones.
 

Spirit

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Are color-change stones only non-heated, or can you get a color -change stone in a heated stone?
 

zeolite

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Date: 4/21/2009 10:39:01 AM
Author: Spirit
Are color-change stones only non-heated, or can you get a color -change stone in a heated stone?
As far as I know, no garnets are heated. It doesn''t seem to make any change or improvement in the garnet.

Sapphires and rubies are heated to dissolve the many rutile crystals inside, and to improve the color. Tourmalines and zircons can be heated, to lighten the tone. Aquamarines are heated to remove the yellow component and change the aqua from green or blue-green to blue.
 

zeolite

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Concerning the cause of the color in the very rare blue garnet:

I am quoting from page 5 of Garnet: Great Ball of Fire book, which I and Pandora ordered:

The extremely rare blue garnets from Madagascar, actually pyrope-spessatine, derive their color from a combination of the Mn2+ in the spessartine (imparting orange), and traces of vanadium in the prrope (imparting green). Heating in a reducing environment will mitigate some of the brown and yellow tones of "demantoid". But irradiation does not seem to have any impact on garnet color (George Rossman, personal communication).
 

cushioncutnut

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My jeweler showed me a gorgeous color change garnet today! I have to say, your collection takes the cake!!
 

zeolite

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Date: 4/21/2009 4:04:46 PM
Author: innerkitten
Cool color change photos! That blue color is really neat.
There is an extensive article on Bekily CC garnets in Gems & Gemology, Winter 1999 (volume 35, no. 4) on pages 196-201, with good pictures of these garnets. Ask GIA for reprints.

It is a difficult read for a non-gemologist. To summarize, it is slightly more pyrope than spessatine content, with high vanadium content (about 1.25%) and lower chromium content (about 0.25%), which causes the color change.

It is interesting that all of their examples are described as blue-green to purple, whereas mine is blue (or purplish-blue) to pinkish purple. I assume then that mine has even more vanadium and less chromium. With this better yet ratio of vanadium to chromium, mine is closer to the elusive perfect blue garnet. Mine has a refractive index of 1.761, right in the middle of their test data.
 

zeolite

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More fun with CC garnets and my camera, just in case anyone thinks the colors are manipulated:

Here are three photos with both light sources on in the same picture at the same time. These pictures were taken with no diffusion, so the lighting is harsh. This is actually what you see with your eye!

But the effect seems enhanced for two reasons: the daylight fluorescent to incandescent shows a stronger change than daylight to incandescent. This is because daylight has more red than daylight fluorescent. But the second, much stronger reason is that the human eye has an automatic, very fast white balance correction. If you view in fluorescent and then one second later shift to incandescent, you eye corrects, and the color change effect seems weaker. When both lights are on at the same time, the eye can''t correct. You eye is forced to see what the camera sees.

1.98 ct shield cut

4844shieldcc.jpg
 

zeolite

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Here is the 0.71 ct Bekily blue:

4843bekily.jpg
 

zeolite

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It is hard to get both light sources and a large camera within the field of view of these round cuts. So for this picture, I placed them all table down and photographed the two colors reflecting off of the big table facet.


2.12 ct, 1.27 ct, 0.89 ct


4845_3round.jpg
 

stepcutnut

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Date: 4/22/2009 4:09:06 PM
Author: zeolite
More fun with CC garnets and my camera, just in case anyone thinks the colors are manipulated:


Here are three photos with both light sources on in the same picture at the same time. These pictures were taken with no diffusion, so the lighting is harsh. This is actually what you see with your eye!


But the effect seems enhanced for two reasons: the daylight fluorescent to incandescent shows a stronger change than daylight to incandescent. This is because daylight has more red than daylight fluorescent. But the second, much stronger reason is that the human eye has an automatic, very fast white balance correction. If you view in fluorescent and then one second later shift to incandescent, you eye corrects, and the color change effect seems weaker. When both lights are on at the same time, the eye can''t correct. You eye is forced to see what the camera sees.


1.98 ct shield cut
I''m in love!!!
 
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