Confused about color change - please help!

[drive_yugo]

I am a semi-educated newby interested in color-changing diamonds. Now, my understanding has been that in diamonds - under "normal" lighting conditions that won''t kill you or your retina - this effect is limited to chameleons, which change color based on (a) temperature; or (b) light exposure. In particular, with light exposure the diamond displays a different color after being kept in the dark for a while, but quickly reverts back to the main color when exposed to light again. In my (limited) understanding, these were the only color change mechanisms in diamonds. (Some could also display a different color under UV, but that''s not "normal" lighting.)

However, recently a friend of mine - who has a degree in some "geological" (not "gemological") science - has insisted that there also are diamonds that display an Alexandrite-like effect. That is they can display a vivid change of color (e.g. same clear "green" "yellow" transition as chameleons), but in a light-dependent manner and _without_ reverting to main color after exposure (i.e. green in day-light; yellow under incandescent - with coloration display lasting indefinitely as long as the light source does not change). My friend claims to have seen a couple of such stones, but I''ve never even heard of something like this - either from people interested in diamonds OR in alexandrite (and they ought to know as they are constantly pre-occupied with possible alexandrite "substitutes"

)... Is this really possible??? (And, if so, what is the mechanism and how frequent/rare such stones are? What are the color pairs seen?)

Thanks for the help!

dy

 

[dkodner]

Hi DY-

Your friend may have seen diamonds with such strong fluorescence that when they were in direct daylight, the fluorescence appeared to change the color, and then again as he went into incandescent light. I have dealt with and own quite a few Chameleons and other colors, and have never personally seen a diamond other than a Chameleon have a true color change affect. However, I do know that there have been diamonds discovered in the Argyle Mine that also apparently have a natural color change, although I believe they are mostly bluish-grayish or olive gray stones. I believe they attribute the color change to high amounts of Hydrogen. These would be very rare stones, and probably only seen by a few people. I don''t know that there is a lot of data on these stones, and I have never seen one personally. I would think your friend saw something other than what he described, possibly even a stone that he was told was a diamond but was not. That being said, I would love to know more about these "diamonds" if they do exist. Ask your friend for more information please, as to where he saw these, and where they came from. Hope that helps.

D

 

[drive_yugo]

Thanks David - this helps quite a bit.

I also thought of the underlying fluorescence as a possiblity, but it seemed like it would have to be crazy-strong to overwhelm the natural color!! I will follow up with my friend and report back if I get any concrete information.

Also, should you or others come across anything like this (pictures, links, etc.) - please do post them!

dy

 

[Rockdiamond]

Hi All!
I agree with David.
We''ve had our share of chameleons as well. They are desirable for this characteristic- but our experience is that it''s actually more difficult to see a chameleon change color than it is to see the color change in a fluorescent diamond- a fluorescent yellow diamond in particular.
Some of the more faint yellow diamonds with strong blue can display quite dramatic color change effects.

I''ll see if I can find a photo showing this.


In my experience, GIA is actually tougher on yellow diamonds with fluorescence. For example a Fancy Yellow with strong blue may look quite like an Intense Yellow in room lighting but get a lot lighter in sunlight.
All this makes fluorescence one of the more "interesting" aspects of colored diamonds.

 

[drive_yugo]

David, you bring up several interesting points! Could you elaborate why is it more difficult to see chameleon change color - is it because the change is weaker or because they lose the alternative color too quickly after being moved into an illuminated area? (Incidentally, in your experience - other David''s or anybody else''s - how long do they typically hold the alternative color and how long does it take them to "recharge"?)

Wrt fluorescence - as someone with a bit of a physics background I find it pretty amazing that you can induce a sizable crystal to fluoresce with a white light source to the point where this would create a complete change away from the basic reflected color. This could certainly explain the alexandrite-like yellow to green (yellow+blue) shift, so it would be great if you could post some side-by-sides of a stronger color changing stone or two!

Finally, a real newby question: As I understand it, GIA grades under a fluorescent source - which would explain them being tougher on coloration of fluorescing yellows - but do they test for chameleon (and/or any other "rare" properties) by default? (I.e., never having done this, I am wondering do you have to specify that the stone might be a chameleon when you send it to them or do they test it regardless under some sort of criteria?)

Thanks much!

dy

 

[oldmancoyote]

On speed of change: "my" chameleon takes between 10 to 20 minutes to change completely (yellow -> green) after being in the dark for a couple of days. Speed of change varies depending if exposed to natural or artificial light. "Recharge" time in darkness is about overnight, but I can''t say I ever bothered to get up at 3 am to see if it had turned back.

I think there are certain giveaways to chameleons in terms of the IR and UV absorption spectra that GIA would pick up by default when testing colour origin in greens/yellows/browns, but someone more versed in diamond testing may correct me.

 

[Rockdiamond]

Without question OMC has more patience than me.
When I've needed to show the color change in a chameleon, I have kept it in the dark overnight.
I get the camera ready before I open the safe, and immediately snap a photo.
You really have to be fast with that one- as you need light to get a good photo- so the change is already starting.

Instead of simply sitting around like a Coyote waiting for a Road Runner- and we all know how that one's going to play out- I accelerate the process.
I take the diamond and put it table down on a galvanized diamond scoop, which I am holding using a pair of tweezers.
Then I take a simple cigarette lighter, and heat up the bottom of the scoop till I can't take the stand the heat with my lighter hand.

A diamond is one of natures most efficient substances at transmitting heat. At this point the diamond would sear your skin in an instant if you touched it.
Somehow I was able to pick it up, red hot, and get the photo on the right.



In this case, the diamond really looks almost green after you've taken it out and it's adjusted to normal room temperature.

Basically, you can "induce" a more dramatic color change, but normally the stone will stabilize at it's normal color once it's been exposed to light for about 10 to 20 minutes. Thank goodness Coyotes can , at least, keep time!

The reason I feel fluorescence is a more easily seen color change is that it's instantaneous, requires no preparation, it's repeatable- and can be quite distinct.

 

[Fly Girl]

Date: 6/1/2009 12:55:15 PM
Author: oldmancoyote
On speed of change: ''my'' chameleon takes between 10 to 20 minutes to change completely (yellow -> green) after being in the dark for a couple of days. Speed of change varies depending if exposed to natural or artificial light. ''Recharge'' time in darkness is about overnight, but I can''t say I ever bothered to get up at 3 am to see if it had turned back.

I think there are certain giveaways to chameleons in terms of the IR and UV absorption spectra that GIA would pick up by default when testing colour origin in greens/yellows/browns, but someone more versed in diamond testing may correct me.

My chameleon changes color the same as yours, OMC. But it also looks green in natural or fluorescent lights, and brown under incandescent lights. So, I figure it could be considered a color change diamond as well. It does have strong green fluorescence.

 

[Fly Girl]

Platinumrock has posted pictures of her peachy gray cleftless heart. Link

Wouldn''t a diamond like this be considered a color shifter?

 

[oldmancoyote]

Date: 6/1/2009 8:06:40 PM
Author: Rockdiamond
[snip]
Instead of simply sitting around like a Coyote waiting for a Road Runner- and we all know how that one''s going to play out- I accelerate the process.
[snip]

See? Here I am, reading about chameleons, and look what happens???

(threadjack over)