Oct. 24 to 26:SANTA ROSA, CALIFORNIA: Wholesale and retail show; Gem Faire Inc., Sonoma County Fairgrounds
Welcome to the GemologyOnline.com Forum
A non-profit Forum for the exchange of gemological ideas
It is currently Mon Oct 20, 2014 11:41 pm

All times are UTC - 4 hours




Post new topic This topic is locked, you cannot edit posts or make further replies.  [ 25 posts ]  Go to page 1, 2  Next
Author Message
 Post subject: Color Changing Tanzanite
PostPosted: Fri Jul 21, 2006 3:13 pm 
Offline
Site Admin
User avatar

Joined: Sun Oct 16, 2005 12:22 pm
Posts: 14754
Location: San Francisco
I was just thumbing through my copy of Gemstones, Symbols of Beauty and Power by Gubelin and came across something I hadn't heard before.
Page 114: Tanzanite, Blue Patrician from Black Africa:
Quote:
The aqueous calcium-aluminum silicate has strong pleochroism. Depending on direction, tanzanite is either violet-blue, or an unmistakable amethyst color or simply brown. The undesirable brown and violet shades are only removed after professional heating and the radiant cornflower blue is brought to full expression. If this delicate process is only partially successful, a violet tint is left behind that is particularly visible under artificial light. No other gemstone posses this unique ability to rid itself of two of its triple colors by means of heat treatment. If only one of the three colors, frequently the brown, is eliminated as a result of unprofessional heating, a color changing tanzanite is created, similar to color changing sapphire or spinel. In day light it looks blue, in artificial light it looks violet.


So, of course I had to take my tanzanites outside...yes blue indeed and then in the closet with a candle...and they were VIOLET with strong red flashes! :idea: I had never realized. This is super cool. I am so glad my stones were unprofessionally heated!

Is this something everyone is aware of and I've been living in a remote cave? :smt014


Share on FacebookShare on Twitter
Top
 Profile  
 
 Post subject: Tanzanite
PostPosted: Fri Jul 21, 2006 4:50 pm 
Offline
Gold Member
User avatar

Joined: Wed Mar 15, 2006 5:10 pm
Posts: 1338
Location: PA
Im not sure that it has anything to do with "professional" or non professional heating. I have (had) a few un heated tanzanites that were naturally blue, and this color change is very pronounced in them. I also heated a yellowish brown piece, that was on the light side, and the same color change is true, although the finished color of this stone is light purple/blue.
I have on un cut, unheated piece that I'll photograph and post that clearly shows 3 distinct colors.

_________________
Precison Gem
www.precisiongem.com


Share on FacebookShare on Twitter
Top
 Profile  
 
 Post subject:
PostPosted: Fri Jul 21, 2006 7:52 pm 
Offline
Valued Contributor

Joined: Sun Oct 16, 2005 4:25 pm
Posts: 161
Location: Michigan, USA
I've noticed that the nicer pieces I've practiced with did this blue/violet color change but assumed it was a just a standard property of tanzanite. (I have to admit I have the book but have read only parts of it, as I have a hard time getting past the gorgeous photos!)


Share on FacebookShare on Twitter
Top
 Profile  
 
 Post subject:
PostPosted: Fri Jul 21, 2006 11:19 pm 
Offline
Gemology Online Royal Princess
User avatar

Joined: Mon Oct 17, 2005 10:56 am
Posts: 6139
Location: Where did summer go? :(
I remember the first time I finally took my tanzanites outside in the sunshine! They went from what I thought was a pleasant violet color to blue! I try to be sure to take all my colored stones into the sunlight now ... you'd be surprised at what you find out :shock: .


Share on FacebookShare on Twitter
Top
 Profile  
 
 Post subject:
PostPosted: Sat Jul 22, 2006 10:15 am 
Offline
Site Admin
User avatar

Joined: Sun Oct 16, 2005 12:22 pm
Posts: 14754
Location: San Francisco
AS I was standing in the closet with a candle :roll: , I thought, wouldn't it be handy if someone developed a small light box that would mimic daylight and incandescent lighting solely for the purpose of color change.
I suggest the lighting unit fit where the LW+SW UV light goes on the UV light box.

That way one could standardize the perimeters.


Share on FacebookShare on Twitter
Top
 Profile  
 
 Post subject:
PostPosted: Sat Jul 22, 2006 12:04 pm 
Offline
Platinum Member

Joined: Tue Nov 29, 2005 2:02 pm
Posts: 2647
That's a $$$Capital idea$$$. In fact make the light sources all one unit. Simply flip over for LWSW or flip again for incandescent/fluorescent option.

Shouldn't be difficult to engineer at all.


Share on FacebookShare on Twitter
Top
 Profile  
 
 Post subject:
PostPosted: Sat Jul 22, 2006 1:19 pm 
Offline
Valued Contributor

Joined: Sun Oct 16, 2005 4:25 pm
Posts: 161
Location: Michigan, USA
Invent a "third hand" for maglites while your at it, please. (I run out of ways to hold everything!)


Share on FacebookShare on Twitter
Top
 Profile  
 
 Post subject:
PostPosted: Sat Jul 22, 2006 2:14 pm 
Offline
Gemology Online Royal Princess
User avatar

Joined: Mon Oct 17, 2005 10:56 am
Posts: 6139
Location: Where did summer go? :(
I'll bet you could get something like this from Kassoy or another dealer, then buy a regular bulb to go along with the daylight bulb:

http://www.kassoy.com/gemology02.htm


About half way down the page!


Share on FacebookShare on Twitter
Top
 Profile  
 
 Post subject:
PostPosted: Sat Jul 22, 2006 3:09 pm 
Offline
Platinum Member

Joined: Tue Nov 29, 2005 2:02 pm
Posts: 2647
That may be good for portability issues if you can find an incandescent light source for it.

For the lab, I have the exact same unit as the one first pictured on that Kassoy page.

Notice how the LWSW bulbs face down into the cabinet. Now if the top of the light unit had a similar bulb arrangement for incandescent/fluorescent, independently switched, how easy would that be? No bulbs to change.

The enclosed cabinet would ensure no extraneous light would be involved.

Just a thought for inventors.


Share on FacebookShare on Twitter
Top
 Profile  
 
 Post subject:
PostPosted: Sat Jul 22, 2006 4:37 pm 
Offline
Gemology Online Royal Princess
User avatar

Joined: Mon Oct 17, 2005 10:56 am
Posts: 6139
Location: Where did summer go? :(
Great idea, JB, but until the inventors get going--IF one could find an incandescent bulb shaped like a flourescent bulb, could they be used in place of the LWSW UV lights in your cabinet? I realize that wouldn't exactly be portable, but for lab use, as you said.

This would probably have to be a do-it-yourself set-up, since the use of such an item would most likely be limited to a small buying group.


Share on FacebookShare on Twitter
Top
 Profile  
 
 Post subject:
PostPosted: Sat Jul 22, 2006 5:59 pm 
Offline
Platinum Member

Joined: Tue Nov 29, 2005 2:02 pm
Posts: 2647
I refuse to change light bulbs! lol

Seriously, If someone thinks they can make a buck on it, they'll probably give it a go.

If not, penlight and flourescent.


Share on FacebookShare on Twitter
Top
 Profile  
 
 Post subject: heating
PostPosted: Tue Jul 25, 2006 6:27 am 
Offline
Gold Member
User avatar

Joined: Wed Apr 26, 2006 12:44 am
Posts: 1898
Location: San Francisco
The heat treatment sounds pretty simple.. put the cut stone in investment casting, w/ 3 " thick all around.. heat to 1200 degrees ramping 100-200 deg/ hour and same for cool down, and voila.. from the guys that sold me some excellent rough I haven't cut yet.. (tom schneider gems).


Share on FacebookShare on Twitter
Top
 Profile  
 
 Post subject: Re: heating
PostPosted: Tue Jul 25, 2006 1:54 pm 
Offline
Platinum Member
User avatar

Joined: Fri Feb 24, 2006 1:20 am
Posts: 2558
Location: Southern California, U.S.A.
jleb wrote:
The heat treatment sounds pretty simple.. put the cut stone in investment casting, w/ 3 " thick all around.. heat to 1200 degrees ramping 100-200 deg/ hour and same for cool down, and voila..

It is and I've done it several times. The color change seems to depend on the intrinsic nature of the material being treated. My observation is that the darker the original brown color, the darker the tone and saturation of the blue/purple color. When finished I've always just turned the oven off at 1200 and let it sit unopened for at least 12 hours instead of ramping down. No problems yet.

I have issues with this topic and haven't posted to the thread previously because my book research hasn't yet resolved some of my questions. Does anyone have any cites as to how heat actually changes blue zoisite's pleochroism? What happens on an atomic level?


Share on FacebookShare on Twitter
Top
 Profile  
 
 Post subject:
PostPosted: Wed Jul 26, 2006 10:09 am 
Offline
Gemology Online Royal Princess
User avatar

Joined: Mon Oct 17, 2005 10:56 am
Posts: 6139
Location: Where did summer go? :(
I don't know why my brain wasn't working earlier in this thread, but I just remembered -- someone does make a box with both flourescent and incandescent lights. I saw quite a few at the Tucson show ... they were used to show the color change in zandrites, garnets, and alexandrite. Don't know where they obtained the boxes, but they did look rather professional, if memory serves me correctly (which, as you all know, it doesn't always :oops: ).


Share on FacebookShare on Twitter
Top
 Profile  
 
 Post subject:
PostPosted: Wed Jul 26, 2006 6:09 pm 
Offline
Platinum Member

Joined: Tue Nov 29, 2005 2:02 pm
Posts: 2647
Quote:
Does anyone have any cites as to how heat actually changes blue zoisite's pleochroism? What happens on an atomic level?


That was a good question ROM. I've searched quite a bit and so far the only site that even hinted at the mechanism stated that heat alters the yellow green trichroic crystal axis leaving a more face up blue color.

As to what happens in this chemical alteration....don't know yet.


Share on FacebookShare on Twitter
Top
 Profile  
 
Display posts from previous:  Sort by  
Post new topic This topic is locked, you cannot edit posts or make further replies.  [ 25 posts ]  Go to page 1, 2  Next

All times are UTC - 4 hours


Who is online

Users browsing this forum: No registered users and 4 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Search for:
Jump to:  
Powered by phpBB © 2000, 2002, 2005, 2007 phpBB Group
Gemology Style ported to phpBB3 by Christian Bullock