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A Christmas wish, researching tourmaline color.
https://www.gemologyonline.com/Forum/phpBB2/viewtopic.php?f=13&t=24864
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Author:  bruce_tourm [ Thu Dec 20, 2018 2:05 pm ]
Post subject:  A Christmas wish, researching tourmaline color.

My Christmas wish has to be about research with color and tourmaline. My focus will be on cuprian, paraiba type, and Paraiba (copper bearing) tourmaline and research that will probably never be done until synthetic tourmaline is commercially available. The natural gemstone has become too expensive to be sacrificed for testing. The following list of facts is put in general terms and not intent to be anything more than brief ideas I have discovered in papers, communications or from working with tourmaline myself.

1,The copper ion (Cu+2) found in copper bearing tourmaline can be effected by heating. The effect of improper heating leads to a less vibrant gem.

2, The copper ion (Cu+2) found in copper bearing tourmaline is unaffected by heating. This result of observation is the generally accepted fact.

3, The heating of copper bearing tourmaline reduces the red vector in its color by reducing manganese ion (Mg+3) to (Mg+2).

4, The heating of principally Paraiba can be difficult because even the best grades can have a slight grayest cast and over heating is a constant threat. This can lead to multiple cycles of heating of different duration to get the best gem.

5, Manganese is in its Mn+2 oxidation state when tourmaline is crystallized and natural radiation converts it to Mn +3.

6 Some green copper bearing tourmaline can be heated to reveal the cyan color from copper .

7 Some green copper bearing tourmaline can NOT be heated to reveal the cyan color from copper.

8 A large percentage of copper bearing tourmaline does not contain enough iron or titanium to have them as chromophores.

9, Irradiation induced color centers (O- hole center) can cause a yellow color vector in copper bearing tourmaline that can be eliminated threw heating.

10, Manganese that is incorporated into the Tsalisite structure that would be resistant to heating could cause the yellowish vector in copper bearing tourmaline.

11 Purples, the most distinctive color range in copper bearing tourmaline can be modified by heating without eliminating Mg+3's red vector.

12 Copper in tourmaline can not produce both green and cyan color no matter its concentration.

13 Incandescent/yellowish light greatly enhances the vividness of copper bearing tourmaline in the Paraiba color range of green to blue.

As you can see not all the listed "facts" can be true and my Christmas wish is to really understand what is happening in the complex and wonderful world of color in copper bearing tourmaline. I think that the early work on Paraiba was incomplete and based on a very limited set of specimens. Follow up work has been done on heating the many colors of copper bearing tourmaline and the resultant change in color, but I have not found any scientific work that address why the vividness of some copper bearing tourmaline can be reduced by heating.

So here comes my speculation. I present it with some trepidation because I can not have it tested. But maybe in the future when synthetic tourmaline can be manufactured with the right properties answers will be found. I think that either the color centers (O- hole) or Tsalisite can effect the vividness of copper bearing tourmaline. I think the commercial heating of copper bearing tourmaline can be complex because you are doing with more than just the reduction of manganese +3 to +2. You have to retain the enhancement of the yellowish vector from either the O-hole color centers or Tsalisite to get the most vivid gems. The copper chromophore in copper bearing tourmaline is stable in regards to both heat and color.

Bruce

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