Anybody know the answer?

[LD]

Ok, you know you''re obsessed by gemstones when you wake up with a question about them you NEED answering! So .....

Question:

Natural sapphires will sometimes shift in colour (pink/purple teal/violet etc etc). However, do BE diffused sapphires shift in colour also?

My thinking is that if you take a natural sapphire (that was a colour shifter) and bombarded it with diffusion you are essentially impregnating a colour - does this mean it will stop the sapphire from shifting because the colouration alters the properties of the sapphire?

or

Will the sapphire still shift despite the treatment because it''s the natural way that it responds to light?

 

[zeolite]

Keep in mind the following answer is theoretical; I have no actual experience in this specific question. However, as a physicist, I have a very strong educational and work experience in optics, plus a gemology degree.

The main criteria for a color changing stone, is that when it is viewed both in light high in blue (daylight) and also light high in red (incandescent – light bulb), that it MUST have an absorption band in the yellow region. This explanation was given to me in person by Dr. Jim Shigley, then head of GIA research department.

Since daylight has less red, and the yellow region is blocked, the gem looks more blue or green. When the same gem is viewed in incandescent light, which has less blue, and yellow is blocked, the gem appears more orange or red. The yellow blocking region is created by trace metals, vanadium and/or iron.

So there are two parts to the answer to your question. If the sapphire, before the BE diffusion, did not have the color changing yellow absorption band, the BE treatment would have no effect. It would not suddenly become a color changing gem.

Now take the case of a color changing sapphire that gets BE treatment: BE diffusion is usually applied to a pink sapphire, and has beryllium atoms substituting for the aluminum atoms in the Al2O3 sapphire structure. This imparts an orange filter on the gem. Orange filters will pass orange and red, and block blue and green.

So the gem will still be a color change or color shift gem, but both colors will shift slightly toward the orange red region. So if the original gem might shift from blue to orangy- red, after BE treatment, it might be more blue-green to red.

 

[Lady_Disdain]

Very interesting, zeolite. Thank you for sharing the information with us.

 

[LD]

Thank you - that makes absolute sense.

Just one further thought ............ my understanding (and am totally prepared to be corrected) is that most sapphires that are used for BE treatment, start as a yellow or brownish colour rather than pink. So, if that''s the case, would that affect the absorption levels since yellow is an important part in the process? I hope I''ve explained/phrased that correctly?

 

[zeolite]

Date: 12/30/2009 2:31:56 PM
Author: LovingDiamonds
Thank you - that makes absolute sense.

Just one further thought ............ my understanding (and am totally prepared to be corrected) is that most sapphires that are used for BE treatment, start as a yellow or brownish colour rather than pink. So, if that''s the case, would that affect the absorption levels since yellow is an important part in the process? I hope I''ve explained/phrased that correctly?

LD, I just did a google search on "beryllium sapphire treatment", below. It appears that most references quote a beginning pink core. However the first reference below quotes an intriguing yellow or green core. The final color seems to vary according to the trace metals in the original sample.

Keep in mind these only discuss BE treatment on fairly common sapphires. My guess is that a CC sapphire is rare enough and expensive enough, that it would bring a higher dollar value if it is left untreated, since it is so rare.

http://www.gemselect.com/gem-info/berylliumtreatment.php

Thus bright yellow or orange sapphire can be produced from weak yellow or greenish gems.

http://www.australiangemmologist.com.au/agnews02.html

research soon discovered that these padparadscha coloured sapphires were in fact pink sapphires that owed their orange colour to a rim of sapphire of induced yellow colour

Subsequent examination of the immersed sapphire, with magnification, allowed observation of a circumferential rim of yellow sapphire surrounding the original pink core of the sapphire.

http://www.palagems.com/gods_graves_sapphires.htm

The AGTA lab’s Ken Scarratt had also obtained samples of these citrus sapphires and discovered disturbing orange color rims surrounding pink cores.

 

[LD]

Thank you again. I am familiar with BE/lattice diffusion and I think you have to be nowadays because the majority of sapphires on sale (with the exception of our forum vendors etc) unfortunately have been treated.

I think however you may be right that a colour shift sapphire may well be more expensive than a normal single colour sapphire and so is unlikely to be a candidate for BE treatment. I have no idea why I even thought of this question this morning but it intrigued me!

Thanks again for imparting your knowledge. Most appreciated.

 

[Michael_E]

Here''s a good article by the GIA: GIA BE diffused blue sapphire

 

[LD]

Thank you Michael. I''ve read the research with interest. I wonder if you''ve had any experience with BE and colour shift sapphires please?

 

[deorwine]

Wow, Michael_E, that was really neat. Thanks.

 

[Michael_E]

Date: 12/30/2009 5:07:21 PM
Author: LovingDiamonds
Thank you Michael. I''ve read the research with interest. I wonder if you''ve had any experience with BE and colour shift sapphires please?

I haven''t had any experience with this. I think that I''ve only handled a dozen or so of what I would consider really good color change sapphires and none were treated. From the radical changes that I''ve seen in research papers concerning BE enhancement I would suspect that most enhanced stones,( the orange to pink color ranges), would no longer show the same color change as they had originally. I suppose that one could go from pink to orange though ? The enhanced blue stones may be a different story though, so if you''re thinking of getting one make sure it has a cert and that the stone matches the cert.

 

[LD]

Date: 12/30/2009 6:27:46 PM
Author: Michael_E

Date: 12/30/2009 5:07:21 PM
Author: LovingDiamonds
Thank you Michael. I''ve read the research with interest. I wonder if you''ve had any experience with BE and colour shift sapphires please?

I haven''t had any experience with this. I think that I''ve only handled a dozen or so of what I would consider really good color change sapphires and none were treated. From the radical changes that I''ve seen in research papers concerning BE enhancement I would suspect that most enhanced stones,( the orange to pink color ranges), would no longer show the same color change as they had originally. I suppose that one could go from pink to orange though ? The enhanced blue stones may be a different story though, so if you''re thinking of getting one make sure it has a cert and that the stone matches the cert.

Oh no Michael - I''m not buying anything but thank you for your concern! I literally just woke up this morning with this burning question!

Actually I have a large (ish) collection of colour change gemstones, including sapphires. To my knowledge (and I can always have fallen foul along the way), none of them are BE treated thank goodness. However, in the UK there is a huge trend of selling treated sapphires without disclosure.

I''ve yet to see a colour shifting sapphire be sold in that manner but I think that may have prompted my question. In fact, with the exception of a few Vendors listed on this site, I haven''t seen many colour shifting sapphires for ages!

 

[chrono]

LD,
I''ve not heard of any colour change sapphires that are BE treated but I''m not 100% sure if it exists or not. As for the candidates for BE diffusion, for padparadschas, the sapphires originally start off as pale pinks so the treatment only needs to add the orange component.