Diffusion of star sapphires?

[pregcurious]

I got a query on stone I am selling on Preloved, and the question was if no treatment meant no diffusion. The potential buyer said that she had heard that diffusion can improve a star. I responded: "I have never heard of diffusion treating to enhance a star. My understanding is that diffusion treatment with Beryllium is done at extremely high heat. I am not sure if the inclusions that cause the star of a star sapphire would survive high heat."

Has anyone else heard of diffusion used to improve a star? Thank you!

 

[chrono]

Surface diffusion can be done but not lattice diffusion. I don't think it is done to improve the star, only the body colour.

 

[VapidLapid]

I believe star sapphires are diffused under vacuum with Titanium vapor which improves the star. I can only guess at the cooking process. Since high temp heating of the sapphire would melt/dissolve the star causing rutile (titanium dioxide), but titanium has a high melting point, I imagine the sapphire is placed near the top of the vacuum chamber and the titanium is vaporized with like an electron beam gun. that way the sapphire could be held at lower heat, but still become diffused.

http://www.gemrockauctions.com/learn/gemstone-articles/star-sapphire-treatments

 

[pregcurious]

THanks, VL. I've never heard of that. I just emailed the prospective buyer your info (and previously the link to this thread).

 

[VapidLapid]

I looked at your stone. Didn't realize it was from tgt. Certainly a vendor I trust, and he did state it was no treatment. It also doesn't have the look I expect in treated stars. Diffused stars are generally hard, contrasty and complete in all legs. Ideally one would want a lab report, but at this price point a lab report is not a must(for me). If I were buying it I would be satisfied with brad's word.

 

[pregcurious]

Thanks, VL. At this price point, it was not an issue for me, but I cannot speak for other buyers. I learn something new all the time on PS.

Chrono, I was with you. Titanium diffusion is news to me.

 

[JewelFreak]

Something new for me too, interesting info. I agree with VL, Brad's word is good; he's one of the trustworthy ones.

 

[chrono]

From what the website noted, including several other sources, the diffusion of corundum is done to help bring out a better star and improve the body colour but is only surface diffusion which isn't deep into the stone. On a positive note, it is much easier to detect surface diffusion than lattice diffusion. I hope that the potential buyer has the same trust as we do in TGT. I would be more cautious about diffusion in a faceted sapphire over a star sapphire because of the type of diffusion possible is different.