Silk

[JewelFreak]

I've been reading here & in articles I looked up about silk, especially in sapphires. I get what it consists of & that it increases sapphire value as evidence of lack of heating, but I'm not sure how to spot it. Could somebody show an example of silk? Or link to it? Many thanks.

--- Laurie

 

[chrono]

Excellent write up complete with pictures. In general, you’ll not only need high magnification but know what to look for as shown in the pictures.
http://www.cresla.com/Library/index.htm

 

[T L]

Thanks for the web page Chrono. That page really shows you how much corundum can undergo as far as treatment is concerned!!

 

[Nashville]

Thanks for the page Chrono, fascinating information.

 

[soberguy]

I think the best examples of rutile silk can be found in Kashmir sapphires. Heating does NOT necessarily destroy all the silk, so it isn't necessarily a certainty that a sapphire that exhibits silk has NOT been heated. But look at these stones:

http://kashmirblue.com/

 

[soberguy]

Here are some great pictures!

http://kashmirblue.com/Research/inclusions.html

 

[chrono]

I think the best examples of rutile silk can be found in Kashmir sapphires. Heating does NOT necessarily destroy all the silk, so it isn't necessarily a certainty that a sapphire that exhibits silk has NOT been heated. But look at these stones:

http://kashmirblue.com/

That is correct; sometimes when heated with “low” temperatures, the rutile isn’t completely dissolved and can still be seen, which is why one has to know what to look for.

 

[chrono]

Here are more interesting pictures of heated versus unheated, but also includes other gem types and interesting inclusion pictures.
http://www.gemologyproject.com/wiki/ind ... Inclusions

 

[chrono]

There are many pages to this article but I think should explain what a gemologist looks for as tell-tale signs of heating versus unheated, complete with pictures.
http://www.gaaj-zenhokyo.co.jp/research ... _01en.html

 

[soberguy]

The Be treatment inclusions are really interesting to me.

 

[Aoife]

Wow, those are wonderful sources, Chrono, thanks for linking to them. I'm going to bookmark them before they disappear into the PS cloud.

 

[JewelFreak]

Agreed -- great articles & much info I didn't know. Thank you!

-- Laurie

 

[jleb]

It takes 3200 degree F to convert the rutile into the Titanium color centers, and this must be done in a reducing atmosphere. The result is increased blue. Heating to 1700 degrees in an oxidizing atmosphere will convert the Iron to a lower oxidation state and turn pale stones into vivid yellow. That does nothing to the rutile however. The biggest indicator of heating is a "Saturn" ring, where a halo appears around the rutile crystal as it expanded and cracked the lattice allowing the Titanium ion's to diffuse into the stone. So that's how it works in a nutshell. I've done the low temp heating, but not the high temp ( no furnace that will reach that handy), and it works great on rock creek sapphires from Montana.

 

[chrono]

Jleb,
Thanks for the explanation. It’s always nice to have lapidaries and gemologist share their knowledge and explain in greater detail.

 

[Arkteia]

Very interesting, Chrono.

You have posted these links recently. Of interest, I bought an unheated sapphire with AGL memo and (as I always play with fluorescence) noticed a faint green fluorescence. Now I am sending it to the GIA to confirm that it is unheated. Because chalky-green fluo has been discussed in the "cresla" article if I am not mistaken.

 

[chrono]

Crasru,
When the labs determine if a sapphire has been heated or not, they also take other factors into consideration, not just based on the result of the fluorescence. Also, just because it has a slight green fluorescence isn’t enough proof that your stone is heated per the article linked below written by Richard Hughes below, complete with picture examples. As noted, the test can be invalid if the stone is dirty because soap and other chemicals can throw the results off. The last thing to note is that this effect is also sometimes seen in untreated Madagascar blue sapphires and the effect is slightly different than a heated stone.
http://www.ruby-sapphire.com/heat_seeke ... scence.htm