Dissolved Silk Inclusions in Sapphires

[Double E]

What does it indicate when a sapphire has dissolved silk inclusions? Heavily heated or even treated? What are those silk inclusions being dissolved actually?

 

[thirdrock]

“This partially-dissolved silk may be indicative of heat treatment. However, minute exsolved particles, which can occur naturally, may be confused with the partially-dissolved silk of heated gems. The presence of long needles and dart- and arrow-shaped rutile is a strong indication that the gem has not undergone high-temperature heat treatment.”

Rutile in Corundum • Following the Silk Road • Lotus Gemology

A discussion of rutile silk in corundum and its use in detecting artificial heat treatment. Examination of these "silk" inclusions can identify heated gems.

www.lotusgemology.com

 

[demantoidz]

Important to mention that a sapphire with dissolved rutile can still be diffused and doesn't mean heat-only.

 

[Double E]

“This partially-dissolved silk may be indicative of heat treatment. However, minute exsolved particles, which can occur naturally, may be confused with the partially-dissolved silk of heated gems. The presence of long needles and dart- and arrow-shaped rutile is a strong indication that the gem has not undergone high-temperature heat treatment.”

Rutile in Corundum • Following the Silk Road • Lotus Gemology

A discussion of rutile silk in corundum and its use in detecting artificial heat treatment. Examination of these "silk" inclusions can identify heated gems.

www.lotusgemology.com

Thanks for posting the link. I actually read the article, it’s a bit technical. One of my main question is that does dissolved silk only apply to high heat, but not low heat? Assumed it’s heat only.

 

[Double E]

And other than rutile what can that dissolved silk be?

 

[demantoidz]

Thanks for posting the link. I actually read the article, it’s a bit technical. One of my main question is that does dissolved silk only apply to high heat, but not low heat? Assumed it’s heat only.

It seems like low heat as defined by Lotus does not dissolve rutile.
"While some dealers that we spoke to defined low-temperature treatment as below 1000°C, for research purposes we define it slightly differently. High-temperature treatment involves the dissolution of secondary-phase microcrystals, while low-temperature treatment does not. The most common of these microcrystals in corundum is rutile silk."

They define low heat as 800-1100C, intermediate 1300C, and high 1500C.
Under the 'Inclusions' subtitle they show and describe clarity changes with low heat.

The above quote also helps answer your second question of what else can dissolve during heat, as they mention high heat dissolving 'secondary-phase microcrystals' - rutile being the most common example. However, I am not sure if 'silk' is generally used to describe anything other than rutile.

Madagascar Sapphire: Low-Temperature Heat Treatment Experiments

Madagascar is one of the world's top sources for fine blue sapphire. Lotus Gemology conducted heat treatment experiments to better understand this material and how it responds to heat treatment.

www.lotusgemology.com

 

[thirdrock]

Thanks for posting the link. I actually read the article, it’s a bit technical. One of my main question is that does dissolved silk only apply to high heat, but not low heat? Assumed it’s heat only.

Here’s a quote and another article that may help.

Defining “Low” Temperature​

“While some dealers that we spoke to defined low-temperature treatment as below 1000°C, for research purposes we define it slightly differently. High-temperature treatment involves the dissolution of secondary-phase microcrystals, while low-temperature treatment does not. The most common of these microcrystals in corundum is rutile silk. Rutile dissolution can occur around 1200–1350°C, which we use to define the approximate boundary between low- and high-temperature treatments (Hughes et al., 2017). Because of this, we focused our experiments on four “lower”-temperature rounds of heat ranging from 800 to 1100°C, one “intermediate” round at 1300°C, which we can consider a borderline area, and one “high” round at 1500°C for contrast.”

Madagascar Sapphire: Low-Temperature Heat Treatment Experiments

Madagascar is one of the world's top sources for fine blue sapphire. Lotus Gemology conducted heat treatment experiments to better understand this material and how it responds to heat treatment.

www.lotusgemology.com

 

[thirdrock]

It seems like low heat as defined by Lotus does not dissolve rutile.
"While some dealers that we spoke to defined low-temperature treatment as below 1000°C, for research purposes we define it slightly differently. High-temperature treatment involves the dissolution of secondary-phase microcrystals, while low-temperature treatment does not. The most common of these microcrystals in corundum is rutile silk."

They define low heat as 800-1100C, intermediate 1300C, and high 1500C.
Under the 'Inclusions' subtitle they show and describe clarity changes with low heat.

Madagascar Sapphire: Low-Temperature Heat Treatment Experiments

Madagascar is one of the world's top sources for fine blue sapphire. Lotus Gemology conducted heat treatment experiments to better understand this material and how it responds to heat treatment.

www.lotusgemology.com

Funny, I was posting the same thing. Great minds think alike. I can’t believe we even used the same quote.

 

[demantoidz]

Funny, I was posting the same thing. Great minds think alike. I can’t believe we even used the same quote.

This is the second time recently me and someone else posted almost the same thing. So my mind is twice as great!