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Cat's eye Sapphire conclusion?
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Author:  arms [ Mon Mar 01, 2021 8:51 pm ]
Post subject:  Re: Cat's eye Sapphire conclusion?

Oh right. Thank you.

Author:  1bwana1 [ Mon Mar 01, 2021 9:28 pm ]
Post subject:  Re: Cat's eye Sapphire conclusion?

glhays wrote:
I would not think that dopping heat would even be detected by the GIA. If that were the case almost all will be considered heated on the reports. Takes a great amount of heat to burn silk in corundum, something like 1850 °C, not sure if that is completely accurate but somewhere in that range. So anything below that might be done just to try and effect color.



Low temperature heat treating is in the range of 900 to 1200 C. It is used normally to lighten or brighten color. You are correct high temperature heat treatment around 1900 C +- is used to melt rutile.

Author:  Christopher P. Smith [ Tue Mar 02, 2021 9:47 am ]
Post subject:  Re: Cat's eye Sapphire conclusion?

Hello all,

This has transitioned into an interesting side discussion. Depending on the color-causing mechanisms involved, colors can be removed or increased via the application of relatively low temperature heating. In general, when we discuss relatively low temperature heating versus relatively higher temperature heating, we are using the threshold were rutile silk begins to dissolve. This is not an absolute temperature, as several factors will have an influence on when that process begins in any given stone. However, in general we are talking about temperatures +/- 1300-1350C. And of course, at even higher temperatures, the process of dissolution is accelerated.

Below this temperature threshold, the charge compensation between iron and titanium can be very effectively broken, thereby removing or reducing a blue color or color component. In addition, trapped hole centers can be introduced or removed with heating under relatively low temperature conditions, removing, reducing or increasing a yellow color or color component.

Best regards to all,
Christopher P. Smith

Author:  1bwana1 [ Tue Mar 02, 2021 10:28 am ]
Post subject:  Re: Cat's eye Sapphire conclusion?

Christopher, What was the indicator you relied on to make the heat treatment call?

It is my understanding that much above 1200 C and the dissolution and absorption process will have already started resulting in the darkening of color. So, my threshold between low and high temperature treatment is a bit lower.

Here is some interesting research on the subject for those interested.

https://www.gia.edu/gems-gemology/summe ... xperiments

Author:  Christopher P. Smith [ Tue Mar 02, 2021 10:40 am ]
Post subject:  Re: Cat's eye Sapphire conclusion?

I cannot speak for any of the criterion that the GIA lab uses when making such determinations.

Here at AGL, we have had robust criterion in place for the detection of relatively low temperature heating for more than 10 years. However, other labs have only more recently been exploring this topic and developing criterion for its recognition.

While we do not share our specific criterion, I can say that our criterion is dependent upon a variety of factors related to the color and geologic setting of stone being tested. Additionally, due to the relatively lower temperature conditions involved, such treatments are not always detectable. This is a key reason why labs have chosen the specific wording of disclosure which states: No indications of heating. or No gemological evidence of heat.

Best regards,
Christopher P. Smith

Author:  arms [ Thu Mar 04, 2021 1:27 am ]
Post subject:  Re: Cat's eye Sapphire conclusion?

The sri lanian dealer says many heated stones come back as unheated 90% of the time from labs.

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Author:  glhays [ Thu Mar 04, 2021 2:36 am ]
Post subject:  Re: Cat's eye Sapphire conclusion?

"from labs" seems like a vague argument. Would imply all labs have no idea what they are doing when it comes to detecting heat treatment.

Author:  Christopher P. Smith [ Thu Mar 04, 2021 10:33 am ]
Post subject:  Re: Cat's eye Sapphire conclusion?

Hello all,

As 'Gems Garden' has indicated, this is a very broad statement. The detection of low temp heating is different from the detection of relatively higher temperature heating. There are some labs, such as AGL or GIT, who have had criterion in place for a much longer time than other internationally recognized labs. I can speak for AGL and there was a period of almost 10 years where we would call low temp heating when the same stone received a 'No indications of heat' determination from a number of other labs. However, as I mentioned earlier, more recently other labs have progressed in the recognition of low temp heating, so we are finding less situations like this taking place. A bigger issue is how stones tested previously are being handled when they come back and/or are being updated. Do these labs honor the previous result or do they apply the standards/criterion of today? This may seem like a straightforward question to answer however it is more complicated than that.

Relating to the 'blow pipe' process, this has also been well-known for a long time now. For those who have done specific work on the detection of this method, there is the potential to detect in many instances. Although also as I had mentioned previously, the low temp heating of corundum may not be detectable in all instances. The blow-pipe method is not typically employed on all color varieties of corundum either. The Sri Lankan treaters have a depth of experience here that is unrivaled and so they know very well which kinds and colors of corundum respond best to this particular treatment.

This is a very interesting and complex topic that has a number of variables that influence the relevance of certain statements, so broad general statements will almost certainly be valid in for some instances, while also being inaccurate for others.

I also want to say how valuable a resource GemologyOnline is for its members. This is a great platform to get input from so many sectors of the trade. I learn things here all the time from all kinds of members and their posts, and I am happy to contribute whatever I can when I feel I have something useful add.

Best regards to all,
Christopher P. Smith

Author:  glhays [ Thu Mar 04, 2021 5:40 pm ]
Post subject:  Re: Cat's eye Sapphire conclusion?

The report Arms has uploaded distinctly states "Heated". Many of our stones that have been reported on by the GIA states just as you commented on "no indication of heat, and others indications of heat, and some just like this one heated, we understand this completely as experienced trade people. So how would Arms in this case where the report seems very distinct that the stone is heated, be able to claim to the seller that the stone you sent me is heated, with what appears to be a dispute. It might make sense to send off to another lab for opinion? I understand why Steve asked the question of what comments were made on the call of Heated. This seller/dealer is persistent on the claims the labs are wrong 90% of the time. Of course this is just based on the trivial info given here in this instance. This is a very interesting topic, and all input should be welcomed.

Author:  Christopher P. Smith [ Fri Mar 05, 2021 12:23 pm ]
Post subject:  Re: Cat's eye Sapphire conclusion?

If the seller is not prepared to accept GIA's results, then I would suggest the buyer send it to another lab to get their opinion.

Best regards,
Christopher P. Smith

Author:  arms [ Sun Mar 07, 2021 2:21 pm ]
Post subject:  Re: Cat's eye Sapphire conclusion?

Im fine with the result. Its just the seller thought its an unheated cab. But came back as heated. Just unexpected. I trust GIA more than the seller. But also i think that mistakes happen too.

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