Rutile/Silk - heat treatment

[Pandora II]

Just wanted to share a couple of things I learnt the other week from Christopher Smith the President of AGL.

First of all, I had always been lead to believe that whilst you could never declare 100% that a stone was unheated/treated, the presence of rutile and/or silk was a pretty good indication that it had no been heated.

Well, this is apparently erroneous. Rutile doesn't begin to melt until 1400 degrees and corundum is regularly heat-treated to improve colour at 1100 degrees, so rutile/silk inclusions are not reliable indicators of no heat.

The other issue he raised was the routine oiling of rubies. I asked whether this would be disclosed routinely on a lab-report and thde answer was that AGL do disclose but many other labs do not.

Just thought I'd throw that out there as many websites have statements alongside stones saying that they have rutile inclusions and this verifies that they are unheated - sadly not the case...

 

[chrono]

Absolutely correct - the presence of rutile does not automatically mean that a corundum is unheated because it could be heated to temperatures not high enough to melt the rutile. It is best to have the lab or gemologist look at other indicators to rule out heating.

 

[m76steve]

Absolutely correct - the presence of rutile does not automatically mean that a corundum is unheated because it could be heated to temperatures not high enough to melt the rutile. It is best to have the lab or gemologist look at other indicators to rule out heating.

i agree-another good example is rutile quartz & russian demantoid w/horsetail inclusions-i think the same condition would apply-steve...quick question-i see namibian demantoid garnet listed with horsetail inclusions-i have been told that these do not exist in nature-the only material with the horsetail material is the russian demantoid-is this correct? thanks-steve...

 

[T L]

More reasons that I trust AGL above most other labs for the verification of colored gems. Thanks for the info Pandora.

 

[LD]

Absolutely correct - the presence of rutile does not automatically mean that a corundum is unheated because it could be heated to temperatures not high enough to melt the rutile. It is best to have the lab or gemologist look at other indicators to rule out heating.

i agree-another good example is rutile quartz & russian demantoid w/horsetail inclusions-i think the same condition would apply-steve...quick question-i see namibian demantoid garnet listed with horsetail inclusions-i have been told that these do not exist in nature-the only material with the horsetail material is the russian demantoid-is this correct? thanks-steve...

No. Namibians are now found with horsetail inclusions although they are usually smaller and not so prominent. The colour of Namibians is also more yellow or brown than the bottle green Russians.

 

[LD]

Thanks Pandora. Unfortunately nothing is sacred now is it? Looks like it's AGL for important stones then!