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 Post subject: Rubies and Acid
PostPosted: Fri Sep 29, 2006 7:16 pm 
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Hi all,

I was recently on a trip buying ruby rough here in thailand and saw rough stones being soaked in acid prior to heat treatment. is this considered common practice?

I was told that this was to remove any rust particles on the surface of the stones. was not able to get an answer as to what type of acid was used. i guess just knowing that it was acid was enough for the guy in flip flops who was doing the soaking. lol.


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PostPosted: Fri Sep 29, 2006 7:27 pm 
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Hi!
If it was made only for removing iron oxide, then it probably was oxalic acid since it is effective and cheap. It is the relatively strongest organic acid, but still not very dangerous to handle. I use it to clean up quartz specimens.

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PostPosted: Fri Sep 29, 2006 8:59 pm 
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Interesting, I'd never heard of this practice. I love this forum, you always learn new things. :) Thanks for the info!


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PostPosted: Sun Oct 01, 2006 9:57 pm 
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Hello,
This is a very common practice, it is even necessary in order to remove as much as possible most of the foreign substance which could fill any cavities or fissures. This is performed for rubies and for sapphires and not only in Thailand. Usually they use hydrofluoric acid for few minutes to 24 hours. The fact is that rubies and sapphire are not affected by acids even the most powerful ones.
You can have a look to the typical heat process using the Thai way and starting with some acid work on the following page:
http://www.fieldgemology.com/showpic.php?sub_id=58&type=school

This page show you step by step the way traditionally sapphire are heated since the discovery of this type of heat treatment by Samuang Kaewen in 1968 in Chanthaburi, Thailand.

All the best,

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Vincent Pardieu

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The views expressed here are V. Pardieu’s opinions and do not necessarily reflect those of GIA Laboratory Bangkok (http://www.giathai.net)where he is an employee since Dec 2008.


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PostPosted: Mon Oct 02, 2006 4:17 am 
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Exellent pictures, Vincent!
Do you know what concentration they use? Hydroflouric acid is scary...in high concentration it is used to etch glass, but is so dangerous to handle that it has not been allowed in Sweden for use outside the universities' research labs since the 60's!

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PostPosted: Mon Oct 02, 2006 5:00 am 
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Hi,
Well they use the higher concentration they found...
It is also used to remove glass filling in rubies after heat treatment with borax or other fluxes.
But as I say for sure this has to be handle with care. Whatever heat treatment of rubies and sapphire is "a little bit more dangerous than cooking" as do be performed correctly it needs to handle several security and health hazard. I do not advise people without experience and training to try to heat gemstones like trying to cook potatoes.
All the best,

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Vincent Pardieu

www.fieldgemology.org
www.conservationgemology.org

The views expressed here are V. Pardieu’s opinions and do not necessarily reflect those of GIA Laboratory Bangkok (http://www.giathai.net)where he is an employee since Dec 2008.


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PostPosted: Mon Oct 02, 2006 5:04 am 
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Scary was the word... Is there any possible threat in leakage from remaining acid in fissures, to the customer? Even one drop will eat through the flesh.

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PostPosted: Mon Oct 02, 2006 7:02 am 
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LOL
No not at all,
As you can see the stones are heavily washed after being cleaned by the acid and then they are heated. Nothing to worry about as the acid does not penetrate corundum...
All the best,

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Vincent Pardieu

www.fieldgemology.org
www.conservationgemology.org

The views expressed here are V. Pardieu’s opinions and do not necessarily reflect those of GIA Laboratory Bangkok (http://www.giathai.net)where he is an employee since Dec 2008.


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 Post subject: HF
PostPosted: Mon Oct 02, 2006 12:01 pm 
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Hydrofluoric acid won't just "eat through skin", however that doesn't mean it's not dangerous. If it does get on the skin, it can cause a systemic poisioning effect which can be fatal. This must be medically treated as soon as possible.. here's the link..

http://www-safety.deas.harvard.edu/advise/accident.html

so wear an apron, rubber boots and be very very careful..


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PostPosted: Mon Oct 02, 2006 12:23 pm 
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It will not "eat up" the skin, like other acids, but it will eat through it very quickly and fall out as salts that is very hard to disolve and cause tissue death.

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PostPosted: Thu Oct 05, 2006 9:58 am 
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Thanks for the info Vincent. gotta love seeing people play with acid wearing no gloves, nomask/glasses and flip flops. i still remember my lab teachers lectures on safety in the lab at my university, goes right out the window over here. i guess when in rome... :roll:


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PostPosted: Thu Oct 05, 2006 9:24 pm 
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Hi,
Well on the photos about heat treatment in cambodia, the burner does not use any protection, that's correct but in other places I was able to witness that like in bangkok or Chantaburi, it is not the same: They use gloves, masks and operate in places with a good ventilation...
All the best,

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Vincent Pardieu

www.fieldgemology.org
www.conservationgemology.org

The views expressed here are V. Pardieu’s opinions and do not necessarily reflect those of GIA Laboratory Bangkok (http://www.giathai.net)where he is an employee since Dec 2008.


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