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 Post subject: heating paste for reducing atmosphere?
PostPosted: Mon Sep 27, 2010 5:16 pm 
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Hi,
I'd like to make a few experiments with heating stones in reducing atmosphere, thai burners use a paste to get such an atmosphere, do you know what ingredients should be used to make such a paste?

Also, I guess I should place the stone in a small airtight closed container, right? (so to limitate the O2 supply)

On the other hand, if I want to heat the stones in oxidizing atmosphere, should I just place the stone in the oven/furnace (as there's already some air inside the oven), or should I use another oxidizing paste to get even more oxygen inside the oven?


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 Post subject: Re: heating paste for reducing atmosphere?
PostPosted: Tue Sep 28, 2010 12:19 pm 
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I remember Steve Lembeck telling us a story about a reducing atmosphere heating session gone smokey. If I'm not mistaking he packed the stones (zircons in that particular case) in an airtight crucible filled with charcoal... The carbon being an O2 sucker...


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 Post subject: Re: heating paste for reducing atmosphere?
PostPosted: Tue Sep 28, 2010 1:34 pm 
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yeah, for reducing atmosphere, I was thinking of charcoal, maybe additioned with steel whool (steel whool combustion inside a closed jar will consume all of the present O2), and place the whole thing inside a tightly close the container. I'm only worried by the possibility of an explosion if I close the container.

also, am I right to say I don't need nothing but placing the stones in the oven if I wanna get an oxidizing atmosphere (with no need of an O2 producing paste beeing used)?


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 Post subject: Re: heating paste for reducing atmosphere?
PostPosted: Tue Sep 28, 2010 5:08 pm 
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Quote:
also, am I right to say I don't need nothing but placing the stones in the oven if I wanna get an oxidizing atmosphere (with no need of an O2 producing paste beeing used)?


It depends mainly on the type of heating. Electrical ovens will be better than gas for an oxidation atmosphere, but there still has to be some air flow in. Most of my experience with this ( except for one time with some dark high zircons) is in ceramics where I had to control the atmosphere for the glaze to form the correct coloration ( mainly copper glazes). Even in the electrical kiln, I had to remove most of the plugs and prop open the lid a little to get oxidation. With the gas kiln for reduction, it had to be adjusted to a smokey flame. They use to throw moth balls into the electric kiln to make it reducing, but the danger soon eliminated this for most. The teacher said in olden days, they would throw a dead animal into the kiln to utilize the oxygen and make it reducing. We did try left over turkey skin once, and it smoked like crazy :) I would try it in a portable electrical oven outdoors to open the door a little and not affect the kitchen.

For the zircons I did it in a lab situation with a ceramic crucible and 2 large gas burners. I surrounded the test zircons with powdered lab charcoal, and when the smoke died down a little, I put a matching ceramic lid on the crucible and heated for 10 minutes, which I think was too long in retrospect as later I experimented and found I could change the color of a single zircon by holding it in tweezers heating with my little hand butane torch to almost colorless, and even with a butane firestarter, I could change one from honey to red or yellow. You do seem to need the reducing atmosphere though to change it to the blue side.

I could be wrong, because each stone can be a little difference, but I have had more pitting and cracks when faceting with the heated stones than the unheated ( which facet with no trouble).

Maybe the reducing paste is mainly animal fat and such :( Leftover french fry oil ?

Jim


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 Post subject: Re: heating paste for reducing atmosphere?
PostPosted: Mon May 09, 2011 12:24 am 
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It's really quite simple I crush charcole in to a fine powder then drop rough stones into crusible then add a fine mix of dried fine beach sand and charcole powder 50/50 then 25(charcole /75 sand filling it right up gave me best results ands it's so cheap I was able to get Nigerian zircon a nice blue with a certain amount of time at certain temps


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