Capped silver foil & fuming - WarmGlass.com

Capped silver foil & fuming

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Kinsey K
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Capped silver foil & fuming

Postby Kinsey K » Wed Oct 20, 2021 9:56 am

I know that when firing a piece with silver foil, there is the risk of contaminating the kiln shelf. Is that still true if the glass is capped? I'm hoping the cap would contain the fuming so it doesn't extend to the shelf and neighboring pieces.

Also, does it make a difference whether one caps with Tekta, clear transparent, or crystal clear?

N.b. I do have one shelf dedicated to silver pieces, but I'd like to know if capping is an option so I can prepare a new load while the other one cooks.

Brad Walker
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Re: Capped silver foil & fuming

Postby Brad Walker » Wed Oct 20, 2021 10:05 am

If you cap so that fumes can't get out, then you shouldn't have a problem. Shouldn't make a difference what you cap with.

Buttercup
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Re: Capped silver foil & fuming

Postby Buttercup » Thu Oct 21, 2021 3:28 am

Hi Brad, reading this thread with interest. Is it just contamination of the shelf one has to worry about or can the kiln become contaminated such that it would damage future firings. I've kept a separate shelf for silver stain in the past. Is that sufficient for silver foil, too? Thank you.

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Re: Capped silver foil & fuming

Postby Brad Walker » Thu Oct 21, 2021 9:50 am

Buttercup wrote:Is it just contamination of the shelf one has to worry about or can the kiln become contaminated such that it would damage future firings. I've kept a separate shelf for silver stain in the past. Is that sufficient for silver foil, too? Thank you.


A separate shelf makes sense if you use a lot of silver stain or foil, but it's probably overkill for the occasional user of foil.

The only "damage" I've seen from silver contamination is that the silver causes dark areas when it comes into contact with a glass that reacts with silver. But that only happens when the glass physically touches the contaminant on the shelf -- it won't happen without the two touching. So silver residue inside the kiln itself shouldn't be an issue.

You can't just scrape old kiln wash off to get rid of the stain. And thinfire paper doesn't help either. But after a few firings it goes away on its own. Or you can fire once to around 1650 to 1700F (around 900C) and that usually does it. But even if you didn't get the silver residue off, it won't hurt anything unless you're using a glass that reacts with silver. And I can't see how it would contaminate the entire kiln.

Here's a photo and another brief discussion of the issue: https://warmglass.com/reaction-on-bottom-of-piece/

Buttercup
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Re: Capped silver foil & fuming

Postby Buttercup » Thu Oct 21, 2021 11:59 pm

Thanks very much, Brad. I'll just stick to the separate shelf solution.

A long time ago, last century at Pilchuck, while taking Painting and Firing with Albin Elskus, an intricate piece on which I'd spent some time became contaminated from silver stain on the kiln shelf. Albin rescued it by masking the painted side and washing the other side with hydrochloric acid. Don't try this at home! Fortunately it worked and I still have the piece.

Kevin Midgley
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Re: Capped silver foil & fuming

Postby Kevin Midgley » Thu Oct 28, 2021 12:07 pm

The acid used was probably not hydrochloric but rather HF. That is most definitely a don't try at home!! It can eat the wires in your studio walls never mind burning your bones.
I have experienced contamination by silver months later coming out of the refractories in my kiln.
If you think of working with precious metal clays, there you cook the metal inside a closed container surrounded by charcoal.
I really do not trust silver to not cause later problems.

Barry Kaiser
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Re: Capped silver foil & fuming

Postby Barry Kaiser » Sat Oct 30, 2021 6:35 pm

Kevin,
The Charcoal embedding is used with copper containing metals (bronze and Brass) as a reducing environment to prevent scaling. It is not generally used with precious metals.

Buttercup
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Re: Capped silver foil & fuming

Postby Buttercup » Sat Oct 30, 2021 9:34 pm

Yes,thanks Kevin, I did name the wrong acid. Here's more info from the archives, explaining why a simple sandblast and refire, or etching cream and refire wouldn't have worked:

http://warmglass.com/phpBB3/viewtopic.php?t=41601

My chosen kiln shelf protection is alumina hydrate so simply dumping it after it's been used for silver, takes care of that problem. No scraping and recoating involved, just a new layer of AH, flattened, and you're ready to go. It's reusable over and over again.

Reserving one shelf for silver, regardless of the coating is still the safest way. It can be as simple as an unglazed terra cotta tile. I have some 400 mm x mm 400 tiles. Some people on this board, use pizza stones.

When Albin rescued my painted and fired piece that had become contaminated with silver stain he did it in a vented, purpose-built booth, that met all safety standards. I watched through a glass pane in the door.


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