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Thread: Silver clay exploding on second firing

  1. #1
    Join Date
    Nov 2019
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    Default Silver clay exploding on second firing

    Hi, I have been making some jewellery from pmc silver flex and they are firing fine, just over the recommended time to make sure they're fired all the way through. Glowing orange etc...
    I have to add jump rings after this and they need soldering closed but... The pieces explode! Literally burst open and fly across the room. I'm looking at selling jewellery with open jump rings which I'm not happy about.
    Does anyone know why this might be happening? Are they too cold? Damp?...

  2. #2
    Join Date
    Dec 2014
    Location
    South Australia
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    I don't work with clay although it seems as though there must still be moisture in the clay and heating will cause it to become steam and it has to go some where
    i'm sure one of the more knowledgeable people will have a different view

    PS I would not include a email address in my user name Just my personal opinion, even if it is a gmail

  3. #3
    Join Date
    Dec 2009
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    Central London
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    7,438

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    I agree with the above on both counts:

    1.As this is an open forum, your email address can attract unwanted messages, so I should ask our moderator to remove it, and remove it from your signature.

    2. I don't do clay now either, but clay when fired is still very porous. The explosion is likely to be steam from reheating absorbed pickle.
    So I would avoid immersing the pieces until all soldering is complete, but just let them air cool.

    The place where the jump ring is to be attached will need freshening with a file. After that, the best way to proceed is to sweat solder. That is to close the jump ring with a little excess solder (easy is OK), hold it against the clay piece and reheat the piece slowly and gently until the solder re-flows. Dennis.

  4. #4
    Join Date
    Jul 2017
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    I'm definitely not an expert in metal clay so a thorough perusal of previous threads about metal clay may provide some answers. But it sounds as though your clay wasn't properly sintered so the first questions to ask are;
    How thick was your piece? Is it possible it wasn't fully dried out before you fired it? Any still damp clay inside will not fire and sinter/ burn off the binders and reduce down to fine silver properly. And damp clay inside a piece can cause at worst a piece that falls apart when touched/polished, bubbles that rise up during firing or as you've discovered an explosion .

    How did you fire it, with a torch or a kiln? Torch firing works for pieces about the size and thickness of a 50p piece, but kiln firing is better. However, neither will do the job if it wasn't properly dry. I started with torch fired pieces but have bowed to the wisdom of those who work with clay pretty much exclusively and have a kiln now - quite an expense but they hold their value. But torch firing is possible with silver clay so long as pieces aren't too big or too thick.

    Did you knead or file the clay at all, causing air to be trapped inside?

    When it comes to soldering fired clay, rather than using a file you really need to burnish it well with a burnishing tool - as I understand it even a well fired (in a kiln) piece is still more porous than the equivalent fine silver sheet piece so you have to burnish well before soldering to ensure the solder isn't sucked into the metal clay piece.

    You don't mention it so hopefully the explosive clay didn't hurt you or your surroundings X
    Deb
    Last edited by misspond; 07-11-2019 at 08:41 PM.

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