Cracks unexpected

With the inlay firing, I thought the thin, sanded tops of the beads might crack, but they did not.

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The fine silver wires were not affected by the firing. However, the thicker tops of these beads cracked away from the sides. (I was going to torch fire a silver inlay.)

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Because of the silver wires, to fire these beads I placed them flat in the charcoal. The inlaid beads I placed vertically in the charcoal as I usually fire most of my base metal clay pieces. I wonder if the positioning caused the cracks in the beads.

Below is a pair of earrings with copper on top of bronze clay: before and after sanding. But before firing. They’re still in the kiln…

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3 Comments

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3 responses to “Cracks unexpected

  1. holly

    those beads on top are lovely! maybe worth all that work!
    it’s funny, i’m trying to fix my bronze cracking problem with laying the pieces horizontally, you’re going vertical!
    i must confess, i went into the studio last night charged up to SEE WHAT HAPPENS….and i… planned out some earrings in sculpy!! heehee. i guess that’s just the way i work!

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  2. I am just beginning with the copper PMC . I have worked up the coolest lesson plan for my 7th grade art students. Tried firing my sample and it didn’t sinter! I only put it 1/2 into the coconut shell. I fired the shell to purify it, then again to test my digital program. Any idea of what went wrong. The piece is 6 cards thick. I think I should have buried it deeper. I did place it so that it was to the back of the kiln. Love your beads. Can you really mix bronze and copper?

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  3. fernald244

    Hi Dale,
    I am still a novice with the copper and bronze clay, so I am still trying to figure it all out. I don’t use Rio’s clay right now, but am using the powdered clay that I buy from Hadar Jacobson. Everything I’ve learned so far has come from trial and error, from reading Hadar Jacobson’s extremely generous and helpful blog, (see the link on this site), and from friends chiming in with their experience.(see comments from LeAnn on “You Ain’t got a Thing…” entry.)

    In my last batch, Some of the pieces sintered and some did not. As far as I can figure, I have my pieces too close together. There should be at least 1/2 ” between pieces in the carbon.

    When you say you fired in coconut shell, was it coconut shell-based activated carbon? (Just plain coconut shell won’t work) Copper and bronze clay won’t sinter unless they are in an oxygen reduction atmosphere. That means totally covered with the activated carbon. If the piece is fired, uncovered, the binder burns off but the metal particles can’t fuse because their surfaces have formed oxides which prevent them from attaching to each other.
    Long response to say, you should have the piece totally covered with activated carbon for most of the firing time. That much I know. I still have a lot to figure out about the whole ramp time and temperature issue. LeAnn made specific suggestions for copper clay firing temperature, so that might be helpful to you. Good luck!

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