Convergent Series

learning, using & teaching metal clay, and other aspects of life

Smart Bronze: By Jove, I Think I’ve Got It! (Post 3 of 6)

Posted by C Scheftic on 2013/06/29

This post continues the story I started telling yesterday, morning and evening….

By the time I got around to trying Smart Bronze again, a newer version of Hadar’s manual was out. Dated May 15, 2013, it told me that my goal in the first trial, 1420°F, was really only 10° below the (latest) recommendation, of 1430°F, whereas I’d intended to aim for 20° below Hadar’s recommended temperature. My second trial had still gone a bit too fast, yes, but it turns out that one really had been at my typical Hadar-clay adjustment of 20° less than the stated goal. That explained all the melting and left me a bit less worried, now, about whether I could get away with dropping my goal temperature some more as I also slowed the ramp speed.

Trial #3: Just after Mid-May in a Brick Kiln

Hadar (by then) said: Ramp at 1400 per hour to 1430°F and hold for 2 hours; total firing should take 3 hours.
I entered: Ramp at 1365 to 1400 and hold for 2 hours. This should have taken over 3 hours; the program completed in 2:58.

Rationale for my new program: (1) Further slowing the ramp should continue to improve the binder burnoff. (2) This was still only 30° below Hadar’s newer target (hold) temperature.

Test pieces: the last (and smallest) two “golden threads” loops that I’d made along with the ones “lost” in the first two trials.

Results (shown, held up inside a slit in some green foam): Both test pieces seemed, at first, as though they might be debindered and sintered. But one small segment did break under very slight pressure (i.e., yes, the “threads” were thin, but this felt like a “normal wear” issue; I had not deliberately test-bent them but, instead, just lightly squeezed a wire-like bit with my fingers to get a good grip on it for polishing). It was hard to see the inside of the small ends. They seemed sintered, but perhaps not fully so. Still, this felt increasingly close to a program that should work.

What to try next: Since there had been so much melting in the previous trial, at 1410, I was hesitant to blame any inadequate sintering on too low a firing (hold) temperature. Since any not-burned-off binder will inhibit sintering, I decided to maintain the temperature and try dropping the ramp-speed a bit more….

Trial #4: End of the third week of May, in Brick Kiln

Hadar said: Ramp at 1400 per hour to 1430°F and hold for 2 hours.
I entered: Ramp at 1350 to 1400 and hold for 2 hours.
Program completed in 2:59.

Test pieces: I wasn’t sure if the thinness of the “threads” might have been a factor in the previous failure. So for this trial I reverted to a simple design I know and understand well: two small, round, simple, stamped butterfly pieces. (One each at 3 and 4 cards thick.)

Results: Debindering seemed to have happened as needed. The pieces sintered into a nice, solid metal. A few small blisters appeared, but they were fairly easy to polish down. The results looked lovely but I have no pictures: sorry! The reason for that is great: As I was finishing their polishing and stringing them up to photograph, a delightful fellow walked into my studio looking for a gift for his twin daughters and bought them both!

Trial #5: Brick Kiln

Hadar (by then) said: Ramp at 1400 per hour to 1430°F and hold for 2 hours.
I entered: Ramp at 1350 to 1390 and hold for 2 hours.
Program completed in 2:59.

Test pieces: I was ready to go for it! I’d had several ring bands ready for weeks! One was made using the “seamless” ring approach; the other was made as a bypass or wrap-ring although I did “connect” the edges of the two ends as they passed each other. I did the latter because I wanted to help keep the piece a bit more stable than it would have been had I left it with “loose” ends.

Results: Both seemed to debinder and sinter beautifully. My only concern was that they had not shrunk by the predicted 2.5 sizes. I was seeing them as not quite 2 sizes smaller. Was that enough? Had I dropped the temperature a little too much? Maybe. Maybe not. But I was hopeful. I first polished the wrap-ring, which looked gorgeous, so I wore that happily while I worked on the seamless ring. When I left my studio at the end of the day, the seamless ring was sitting there waiting to be photographed with its kiln-mate. (It’s shown, here, alone.) I wore the wrap-ring home. The next two days had me moving some furniture and packing-boxes from a recent home improvement project, along with other normal daily activities. I continued to wear the wrap-ring and, half-way through the second day, it suddenly broke into three pieces.

Admittedly, the wrap-ring design did have one “thin” spot. The band was an even thickness all around (which you can see from its greenware-state photo (brown color) above), but it been cut in a tapered shape, so it had the least “height” right where it met the large starting-edge. Which could have been a point of weakness. Which could have explained its breaking open. Or, maybe even breaking into two pieces. But its breaking into three pieces hinted to me that there was another problem somewhere. Less obvious, of course, was the exact nature of that problem.

Should I worry about the pendants I’d just sold? I think not. They were thinner, and less likely than a ring to get knocked around a lot. Still, there was another pause in my testing so I could think this through some more: and another point at which I’ll pause this record too.

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