Convergent Series

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

Smart Bronze: By Jove, I Think I’ve Got It! (Post 4 of 6)

Posted by C Scheftic on 2013/06/29

This post continues the story I’ve been trying to tell for the past two days….

Trial #6: End of May in a Brick Kiln, in which you will see how your tester spaced out momentarily….

Why had that last load’s wrap-ring broken: was there a weak spot, or was the firing program still not right? I didn’t want to risk breaking the seamless ring too, but I thought maybe I’d try firing it a second time just to be safe. I’d also made an open-ended ring “shank” for a double-fire ring that I could put into this load, as well as a couple other simple textured butterfly pendants I’d made up while the last load had been firing. And I’d nudge the hold-temperature up just a tiny bit while I was at it.

Hadar (still) said: Ramp at 1400 per hour to 1430°F and hold for 2 hours.
What I thought I entered (which I’ll explain in a moment):
Ramp at 1350 to 1395 and hold for 2 hours.
Program completed in 2:59.

Test pieces: Now, I had blistering. Just two little blisters on the open-ended shank (shown: first, right). The textured pendants were bubbly all over. So was the seamless band (shown: second, left): it had had a “perfect” finish on it but, since I’d broken the other ring I’d fired with it, I’d stuck it in to see if a second firing would better-sinter it and now it looked a mess. Fixable, I hoped, but still … why?!

My first reaction was, yes, the load had been slightly larger than the previous one, but why so much blistering? Having felt a little bit frustrated at the start of this trial, now that feeling was building up even more. I’d worked on a few pieces in other metals between trials #5 and #6, and succeeded in gaining a bit of positive reinforcement for myself from their success. So I returned to more of those after trial #6. And. as I went to put those in the kiln, and set up the program to fire those, that’s when I noticed that I’d somehow spaced-out entering the program for trial #6, and gotten wrong both the goal temperature (slipping back to the previous trial’s number) and the ramp (where I’d entered the (wrong) goal number, not the ramp number). And, somehow, the firing time came out to be the same as other test loads, so that was no clue either. Argh…. ( I had actually been starting to wonder if, somehow, the load-timer was malfunctioning and always just returning the last reliable number it had ever had….) But, now, here’s what I’d done:

What I meant to enter: Ramp at 1350 to 1395 and hold for 2 hours.
What it seems I entered: Ramp at 1400 to 1400 and hold for 2 hours.

Little differences can mean a lot! What can I learn from my observations, both before and after I realized my mistake? The textured pieces had bubbles that clearly did not belong to their textures. Ugly! But, though the rings both, at first, looked fix-able, I was even more disappointed by them! The seamless band had blistered, but I was able to work away at it (for a very long time!) with various sanding attachments on my rotary tool until I got it back to a nice condition. Not as pristine as it had been after its earlier polishing, but still very nice. And, it had shrunk another whole size (meaning it had gone down by a total of three ring sizes), which told me that the refiring had resulted in more sintering. At least that was a good sign. But the open-ended band, on the other hand, did not seen to have shrunk much, if at all; worse yet, it broke into three pieces when I slipped it (carefully!) onto my ring mandrel to check its size. Even though it looked at least reasonably well debindered, was it possible that the faster ramp had prevented all the binder from burning out? Or … what?! Of course, I’d made a mistake. It was just “little differences” here and all I needed to do was to go back to the pattern I’d been developing and it should work. I kept telling myself that.

So, let’s take a little break here, to clear our heads….

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