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Friday, June 8, 2012

Round 5 Testing Firing Schedule for Bronze Metal Clay

Round 5…

The set-up…
Media: bronze and copper together, pieces 6 cards thick and little ball
Kiln: top loading brick
Firing Container: round fiber firing container, no lid (phase 2)
Charcoal: coconut shell carbon, acid washed
Phase 1 Firing: Shortened Phase 1 was 20 minutes on a camping stove with a lid (see previous post)
Phase 2 Firing: full ramp to 1300 external pyrometer reading (kiln setting 1200), hold for 1 hour

So far, I’m up to October 2010 in reading every post on Hadar’s blog.

Today during Phase 1, the test pieces started smoking a few minutes soon than yesterday (maybe around 12 or 13 minutes… I don’t remember now). And once again, when I tried to turn the knob to lower the flame to minimum at that point, I managed to turn it all the way off. GAH! I hate that. Because I hate taking my lighter and lighting that camp stove when it’s REALLY hot. It gets so hot, in fact, the on/off knob melted. Hmph! I may look into a higher quality camp stove.

Anyway, the pieces didn’t seem to smoke for very long compared with yesterday. Unsure how to interpret that.

So to reiterate, Phase 2 is at 1300 degrees for one hour.

I also figure that it’s okay to open the lid completely once the cycle is over because anything I can do to help cool the charcoal down may be good (considering I’m STILL over-firing).

So I open the lid and the charcoal is bright orange (not on fire, though). Also, it’s about one inch shorter.

Fingers crossed… can’t wait to finally have test pieces someday that aren’t over-fired.

Here is before (green state) and after firing (as well as brushing, grinding, sanding, and adding patina):

As you can see, I was at the end of my created test pieces. That ball of copper in bronze was just what was left of the two clays. I suppose I could have spent more time smoothing my test pieces out, but I was getting tired of spending time on things that were just frying up in the kiln.

The cracks you see in the “after” photos were the same cracks as in the “before” photos, so my pieces didn’t crack during the firings. But I’m curious what I can do to minimize that visible bit of separation between the copper and the bronze.

I do wonder if (well, I pretty much imagine) larger and/or thicker pieces WILL need more… something. More time, more heat. ??? We’ll see.

Remember, my crop circle, not a small piece by any means, came out fine (the second time… don’t think it sintered in the first firing, so repaired and refired).

But still, it was fired at a “kiln” temperature reading of 1470 (which would have really been about 1550), but that was in a steel container, not the new fiber box which requires slightly lower temps. But still… 1550 seems excessive for bronze metal clay.

Honestly, this stuff CAN get confusing.

Anyway, much better results than before. Now I will work to refine the whole system. Oh yeah, and I have two more crop circles to fire. I’m totally guessing they will not sinter at 1300 degrees.

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