Thursday, October 31, 2013
Day 4 of Metal Clay Sintering Tests
I’m probably getting closer to my ideal phase two firing temperature now, so I’m going with:
2-cards thick ¾ x 1½ inch rectangle
7-cards thick ¾ x 1½ inch rectangle (“7” was more mid-way than “8”)
12-cards thick ¾ x 1½ inch rectangle
Ramp 1 500°F/hr
Holding Temp 1 1420 for 1 hour
Carbon Under ½ inch
Carbon Over ½ inch
Ramp 2 full
Holding Temp 2 1470 (was previously 1450) for 2 hours
I’m anxious to find my best phase two temp so I can start messing around with phase one methods and temps.
I supposed I should confirm that my first test pieces are fully sintered by doing the sanding test. After all, I’m keeping the phase one temp at 1420 because of my assumption that the pieces are sintered.
I was in the middle of an online class when phase two finished, so I didn’t get to the kiln until it had already cooled to 500 degrees, but I don’t really think that made any kind of difference.
The 2-cards thick piece had some blistering. The 7-cards thick piece had a lot more blistering. The 12-cards thick piece had no blistering, but all three pieces showed pitting on the bottom (the surface facing downward in the carbon).
The 12-cards thick piece has more pitting because it's heavier than the other pieces so more weight is pressing into the carbon than the lighter pieces.
This is good. We now know that 1450 works (for these particular bronze pieces) and 1470 is too high.
For my (hopefully) final test of phase two firing schedule for Brilliant Bronze, I only made one 7-cards thick piece.
The piece is currently in the kiln for phase one, then after cooling I’ll run phase two at 1460 to determine the final optimal phase two temperature for mid-fire schedule.