WOODFIRING DEC 2011

Kiln Club Woodfiring

10th December 2011.

Packing

Packing on the 6th December was relatively simple, as there was barely sufficient work to fill the kiln. That said, after the April firing we did note that we should have a more open pack. A few pieces were put underneath the floor, as last time. The same thermocouple as the last firing (2nd April 2011) was used, although it had to be repaired: we had said in April that perhaps we needed a new one: we definitely do now!

Firing

Firing started on a very cold (00C) morning at 0600. A gas torch was used to light the wood. Temperature rise was encouraging and 12000C was reached (according to the thermocouple) at about midday but then, however we stoked, the temperature remained about the same (although 12600C was reached momentarily at about 1430). Unlike the April firing (chart 2 below), it was the bottom of the kiln which appeared to be the hottest. Thus, the 8, 9, and 10 cones at the top of the kiln were unaffected when the firing was curtailed after 12hours, yet the 8, 9, and 10 cones at the bottom were down (8, and 9 some two hours earlier) (see chart 1 below). That aside, there is little difference between the two plots. Throughout the firing, most of the wood used was relatively thin: this may be something we need to consider in future firings.

Front (during firing) Rear (post-firing)

Top 06, 5 [8, 9, 10] 06, 5, 8, 9, 10 down (all melted)

Middle 06, 5, 8, 9 [10] 06, 5, 8, 9, 10 down (10 bent halfway)

Bottom 06, 5, 8, 9, 10 down (all melted) No cones

Results

Some interesting results. It is obvious from the cones (above) that parts of the kiln (top back, bottom front, and possibly bottom back – where there were no cones) fired to well above cone 10 – so, depending on the ramp rate, possibly somewhat over 13000C. This seems likely when one looks at some of the pieces which look decidedly well fired. Perhaps the pack, with a series of large shelves at the front, in some way kept the top front of the kiln cool?

Many pieces were stuck to shelves and others had been heavily “dripped” on. It seems unlikely from looking at some of these pots that it was heavy ash – more likely is that a non-stoneware pot crept into the top right of the kiln and melted.

It seems unlikely that this is due to wood ash!

Below is a selection of pots: better images will be added as people take photos of their work.

Next time

We did not bother with an air blower this firing. As we raked out embers close to ten times, might we try air blowing next time. Perhaps something like this – used by Mateusz Grobleny at ICF Aberystwyth this summer.

It seems obvious that our temperature readings (thermocouple and meter) need to be recalibrated (or we need new kit). Either that or we accept that all we need do is get to 12000C and then just watch the cones. And with that in mind, is there any way of being able to see cones placed at the rear of the kiln?

Conclusion

In some ways, an excellent firing as Bertha obviously can get to well above 13000C well inside 12 hours. However, we still need to find some way of ensuring that the temperature range throughout the kiln is narrower and that we reduce the need for so much raking of embers.