This is a video clip of a group from The Pottery School in Pioneer Square doing a pit fire at the beach in late July.
The firing was pretty similar to the Vashon Island firing except most pieces had no terra sig on them. They were all bisqued to cone 06. Here is what I have written down in my notebook about the pit layout:
- pine sawdust: ~3 inches
- horse dung: ~ 1/4 to 1/2 inches
- copper carb: ~ 1/2 coverage of pit bed
- baking soda: sprinkled around (but not on top of) some pots (not a lot)
The pots were mostly in a single layer (only 2 small pots were on top of other pots.) Copper carb was used more sparingly than the Vashon firing, and there was none on top of the pots. Besides the usual salted raffia, Chore-Boy copper netting, and steelwool strands that I brought, the participants also used copper wire of different sizes, inclulding some heavy gauge ones, as a fuming material.
The firing schedule is basically comparable to the Vashon firing as well. Below is the firing schedule in more detail:
- 8:30 am:lit the fire
- 10:30 am:stopped feeding the fire
- 2:00 pm: started to pull pots out
- 2:30 pm: all pots out
Around 11:00 am we noticed some exposed pots looking rather pale, without any color flashes or smoke marks, and we thought perhaps we could create some local reduction by dumping horse dung directly on those pots. Well, it was a good try but didn’t seem to have produced any noticeable effect. My guess is that to make this work, we would have to have dumped the dung (and dumped a lot of it, too) while the fire was still raging hot, not after it had already died down. Well, it’s something to try next time perhaps — probably we’ll need to do the whole pit and not just select a few pieces here and there, though.
Most pieces from the firing turned out well color-wise, with strong black (from the sawdust and dung) and red (from copper carb) as expected. An unexpected result was some very pretty bright green on many of the pots, which some thought to have come from the heavy gauge copper wire. But I had gotten some similar green without copper wire before, too. In any case, this green — like the one I had before — later faded away in just a couple days. I wonder if a coat of timely applied wax or some other kind of coating would have preserved the color? It certainly would be worth a try.
A major disappointment in this firing, however, is the very high breakage rate. One participant, in particular, had fine cracks on all but one of her 7 thin and evenly thrown pots — the kind that you’d expect to be able to withstand thermal shocks pretty well. The only thing I could think of is that all those pots have fairly wide mouth, and the pots were all stacked right side up in the pit. Furthermore, when they were taken out from the pit, they were also left to cool right side up on the sand. I would have kept them upside down in both instances. A wide mouth facing up is an invitation for cold air to come in and cool the rim while the bottom of the pot is still hot — not a scenario you’d want to subject your pots to!
This high breakage rate also got me to rethink the whole idea of fast firing in general. I have been getting away with this until now, but I also have not fired large or delicate pieces so far. Taking pots from the hot pit to cool in open air is certainly asking for trouble. Even leaving a pit uncovered so it will cool quickly also seems a pretty bad idea now. But having a pit total covered up to let it slowly cool overnight is just not a practical solution for me at this point in my life, i.e. I’m not quite ready to move to the country yet. :-(
Well, supposedly there are compromise solutions available, e.g. using shards to create local covers, so we don’t have to cover up the whole pits, and yet delicate pots are protected from being hit by cold draft directly. Or try to make the clay more open, e.g. wedging in some grog and sand — or switch to a different claybody all together. Perhaps it’s time to start experimenting with some of these schemes, eh?