I packed seven of the big pots into the kiln on Thursday, trying to make plenty of space between them for the heat to move around. Perhaps there were too many in there – none of them were more than an inch short of the roof, and some just about touching. the firing certainly went differently. I had noticed that when I bisque fired them the kiln seemed a little slow, and the firing was quite uneven, as the black clay had started to go black near the top of the pot. the glaze firing was very awkward – with the flue as closed and the pressure as low as I had it on the last two firings at 1030 C the temperature stuck and even went down. in the end more pressure and a wider opening to the flue worked better, but I found that I needed to lose the visible signs of reduction to get the temperature to rise quite frequently. the firing took longer – about two hours longer.
in fact the amount of reduction was fine, and I was very pleased with all the pots, except that the black clay large bottle with wirebrush vertical scoring, on which I used the barium carbonate glaze, cracked right open across the base.
the crack ran right up the front of the pot and opened it up across the shoulder seam, which broke off half the neck as well. this is quite a disappointment. I think the clay of the base melted into the kiln shelf slightly, which prevented the pot shrinking as it cooled. I will have to put any big pots like this on the shelf with either clay supports or pieces of kiln brick under them in future.
you can see the dark rings made by the two black clay bottles, and a dust track from the snap right across where it broke.
the crawling shino worked really well on the other black clay piece.
the dolomite/tin copper glaze behaved as it has been doing for the past couple of firings, where I have dipped in and out with no hanging about and got a thin coating. on the pale stoneware the coppery ginger is breaking where the surface of the clay is disturbed on this side of the pot, which was close to the front of the kiln, but on the other side it is all over rather than just on the scored lines.
I overlapped the two dolomite glazes, the green/orange, and the blue/grey in these two bottles, which were both at the front of the kiln. this is the st thomas reduction clay, which gets quite toasty and makes the glazes darker. I picked this section of the pot for a close-up to show off my scored lines.
on the photos of the whole pot it’s hard to see the blue of this glaze where it breaks, but in real life it is quite noticeable. I’m very pleased with it, a blue that is just green enough.
this is a reprise of what I did in the summer with porcelain; plastered gooey porcelain over the surface of a buff stoneware, sprinkled it with china clay powder and rolled it in, before making the pot, and then glazed with barium carbonate.
here is the dolomite/tin/copper glaze doing something completely different – it is over a very white stoneware full of molochite grog, on very thin, and in the middle of the kiln. a gorgeous pumpkin orange, where over the edge of the buff underneath, it is just brown.
apart from the sad state of the big black bottle, a very pleasing firing. you can see the pots here