saturday’s firing was very very hot indeed. when I turned it off, I knew the temp was well over cone eleven; the light from the burner ports was much whiter than usual. the problem with saggar firing is that you can’t see any cones which are inside the saggar. the ones on the outside had in fact disappeared from view – they had fallen off their perch, but you can see that they give a very inaccurate idea of what was going on as ten and eleven are hardly affected.
inside the saggar though, cone eleven is well melted, never mind over.
I photographed the beautiful green flame shooting up from the flue at the end of the firing. this was from the copper carbonate I sprinkled around the sawdust.
the pyrometer registered 1277 centigrade before I turned the burners off. that is the lower end of what you expect for cone eleven, but it’s almost the highest I have fired the kiln to, on one other occasion it got to 1280 before cone eleven went over – with the cones visible. usually it goes to between 1250 and 1265 before cone eleven is bending enough for me to finish the firing. the cone works on a combination of time and heat – the longer it takes to get to temperature, the lower the actual temperature that the cone will bend at. however, without establishing some records, and trying out the parameters, I won’t know what goes on inside a saggar. so to take the kiln up to this white heat taught me some vital clues.
everything survived okay, except the tall vessel in the rear left hand corner had started to bubble and melt, as it is made of the orange terracotta I was given by the Tinajeria in Extremadura.
there is none of the black and grey carbon marking I expected, and I don’t know if it burnt off because of the high temperature, or the fact that the saggar was open at the top – and the top sections of the box, which were lightweight ceramic insulation board – had leant outwards, making it even less enclosed, which may mean that it failed to hold in the effects of the sawdust. there was a good deal of mess from the copper carbonate and from the steel wool I put in, and the only trace of the sawdust is some bits of green ash glaze caught around the feet of some of the pots. (this is an old kiln shelf on the floor, one side is already pretty much ruined).
this bottle at the front with the black markings had a big clump of steel wool settle on it – quite a dramatic effect.
this big layered clay jar, whose siblings have all been glazed with the green and orange version of the saltmarsh glaze, (copper/tin/dolomite) has worked very well; the white stoneware has picked up some very subtle flashing and sawdust markings, the extra heat has just softened the form a little and the crank of the underlayer is a gorgeous toasty rust.
the finger-applied porcelain on these funnel topped vase shapes is less dramatically changed by the firing than the pieces in the first saggar firing, and I must admit to being disappointed by them, but I think they still work a lot better than if I had glazed them. I am re-firing one in the next attempt
which will be the back half of the kiln in a vertical slice. I am just a little nervous about keeping these big shelves upright during the firing, but the slight weight of the lid, made of ceramic insulation board, plus tall props wedged behind them, and a shelf against the front one should keep them in place, and I plan to have cones inside, and ones outside which will stay in place, as the front of the kiln will hold a normal glaze firing.
a piece of card to keep the sawdust in place until I can shut it off with the final kiln shelf.
you can see the rest of the pots here.