|What my kiln shed looked like at some unearthly hour this morning.|
|Our back door steps with flowers nicely lit up by our porch light. This is what I see when I return from my kiln shed!|
|The Red Planet......|
There are still some potters who fire "by eye" and don't use modern gadgets at all, but these would mostly be doing stoneware temperature wood firings, sometimes over several days, or raku firings, where accurate control of temperature may not always be the most important thing. With raku, it is more about firing until the glaze looks shiny. In this case, the maturity of the glaze is far more important than if it happens at 850 degrees, or 950! There is a rather nice account, in an old Ceramics Monthly magazine, of a group of American potters visiting a traditional pottery in China. There, through an interpreter, and old man firing a kiln was asked what temperature he fired to. He evidently looked puzzled as if this had little relevance, and said, "until the glaze goes shiny". He was asked how long he fired for, and again answered, "until the glaze goes shiny".
Unfortunately, crystalline glazing calls for accuracy of time and temperature, and even 5 degrees over or under a target temperature can make a lot of difference. It would be very useful to be able to watch what was happening to the glaze and the crystals throughout the firing, then I could fire "until the glaze goes shiny"! Some potters have experimented with taking photos of crystalline glazes as the crystals are forming. Unfortunately this is not a simple process, and needs special equipment. The pots are at such a high temperature that they are very hard to see at all, even through welding goggles. Everything glows like the surface of the sun!
|Blue Crystalline Vase, 6 3/4 x 6 inches (172 x 152mm)|
I am still working on some blue crystalline glazes. Last firing I managed to get most of the pots to produce crystals (which was a great improvement on the firing before), but I still have to fine tune the peak temperature that I am firing to, and the amount of time the kiln remains there. The time spent at the peak temperature is an important influence on how many crystals grow on the pot. I want to achieve a nice visual balance between crystals and the glaze that surrounds them. Some of the pots came close to success in this firing, but only one was saleable.
|Some of the other "blue" pots from the last firing. Yes, the one on the right is supposed to be blue!|
One problem that I ran into with several of these pots was uneven distribution of crystals. I had initially applied the glaze by pouring. This had resulted in some areas of glaze that were double thickness, the sort of thing that can give nice colour variations on a stoneware pot, but in this case the variations in thickness caused areas that were oversupplied with crystals, in a way that was ugly, rather than something to celebrate! I think that holding the kiln for slightly longer at peak temperature would have helped the glaze even out somewhat and made this less of a problem, but I will have to be more careful with glaze application in future.
I will try re-firing the pots that did not work out in the previous firing. Sometimes this can produce wonderful results. I have put the tall blue vase, that is in the photo above, in the kiln again, and we will see what happens to it a second time around!
To give you some idea of what the pots look like before they go into the kiln, here is a photo of the pots that I was getting ready for the firing that I am doing at the moment. The glazes are mostly a powdery grey colour at this stage. The smallest pot, on the right of the photo, is the only pot to not have a blue glaze. This one should be a warm honey-brown colour.
You will see that the pots on the left of the photo have a rusty red coloured glaze inside them, this should be a very dark brown, almost black, when we see them again after the firing.
The glaze has to be applied very thickly for crystalline glazing. Lots of it will run off the pot when the firing is at its hottest, and there is a glaze catching saucer under each pot. I have applied the glaze by pouring a layer over the pot, then brushing glaze on top of that. The glaze will be about 3 mm thick in the top third of the pot, and about 1 mm thick near the bottom, this should even out when the pot is fired.
Well, must go and check the kiln again. It is now 11.30 in the morning, and I am mid way through growing the crystals.