Wednesday, May 24, 2017

Blessings from the Kiln!

Detail of a wood fired copper red bowl from the recent firing of the kiln.

 I am often a little depressed before the opening of a kiln, which may seem odd or be odd... I couldn't possibly say. There are just so many unknowns and variables when glazing and firing pots, especially in a wood fired kiln, that I can only do my best with everything I do, the making, glazing, packing and preparing of the kiln, and the firing, and then wait for 2 or 3 days for the kiln to cool, and the jury to reach its verdict!! The waiting is not an easy time, but it is a time when studio floors can be cleaned, shelves in the store room organised, and some glazing materials put away.

Most of the glazes used in this firing were copper reds, Shinos or celadon. All require an atmosphere in the kiln where oxygen is in limited supply for transforming magic to happen to them, and it is like magic! Green copper carbonate can be transformed to cherry red or pink, a rather nondescript white Shino glaze can become rust coloured or golden, and a honey coloured iron bearing glaze becomes green or grey green, or even blue-green celadon.

Copper red, pink and celadon glazes.

 The firing has been a careful one, abundant oxygen until about 800 Celsius (1472 F) was achieved, and then a deliberate choking and slight over stoking of the kiln until temperatures had climbed to their peak of about 1300 Celsius (2372 F). Firing was about temperature, and time taken to get there, but also about atmosphere, and atmosphere was monitored by eye. Was the chimney smoking, did flames come out of spy holes under pressure, or was air sucked in? Was the flame in the chamber of the kiln hazy, or was visibility in the chamber clear and bright? These are the sort of things that had to be constantly observed and considered throughout the firing.

So there is the firing, and then the waiting for the kiln to cool. Days pass. It is winter and snow falls. There is sleety rain and wind.

Laura having a peep into the kiln.
On the third day after the firing the kiln door is unbricked carefully, one brick at a time. The opening breathes warmth. Hands are put into the darkness of the kiln chamber to check pots for warmth. It is the first contact with the pots. The surface is smooth with a slight dust of wood ash. The pots have a lingering warmth that is almost blood heat. More bricks are removed, and weak sunlight enters the kiln and there is colour and form.

As to the work in the kiln... most things turned out well, or very well, and there was a copper red bowl and a Shino pot that went above and beyond anything I could have anticipated and I will hold onto them for a while and enjoy them!

Bowl approximately 30 cm diameter (12 inches). Copper red and Shino glazes. Stoneware.

The thick copper red glaze was extraordinary.

Stoneware pot with poured Shino glaze. 29 cm high (11.5 inches).

 Those two are keepers. For now!

Shino and celadon platter. 30 cm (12 inches). Stoneware.

Shino platter with sprinkled wood ash decoration. 30 cm (12 inches). Stoneware.

Copper red vase. 26.5 cm (10.5 inches). Porcelain.

Detail of copper red showing pale purple flecks in the glaze.

Copper red and celadon with splash of copper/rutile blue. 18 cm (7 inches). Porcelain.

Carbon trap Shino bowl with copper/rutile blue splash. Dia. 11.5 cm (4.5 inches). Stoneware.

Carbon trap Shino glaze over porcelain, the result is much quieter.  24 cm (9.5 inches).
Inside the pale Shino vase, the same glaze is much warmer in colour.

Vase with poured black Shino glaze. 22 cm (8.75 inches). Stoneware.

Sculptural vase. Copper red glaze on porcelain. 22.5 cm (9 inches).

I was delighted to be contacted by Jane, a potter living in Vancouver Island B. C. when I was glazing pots for this firing. She asked for some thoughts about a tricky copper/rutile blue glaze that she was using, sometimes with great success, but not all the time! She sent the glaze recipe with the email, so I was able to try it and see if it worked for me.

The results were most interesting and rather beautiful, and I have greatly enjoyed corresponding with her by email about the glaze. From time to time the internet can be a wonderful thing, and it is very nice to feel part of a much wider community of potters and other interested people from around the world. It has been a joy to have met some of the readers of this blog too when they have ventured to the East Coast of the South Island of New Zealand.

I recently watched a documentary about an 83 year old Korean potter and his sons who were making celadon glazed pots. The documentary was made a few decades ago and the colour is somewhat faded, but I found it quite a moving glimpse of the life of potters working in a traditional manner, where making and firing pots was really a form of prayer. The heart and life and work of the potter was conducted in a spiritual manner, in a way that goes far deeper than a particular religion or dogma.

*Technical Notes about the firing (for those who might be interested in such things!!).

All areas of the kiln had good reduction, and the temperature variation from top to bottom of the kiln was about 2 cones, from an estimated cone 11 at the top to cone 9 at the bottom, and most of the kiln being an even cone 10. In every day terms, that is about a 30 degree Celsius (86 F) temperature variation. This was a marked improvement from the firing before that had a 3 cone variation from top to bottom, or something in the order of 45 degrees Celsius (113 F). The improvement had been achieved by spacing the lower shelves wider apart than in the first firing, so as to let a greater flow of flame through the setting there.

Sunday, May 21, 2017

Second firing of the Redesigned Wood Fired Kiln.

We managed to fire the wood fired kiln on Thursday this week, a 10 hour firing that finished about 20 minutes before winter arrived.

 Still photo taken from the Leith Saddle Traffic Cam.

The road to Dunedin was closed due to snow for a few hours yesterday, and it was nice to walk outside in the chilly air to visit the cooling kiln and bask in the gentle heat radiating from its walls!

I hope to unload the kiln today.

This second firing of the wood fired kiln since the major interior rebuild and design was more controlled than the first, it had to be... because there were much larger pots and bowls on board than there were on the test firing. The kiln was loaded over a two day period. The loading took a little longer than anticipated, because I had the interesting job of sorting out how best to stack a mixture of large and small pots, and I changed my mind a couple of times!

Our friend, Mark, kindly welded together a lovely door for the fire box, made from scrap angle iron and I fitted insulating fire brick to it, and managed to install it by torch light the evening before the firing. I then lit a small fire in the ash pit to pre warm the kiln.

The firing began the next morning in darkness at 6 am. The first 300 degrees or so is fired completely from the ash pit, with a small fire in there being progressively built up over the course of three hours or so. At about 350 degrees the first wood is put into the firebox, and this starts to take over as the main source of heat after 450 degrees is reached. From that point onwards, the fire in the ash pit is allowed to burn out, and is replaced by hot embers from the firebox above it.

On the first firing the kiln climbed happily at about 400 degrees Celsius (752F) per hour until well over 1000 degrees (1832F), which was OK for a test, but I needed to fire a lot slower than that for this firing. I managed to average about 250 degrees (482) per hour from 400 to 1000 degrees, then slow to 150 (302F) degrees per hour to 1200 (2192F), and then spend one and a half hours or so above that temperature. The kiln will have reached 1300 (2372F) and I was able to hold for 45 minutes near peak temperature. I would have liked to have climbed slower than I did, but I was pleased that this firing was considerably more under control than the previous one, so things should improve with experience!


Hotter Still!

I fear that I may have over fired the pots at the top of the setting, but all will be revealed when the kiln is opened a few hours from now. The top of the kiln still fired hotter than the bottom, but I think the difference was about 2 cones on average, where as it was 3 cones on the test firing. I may not worry too much about trying to even things out more than that, as it gives me the chance to fire a range of stoneware glazes. I just have to be organised about making and glazing work for the hotter and cooler parts of the kiln.

I had better go and see if I can take some bricks out the door now to finish off cooling the kiln!