Friday 14 March 2014

A gas-fired, glaze test kiln

Yesterday, I built and tested a very small gas kiln, partly to see how fast I could fire it to cone 9 temperature! The kiln was built simply using high-temperature insulation bricks, nothing else..even the roof was made using bricks:


Only two small pots were placed in the kiln:


This was meant to be a crackle shino over a dark, iron-oxide slip. A little (1%) iron oxide added to the glaze has made it flux, losing most of the cracks. It has also bubbled rather alot, possibly a sign that the atmosphere was not reduced sufficiently. This is probably because it was positioned directly under the exit flu..unavoidable in a kiln of this size.



This piece was more successful. The glaze was made with kaolin, AT ball clay and raw wood ash and has come out rather like a traditional, Japanese shino. Wood ash was also aplied to the top half of the pot (glue was sprayed on and the pot dipped in a pile of ash). It actually looks very much like an anagama-fired piece with a variety of surface colours created by the melting ash. But this kiln was fired to approx 1275 Centigrade in two hours. Some wood was introduced to the gas flame by placing bamboo into the burner port..interestingly, each time this was done, the temperature would drop very quickly by 30 to 42 degrees C. It would then take about 10 minutes for the temperature to get back up as the bamboo ash burned away. The kiln was so small, I had to pull the weed burner head about 7-8 inches away from the kiln to get the hottest part of the flame inside the chamber. Optimising this distance was critical to achieving a rapid temperature rise.

Here are a few other pieces I fired recently in the electric kiln:

Carved tea caddy, fired to cone 8/9

Carved tea caddy, approx 4 ins tall

This tea caddy was carved from a solid block of clay. It took a very long time to finish so I was relieved there were no firing cracks!

Carved incense burner, fired to cone 8/9
Black tea bowl, fired to cone 8/9
Thanks for reading.







7 comments:

  1. oh Mark you have inspired me I have always wanted a gas kiln and I think I could afford something small, what kind of burners did you use? Maybe I could build a small wood kiln, oh the possibilities, love how your pots are coming out of your firings. I like that bubbly pot

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    1. Hi Linda, thank you! This tiny kiln is only really useful for glaze tests but no reason why a larger version couldn't work, with kiln shelves or fibre for the roof. I'm thinking of making a much bigger one and cementing the bricks, which would give better reduction. The single burner was simply a roofing torch/weed burner resting on concrete blocks: http://www.ebay.co.uk/itm/271217616910?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649 . Not the safest option but okay if you are careful and watch the kiln constantly.

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  2. Your carved tea caddies are so beautiful! And the black tea bowl looks like the night ocean. I just love that you made a small gas kiln---so many possibilities to just check out different glazes. Nice!

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    1. Hello Charlene, thanks for the kind words. Yes, I find the possibilities of small kilns quite exciting..you can experiment with much less investment and risk. Looking forward to my next project which will be a kiln fired with gas and wood :)

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  3. You are the king of experiments, Mark! How wonderful! : ) I love the way the second pot came out. That was a quick firing! Surprising!

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    1. Hi Midori, thank you! Me too, I was really surprised how nicely the ash and glaze worked together. Even the unmelted ash works well on this piece. More experiments on the way soon :)

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