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An alternative to woodfiring using gas at cone 6: Minori Thorpe shares her firing technique.

FOR THE PAST 13 YEARS CERAMICS HAS BEEN my hobby. The career for most of my life was as a nurse anaesthetist. The working conditions were tense and failure was not an option. Clay became my outlet because of its versatility and my experimentation. I was able to relax and make mistakes while learning new processes and techniques. Recently I have experimented with soda firing at cone 6 in an outdoor kiln that was made from an old electric kiln using propane gas. Each of the three rings in the kiln is 28 in. (70 cm) in diameter and 9 in. (22.5 cm) in height. For the bottom of the kiln I used hard brick and made it 28 in. (70 cm) in diameter and 11 in. (27.5 cm) high. I made six holes at varying levels for the fuel and the soda spray to be distributed equally. The bisque pieces that go into the kiln are glazed on the inside with cone 6 glaze. The outside is sprayed using an atomiser containing a mixture of wood ash, water and colourant such as: red iron oxide, cobalt, or copper. Once the pieces are dry they are placed in the kiln using wadding on the bottom so that the pots do not melt to the shelves. The single batch of soda spray mixture that is sprayed during the firing consists of 250 grams of sodium bicarbonate, 250 grams of soda ash, 50 grams of borax and water that adds up to be about 1500 ml. Each batch is made separately so that all the particles do not settle to the bottom. Once cone 6 is down I start the first spray of the soda mixture in all the holes, making sure to coat the pieces as evenly as possible. About 20 minutes later I start the second spraying of the soda mixture in the same fashion as the first. I wait about 15 minutes and then start the heavy reduction for about five minutes which then ends the firing. The Blue Pitcher is a result of this firing.

In 2012 I visited Japan after retiring from my job. I visited an artist exhibition in Tokyo where a ceramics artist was displaying work that was fired in a wood kiln to cone 10-11. The work was impressive and beautiful which made me interested in his technique and process. I learnt that he used more than 4000 bundles of red pine to complete the woodfiring that lasted about 10 days in the Noborigama. When I heard about this part, I started questioning if there was a way to use less wood and limit the amount of time, but still produce the same results. When I came back from Japan I started experimenting in my outdoor soda-firing kiln. I used propane gas for the fuel and I used sieved wood ash that came from my friends' fireplaces. The spray mixture that I sprayed on during the firing consisted of two cups of wood ash, a small amount of Ferro Frit 3110 and water, which totals to about 700 ml. The first spray is at around 1750[degrees]F (955[degrees]C) and the second spray is again with the wood ash mixture at 2014[degrees]F (1100[degrees]C). The next spray after the second wood ash spray would be the soda ash spray once cone 6 has fallen. About 15 minutes after the soda ash spray, I will spray the third wood ash mixture. I again wait about 15 minutes and spray the second and final soda ash spray. After the last spray, I hold the kiln for 45 minutes at 2230[degrees]F (1220[degrees]C) and the do five minutes of heavy reduction before turning off the gas. I was pleased that the results were similar to the cone 10 woodfire soda sprayed pieces that I have seen in the past at exhibitions and magazines.

I want to share this technique and process to help people achieve the appearance of cone 10 woodfired soda sprayed pieces without having to use a lot of resources and time.

Minori Thorpe immigrated from Japan to the US in 1969. For the past 13 years she has turned to ceramics as her creative outlet to help balance her career as a nurse anaesthetist. Since retiring about one year ago she has been experimenting with soda firing and alternative woodfiring (

Thank you to Ashley R Barber and the University of Delaware for all their help.
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Author:Thorpe, Minori
Publication:Ceramics Technical
Date:Nov 1, 2013
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