Woodfiring on Saturday 30th October 2010
The kiln packing took place on Wednesday 27th October to give us a couple of days calm before the storm! The pack was adjusted from the previous firing, according to the notes we’d written from the in the hope of balancing out the temp in the kiln. More spy holes were put in to enable us to get a better overview of temperature difference.
On Saturday the firing was started at 5.15am on an autumn morning by Gareth, Ashley and Ian. A steady climb in temperature was maintained (around 100c an hour) so as not to cause any thermal shock to work that was being refired.
Ian kept a detailed log throughout the whole firing, which gives a valuable insight into how each firing compares and differs. This enables us to see if there are patterns reoccurring with each firing and how we can adjust and respond to the kiln.
Throughout the morning old and new kiln clubbers arrived and all joined in with stoking and raking Bertha. The enthusiasm of the members is truly inspiring, and it’s great to see people travelling from near and far to participate in the event. In addition a tempting array of food always appears which certainly keeps us going into the night!
The first of many ash raking was at 12.30pm when the temp was 943c, and this continued throughout the firing around once every hour. One of the main challenges with Bertha is that she needs air, but wood falls down from the fire bars much sooner than it should and as a result the fire box clogs up with fuel. In order to keep the temperature rising the fire box needs to be raked out at regular periods.
As the firing continued into the evening it became a real battle to get any prolonged and sustained temperature climb, no matter how we stoked and raked, but still we continued on!
It became evident by looking at the cones that there was a significant difference in the temperature throughout the kiln. By the end of the firing the base of the kiln had reached 1280c whereas at the top of the kiln only the 1200c cone had gone.
In the end the highest temperature reading was 1127c and it seemed no matter what we did the temperature would not climb. The decision was made at 9pm to end the firing.
What a great advert for woodfiring!
When Bertha was unpacked the following week one of the things that became apparent was that due to the length of the firing there was a large build up of ash, which once the work was refired to the correct temperature created some beautiful effects.
It was decided that we will try one more firing with modifications to the kiln and depending on the result continue firing Bertha or dismantle her and build a new one.
Post firing. Note the difference in the cones at top and bottom
Table of goodies! Maturing of glazes has taken place on some pieces
A few notes ready for the next firing:
• More bars put into the fire box to prevent wood dropping down into the ash pit so quickly
• Block up right hand corner under floor space
• Position cones further back into the kiln to reflect true temperature rather than possible cold spots
• At the top of the kiln keep the pack very open and leave space above
• Make work of all sizes and shapes using stoneware clay. Remember to leave a good gap between the bottom of your glaze and the base of your work, approx 2cm.
• Wood prep day 5th February. Wood firing 19th February. If you want to be involved please email me on schapman4@ucreative.ac.uk at least one week in advance.
Sam