A series of posts documenting the making of my wood-fired ceramics
A crucial part of the wood firing process is the packing of the work in the ware chamber. How and where each piece is placed affects the flame path and also how the kiln fires, and as a consequence how the work will finally look. With many different factors to consider it can sometimes feels like a huge complicated jigsaw.
Packing the Kiln
The packing can take 4 to 5 days to complete depending on the shape and complexity of the pieces. I tend to pack the kiln quite tightly so that I can get as much in as possible. I unfortunately lost 5 large pieces of work during the earlier bisque firings which meant I had extra space to fill (the pieces weren’t bone dry and the firing cycle was too quick). Fortunately, prior to the wood-firing I had just taught a throwing course at the nearby Aberystwyth Arts Centre and suggested to the students that I could fire their work in my wood-kiln instead of the centre’s electric kilns.
There are many factors to take into account when packing the kiln. Certain glazes will only mature in the hotter areas whereas other glazes work better in cooler areas. The size and shape of pieces can affect how the flames travel throughout the kiln which in turn can affect heat distribution. All the time I am packing I am thinking about where the flames will travel and how I can persuade it to go where I want it to go. The flames leave marks on the surface of the the work and I try to plan how I can make the most of this. You can tell the direction of the flames on a piece of work as the bare clay on one side will be more ‘toasted’ than the other.
The vast majority of pieces are placed on kiln shelves, however I have always placed a few pieces around the firebox inlets. These areas have the most direct flames from the firebox and attract more wood ash accumulation. Although some really interesting effects occur here, I am unfortunately limited to the amount of pieces I can fit.
I tend to have a kiln shelf outside the kiln which I use to mock-up each stack. This makes it easier and clearer for me to work out the best way to get all the shapes and sizes to fit and work together. The whole process is like a giant jigsaw puzzle but without the picture on the front of the box to help me…
Most of my glazes are runny and to help reduce the chances of pieces sticking to the kiln shelves I use little ‘wads’ to elevate the work off the shelf. They also allow the flame to get underneath the work and produce a nice toasting effect.
For years I have been using a wadding mix recipe that Phil Rogers gave me. It has served me very well over the years, however it is expensive to make and sometimes leaves undesirable white marks on the base (I think the recipe is more suitable for salt or soda firing). For this woodfiring I decided to change my wadding recipe after having some work recently fired in another potter’s kiln. Tim Copsey lives about a half hours drive from my studio in Sowerby Bridge and fires a small anagama style kiln and he kindly let me fire a few pieces alongside his own work. His 1/3 Fireclay, 1/3 Sand, 1/3 Sawdust wadding recipe is much simpler, easily removed from the work, and leaves a more pleasant mark on the base.
As well as the wadding, I also use shells to support some of the work as it can leave some pleasing marks on the work. I tend to use the shells when supporting the slabbed platters in a vertical position.
I decided last minute to put a couple of pieces right down in the bottom of the fireboxes to see what would happen to them - I’ve had pieces fall down into the fireboxes by accident and although they tend to be underfired, they do come out with some interesting effects. The two pieces are older test pieces so I’m not too worried if it doesn’t work.
There are two ways of measuring the temperature within the kiln chamber: air temperature and heat work. The air temperature is measured by the pyrometer, the heat work is measured by using pyrometric cones. These little cones are designed to melt at very specific temperatures and represent the heat work occurring in the ceramic material. The air temperature can fluctuate dramatically but it takes time for the ceramic to absorb the heat and as a consequence it isn’t necessarily at the same temperature as the surrounding air. The cones are a more accurate way of seeing what’s going on in the kiln. The are placed in little clay boats which will contain the melted cones.
I also make little rings of clay which I can draw out at different times during the firing to get an idea of how the clay and glazes are reacting. They are mainly used during the ‘body reduction’ phase which I’ll talk about in the next blog post. Both the cones and draw-rings are placed as close as possible to the spy holes for easy access and visibility.
Kiln Pack Finished
Now that the kiln is packed, all that is left to do is to brick up the door (more commonly know as the ‘wicket’), and then put the secondary insulation in place. I’ll go and spend some time planning the firing schedule and once everything is ready, start the firing.
In my next post I’ll write about the firing and the moment I will have been working towards over the last few months… the unpacking.