Raku firing is one of the most exciting processes in ceramics. After you place your pottery into a raku kiln, the anticipation builds as you wait for that final moment when the intense heat begins to melt the raku glazes. Something that I hate is waiting and the great thing about raku firing is that you pop it in the kiln and just a few hours later you have the final piece in your hands; something that you can’t get with normal firing.
Preparation is key for safe firing with raku, you should be appropriately dressed and covered, wearing health and safety equipment.
All types of clay can be used, including porcelain, but experimenting will be necessary. Gorged clays are probably the best bodies to use. Work must be bisque fired and glazed with raku glaze or slips prior to the raku firing. For the first firing warm the kiln for ten minutes by igniting the burner on a gentle flame for the first five to ten minutes. The burner connection should be fitted with a pressure gauge, which reads the amount of gas flowing into the kiln. The heat rise should be gradual and can be turned up in two stages during the firing, but how much will depend on the size of the kiln. The first firing, before the kiln has warmed up, will take longer than the next ones. Once you see the glaze surface go shiny, turn the gas down for a few minutes to allow the kiln to soak so that there is a even melt. Turn off the gas supply and lift off the lid, ideally placed to one side on the kiln shelves. While the inside of the kiln is red hot, lift out the work using long handled metal tongs and place it in the dustbin, which should have a layer of sawdust in it. Once the dustbin is full f work, throw in large handfuls of sawdust and replace the lid, making sure it’s a tight fit.
Once you have placed the lid on the dustbin, do not take it back off to check, the flame will burst back into combustion with the oxygen and great a large, high flare (yes, almost lost my eyebrows). Wait until the sawdust has had a chance to burn down and then gently take off the lid. By placing work in a pit, you will have a greater control over the reduction and coverage of the developing black. The work that is controlled in this way will usually have a much lighter and subtle tones of greys and blacks. All workweek still be very hot, so use small metal tongs to take it out of the pit. Work can be cooled down on water and cleaned off to unveil the interesting surfaces and marks.
The slip resist technique can offer great mark-making potential, which produces finely controls surface detail. To produce this effect, you coat your piece with a layer of resist slip; different thickness of slip will produce a varied tonal surface. Then add a layer of raku glaze which will chip off but will protect the slip. While the glaze is still damp you can draw very precise lines. Then just fire it away and be amazed with the wonders of raku firing.
I mixed a raku glaze from Christine Constant & Steve Ogden book, The Potter’s Palette during my glaze induction and finally had an opportunity to fire it. I was expecting a crackled aqua colour which you can notice on the tip of the spout. Really interested how the colouration turned on the tea pot, and just comes to prove how unpredictable raku can be. Just a shame I can’t use the tea pot. Just a nice way to end this busy and productive term full of new techniques and experiences.