K is for Kiln

Like the alchemists of medieval times who sought to turn base metals into silver and gold, potters seek to transform clay into vessels of beauty and function. And they do. They dig raw material out of the ground, mix oxides into glazes, and forge their wares with fire.

Amongst the 'primitive' firing techniques thre is a technique called Black Firing This method involves heating a primitive gas-brick kiln to about 1000oC (these days with gas) and then adding copious amounts of sugar, which then volatilize and impregnate the clay with carbon, giving it a matt black surface. Glazes may also be used with this method, which can result in some interesting effects. The required temperature is usually reached in about five hours. The gas is then shut off and flue and any cracks sealed. Sugar is pushed into the burner port and volatilizes. Then the burner port is quickly sealed with bricks and fire clay. The kiln cools slowly and can be opened the next day.

Black Firing Tips

  • Build the kiln with two walls. On the inner wall use soft bricks and the outer house bricks. Fill the gap with sand. Seal the kiln with kiln wash or a mixture of sand and slip 4:1.
  • Use old shelves and wads of fire clay to stack the work, as the glaze can become very fluid.
  • Use gloves when glazing, as Copper Carbonate is toxic.
  • Stack the kiln carefully so that flames will wrap around the work and exit the flue. Be sure not to stack too empty, as the kiln will take too long to reach temperature. Work placed near the flue will receive more heat.
  • Place glazed test rings near the spy hole to check the glaze maturation during the firing.
  • Place a cone 013 (855o C) in the kiln and insert a pyrometer.
  • Begin the firing slowly for the first hour and then turn up the gas pressure every hour.
  • You should reach the required temperature in about five hours. Shut off the gas and seal the flue and any cracks. Push in one kilo packages (5-8 kgs) of sugar into the burner port and then seal the port with bricks and fire clay.
  • Make sure all cracks around the kiln are sealed with fire clay as well as possible.
  • Use a gas mask during this process as toxic fumes are unavoidable.
  • Allow the kiln to cool overnight and open the next day. Remove the work with rubber gloves and remove excess scum with a wire brush under a running tap.
  • As the glaze is unstable and can change, it is best stabilized with PVA glue, Bondcrete or another ceramic fixative.
  • Special effects, e.g. green patina can be achieved by leaving the work in the open
  • The glaze can be post-firing treated with a gas burner, creating an 'oil-spill' effect.

Firing Your Imagination

The Chinese Alchemists practised mild forms of gymnastics and self massage to unblock the flow of energy, to nourish the life force and to circulate the chi. Quigong and tai chi are only part of a variety of technniques directed to nourish, to act as bellows and fan the fire within. The aim is to preserve the three primary 'vitalities' known as the three treasure: shen (spirit or mental activity), chi (energy or the breath of life) and ching (semen and sminal essence).

Here at Soul Food you can enter a special gymnasium and undertake some mild gymnastics that will help your flow of energy and fan the creative fire. And then there are the more energetic activities that are housed in special projects.

Anita Marie Moscoso never ceases to take my breath away with her take on some of these prompts. Her Cold Storage is quite literally overflowing with wonderful responses.