Black Firing Tips and Tricks

mongst the 'primitive' firing techniques you will find the technique of 'Black Firing'. This method involves heating a primitive gas-brick kiln to about 1000^oC and then adding copious amounts of sugar, which then volatilize and impregnate the clay with carbon, giving it a mat black surface. Glazes may also be used with this method, which can result in some interesting effects. This weeks feature offers a black firing glaze and some tips and tricks for a successful black firing.

Salvatoris Rusty Red Black Fire Glaze

Copper Carbonate Borax Sodium Bicarbonate Cobalt Carbonate

60.0 40 40 5.0

• Bisquefire work to 1100^o C
• Mix glaze same day as firing
• Apply glaze thickly
• Dribble glaze on thickly for effects

• 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 (855^o 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.

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