Step 5: Glaze
Firing.
After the glaze is applied, the ware is loaded into the
kiln again and given its final firing. This melts the glaze on the
pottery into glass and vitrifies the clay into an extremely hard and
durable pot. This firing process takes 24–48 hours. During the first
6–20 hours the temperature of the kiln is slowing raised. Once the
maximum temperature is reached, the kiln is turned off and allowed to
cool for 18 – 36 hours. In general, the kiln is not maintained at a
specific temperature (as you would when baking a cake) but rather the
kiln is turned off as soon as the desired temperature is reached.
A note about cones. The firing process is measured using pyrometric
“cones” instead of a high temperature thermometer. These cones are
small pyramids of ceramic materials with each cone formulated to bend
at a specific temperature. A group of 3 cones is used. If firing to
cone 10 then cones 9, 10, 11 would be used. When 9 bends it is close,
when 10 bends, you are done, if 11 bends you went too far. The photos
below show cones before firing and anfter firing to cone 10.
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