What is Raku Pottery?
The colors and luster of raku pottery are so fabulous! When I am at shows, customers always ask me how I get these effects. I love explaining the process, but I always start by saying, "I LOVE PLAYING WITH FIRE!"
Raku is an ancient technique of firing clay, the roots of which go back to early 16th century Japan. Unlike other glaze firings where the kiln is slowly brought up to temperature and then allowed to cool slowly, raku is fired very quickly--from room temperature to 1750 and back to room temperature in about an hour. When the kiln has reached the correct temperature, it is opened, the pieces are removed using long tongs, placed in a pit lined with sawdust, and quickly covered with a metal pot or container that is lined with straw.
The combustibles use up the oxygen in the container, producing beautiful metallic colors. Think of a brand new shiny copper roof that has not yet been exposed to the elements including the oxygen in the air.
This type of firing is called a reduction firing because it reduces or eliminates the oxygen in the container. In this anaerobic environment, the glaze interacts with the flames of the burning organic matter.
The beautiful patterns that result are surely "preserved fire," because, if you look closely, you can see the pattern of the flames.
The unglazed areas of the pot absorb carbon from the burning organic matter and become black. If the metal container is lifted at the correct moment during cooling, oxygen is added to the environment. The copper in the glaze oxidizes just as a shiny copper roof does as it turns green and grows duller over time. The cool air causes the glaze and the clay cool at different rates, so the glaze cracks, causing a gorgeous crackle pattern without the luster.
The crackle pattern shows up beautifully
as the cracks in the glaze absorb carbon
from the burning organic matter.
Which effect do you like better, the metallic luster of the reduction firing or the oxidized crackle effect?