The Raku process originated
in Japan in the 16th century. The term raku is derived
from the Kanji character meaning "enjoyment" or "ease".
In the Raku process, glazes containing metal oxides are applied
to the Bisque fired ceramic piece, which is then placed in a
kiln and brought to approximately 1800 degrees Fahrenheit very
quickly. When the glazes are melted and shiny, the piece is removed
(with tongs) and placed in a combustible material such as wood
chips, pine needles or dry leaves. The material immediately bursts
into flames from the heat of the piece creating a reduction
environment. |
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| A reduction environment
is a condition created in an enclosed space to produce specific
effects on the ceramic wares being fired. A reduction atmosphere
is produced in a container partly filled with a combustible material,
which flame up and deprive the container of oxygen. This reduced
level of oxygen causes incomplete combustion of the fuel and
raises the level of carbon inside the container. |
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At high temperatures the
carbon will bond with and remove the oxygen in the metal oxides
used as colorants in the glazes. This loss of oxygen results
in a change in the color of the glazes because it allows the
metals in the glaze to be seen in an unoxidized form.
The piece is removed from the container and is allowed to cool
to ambient temperature. An abrasive pad or fine steel wool is
used to clean the excess carbon and debris from the piece. The
piece is then rinsed in water and dried. |
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