The Art of Raku
Raku is attributed to Zen Buddhist Monks of 16th Century Japan and was favored for the
tea bowls of the great tea masters. In that culture and time Raku was much more than a
method of making and firing pottery, it was a philosophy. The Japanese symbol for Raku
can be translated as "enjoyment of freedom." However, as is often the case with other
cultures' philosophies, we in the West have distilled Raku to a technical process. Raku is
now generally accepted to mean a method of rapid firing and cooling of ceramic ware,
and names the finished product.
Raku is the firing method used at The CLAY CELLAR. The process as we employ it involves
the following: forms are either slip cast, wheel-thrown or hand built, using a white Raku clay
body formulated to withstand great thermal shock. Metallic stains and engobes (colored clays)
are often brushed on the green ware forms for decoration. When trimmed and dried, the vessels
are bisque fired to cone 04. The forms are then glazed with either crackle white glaze or a variety
of metallic luster glazes. When thoroughly dry the forms are gas-fired to 1700-1900 degrees.
Once glaze-mature temperature is reached, the kiln is opened. The forms are removed with Raku
tongs and placed in a reduction sand pit on a bed of paper and sawdust. The hot form ignites the
combustibles, and a lid is then put over the hot ware, smothering the fire and starving it of oxygen.
The forms remain in this smoky environment for five to 20 minutes. Three important reactions are
occurring. First, the glazes are being reduced. Since a fire needs a sufficient amount of oxygen to
burn properly, the oxygen molecules contained in the clay and glazes are being robbed from their
oxidized state, thus reducing the glaze. This produces the rich metallic luster colors ranging from
oxidized copper greens through reduced copper blues, purples, plums, reds, and copper penny
which are the hallmark of metallic luster raku glazes. Secondly, carbon from the smoke is being
trapped in the white clay body, turning it gray to black wherever the glaze cracked or the body
was left unglazed. This reaction creates the traditional Raku crackle effect. The third important
reaction is the additional cooling of the form. This helps prevent massive thermal cracks from
occurring when the form is removed from the reduction barrel and quenched in water. The
quenching is more important with metallic luster glazes than crackle white, because the water
freezes the color and prevents re-oxidation from occurring. The form is then washed, exposing
the rich colors that lie beneath the carbon black. The Raku experience is serendipitous and more
often than not yields spectacularly brilliant results.
There are three very important WARNING DISCLAIMERS we want to state very plainly. Due to the glaze chemistry and low firing process used:
- 1. RAKU IS NOT FOOD SAFE!
- 2. RAKU IS NOT WATER TIGHT!
- 3. RAKU IS FRAGILE!
The metallic luster glazes we use contain carbonates, oxides, and nitrates that will leach out if
in contact with food acids. Therefore, NEVER USE A RAKU METALLIC LUSTER VESSEL
WITH FOOD. Consider them as vessels for visual pleasure and enjoy them in the love with
which we make them. It should also be stated that even though their form may imply a
function, that function is limited by the fragile nature of the non-vitrified clay body.
Specifically in the case of vases, if used as a fresh cut flower vase, water would eventually
leach through the porous clay and leave a stain on a wood table. If the vessel is used with
water, please use a plastic liner or place the vase on a glass plate to protect your furniture.
Additionally, ultra-violet light is very bad for metallic oxide glazes used on Raku, therefore
please do not place the work of art in a location where it will receive direct sun light.
Raku should always be handled with care as it does not have the strength of stoneware. Whenever possible, use both hands to pick it up. Raku may be dusted by rinsing it with water and drying it with a towel. The metallic glazes will "tarnish" in time, but please do not use commercial cleaners.