The Clay Cellar: About Raku

he Art of 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 adapting the philosophies of other cultures, 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.

vessel09-sm.jpg - 16763 Bytes vessel01-sm.jpg - 8852 Bytes Raku is the firing method used at The CLAY CELLAR. The process as we employ it involves the following: forms are either 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 greenware 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 1660-1800 degrees.

firing02-sm.jpg - 11043 Bytes Once glaze-mature temperature is reached, the kiln is shut off and opened. The forms are removed with raku tongs and placed in a reduction sand pit lined with paper. The hot form ignites the combustibles, and a lid is lowered over the ware, smothering the fire and starving it of oxygen. The forms remain in this smoky environment for 5 to 20 minutes. Three important reactions occur: First, the glazes are reduced. Since a fire needs a sufficient amount of oxygen to burn properly, the oxygen molecules contained in the clay and glazes are being removed from the glaze mix, thus reducing the glaze.

detail01-SM.jpg - 30032 Bytes 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.

v-detail01.jpg - 8310 Bytes This reaction creates the traditional Raku crackle effect. The third important reaction is the additional cooling of the form. This helps prevent massive thermal shock 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 thoroughly 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 WARN!NG 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 METALIC 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. Therefore if used with water use a plastic liner or place the vase on a glass plate to protect your furniture.

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 and never pick a piece up by its lip. Raku may be cleaned with a mild soap and water or lightly buffed with very fine (0000) steel wool.