River Market ArtSpace

How'd They Do That? -- Clay

There are many different ways of transforming clay into masterpieces of art. One of the most popular types is Raku clay. If you’ve ever seen a vase with brilliant, metallic colors or grayish colored lines that appear as cracks in the clay, you’ve probably seen a piece of Raku clay.

The term Raku refers to a firing technique which dates from 16th century Japan, and was originally associated with the tea ceremony. Unlike stoneware firings, which can take up to several days, the Raku glaze may take only minutes. The formed pot, covered with a glaze, is placed directly into a red-hot kiln and observed as the glaze melts. At the exact moment that the glaze matures, the kiln is quickly opened and the hot piece is removed with a pair of long tongs. At this point the pot is placed into a container of combustible materials, such as sawdust, leaves, or wood shavings that ignite. Once placed in the container, it is covered to reduce the amount of oxygen available for the fire to burn. This captured carbon (smoke) becomes saturated in the clay body and in crazed areas which occur in the rapidly cooling glaze. The pot is removed from the container after 10 minutes or so and cleaned so that the colors set and don’t re-oxidize.

Raku glazes melt at approximately 1800 degrees Fahrenheit and use metallic oxides as colorants. Many artists use Cobalt Carbonate to get deep blue colors, Copper Carbonate to get luscious greens, and Silver Nitrate for gold and silver. Black comes from Carbon staining the bare clay of the pot, and metallic luster is produced in the firing and smoking process and are made up of the copper, cobalt, and silver metals.

The firing process involved in Raku clay allows for much variation. Each piece is unique and individual, as are the artists who make them!

Another popular type of clay is called stoneware. Stoneware clay is used in many different pottery techniques; it can be functional as well as decorative. When thrown on a potter's wheel, it passes through many stages before the final piece is finished.

First, the clay is wedged so as to remove any air bubbles in the clay (if bubbles are left in, the piece would blow-up in the firing), then it can be thrown on the wheel. When the clay has been manipulated and centered on the wheel, the potter then begins pulling and shaping the form. After the desired shape has been achieved, it must sit until it is leather hard (still pliable, but won't collapse if picked up). At the leather hard stage it is flipped over and the bottom is trimmed. Also at this stage, any additions of decorative clay shapes may be added like leaves and vines as in seen in Janet Donnangelo's work. After any additions have been made or not, the pieces must set out to dry completely - this may take days or weeks depending on how thick or large the piece. When the pottery is bone dry it is placed into an electric or gas kiln and fired to approximately 1800 degrees Fahrenheit, this is called the “bisque-fired” state. The bisque ware is then glazed, maybe by painting with a brush or dipped into a bucket of glaze or sprayed on with a spray gun. The glazes are combinations of different chemicals that give it color whether it's shiny or matte finish. Then it is placed back into the kiln and fired to 2300 degrees or more, depending on the glazes used. The final firing can take almost a day to reach temperature and a couple of days to cool down before it is removed. So, from start to finish one piece may take weeks or months before it turns into the masterpiece that is envisioned.