|For improved bonding, I use additional coils and always work the clay in the same direction (figure 1). When the walls reach higher than the mold, I insert a balloon for support (figure 2).
Super-sized balloons can be ordered online or through party or flower stores. For extra strength, it is sometimes helpful to insert one balloon into the other and inflate them only to two-thirds of their maximum size. With care, they can be reused several times.
This post was excerpted from Ceramic Art: Innovative Techniques, available now in the Ceramic Arts Daily Bookstore. The full article includes information on how Ursula finishes these pieces by wood or raku firing them.
Once the basic form is complete (figure 3), the drying process needs to be closely monitored. It is important to let air out of the balloon periodically to give the clay room to shrink. If the air pressure is too high, the drying clay cracks as it shrinks; if the balloon deflates too quickly, the whole structure could collapse.
While the clay is still leather hard, I paddle the sphere with the balloon inside to strengthen joints, or to alter shape and create additional texture. If one has not been left in the forming process, an opening big enough to insert a hand is carved out at this point. I remove the balloon and continue to work inside and out on form and texture, often adding found pieces of granite, glass and/or metal.
Special attention needs to be paid to how, when and where to incorporate such materials, because they dry, mature or melt at different rates and temperatures than the clay body. For example, to include a larger piece of rock or metal, I work like a jeweler putting a diamond into a setting of gold (shrinking clay). Volcanic rock keeps its form when raku fired but becomes a stream of lava in the much hotter anagama wood firing. Some metals run at mid-range temperatures, while heavier pieces of steel survive stoneware temperatures. Rocks can explode, while beautiful seashells dissolve into powder.
Once structure and design are completed, the opening is (partially) closed to form a small neck. The clay is then allowed to dry completely before firing.