Circular Logic: Using Balloons as Molds for Spherical Handbuilt Ceramic Sculpture Ursula Goebels-Ellis

She also shares a clay body recipe that she tweaked to work perfectly for this technique. - Jennifer Poellot Harnetty, editor

Materials

I work with a clay body modified from a Stephen Kemenyffy recipe: 30 parts Virginia Kyanite (35 mesh); 33 parts Cedar Heights Goldart; 33 parts Frederick Fireclay. Since plasticity is essential in my handbuilding process, I substitute mullite for kyanite and add 1 1/2 to 2 parts paper pulp (dry weight). Toilet paper dissolves most readily into a soft pulp that can be mixed with dry ingredients or wedged into a commercial clay body. After adding the paper pulp, I allow the clay body to mature for a couple of days. I have kept this mixture for almost a year in plastic bags in an airtight container without excessive bacterial growth; however, it does not recycle well.While traveling, I collect indigenous materials from the depths of the oceans and the rims of volcanoes. At home, I work them into the clay, along with pieces of glass, scraps of metal and machine parts.

Process

I start each sphere by covering a concave mold with a piece of cloth. The mold can be a cracked bowl or a hemisphere made from plaster or recycled clay. I prefer the latter. The cloth prevents plaster chips from contaminating the clay body and assists in rotating the sphere without disturbing the surface; it also is useful in carrying the finished form to a place where it can be stored, glazed or fired.

A flattened piece of clay - the thickness varies from 1/2 to 3/4 inch, depending on the size of the sphere- is cut into a round shape for the base. Slabs are then attached to the base to build the sides. During the forming process, the edges are kept soft by covering them with small strips of plastic.

I use a fork to score the edges, apply slip and press the overlapping clay against the wall of the mold

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, which is available in the Ceramic Arts Network Shop. 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.