A clay body is a combination of clays and other earthy minerals that are blended together for a specific purpose. Compatibility is a function of not only of the coefficients of expansion but the viscosity of the fused components. (Runny or stiff). The clay and the glass must have the same COE, or the viscosities must be mismatched in a way that counters any mismatch in COE to make them compatible.
What I have done is to develop a clay body that expands and contracts when heated and cooled at the same rate as glass. When the clay and glass are fused together there is no stress. I have developed special clay bodies to be used with different glasses. When wet the clay body is plastic and can be manipulated by a number of traditional clay forming techniques. When dried and fired the clay becomes a rigid vitreous ceramic object.
Stepping is a buffer between the glass and clay to step between COE’s. This stepping agent can be glass frit, or a mixture of materials like a glaze that gradually ease the non compatible components together. As I discussed in compatibility the viscosities must be mismatched in a way that counters any mismatch in COE to make them compatible.
I formulated a clay slip that I applied to a commercial bisked tile, (dall Tile). This layer of slip allowed me to step and fuse a COE 90 glass to to its surface. The COE 90 glass will crack when fused directly to the tile.
Fusible clay can be used like any other clay. It is plastic and can be manipulated by a number of traditional clay forming techniques. As long as the clay is not fired it can be re-wetted, mixed, and used over.
When the clay dries it will shrink and crack like dry mudflats. This is an exciting aspect of clay fused with glass because you can see through these fissures and know that something uncharacteristic of glass is happening. When blowing the glass, these fissures open up and constrict depending on the manipulation of the glass.
Fused sheets of glass can be scored and cut by hand or with a waterjet machine which can cut the glass into most any desired shape. Cut shapes and clay elements can be re-fused into new compositions. New layers of glass, or clay, can be added and fused to provide shape color and texture. Clay can be fused with glass in sheets and then blown using the roll-up process. Glass can be gathered onto a pre-fired clay shape.