Fused or kiln-formed glass art is made by firing glass in an electric kiln, at temperatures ranging from 600 to 825 degrees Celsius (1100 to 1525 degrees F), and then cooling it slowly to relieve internal stresses. It usually takes several separate firings to create a single piece of art glass.
When Bob first started working with kiln-formed glass, he used traditional stained glass techniques to cut and reassemble sheet glass before fusing and shaping (slumping) the resultant pieces in the kiln. However, when glass powders became available, he quickly realized the possibilities for developing new techniques which resulted in his signature “crackle” style for colouring and designing with glass.
Bob now thinks of a sheet of glass as his canvas, and coloured glass powders as his paint. He applies layers of powder to sheet glass and manipulates them using a variety of techniques before firing his pieces. The unique, textured appearance of a sheet of glass created this way depends on what colour combination of powders is used, how the powders are applied, and how the glass is heated in the kiln.
An important part of the process for Bob is blending powders to create a unique colour palette. This includes understanding and using colours that form as the result of chemical reactions, layering powders to create colour transitions, and adding coloured design elements such as distinct colour patches and veining.
Bob’s approach to assembling pieces also involves the extensive use of "elements." These small pieces, made in advance and later included in larger compositions, include paper-thin powder wafers, rods, small symbols and patterns, and sheet glass cut into strips. When completing a piece, Bob positions or layers these elements onto a previously created textured glass sheet. This construction technique allows Bob to impart a sense of spontaneity to each piece.
The next step Bob takes is to shape or slump the newly created sheet glass by slowly warming it in the kiln so that it bends in response to gravity to assume the shape of the underlying mould.
Bob also uses several important techniques to add finishing touches to the shaped glass when it has cooled to room temperature. These are called cold-working techniques and include altering the cooled glass surface by sandblasting to create a matte or carved surface, cutting with diamond wheels, and/or polishing to a high gloss with pumice and cerium oxide. Cold working can be done at various stages throughout the creation of a piece of glass art but most often is done as the final step.