Material Science
A Little Information, or What We Do and How We Do It
Kiln-formed glass is glass that is altered, fused, shaped or textured by extreme heat generated in a kiln. The heat generated at extreme temperatures allows kiln glass to melt and bond. After fused glass cools, it may then be slumped into forms using a variety of molds. During slumping, glass heated in a kiln conforms to the shape of the mold.
Fusing begins with flat sheets of colored glass that have been tested for compatibility, or COE (coefficient of expansion) - the glasses must have a similar COE or they will crack during the fusing process.
Before fusing, an artist typically cuts, smashes, breaks, builds, piles, paints, and/or designs shapes and images that she then layers onto another glass sheets or shape. The glass is then placed on a kiln shelf, which has either been coated with kiln wash, or topped with fiber paper or graphite, to prevent the glass from adhering to the surface.
The glass is then kiln heated to between 1300-1700 degrees F (depending on the desired outcome), until the layers have melted together and become one piece. Different fusing temperatures and fusing times can produce anything from stacked and textured glass, to entirely smooth and rounded sculpture.
After the initial firing, kiln glass must be annealed. The annealing process is critical to maintain stability and integrity. During annealing, the kiln is set at a lower temperature for a period of time that allows the glass to cool slowly. This process enables the glass to cool evenly, thus relieving internal stresses in the glass that might otherwise produce cracks and instability.
Depending on the artists desired design, a piece may go through several different fusing before moving to the slumping process.
After fusing is completed, an artist may then slump his piece by placing it back on a mold, and then placing the mold back into the kiln. Molds, which come in all shapes and sizes, are generally made from ceramic, steel or other materials that will not bend, warp, deform or explode at high temperatures. The more complex the mold form, the more technically difficult it is to cut, design and complete a final fused product.
After the fused piece is placed on a mold and placed back into a kiln, the artist fires it to a lower temperature, but one still hot enough to cause the softened glass to conform, or "slump" into the mold.
After the fusing process is complete, and a piece has cooled, an artist can 'cold-work,' or add finishing touches to it if so desired. This includes etching, sanding, carving, engraving, and polishing techniques that add to the piece's unique look.
Dichroic Glass
Dichroic Glass was developed in the 1960's as an interference filter for use with lasers, and is a product of technology called "thin film physics." It was, and is still used by the laser industry, for camera filters, by NASA and various in other commercial applications other than fine art and jewelry.
Dichroic fused glass is produced by evenly layering molecular films of metal (primarily silicon and titanium oxides) onto the surface of a sheet of glass in a vacuum chamber. These materials are then vaporized in a crucible onto the glass, rotating above, by a high voltage electron beam. The process causes the dichronic glass to become mirror-like by allowing only select narrow bands of light to transmit; other rays are rejected through reflection and absorption. As the light rays transmit through the glass at a right angle they are less effected by refraction than when passing at an extreme off axis angle where they have to travel a greater distance through the coated material. This greater distance causes a shift of color.
Layers of metal oxides also make dichroic glass stiffer than other fusible glass, and the types of metals used, as well as the order in which they are deposited, are factors that determine which colors the glass filters and passes.
When fired in a kiln, dichroic glass colors shift with the heat. By varying the firing temperature, an artist can produce different colors from the same sheet of dichroic glass. As a result, each firing produces a unique piece of art, plate or jewelery.