A Glass Compendium
(compiled for your information from various sources)
Glass is, essentially, a liquid that hardens into an uncrystallized state without ever becoming a true solid. It is also a magical substance that stores and transmits vibrations.
Glass is an amorphous substance made primarily of silica fused at high temperatures with borates or phosphates. Glass is neither a solid nor a liquid but exists in a vitreous state, in which molecular units have disordered arrangement but sufficient cohesion to produce mechanical rigidity. Molten glass is cooled to this rigid state and heat can reconvert it to a liquid form. Glass can be transparent, translucent, or opaque; its color varies with its ingredients. Glass is also found in nature, as tektite and the volcanic material obsidian .
Adding different metal oxides to sand, soda and lime, the basic formula for glass creates different colors.
- Iron - greens and aquas
- Iron & sulfur - amber and brown
- Copper - light blues
- Cobalt - dark blue
- Manganese - amethyst
- Tin or calcium - opaque white
- Selenium - reddish
- And more...
Kiln-formed glass is that which is altered, fused, shaped, or textured by the extreme heat of a kiln. Fusing is the heat bonding of glass. Slumping is the procedure in which glass heated in a kiln conforms to the shape of the mold.
The fusing process begins with flat sheets of colored glass which have been tested for compatibility - the glasses must have similar COE (coefficient of expansion) so they will not crack. The shapes to be fused are cut from the glass sheets. Two or more layers of glass are placed together, when fused the glass will form thick soft rounded edges. The cut pieces of glass are put 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. In the kiln the glass is heated to anywhere from 1300-1700 degrees F until the layers have melted together to become one piece. Next follows the critical annealing process during which the glass is cooled slowly to allow the entire thickness of glass to even out in temperature, thus relieving internal stresses in the glass.
If a curved shape is desired, such as a bowl, a mold of ceramic, steel or other material that will not bend, warp, deform or explode at high temperatures is used. The glass is placed on the molds, put in to the kiln and fired to where heat and gravity allow the softened glass to conform or slump to the mold. During the fusing and slumping it is necessary to look into the kiln in order to determine the moment the desired result occurs. Protective clothing, gloves, and glasses are essential.
Invented over 100 years ago and developed in the 1960’s as interference filters for use with lasers, dichroic glass is a product of the technology called “thin film physics” . Dichroic glass is used in art glass as well as the laser industry for camera filters, by NASA and various other commercial applications.
The coatings are made with molecular films of metal (primarily silicon and titanium oxides) evenly shuffled into multiple layers. The coating layers of metal oxides make the glass stiffer than other fusible glass and so requires special handling. The types of metals used and the order in which they are deposited are factors that determine the colors the glass filters and passes. The coatings are produced by depositing thin layers of a variety of metal oxides such as titanium, magnesium and silicon to the glass in a vacuum. A vacuum chamber is needed in order to produce a pure environment for the vapors to travel. The materials are vaporized in a crucible by a high voltage electron beam onto the rotating glass above. The glass must rotate to achieve a uniform coating. This process causes the glass to become a partial mirror by allowing only a select narrow band 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 and when dichroic glass is viewed at even slightly different angles, you will see differing colors.
When worked in a kiln the color range shifts on the glass with the heat. By varying the firing temperature different colors can be produced from the same sheet of dichroic glass. Each fused dichroic piece is truly a unique piece of art, impossible to duplicate.