Fused Glass 101

Glass Fusing — joining pieces of glass  together by melting them in a kiln.This is usually done roughly between 700 °C (1,292 °F) and 820 °C (1,510 °F), and can range from tack fusing at lower temperatures, in which separate pieces of glass stick together but still retain their individual shapes, to full fusing at higher ones, in which separate pieces merge smoothly into one another.

Slumping —a technique in which items are made in a kiln by means of shaping glass over molds at high temperatures. The slumping of a pyrometric cone is often used to measure temperature in a kiln. The glass used is already colored.

There are four main types of glass used in glass fusing:

• Opalescent Glass — opaque glass that you can’t see through
• Cathedral Glass — transparent glass
• Iridized Glass — glass coated with a metallic coating made of tin. This coating can be silver, gold or have a rainbow transition from gold to silver, too purple, blue and green.
• Dichroic Glass — This layers of metallic oxides are deposited upon the surface of the glass at a high temperature.
• Vacuum Furnace Glass — glass coated with a metallic coating made of tin. This coating can be silver, gold or have a rainbow transition from gold to silver, too purple, blue and green.

The glass is purchased in sheets of varying thickness and includes crushed glass (fit), powdered glass, thin rods (stringers) and thin shards of glass (confetti).

Any glass fused together has to be tested “compatible” or it will crack upon cooling. Glass has to be heated slowly, and can be brought to specific temperatures to achieve different effects.

It then has to be cooled slowly to compete the annealing process. The kilns for glass fusing are usually computer controlled to achieve consistent results. However, in spite of this, each handmade glass item will be different. Certain inconsistencies or imperfections are part of the mystery and beauty of this process.