Kiln Formed Glass
Kiln-formed glass is the process of creating art glass pieces by applying controlled heat to reshape, bend and fuse components of compatible glass (same COE) together in a glass fusing kiln. The individual components could be glass powders, frit (glass chips), stringers (thin tubes), rods, confetti (thin glass shards) or most commonly sheet glass. The physical melting process of the art glass is called fusing, but casting the glass into moulds or slumping the already fused pieces into three dimensional shapes or draping the glass over a mould also forms part of kiln formed glass, sometimes called warm glass, fused glass or slumped glass.
In contrast to blowing glass or lamp / flame working, fusing glass is more a process of creative decision-making before energy is applied to the material. Based on knowledge and experience, the hoped-for end-result is envisioned, designed, planned and executed before it is placed in the kiln where extreme heat without the touch of a human hand transforms the vision into a reality. The good news is that the kilns used at Lea’s Loft Glass Art Studio have built-in inspection holes which at least allows for a sneak peek during the firing process to monitor that the desired result is achieved.
Most kiln formed glass art pieces are fired in the kiln at least twice with a single firing taking between 18 and 24 hours to complete, which includes about 10 hours of natural cooling down to room temperature before the kiln can be opened. The pieces fuse nicely (or sometimes not so nicely) at temperatures of up to 900°C, but mostly somewhere between 700°C and 820°C. An important step during the cooling down phase is when the pieces are carefully annealed at around 500°C for 30 minutes per 3mm thickness in order to allow the glass to regain its strength and toughness. Glass requires carefully controlled heating and cooling cycles in order to prevent breakage and weaknesses in the final piece.