Fused glass is an ancient art form. My pieces are a result of the merging of shapes and colours, the interplay of light and shadow and the use of extreme temperatures within the kiln.
Compatible glass which is to be layered into a pattern or design and then fused to temperatures of up to 850degC in a kiln is called Fused, Kiln-Fired or Warm Glass. The resulting flat product can then be slumped or bent into a shape using a mold in the kiln at a lower temperature.
There are a few important facts that need to be followed in order to produce a good piece of FUSED glass.
1. The different glass layers used need to be compatible with each other,i.e. they should have the same or similar COE (coefficient of expansion).
2. The glass must be as clean as possible.
3. It is essential that the kiln shelves are smooth and primed with kiln wash to stop the glass from sticking to them.
4. All precautions must be used to safeguard against possible added stresses being inbuilt in the glass.
The fusing process involves both time and temperature. A lot depends on the kiln and its settings. I use a small Sierra 1100F (about the size of a large microwave cabinet) which has a maximum temperature of 1093degC and 2 programmes. Once the glass has been prepared, it is carefully laid on the kiln shelf and the programme set, the cycle may take up to 12 hours. Generally, she use a 4 ramp cycle with the initial temperature rise being up to 520degC from room temperature and then up to a high of 835degC. The size of the piece and its thickness affects the final appearance of the product. Consistent success in fusing glass pieces is directly related to a good understanding of the heating (fusing) and cooling (annealing) processes. In her work, there are 6 stages where there are 2 heating (initial heat and rapid heat) and 4 for cooling (rapid cool, anneal soak,anneal cool and cool to room temperature).
The final important point to mention is that the controlled cooling of the glass is there to eliminate and prevent unwanted stress (thus no cracking) of the finished item.
Once the glass piece has been fused and it is satisfactory (it could be re-fused if required), it may then be altered from a flat piece to one with some shape. This can involve a whole new 12 hour cycle in the kiln at lower temperatures where the flat item is put in or over a mold. Molds can be hand made but to simplify matters for a novice glass fuser, they can be purchased and re-used.