There are many forms of glass art. Fusing is one of them and dates back to ancient times. The Egyptians are thought to have developed the technique around 2000 BC.
Glass that is fused has been fired to high temperatures in a kiln, up to 816 °C or 1,501 °F. The word ‘fusing’ is used to describe the combining of different pieces of glass into one piece, but can also include the bending and shaping of glass such as kiln casting or slumping, where a mould is used to cause the glass to take on a shape. As the kiln increases in temperature the glass softens and then becomes more fluid and flows together. Most pieces are comprised of 2-5 layers to build up the design. Some fused glass pieces need to be fired more than once in order to achieve the desired look. The fusing and cooling process can take over 12 hours.
When fusing glass all the pieces must be of the same co-efficient-of-expansion (COE), or the different types will cool and contract at a different rate, and may exhibit stress fractures and shatter. Sometimes weeks or months later. The glass I use is sold by specialist suppliers which guarantee it to be of the same COE. Other glass such as bottles can be fired in a kiln to be flattened or ‘slumped’ into a mould, but these pieces cannot be combined with other glass as their COE is unknown.
An inclusion is an object that is fused inside the layers of glass. This material may have different characteristics so needs to be thin or weak enough to allow the piece to expand and contract normally to ensure that it doesn’t crack as it cools, or leave a large air bubble around it. Materials that don’t completely carbonize from the heat of the kiln can be used, metals such as copper, aluminium, brass, gold and silver are used in the form of foil, mesh, wire and metal leaf. Other objects that can be used include enamels, mica and fiber paper.
Air bubbles are caused by air that has been trapped between the layers of glass. This can be encouraged as part of the design and it is possible to create more or manipulate bubbles, but it is very difficult to totally eliminate them all. Unless they are an intended part of the design I try to make pieces to be as bubble free as possible. These are small and do not weaken the final piece.