Glass casting, or kiln casting, is the method of creating glass sculptures by placing glass into a mould and heating it to allow the glass to take on the shape inside. The technique has been used since the Egyptian period. Modern cast glass is formed by a variety of processes, here a some of the main methods:
- Core casting – is one of the more complex forms of casting. Firstly a plaster mix model of the object is made. The plaster model is then placed into a plaster outer framework. Glass is added to the area around the plaster model and heated in the kiln. The molten glass solidifies around the inner model and outer framework. After firing the outer frame is removed as well as the inner plaster core. You are then left with a solid glass form with a hollow void that is the shape of the original model.
- Lost wax casting – starts with making a wax model of the item to be cast. A plaster mould is then formed around the carved wax. The carved wax is then melted out of the plaster and the cavity is filled with molten glass and annealed inside a kiln. This method is used for more complex forms or pieces with a lot of fine detail.
- Open casting – involves firstly making a model of the item to be cast (typically made from clay). A frame is made around the model and a plaster mix is poured over the model. Once the mould mix has set the clay model is removed and the cavity cleaned. Glass is then placed into the mould and heated in the kiln and allowed to anneal. The glass melts and fills the void. This technique is normally used for less complex forms.
- Pâte de verre – translated as glass paste, tiny pieces of glass are placed inside an open mould and fused in the kiln.
- Sand casting – involves making an impression in damp sand that is contained within a boxed frame. Molten glass is then poured directly into a mould. The moulded glass is then left to anneal in a kiln.