Making glass, bronze and polythene sculptures
The clay sculpture is used to make a rubber resin mould which is then used to make a wax copy. I first determine where I can pour the wax so that it fills all parts of the mould without creating air pockets, and then cover the clay in rubber resin. This is reinforced with a plaster outer mould.
After removing clay from the mould, I pour molten wax in and out of the mould several times, allowing the wax to cool between pours. The wax needs to be 3mm thick for bronze sculptures. If it were much thicker, the bronze would fracture as it cooled down. For hollow cast glass, I aim to eventually have 15-20mm thickness of wax.
By holding the wax up to the light I can determine areas of the wax that are too thin. These areas are built up to the desired thickness after heating the wax and pushing it into the sculpture. It takes a while, removing air bubbles and other artefacts, to make the surface of the wax smooth. With hollow glass sculptures, I pour the wax into the sculpture an extra time using a different opening to ensure the interior is smooth and of the desired thickness.
Working with glass
A wax reservoir is attached to the sculpture, which will eventually funnel the molten glass into the mould. In the areas that may produce bubbles, I attach risers to allow the air to escape during the casting process.
I seal all openings, before applying the initial plaster and silica layer. Soon after this has set, I remove the seals and pour the core ensuring that no bubbles are left inside. As this starts to set, I insert several stainless steel screws to keep the core in place. If the screws are not long enough, the core can easily break away from the mould and float to the top of the glass.
It is important that the mould has dried completely before it goes into the kiln for casting. The mould is loaded into the kiln with a plant pot containing glass billets positioned above the mould reservoir. To be on the safe side I run a drying programme in the kiln before casting the glass. The firing schedule for hollow sculptures takes 5 days. With large solid pieces, it takes 11 days. Glass requires sufficient time to slowly cool down so that it can anneal without introducing stress in the solidified glass.
The investment material is removed from the glass and recycled. To remove the core, I use a blunt screwdriver followed by angled plastic brushes together with water blasting.
The glass is cold worked using diamond burs and then sanded by hand with diamond pads. The casting process introduces air bubbles in the glass, particularly in the hollow sculptures. This creates more texture and interest in the piece. In areas where there are excessive amounts of bubbles, I remove bubbles from the surface of the glass by grinding away the top few millimetres. For polished sculptures, it takes at least a day to hand sand and polish using an angle grinder and cerium oxide. All other sculptures are sandblasted and, if needed, sent away to be acid etched.
Working with bronze
Thick wax strips are added inside the base of the wax sculpture so that it can be bolted onto a stone plinth. After the waxes have been cast at the foundry, I sand and polish them using power tools. The bronze plate inside the base is drilled and tapped so that it can be secured to the stone plinth using bolts. I finish by applying a patina to the sculpture and seal with wax polish.
Making polyethylene lamp sculptures
The polyethylene lamp sculptures are based on sculptures that I have previously made in either glass or bronze. They are rotationally moulded by a local manufacturer. To produce the aluminium mould to make these sculptures, involved first constructing a fibreglass and polyester resin prototype. From this, I designed a detachable base unit to carry the light and cable.
After determining the parting lines of the mould, I started building the pattern. This is made by applying plywood and car body filler to the fibreglass prototype. Most of my patterns are in three pieces with tongue and groove flanges.
The pattern is then used by the foundry to cast the aluminium mould. After this, it goes to a production design engineer to finish the mould parting lines and build a steel frame to hold the mould together. I then sand and polish the inside surface to a perfectly smooth finish ready to go to the factory for the rotational moulding process. My future polyethylene lamp sculptures can be seen in ‘New Projects’.