Technical Notes on Castings

Process Overview

Typically the lost wax method is used for casting bronzes in, or with the possibility of, limited editions. The process being;-

1. The sculptor constructs the work in some intermediate non-precious material (plaster, plasticine, clay etc.). 2. A flexible mould is then taken from the original. 3. A wax surface is then built-up on the inside of the mould and the flexible mould removed. 4. Runners (tubes for the molten bronze to descend) and riser (escape vents for excess gases pushed out by the liquid bronze) are then added to the wax. 5. The wax is enclosed in waste mould, made from an refractory material, such as a ceramic shell. 6. Firing. The wax is burnt out of the refractory mould and the ceramic shell fired to 900oC. 7. The molten bronze is poured into the cavity. 8. The waste mould / ceramic shell is knocked off. 9. Then the bronze is "chased" (cleaned up) runners and riser cut off and the metal cleaned. Then maybe patinated, polished or lacquered. 10. Because the flexible mould still exist more wax patterns maybe taken, thence bronze editions of the work can be made.

Wax Originals

All the bronzes in this exhibition are UNIQUE bronze casting done by a lost wax method. Unlike the typical process above there is no intermediate work and flexible moulds, as I work directly with in the wax. I find fabricating directly in the wax allows me the expression of more open and fluid original forms.

I use different two waxes (which from memory ) are;
      1. A yellow /amber microcrystalline wax called Microystal 2305 (or 2306) from Mobil Oil Australia
      2. 'Burma' Victory Brown, from Dussek Campbell Pty Ltd.

The yellow is the cheaper (always an important point) and tends to have the greater tensile strength of the two, unfortunately the butter like surface is very difficult to see detail on. The Victory Brown is great for detail though a little soft at times.

Castings

The one-off wax orginals are then taken to a foundry for casting. The foundry use the ceramic shell method. The ceramic shell, is basically a porous shell produced by dipping the wax patterns (the work with runners and riser attached) into a slurry of fine (approx. 200 mesh) refractory clay then stuccoed with a coarse grit of similar material. The process is repeated building the shell up in layers ( 5-9 layers depending on the size of the piece).

The ceramic shells still containing the wax are then fired, burning the wax out in the process. While the moulds are still hot the molten metal is poured in. The metal used is a "Silicon Bronze", approximately 95% Cu, 4% SiO₂, 1% Mn.

All my bronzes casting is now done by;-

Alan Crawford, Crawford Casting P/L 27 Madeline Street, Enfield NSW, Australia 2136

Work phone (+61) 2 9642 1849 {Best 9am to 4 pm EST}

Copyright Shaun Gray (c) 1997

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