The Process
Casting an object in bronze is a many-stepped process requiring highly specialised equipment and craftsmen.
The process used at Fundere Foundry is called “Lost Wax” casting, using a ceramic shell mould. Lost wax casting dates back to the Bronze Age. Today the essence of the process remains the same, though moulding and chasing (finishing) processes have become highly advanced.
At Fundere Foundry we predominantly use the Ceramic Shell process which is at the technological forefront of fine art casting. The mould is lighter, thinner and holds the finest detail. It is easier to handle than an investment mould and is less wasteful of both materials and resources. As a non-ferrous art foundry we predominately cast in bronze and aluminium but have experience with other alloys including precious metals.
MODELLING
The artist’s original model is supplied in wax for small works. For larger works Fundere specialises in silicone-rubber and fibreglass mould making. Once the re-usable rubber mould is created it can be utilised for further editions of the work.
WAX
The object is created in wax or transferred to wax using a silicone-rubber mould. If the object is small, no wider than a clenched fist it can be cast solid. If the object is larger it may need to be hollow. A hollow object is best achieved by casting the object in wax from a rubber mould. The wax object needs a series of sprues (wax pipes) that will carry the bronze to the object and allow the air within the mould to escape. The sprues are made from wax and are attached to the object.
SHELLING
The wax object is painted with a ceramic shell slurry and dusted with ‘en tout cas’ (crushed brick) which works as an aggregate binding the ceramic shell together. The coating is left to dry. This process is repeated 8 to 10 times until a satisfactory shell thickness is achieved over the object. The shell with the object within is heated in a kiln which both fires the ceramic shell and melts out the wax object within, leaving a void for the bronze to fill, hence the name lost wax.
CASTING
The alloy being cast is melted in our furnace, for silicon bronze we heat to 1100 C. We have the capacity to cast 250kg of metal in one pour, more than enough for any project. The shell investment is buried in a pit and the liquid metal is poured into the ceramic shell, filling the void within - always an exciting moment.
CHASING
After the Ceramic Shell has been removed the bronze cast needs to be chased (metal finished) where the sprues are cut off and recycled. The surface of the bronze is re-worked where necessary using T.I.G. welders, grinders, die grinders, chisels and files. This is a highly specialised process requiring skilled technicians to replicate the hand of the artist.
PATINATION
The finished bronze is then patinaed. This is the colouring of the surface of the bronze through a process of oxidisation. Different chemicals produce different hues.