< NICKEL BRONZE
LIGHT METALS
After copper alloys, light metals and in particular aluminium, are perhaps the most popular materials for casting sculpture. Refined aluminium has evolved from it’s mid nineteenth century origins, when it was considered a semi-precious exotic material, to become the common place and relatively inexpensive material of the present day [ref 1]. The earliest recorded use of aluminium (in an architectural feature), was for the pyramid cap of the Washington Monument (1884), though perhaps the best known of all (cast) aluminium sculptures is the 1892 ‘Shaftesbury Memorial’ – or ‘Eros’ by Alfred Gilbert (1854-1934), this landmark sculpture being famously situated within the environs of London’s Piccadilly Circus [ref 2 ].
Possibly on account of being a relatively modern material, the inclusion of aluminium within an artwork is often associated with innovative artists and progressive modernist movements; Vladamir Tatlin (1885-1953?) for Russian Constructivism, and later, Donald Judd (1928-1994) for Minimalism are leading examples. Likewise the architectural designs of Mies van der Rohe (1886-1969), and others of the International Movement, made extensive use of this material within their determinedly modern built constructions from the 1920’s onwards.
Light metals melt at significantly lower temperatures than copper alloys (the melting points of elemental copper, aluminium and zinc are respectively: 1085°C, 660.4°C and 419.6°C). Care must be taken during melting to prevent the molten charge from overheating, at which point it absorbs excessive quantities of oxygen and hydrogen gas. If absorbed in the charge, these gases could adversely affect the quality of the cast. Over-heating the charge can also induce the rapid BURNING OFF of alloying elements, especially any zinc content as this metal has an exceptionally low melting point.
One particular advantage of using a low melting point alloy is the potential to make low cost sand castings. These sand casts can be produced by either directly drawing into, or pressing forms into a foundry sand, then running in an easily melted alloy such as aluminium. Relatively inexpensive casts may also be produced using a sand encased EVAPORATED POLYSTYRENE LOST PATTERN (EPS) technique. The EPS lost pattern allows a light metal to be poured into a refractory sand mould with little risk of excessive SAND BURN, a fault often associated when using a higher melting point alloy such as copper gunmetals (see SAND CASTING).
Aluminium alloys are sometimes used for constructing substantial master patterns, this is common practice when forming patterns for use with repetitive commercial sand casting operations. Aluminium patterns are preferred here because of their light weight and the ability to withstand repeated handling and the force of sand compaction.
Despite it’s light weight and (generally) lower cost in comparison to copper alloys, it is not recommended that aluminium be specified as a straight substitute for either gunmetal or silicon bronze alloys. Like brass, aluminium offers sculptors many commendable features in it’s own right, but used as a substitute it rarely proves either to be a significantly cheaper, or a more satisfactory option to the more traditional copper based casting materials.
ALUMINIUM ALLOYS 1 >
|
