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INTRODUCTION TO SAND CASTING
Although LOST WAX CASTING is a superlative method of reproducing detailed surface modelling and intricate sculptural forms, premium material and high labour costs makes for a relatively expensive manufacturing process, especially when forming large scale sculpture. A good many monumental sculptures are composed of relatively simple forms and textures. Straightforwards designs like these can often be as equally well produced by an efficient and economic alternative to lost wax casting known as SAND PIECE MOULDING or SAND CASTING.
Few (if any), art foundries specialising in sculpture and design casting operate a sand moulding process to the exclusion of lost wax casting, therefore as a rule, sand moulding is generally practiced in parallel with lost wax casting [ref 1]. Commercial foundries have a different approach to the process of metal casting and it is much less common for a commercial foundry to offer both lost wax and sand processes.
The tradition of sand piece moulding almost certainly owes it’s origins to the civilisations of Eastern Mesopotamia (circa 4000 BC). Through trading links with the Mesopotamians, it is likely that the early Egyptian metalworkers first acquired their skills in both lost wax casting and sand piece moulding – the evidence suggests that sand moulding was practiced in Egypt from about 2575 BC. Murals examined at important archeological sites point to the use of an advanced technique of sand casting in Egypt by about 1450 BC. In turn, the Egyptian’s metal-casting knowledge was passed on to, and had a significant influence upon, the ancient Greeks who had themselves adopted a simple two part (BI VALVE) sand piece moulding technique by the 6th century BC [ref 2].
The principal metal casting technique used in art foundries today – the lost wax process, only regained it’s position of primary importance in relatively recent times. In the United States for example, lost wax art founding was not widely practiced until about 1900. The development of lost wax casting in the US can probably be attributed to the immigration of influential European founders in the late nineteenth and early twentieth centuries, who included among their number the influential Italian craftsman Riccardo Bertelli. Australia’s first professional lost wax foundry was established by the British founder, Joe Lemon (at Moorabin in 1962), who originally trained at Morris Singer (UK), as did Peter Morley who established the more enduring Meridian Foundry (Melbourne 1973) [ref 3].
In general, the use of the lost wax technique for sculpture making throughout the West, prior to the late nineteenth and early twentieth centuries, can probably be best described as patchy. It appears that despite the spectacular sculptural achievements by numerous fifteenth century Italian artists/craftsmen (Cellini, Ghiberti, Brunelleschi et al), a large quantity of the art and design work cast between the end of the Renaissance and the beginning of the twentieth century, was produced by one or another variation of the sand piece moulding process [ref 4 ].
Given the universal popularity of the lost wax technique, an earlier deference to sand casting seems startling nowadays. However, it is important to bear in mind that many of the highly developed and refined materials available to the modern investment founder such as CERAMIC SHELL refractories and moulding rubbers for example, were either unavailable or else uneconomic to use for this work until relatively recently.
An additional factor in the relative scarcity of lost wax casting, is that a detailed understanding of how to successfully cast using the wax based process was retained within a handful of family based companies [ref 5 ]. These often patriarchal businesses typically took some considerable care to restrict wider access to their skills and knowledge, effectively creating a ‘closed shop’. Under these circumstances, the sand moulding process could easily be viewed as a more accessible and reliable option, certainly for large scale and simpler forms.
In contrast to wax founding, which (in terms of technical development had essentially remained static since the end of fifteenth century), sand moulding evolved dramatically with the onset of the eighteenth century – driven forwards by the imperative of the Industrial Revolution and an ever increasing demand for good inexpensive design, effective materials and efficient manufacturing methods.
In an observation on the methods of sculpture founding in Britain during the late nineteenth century, the founder G.G. Adams underlines the (then) prominence of sand moulding.
“The modes of casting in bronze at the present day is totally different to that of the fifteenth century or earlier. We cut our figures into two or three pieces according to the design or form of the work; which are united and rivetted or burnt together as may be best according to our judgement. Sometimes we are enabled to cast an entire work [in sand]; but this is rarely possible in a statue unless modernised purposely or in a simple manner” [ref 6 ] .
Tellingly, Adams’s description highlights the technical limitations of using a sand piece moulding process, drawing particular attention to the difficulty of casting a design in a single section, without first simplifying the form of the master pattern. Unlike rubber moulding materials, sand is a rigid and therefore relatively unforgiving moulding material; this means that studio designed sculptures for the process either have to be constructed in such a way as to release cleanly from the sand mould, or else cut up into more manageable sections that will [release].
With modern processed sands and the ready availability of exceptionally efficient binders, it is now possible to cast relatively complex sculptural forms in sand, transposing detailed surface textures from master patterns into metal. Whilst it is quite possible to cast a small scale artwork by sand piece moulding, the process today is mostly used for the production of large scale monumental sculptures.
Throughout the long history of art metal founding, few truly monumental works have been cast using the lost wax process alone. As a rule sand casting, and occasionally straight fabrication, are preferred construction methods for creating large scale structures. Both of these manufacturing techniques are comparatively direct, requiring fewer intermediate production stages than lost wax casting, offering a potentially significant saving on labour and materials. A good example of such a monumental work is the ‘Rochana’ statue, from temple of Todaiji (Japan 749 AD). This sculpture stands some 53 ft (15m) high, and contains an estimated 300+ tons of metal, with a cast wall thickness of up to 12 inches (300mm). During an address to the Society of Arts in April 1895, W. Gowland, a British expert on Japanese craft techniques, gave a description of the construction methods used to create the Rochana.
“It has not been cast in one piece, but is constructed chiefly of numerous pieces of comparatively small size. Some of the lower portions have been cast by building up the mould on the parts already finished, but the greater part of the image consists of separate casts which have been united by running in an alloy containing large portions of tin and lead between the edges” [ref 7 ].
Gowland’s observations illustrate the two basic techniques used to construct monumental artworks formed in piece moulds. The first method involves an ‘in situ’ sequential casting of the sculpture, typically this is enabled by the use of temporary furnaces, set in close proximity to the designated site. A refractory piece mould section is built on location, and the metal charge is tapped directly into the mould from a nearby furnace. The founder then moves on to construct the next adjacent mould section and so on until the design is completed – in a similar fashion to that of a builder laying down a series of continuous brick courses for a wall.
The second construction method involves the remote (ie workshop) founding of individually cast sections, these sections are later fixed together on-site (in the example of the ‘Rochana’, these separately cast pieces were united by flow welding [see FINSIHING]), usually by fusion welding. A ‘cast/fabrication’ technique of this type can be complemented by the use of an underlying framework, armature or similar sub-structure, both to accurately guide the work’s construction, and later, to help structurally support the dead-weight of the cast. Nearly all modern cast artworks made to a monumental scale (which are too large to be transported in a single section), are made by a foundry cast/on-site fabrication and installation method.
MASTER PATTERNS FOR SAND MOULDING >
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