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History of casting

Historical notes

Historical notes
The first bronze castings date to the mid 3rd millennium BC when a high level of sophistication was achieved in Mesopotamia and Egypt.
At first, the cast metal was poured into open stone or baked clay moulds and the resulting objects had one moulded side and one flat side. Later, double moulds came into use to make three-dimensional pieces.
At the end of the 3rd millennium BC, the first models were made with the lost-wax shaping technique, moulding a clay shell on a wax model. The wax removed by firing creates a cavity in which the cast metal is poured. (Bronze lion of Uruk, late 3rd millennium BC), Dancer in cast copper from Mohenjo-daro, India, second half, 3rd millennium).
In this way, full sculptures of considerable weight were made, which meant that they could not go beyond small sizes. (Flute Player, cm 42 high, mid 6th century, Samo Museum).
The bronze cast technique took a jump forward by the introduction of a wax model with an earth core. The cast bronze, once the wax is removed, takes up the gap between the earth core and the outside form, creating completely hollow works with a thin, even thickness. (Head of Sargon I, late 3rd millennium).
The classic system lost-wax casting with a core was established definitively in 6th century Greek monumental sculpture. On a roughly shaped core, reinforced with a metal framework, the wax is moulded in full detail, and then is supplied with pouring channels and vents and finally covered by a layer of refractory clay (Charioteer of Delphi, 474 BC).
Starting from the 3rd century BC, a system of peg-casting was introduced, which involved first making the peg mould on the clay model, and then, once removed and put back together, a wax model hollow inside was created. This has the dual effect of preserving both the clay model and the mould itself to make more than one piece. In Imperial Rome, increasingly thin pieces were achieved, down to 2 mm, by using more fluid alloys employing tin, zinc and lead.
In the Middle Ages, the latter technique was abandoned, along with other metalworking. There was a return to the simpler system of directly modelling on an earth core, used mainly for casting bells and church doors. At any rate, there was little produced in the High Middle Ages and the technique was decidedly rudimentary. An illustration of this is seen in Florence when to build the Baptistery doors, they had to call in Venetian casters who knew the Byzantine method based on classical methods. The procedures used remained elementary until the late Renaissance, as we can read in the description of the casting of Perseus by Cellini.
Upon close inspection, the bronze works of the Renaissance, though perfect in their aesthetics, required major finishing and correction, evidencing a very low quality of casting. Artists like Donatello and Ghiberti considered the cast work only a rough model to be shaped and sculpted up to as much as the first centimetre of its surface.
At the end of the Renaissance, the peg-casting system was rediscovered, though it did not completely take over, coexisting with more primitive techniques. Both Cellini and Vasari considered it a process of secondary importance, useful to supplement the still popular system. Twenty years later, Vasari understood and praised the superiority of the negative peg method, which did away with the tiresome work of cold finishing, as it reproduced works that were extremely true to the model.
In the 16th century, with Giambologna, this method was adopted systematically as it allowed semi-industrial production that separated the artistís work from that of the caster, though in the Baroque culture, the artistís touch was still indispensable for perfecting the work. Only in the 19th century did the caster begin taking care of the finishing while the artist only corrected the wax models.
In terms of technique, lost-wax casting has survived to our day unchanged, while the introduction of new materials has allowed for further improvement in quality. Silicone rubbers, thanks to their elasticity, replaced the system of peg casting, and refractory clay forms have been replaced by ceramic shells, which are easier to manage, heat resistance and allow for considerable speed of execution.

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