Bronze statues require an intricate process to transform raw materials into lasting masterpieces, known as lost wax casting. It requires artistic vision, skillful craftsmanship, and metallurgical knowledge for successful execution.
At this initial step, the artist unleashes their imagination. Once their clay model is complete, it must be molded carefully to capture all the intricate details.
Clay Model
Artists first express their artistic vision through a clay model when creating a bronze sculpture. This allows fine details to be sculpted into three dimensions while still capturing their intended design expression in three dimensions. Once this stage is complete, molds must be created and cast for larger pieces with support armatures in place as the clay dries.
At this stage, the clay statue must be thoroughly cleaned with water and dried with a soft cloth before molds or castings occur. Any mistakes during this step would be reflected in its final molds or casts. Hence, it is vitally important to remain free of errors – including touching up delicate details and smoothing its surface to perfection.
Once a clay model is ready for casting, it must be covered in a thin coating made up of clay, soil, and sand, reinforced with iron rods and wires for strength, and then coated in wax to preserve original shapes and details while heat melting away wax to form a hollow mold that will allow for pouring of liquid bronze into it. When dry, an additional wax layer can be added for preservation purposes before being de-waxed by heating to produce an open hollow clay mold that can hold it all.
This positive wax replica of the clay model is then attached to a network of wax rods known as sprues and gates, which will serve as channels for pouring molten bronze into it, along with a funnel at its top for running it directly into it. This network will form the basis for creating a bronze cast of the statue.
Sculptors use this time to choose a bronze alloy composition that will determine its final strength and durability, which can only be decided after extensive experience in creating durable bronze statues that can endure the elements. This process requires great skill.
Wax Replica
The sculptor next creates a wax replica of their clay model by melting wax to 210 degrees Fahrenheit, pouring it into a rubber mold, and evenly coating or “slushing” it. This ensures that when casting occurs, the sculpture will be as solid and heavy as possible without compromising the artist’s vision; additionally, this stage also allows reassembling pieces (known as “chasing”) or fixing any flaws or imperfections caused by the casting process.
After the wax model has been chased and approved, a sculptor adds “sprues,” or networks of rods connected by cables known as sprues, that will become channels through which molten bronze will flow. At this stage of creation, strategic thinking becomes important; any mismatch between any given sprue and body part causes the cast to shatter, necessitating careful manipulation using heated metal tools and hands.
Step Two of Sculpting involves applying a mixture of clay and other materials to the spread model that can withstand high temperatures while absorbing gasses. This process is known as investment and creates a rock-hard shell around the wax sculpture that will serve as its mold for casting molten bronze.
This process typically requires several days and requires that the sculpture remains upside down. At the same time, sprue wax is repeatedly submerged into silica slurry and finer grit sand baths, then allowed to dry after each dip. After at least nine such drops, a ceramic shell approximately 2.5cm thick forms around its center.
Once the kiln has baked and cooled, any excess wax spread from the ceramic shell must be removed, and any pieces not connected with the sculpture must be removed. The ceramic body can now serve as a mold for pouring molten bronze.
At this stage, the sculptor must take complete control of the production process and decide whether or not to cast their statue in one large piece, depending on its complexity and size. This decision will have significant ramifications during the finishing and patina stages, requiring technical skill and artistic intuition.
Rubber Mold
Once a clay model has been completed and the artist’s vision realized, a mold must be created to preserve every intricate detail for bronze casting. Rubber molds are often employed due to their flexibility and precise capture capabilities – this step often culminates in rubber mold production.
Rubber mold making involves covering an original sculpture in layers of rubber applied over multiple passes, typically splitting it up into sections for this process. Once complete, this “mother mold” acts as a negative image of its counterpart sculpture, after which molten wax is slushed into it to produce a hollow resin positive of it, which is marked with marker lines indicating where mother mold sections connect; it is then cut up into castable pieces and piped with resin to allow molten bronze into and gasses out from within it – commonly known as sprues are fitted for this step.
Sprues are then sealed off using an investment material made of ceramic shell. Once set, this investment material must be broken apart using hammering or sandblasting to expose and release its raw bronze contents.
At the foundry, a bronze crucible is heated to 2,250 degrees Fahrenheit before a team of workers wearing full safety gear carefully pours molten bronze into a ceramic shell-coated sculpture and allows it to set. Once complete, this bronze-filled work of art can then be set aside until cooling.
Once the ceramic shell has set, it must be hammered and sandblasted again to remove any pieces of raw bronze that remain embedded within tight corners or hollows of the sculpture and any sprues that have formed within.
Wax rods are used to direct the bronze as it enters the casting. A layer of plaster is added inside a ceramic shell to prevent any of its contents from coming into contact with it and damaging the casting process. Finally, this shell is dunked into a ceramic mixture similar to thick cream before drying, creating a protective ceramic cover for bronze that’s ready for casting – though selecting an insufficient combination could cause it to tear or even crack under its weight!
Casting
Working with bronze and other high-temperature equipment requires an enduring dedication to safety. The sculpture process involves many risky steps that must be completed safely; therefore, sculptors and their teams must strictly observe all applicable precautions. Furthermore, bronze casting requires extensive knowledge.
At the center of every bronze statue is its creation, its clay model. This delicate process requires skilled hands, as the sculptor must capture every detail of their original sculpture using various specialized tools, such as wire loop tools, wooden tools, and smoothing tools – each providing different functions that help artists add intricate textures or fine details. Furthermore, they must have extensive experience handling clay materials to avoid mishandling them – even minor errors could ruin their final form!
Once the clay model is complete, its investment requires sealing it in a protective ceramic shell via an investment process known as investment. The asset is vital in guaranteeing that its finished bronze equivalent will be flawless; here, the artist uses every skill at his or her disposal – carefully applying each layer of clay with precision before covering the whole thing in thick layers of wax that “lose” during this stage – hence the term “lost wax.”
At the foundry, this rubber mold is placed into a kiln where a network of wax rods is added, serving as the conduits through which molten bronze will travel to create sculpture. Artists become heavily involved at this point by using heated custom-made soldering irons or tools (dental tools are ideal) to retouch any imperfections before having their wax slushed (an evenly coated layer of excellent wax) into an even surface for casting.
Slushed wax is then carefully dripped into an investment material, hardening and protecting it against the molten bronze about to be poured onto it. At the foundry, great care must be taken so no bronze spills out during running, and once set, it’s time to break apart the ceramic shell by breaking apart its joints; these then have to be disengaged using tools such as hammers and power chisels and removed separately from its ceramic body.
