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The fascinating process of creating the original bronze statue of The Horse from its clay model began when sculptor Nina Akamu and her seven assistants built the 24-foot model from the original eight-foot rendering by using enlarging machines and refining muscle forms and surface details.
Akamu and her team then planned how many mold pieces would be made and how they would be made. The Horse consisted of more than 60 sections, each no larger than approximately four square feet. Metal shims were placed throughout the large model to indicate the boundaries of these sections.
Workers at the Tallix Art Foundry made a rubber mold of the 24-foot model by covering it with a quarter-inch-thick spray rubber and a half-inch-thick layer of polymer resin and fiberglass. After the mixture hardened, the sections were removed between the metal shims.
Most of the statue’s sections were cast with the sand mold process. Foundry workers created positive plaster casts of the inside of each section. The sections were placed individually in a steel molding box. Inside that molding box, a machine rammed each piece with a mixture of sand and binding. After the mixture set, the piece’s plaster cast was removed and scaffolding was placed in its sand imprint. Molten bronze – which is approximately 2,000 degrees Fahrenheit – was poured subsequently into the imprint area, producing a quarter-inch-thick bronze piece. After the finished piece cooled, it was removed from the machine and cleaned.
The few remaining sections were cast with the lost-wax process – the preferred process for creating several tiny sections grouped together. The mane, forehead, ears, and tail of The Horse were cast in this manner. Their rubber mold sections also had plaster casts placed inside them. Multiple coats of how wax were then painted directly inside each piece before a pour spout installed. Each section’s pieces were joined together before more hot liquid wax was injected. Any excess wax poured from the spout. The remaining wax cooled to form a detailed positive copy of the section’s rubber mold.
After foundry workers made any necessary adjustments, each wax mold section was fitted with scaffolding before it was covered with several coats of liquid ceramic slurry over several days. The resulting shell – which would be no less than one-quarter of an inch thick and no more than five-eights of an inch thick – was baked in a furnace at up to 1,450 degrees Fahrenheit. While the shell baked, the melting wax inside it would run out of the shell, or be “lost.”
Each shell piece was then covered in a bed of sand with its pour spouts showing above the surface. The molten bronze was then poured to fill spaces occupied previously by the wax. After the bronze cooled, the outer shell was “cracked” open to expose the finished bronze piece.
After perfecting the edges of each bronze piece, foundry workers began fitting pieces together and tack-welding them. Corrections were made throughout the assembly of the giant, three-dimensional jigsaw puzzle, including the compression and stretching of joints with hydraulic jacks to create exact fittings. Once large sections had been tacked together and double-checked, its seams were welded to finish slowly.
As the statue’s pieces were assembled by one team of workers, another team constructed the stainless steel armature that made up its “bones.” Comprised of type 304 stainless steel, the armature pieces were erected and tightened throughout the sculpting process. A trap door in the belly of The Horse allowed workers to work inside the statue when necessary.
To allow The Horse to stand on two legs, workers also installed inch-thick stainless steel tubes inside those legs that protruded 18 inches below the hoofs. Those tubes would be welded to steel plates in the pedestal in Milan and embedded in concrete. Leonardo probably would have marveled at the fact that The Horse is not held up by its bronze “skin.” All of its weight is transferred through the armature “bones” to its leg tubes to the pedestal.
Once the seven primary sections were completed and shipped to Milan, Italy, they were assembled by Tallix foundry workers, connected to the statue’s pedestal, welded to finish, ground to a smooth surface, and finished with an artificial patina – a film that gives the look of a glorious work of antique art, science, and engineering.