In the late 15th century, upon the commission of Ludovico Sforza, the Duke of Milan, Leonardo Da Vinci spent 17 years devising a plan to cast a 24-ft. tall bronze horse—the largest equestrian statue in the world—in a single pour. The horse, dubbed Il Cavallo, was never completed. After a full-scale clay model and necessary molds were prepared, French troops invaded Milan, forcing Ludovico to use the bronze earmarked for the immense statue to build cannons instead. Tragically, during the conflict, the molds were lost and Gascon archers from the victorious French troops used the massive model for target practice, reducing it to a mound of clay.
In the succeeding centuries, many said the horse would never have been successfully cast anyway. Engineering studies asserted that the casting was impossible because the amount of bronze used in the single pour would result in large pockets of gas and possibly, explosions in the melt.
Il Cavallo may yet have a happy ending. Using Da Vinci’s extensive notes on the project, the Institute and Museum of the History of Science (IMSS), located in Florence, Italy, where the great master apprenticed, worked with Flow Science’s Italian representative, XC Engineering (Cantu), to study the feasibility of Da Vinci’s design. The results, publicized by the Discovery Channel and other media sites, proved once again the genius of Da Vinci.
The most amazing result, apart from the fact that both casting systems developed by Leonardo—vertical and horizontal—could work, is that the pouring of more than 70 tons of bronze would take three to four minutes. This result seems more incredible if we think to another famous casting described by Benvenuto Cellini. A smaller statue, his famous Perseus, seemed to take many hours.
– Andrea Bernardoni, Historian at IMSS
Replicating the Past
Using Da Vinci’s notes on the casting of Il Cavallo, collected in a 34-page handbook, the IMSS and XC Engineering were able to demonstrate that Il Cavallo, often referred to as “the horse that never was,” can be successfully cast as designed.
“At that time, engineers and artists were not used to writing down technological notes,” Bernardoni said, “The notes are not a modern technological plan, but they were files written down to help him understand the best way to achieve his goal.”
The only numerical information in Da Vinci’s notes was the height of the horse—24 ft. (7.2 m). But the notes also provided drawings of the molds, ovens and casting system, as well as the posture of the horse. Da Vinci also detailed his intention to cast the bronze in a single pour without any steel reinforcement, and to make the two weight-bearing legs solid bronze. The mixture of earth used to make the molds and the furnace-opening sequence to cast the statue vertically in an upside-down position also were described in the notes.
Based on Da Vinci’s notes, IMSS built CAD models for the simulation of the casting process with FLOW-3D. “The dimensions of the runners, the external canals from furnace to runners and the bronze alloy were deducted from contextual sources, such as The Pirotechnia by Vannoccio Biringuccio (1540), Cellini’s Treatise on Sculpture (1541) and Lives of the Artists (1551) by Giorgio Vasari,” Bernardoni said. “From Vasari, we know that usually the bronze to cast statues was 10% tin.”
Simulating Leonardo’s Design
The simulations performed by XC Engineering demonstrated that molten bronze would fill the statue’s molds in a few minutes, and that all the metal would have weighed exactly the amount Da Vinci had calculated, according to Stefano Mascetti, who performed most of the FLOW-3D simulations at XC Engineering.
“I have studied Leonardo’s horse case for two years, exploring each possibility, experiment, machine and layer of his drawings,” Bernardoni said. “I had the sensation everything would go in the right way, and the results confirmed my sensation.”
Based on the FLOW-3D results, IMSS hopes to cast the horse in Milan, where Il Cavallo was meant to originally stand. “The result of the numerical simulation reinforced my decision in the end to do the real casting of the horse, following step by step Leonardo’s notes building his foundry,” Bernardoni said.