Casting the Sforza Horse: mould lining and bronze delivery
Burnt-dung ash lining, three-piece moulds, a furnace on rollers, and gunpowder to time the fill
A page of founding notes for the colossal bronze horse. Leonardo prescribes lining the baked mould with ash of burnt cattle-dung, making each rounded member's mould in three pieces so it lifts cleanly off the clay model, and building a furnace on a trestle so it can be rolled between the narrow work-spaces. He then plans the delivery of bronze when the horse is cast upside down, placing gunpowder at the neck-to-back join so its flash signals when the neck is nearly full and the other furnaces can be unstopped.
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Lining the baked mould with ash of burnt cattle-dung
Once an alloy has been made and a cast poured, take cattle dung and burn it. That ash, Leonardo says, is perfect for applying to the inner face of the mould.
Making each rounded member's mould in three pieces
If the mould of each rounded part of any member is made in three pieces rather than two, it can be detached from the clay horse with much greater ease.
A furnace built on a trestle to move on rollers
For working among the cramped furnaces, Leonardo suggests building a furnace up on a trestle of beams so it can be handled on rollers and dragged to wherever it is needed.
Gunpowder flash to signal the neck is full
Casting the horse inverted, he weighs the wax or clay from back to crown and sets gunpowder at the join of neck and back. When the molten bronze nearly fills the neck, the flash of the powder shows it, and the remaining furnaces are unstopped so the bronze stops where it falls rather than running to lower places.