Distributing the Bronze, Choosing Fuel, Freeing the Cope
Matching each furnace's charge to the mould's parts, testing woods, and separating the cope from the model
In this stretch of the Sforza-horse casting notes Leonardo works out how to apportion the bronze so each furnace exactly fills its own region of the mould, calculating the charge by weighing the clay of that place, so that the furnace of the rear legs need not try to help fill the head. He notes to test which wood (willow, alder or fir) alloys best, to keep thin dry fir sticks ready for a furnace running cold, and gives several methods for separating the cope from the model, using ash, ash and tallow, or tallow with forge powder. As throughout, he ends by calling for a trial.
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Apportioning the bronze among the furnaces
Consider by what quantity of bronze each part of the mould must be filled, and give each furnace a matching charge, known by weighing the clay of the place it must serve. This ensures the furnace of the rear legs, once it has filled the legs, need not come to the aid of the head, which would be impossible.
Testing the best fuel wood
Test in alloying which wood is best: willow, alder, or fir.
Aiding a furnace that runs cold
Keep ready thin, well-dried sticks of fir, and add them when the bronze in casting is not sufficiently hot.
Separating the cope from the horse
One may use ash alone; or ash and tallow, heated after the second coat of earth so the tallow leaves the ash and it does not stay sticky; or tallow with forge powder. Pure tallow is good, but give it two coats of earth first and force the fire so the melted tallow runs out between the two earths and leaves its space empty; but test first.