The core vent and the shape of the melting furnace
An exhalation vent in the core, pre-heated furnace floors, and the vault-to-floor proportions
Notes and two figures on the founding of the bronze horse. Leonardo insists on leaving an exhalation vent in the core so that trapped air or moisture can escape, otherwise the fuming moisture would pass through the surrounding bronze and make it boil and spurt. He instructs keeping the furnace floors well heated for six to eight days so the bronze does not chill, and gives the furnace's proportions: half the floor's diameter as the greatest height from vault to floor, with the vault-to-floor angle rounded because the flame stays cold there and the bronze congeals first. A dome-section figure carries the letters a b, and the entrance window is divided a b like the exit window.
On this page
An exhalation vent in the core against boiling bronze
Leave a vent in the core through which the enclosed air or moisture can exhale. Otherwise, once the bronze surrounds the core, the fuming and multiplying moisture would force its way through the bronze and make it boil and spurt away.
Pre-heating the furnace floor for six to eight days
Once the furnaces are built, keep their floor well heated for six or eight days so the bronze does not cool, and do not raise the metal too high within it.
Proportions and rounded vault-angle of the furnace
Divide the floor into two parts, that is its diameter; half the diameter is the greatest height from the middle of the vault to the middle of the floor. Round off the angles where vault meets floor, because there the flame does not work, stays cold, and the bronze begins to congeal rather than in the middle.
Dividing the entrance and exit windows a b
Divide the entrance window into two parts, a b, and make the exit window match each of those. The letters a b are marked on the accompanying figure.