On furnaces: kilns for casting plates and vessels
A furnace sized by its window, a door-and-window opening, and a vented mould
Headed 'On the furnace,' the sheet designs kilns for casting metal plates and vessels. One furnace pairs each plate size with its own window (p q for a 2-braccia plate, r for a 1-braccio plate) to avoid wasting heat; another, two braccia across, opens and shuts like a door and window so the charge can be loaded and fired quickly. Leonardo adds that the form taking the impression should be pierced with dense, minute perforations so the enclosed air can escape.
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Furnace with windows for plates of set diameter (p, q, r)
For a plate 2 braccia across the window p q is used; for one 1 braccio across, the smaller window r. Leonardo argues a smaller plate made through the large window wastes furnace heat beyond its bounds, so each plate should have its matching window.
Furnace that opens like a door and window (immobile / movable / bath)
This furnace, two braccia in diameter, is designed to open and shut like a door and a window so the charge can be inserted and quickly set afire. The parts are labeled immobile, movable, and bath; a second manner of opening is said to be even more expeditious.
Perforated form for venting enclosed air
The form in which the impression is made should be full of very small perforations, dense and close together, so that the enclosed air can escape. This follows the second, more expeditious furnace design.