Re-firing the mold, weighing its earth, and unstopping the furnace
Sinking the furnaces underground, keeping a book of the mold's weights, and the wider mouth of the mold
To re-fire the great mold among the furnaces, Leonardo proposes lowering the ground so the furnaces sit underground, leveling the surface to work and bake the mold on it, then drawing out the earth beneath and lowering the mold into place. He advises weighing, with steelyards, the earth added to each part of the mold and keeping a good account of it in a book, so that the haulings and handlings can be foreseen and planned by force. A final note warns that when unstopping, the mouth of the mold must be larger than the furnace's, because the bronze expands much more there.
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Re-firing the mold by sinking the furnaces underground
The only way he sees is to lower the ground so the furnaces go underground, then fill and level among them; on this surface the mold is handled and re-fired while the furnaces stand in fixed places. When the mold is ready, the earth is drawn out beneath and the mold lowered into place, with earth-covered beams over the furnaces so they are not spoiled.
Weighing the mold's earth to plan the handling force
When the cap is made, use steelyards to weigh the earth added to each piece of the mold: weigh the earthing-up prepared for the neck and head, then the earth remaining in the basin, keeping good account in a book. Done thus, the haulings and handlings are well foreseen and ordered, with the advantage of the water that goes off as vapor.
Unstopping: the mold's mouth wider than the furnace's
When you unstop, remember that the mouth of the mold should be larger than that of the furnace. At the mold's mouth the bronze expands much more than when it leaves the furnace.