Casting proportions: bronze per pound of earth, wax and wood
Material ratios for the mould, and cooked salt dissolved to temper the sandy earth
A page of casting quantities for the bronze horse, set out as a series of ratio questions. Leonardo reckons that 100 pounds of metal answer to 16 pounds of dry earth, or to 20 pounds of wetted earth, and reasons that the 4 pounds of water fill only the earth's pores and are later replaced by air without changing its size. He then gives the metal yielded per ounce of wax, plaster and hard wood such as walnut, all at one pound of metal per ounce. A closing recipe cooks salt, dissolves it in clear water, and uses it to temper the sandy mould-earth, matching the flock-binder to the earth.
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Ratios of bronze to dry and wetted mould-earth
100 pounds of metal correspond to 16 pounds of dry earth, and likewise to 20 pounds of comfortably wetted earth. The 4 pounds of water taken up occupy only the earth's porosity, and when the water departs, air fills the same pores without diminishing the earth's size.
Metal yielded per ounce of wax, plaster and hard wood
In large work one ounce of wax gives one pound of metal; two ounces of plaster give one pound of metal; and each ounce of hard wood such as walnut gives one pound of metal.
Cooked salt dissolved to temper the sandy earth
Cook the salt in a furnace, then dissolve it in clear water and moisten the mould-earth with it. The earth should be sandy, especially the first three coats, and the flock-binder should be matched in quantity to the earth.