HOW CASTS OUGHT TO BE POLISHED.
Make a bunch of iron wire as thick as thread, and scrub them with [this and] water; hold a bowl underneath that it may not make a mud below.
HOW TO REMOVE THE ROUGH EDGES FROM BRONZE.
Make an iron rod, after the manner of a large chisel, and with this rub over those seams on the bronze which remain on the casts of the guns, and which are caused by the joins in the mould; but make the tool heavy enough, and let the strokes be long and broad.
TO FACILITATE MELTING.
First alloy part of the metal in the crucible, then put it in the furnace, and this being in a molten state will assist in beginning to melt the copper.
TO PREVENT THE COPPER COOLING IN THE FURNACE.
When the copper cools in the furnace, be ready, as soon as you perceive it, to cut it with a long stick while it is still in a paste; or if it is quite cold cut it as lead is cut with broad and large chisels.
IF YOU HAVE TO MAKE A LARGE CAST.
If you have to make a cast of a hundred thousand pounds do it with two furnaces and with 2000 pounds in each, or as much as 3000 pounds at most.
Taken from The Notebooks of Leonardo da Vinci edited by Jean Paul Richter, 1880.