Firing the Mould, Lifting the Cope, the Core and the Casting Pit
Shrink-resistant clay, even removal of the cope, filling the core, and ramming earth in a pit beneath the cope's frame
This page of the Sforza-horse casting instructions carries diagrams as well as text. Leonardo prescribes a shrink-resistant clay (pounded brick, ash and fat earth from Santa Maria della Rovere, with river sand) for the part of the mould that must be fired, and explains that the cope must be lifted from the model evenly, every two or three braccia along the joint, opened with wedges, lever or screw, so it does not arc and break at the pole (labeled a in a lower diagram). He then describes filling the core with brick powder, ash or lime moistened with linseed oil and firing it thoroughly, and finally digging a pit deep enough for a man to sit beneath the mould, walled and floored against damp, in which the earth is rammed crosswise beneath the cope's timber frame.
On this page
Shrink-resistant clay for the fired part of the mould
Compose the part of the mould that must be fired from earth that shrinks little in firing. This is done with pounded brick, ash and fat earth from Santa Maria della Rovere, to which river sand may also be added.
Lifting the cope from the horse evenly
The first detaching of the cope must be done equally, every two or three braccia along the joint. If it began from above while the feet were fixed, it would form an arc and the part below the body (the pole) would rise and force the body until it broke. Open the joints with wedges, lever or screw.
Filling and firing the core (maschio)
Fill the core with brick powder, ash, plaster, or better lime powder moistened a little with linseed oil, so the earth stays well compacted when rammed. Fire the core thoroughly inside and out, for even a little moisture would cause great error.
Ramming earth in a pit beneath the cope's frame
To ram the earth between the beams and under the cope, dig the pit deep enough that a man can sit beneath the mould, having first built three walls, one central and two at the ends, covered with planks, then oil and lime against the damp. Then make a continuous wall throughout, two-thirds thick, and ram the earth crosswise.
Diagram of the pole (polo)
A small figure in the right margin is lettered a and marked as the pole (polo), the point below the body identified in the text as the place liable to rise and break if the cope is lifted unevenly.
Wall floor beneath the cope
A caption beneath a lower figure directs making a wall floor beneath the whole cope, two-thirds of a braccio thick, half a braccio near the cope, then rammed earth.