§ 57 The Construction of the Core
The workers then take a rod of iron longer than the whole figure that they wish to make, and that is to be cast, and over this they make a core of clay into which, while kneading it to make it soft, they mix horse dung and hair. The core has the same form as the model and is baked in successive layers so as to draw out the dampness of the clay; this is of use afterwards to the figure, for in casting the statue all this core, which is solid, leaves an empty space that is not filled with bronze, because if it were, the figure could not be moved on account of the weight. They make this core large enough and justly measured, so that when the layers are heated and baked, as has been said, the clay becomes well burned through and so entirely freed from damp, that in pouring the bronze upon it afterwards it does not spurt nor do injury, as has happened many times, involving the death of the masters and the ruin of the work. Thus they go on balancing the core and adjusting and examining the pieces, till they tally with it and represent it, so that there comes to be left exactly the thickness, or, (if we like to say so,) the thinness, of the metal, according as you wish the statue to be.
Frequently this core has an armature of rods of copper across it, and irons that can be taken out and put in to hold it with security and with greater strength.171 The core, after it is finished, is yet again baked with a gentle heat, and the moisture, should any have remained, entirely removed; it is then again laid aside.