The third species called low or flattened reliefs only shows up the design of the figure in the very lowest and most depressed relief. These reliefs are very difficult for they demand great skill in design and invention, and as all depends on the outlines it is a hard thing to impart charm to them. Donatello worked better here than did any other, with art, design and invention.[[167]] In the ancient vases of Arezzo,[[168]] many figures, masks, and other ancient compositions are to be seen in this sort of work: likewise in the antique cameos, in moulds for striking bronze pieces for medals, and also in coins. This style was chosen because, if the relief had been too high, the coins could not have been struck, for the blow of the hammer would not have produced the impression since the punches have to be pressed on to the cast material, and when this is in low relief it costs little trouble to fill the cavities of the punch. Now-a-days we see that many modern artists have worked divinely in this style, more even than did the ancients, as shall be fully described in their Lives. Therefore, he who recognizes in the half reliefs the perfection of the figures so carefully made to diminish, and in the lower reliefs the excellence of the design in the perspectives and other inventions, and in the flattened reliefs the clearness, the refinement and the beautiful form of the figures, will do well to regard them on account of these qualities as worthy of praise or blame, and will teach others also so to regard them.
CHAPTER IV. (XI.)
How Models for large and small Bronze Figures are made, with the Moulds for casting them and their Armatures of iron; and how they are cast in metal and in three sorts of Bronze; and how after they are cast they are chased and refined; and how, if they lack pieces that did not come out in the cast, these are grafted and joined in the same bronze.
§ 55. The Full-sized Model for Bronze.
It is the custom of competent artists, when they wish to cast large figures in metal or bronze,[[169]] to make first a statue of clay as large as that intended to be cast in metal, and to perfect the clay statue as far as their art and their knowledge will allow.
§ 56. The Piece-Mould in Plaster.
When this, which they call the model, is finished and brought to this point of perfection, they then begin, with plaster that will set, to build over it piece by piece, making the pieces correspond to the relief of the model. On every piece they make a key, marking the pieces with numbers or letters of the alphabet or with other signs in order that the pieces can be taken off and register together. So they mould it part by part, oiling the pieces of the cast where the edges have to be connected; till from piece to piece the figure grows, the head, the arms, the body and the legs, to the last detail, in such a manner that the concave of the statue, that is the hollow mould, comes to be imprinted on the inner surface with all the parts and with the very minutest marking which is in the model.[[170]] This completed, the plaster casts are laid aside to harden.
§ 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.