155. Over all this vast field of human skill the laws which I have enunciated to you rule with inevitable authority, embracing the greatest, and consenting to the humblest, exertion; strong to repress the ambition of nations, if fantastic and vain, but gentle to approve the efforts of children, made in accordance with the visible intention of the Maker of all flesh, and the Giver of all Intelligence. These laws, therefore, I now repeat, and beg of you to observe them as irrefragable.
1. That the work is to be with tools of men.
2. That it is to be in natural materials.
3. That it is to exhibit the virtues of those materials, and aim at no quality inconsistent with them.
4. That its temper is to be quiet and gentle, in harmony with common needs, and in consent to common intelligence.
We will now observe the bearing of these laws on the elementary conditions of the art at present under discussion.
156. There is, first, work in baked clay, which contracts, as it dries, and is very easily frangible. Then you must put no work into it requiring niceness in dimension, nor any so elaborate that it would be a great loss if it were broken; but as the clay yields at once to the hand, and the sculptor can do anything with it he likes, it is a material for him to sketch with and play with,—to record his fancies in, before they escape him,—and to express roughly, for people who can enjoy such sketches, what he has not time to complete in marble. The clay, being ductile, lends itself to all softness of line; being easily frangible, it would be ridiculous to give it sharp edges, so that a blunt and massive rendering of graceful gesture will be its natural function: but as it can be pinched, or pulled, or thrust in a moment into projection which it would take hours of chiseling to get in stone, it will also properly be used for all fantastic and grotesque form, not involving sharp edges. Therefore, what is true of chalk and charcoal, for painters, is equally true of clay, for sculptors; they are all most precious materials for true masters, but tempt the false ones into fatal license; and to judge rightly of terra-cotta work is a far higher reach of skill in sculpture-criticism than to distinguish the merits of a finished statue.
157. We have, secondly, work in bronze, iron, gold, and other metals; in which the laws of structure are still more definite.
All kinds of twisted and wreathen work on every scale become delightful when wrought in ductile or tenacious metal; but metal which is to be hammered into form separates itself into two great divisions—solid, and flat.
a. In solid metal-work, i.e., metal cast thick enough to resist bending, whether it be hollow or not, violent and various projection may be admitted, which would be offensive in marble; but no sharp edges, because it is difficult to produce them with the hammer. But since the permanence of the material justifies exquisiteness of workmanship, whatever delicate ornamentation can be wrought with rounded surfaces may be advisedly introduced; and since the color of bronze or any other metal is not so pleasantly representative of flesh as that of marble, a wise sculptor will depend less on flesh contour, and more on picturesque accessories, which, though they would be vulgar if attempted in stone, are rightly entertaining in bronze or silver. Verrocchio's statue of Colleone at Venice, Cellini's Perseus at Florence, and Ghiberti's gates at Florence, are models of bronze treatment.