Hence it follows that the utmost power of art can only be given in a material capable of receiving and retaining the influence of the subtlest touch of the human hand. That hand is the most perfect agent of material power existing in the universe; and its full subtlety can only be shown when the material it works on, or with, is entirely yielding. The chords of a perfect instrument will receive it, but not of an imperfect one; the softly bending point of the hair pencil, and soft melting of colour, will receive it, but not even the chalk or pen point, still less the steel point, chisel, or marble. The hand of a sculptor may, indeed, be as subtle as that of a painter, but all its subtlety is not bestowable nor expressible: the touch of Titian, Correggio, or Turner, [Footnote: See Appendix IV., "Subtlety of Hand."] is a far more marvellous piece of nervous action than can be shown in anything but colour, or in the very highest conditions of executive expression in music. In proportion as the material worked upon is less delicate, the execution necessarily becomes lower, and the art with it. This is one main principle of all work. Another is, that whatever the material you choose to work with, your art is base if it does not bring out the distinctive qualities of that material. The reason of this second law is, that if you don't want the qualities of the substance you use, you ought to use some other substance: it can be only affectation, and desire to display your skill, that lead you to employ a refractory substance, and therefore your art will all be base. Glass, for instance, is eminently, in its nature, transparent. If you don't want transparency, let the glass alone. Do not try to make a window look like an opaque picture, but take an opaque ground to begin with. Again, marble is eminently a solid and massive substance. Unless you want mass and solidity, don't work in marble. If you wish for lightness, take wood; if for freedom, take stucco; if for ductility, take glass. Don't try to carve leathers, or trees, or nets, or foam, out of marble. Carve white limbs and broad breasts only out of that.