d in chalk; on the screen in front of you a large study in
charcoal. In every one of these drawings, the material of shadow is
absolutely opaque. But photograph-stain, chalk, lead, ink, or
charcoal,--every one of them, laid by the master's hand, becomes full of
light by gradation only. Here is a moonlight (Edu. 31 B.), in which you
would think the moon shone through every cloud; yet the clouds are mere
single dashes of sepia, imitated by the brown stain of a photograph;
similarly, in these plates from the Liber Studiorum the white paper
becomes transparent or opaque, exactly as the master chooses. Here, on
the granite rock of the St. Gothard (S. 302), in white paper made
opaque, every light represents solid bosses of rock, or balls of foam.
But in this study of twilight (S. 303), the same white paper (coarse old
stuff it is, too!) is made as transparent as crystal, and every fragment
of it represents clear and far away light in the sky of evening in
Italy.

From all which the practical conclusion for you is, that you are never
to trouble yourselves with any questions as to the means of shade or
light, but only with the right government of the means at your disposal.
And it is a most grave error in the system of many of our public
drawing-schools, that the students are permitted to spend weeks of
labour in giving attractive appearance, by delicacy of texture, to
chiaroscuro drawings in which every form is false, and every relation of
depth, untrue. A most unhappy form of error; for it not only delays, and
often wholly arrests, their advance in their own art; but it prevents
what ought to take place correlatively with their executive practice,
the formation of their taste by the accurate study of the models from
which they draw. And I must so far anticipate what we shall discover
when we come to the subject of sculpture, as to tell you the two main
principles of good sculpture; first, that its masters think before all
other matters of the right placing of masses; secondly, that they give
life by flexure of surface, not by quantity of detail; for sculpture is
indeed only light and shade drawing in stone.

166. Much that I have endeavoured to teach on this subject has been
gravely misunderstood, by both young painters and sculptors, especially
by the latter. Because I am always urging them to imitate organic forms,
they think if they carve quantities of flowers and leaves, and copy them
from the life, they have done all