The Variation of Colour in uneven Superficies, is what confounds an
unskilful Painter; but if he takes Care to mark the Outlines of his
Superficie, and the Seat of his Lights, he will find the true Colouring
no such difficult matter: For first he will alter the Superficies
properly as far as the Line of Separation, either with White or Black
sparingly as only with gentle Dew; then he will in the same Manner bedew
the other Side of the Line, if I may be allowed the expression, then
this again and so on by turns, till the light Side is brightened with
more transparent Colour, and the same Colour on the other Side dies away
like Smoak into an easy Shade. But you should always remember, that no
Superficie should ever be made so white that you cannot make it still
brighter: Even in Painting the whitest Cloaths you should abstain from
coming near the strongest of that Colour; because the Painter has
nothing but White wherewith to imitate the Polish of the most shining
Superficie whatsoever, as I know of none but Black with which he can
represent the utmost Shade and Obscurity of Night. For this Reason, when
he paints a white Habit, he should take one of the four Kinds of Colours
that are clear and open; and so again in painting any black Habit, let
him use another Extream, but not absolute Black, as for Instance, the
Colour of the Sea where it is very deep, which is extreamly dark. In a
Word, this Composition of Black and White has so much Power, that when
practised with Art and Method, it is capable of representing in Painting
the Superficie either of Gold or of Silver, and even of the clearest
Glass. Those Painters, therefore, are greatly to be condemned, who make
use of White immoderately and of Black without Judgment; for which
reason I could wish that the Painters were obliged to buy their White at
a greater Price than the most costly Gems, and that both White and
Black were to be made of those Pearls which Cleopatra dissolved in
Vinegar; that they might be more chary of it.
_Leon Battista Alberti._
[Illustration: _Signorelli_ THE MUSIC OF PAN _Hanfstaengl_]