276

On the colours of derived shadows.

OF THE COLOURS OF SIMPLE DERIVED SHADOWS.

The colour of derived shadows is always affected by that of the body towards which they are cast. To prove this: let an opaque body be placed between the plane s c t d and the blue light d e and the red light a b, then I say that d e, the blue light, will fall on the whole surface s c t d excepting at o p which is covered by the shadow of the body q r, as is shown by the straight lines d q o e r p. And the same occurs with the light a b which falls on the whole surface s c t d excepting at the spot obscured by the shadow q r; as is shown by the lines d q o, and e r p. Hence we may conclude that the shadow n m is exposed to the blue light d e; but, as the red light a b cannot fall there, n m will appear as a blue shadow on a red background tinted with blue, because on the surface s c t d both lights can fall. But in the shadows only one single light falls; for this reason these shadows are of medium depth, since, if no light whatever mingled with the shadow, it would be of the first degree of darkness &c. But in the shadow at o p the blue light does not fall, because the body q r interposes and intercepts it there. Only the red light a b falls there and tinges the shadow of a red hue and so a ruddy shadow appears on the background of mingled red and blue.

The shadow of q r at o p is red, being caused by the blue light d e; and the shadow of q r at o’ p’ is blue being caused by the red light a b. Hence we say that the blue light in this instance causes a red derived shadow from the opaque body q’ r’, while the red light causes the same body to cast a blue derived shadow; but the primary shadow [on the dark side of the body itself] is not of either of those hues, but a mixture of red and blue.

The derived shadows will be equal in depth if they are produced by lights of equal strength and at an equal distance; this is proved. [Footnote 53: The text is unfinished in the original.]

[Footnote: In the original diagram Leonardo has written within the circle q r corpo obroso (body in shadow); at the spot marked A, luminoso azzurro (blue luminous body); at B, luminoso rosso (red luminous body). At E we read ombra azzurra (blue tinted shadow) and at D ombra rossa (red tinted shadow).]

Taken from The Notebooks of Leonardo da Vinci edited by Jean Paul Richter, 1880.

IV * VI
Notebooks of Leonoardo da Vinci
V: Theory of colours.
. . .
other.
263,
264,
265,
266,
267,
268,
269,
270,
271
Combination of different colours in cast shadows.
272
The effect of colours in the camera obscura.
273,
274
On the colours of derived shadows.
275,
276
On the nature of colours.
277,
278
On gradations in the depth of colours.
279,
280
On the reflection of colours.
281,
282,
283
On the use of dark and light colours in painting.
284,
285,
286
On the colours of the rainbow.
287,
288
. . .