The Blue of the Air and the Perspective of Colours
Trattato della pittura, Part Two: colour perspective and the origin of the sky's blue
A text page of the Trattato della pittura (Part Two, folio 73) continuing Leonardo's theory of colour. It opens with the example of a green-walled room where blue light produces a beautiful illuminated wall but an ugly, corrupted shadow, then gathers four short chapters on the perspective of colours in dark places, the agreement of colour-diminution with distance, the loss of beauty in colours lying between light and shade, and the origin of the sky's blue. The blue of the air, it concludes, is born from the illuminated thickness of the body of air interposed between the upper darkness and the earth.
On this page
A shadow corrupted by reflected colour (green wall example)
Leonardo imagines a dwelling with green walls in which blue light, lit by the brightness of the air's blue, makes the illuminated wall a most beautiful blue. The shadow, however, is ugly and not a true blue, because it is corrupted by the green reverberating in it. It would be worse still, he adds, if the wall were of a tawny colour.
Perspective of colours in dark places (a, b)
Chapter a states that in luminous places grading uniformly down to darkness a colour is brighter the nearer it is to the eye and more obscure the farther off. Chapter b holds that the first colours must be simple and that the degrees of their diminution must agree with the degrees of distance, colours partaking the more of their horizon's colour the nearer they approach it.
From what the blue of the air is born (c)
The colour found between the shadowed and the illuminated part of bodies is of less beauty than the wholly illuminated part, so the first beauty of colours lies in the principal lights. The closing chapter explains that the blue of the air is born from the thickness of the illuminated body of air interposed between the upper darkness and the earth.