The window which gives light to a painting-room, ought to be made of oiled paper, without any cross bar, or projecting edge at the opening, or any sharp angle in the inside of the wall, but should be slanting by degrees the whole thickness of it; and the sides be painted black.
Chap. CCLI.—The Shadows of Colours.
The shadows of any colour whatever must participate of that colour more or less, as it is nearer to, or more remote from the mass of shadows; and also in proportion to its distance from, or proximity to the mass of light.
Chap. CCLII.—Of the Shadows of White.
To any white body receiving the light from the sun, or the air, the shadows should be of a blueish cast; because white is no colour, but a receiver of all colours; and as by the fourth proposition[61] we learn, that the surface of any object participates of the colours of other objects near it, it is evident that a white surface will participate of the colour of the air by which it is surrounded.
Chap. CCLIII.—Which of the Colours will produce the darkest Shade.
That shade will be the darkest which is produced by the whitest surface; this also will have a greater propensity to variety than any other surface; because white is not properly a colour, but a receiver of colours, and its surface will participate strongly of the colour of surrounding objects, but principally of black or any other dark colour, which being the most opposite to its nature, produces the most sensible difference between the shadows and the lights.
Chap. CCLIV.—How to manage, when a White terminates upon another White.
When one white body terminates on another of the same colour, the white of these two bodies will be either alike or not. If they be alike, that object which of the two is nearest to the eye, should be made a little darker than the other, upon the rounding of the outline; but if the object which serves as a ground to the other be not quite so white, the latter will detach of itself, without the help of any darker termination.