All colours are comprehended in the synthesis of black, consequently the whole sedative power of colour is comprised in black. It is the same in the synthesis of white; and, with like relative consequence, white includes all the stimulating powers of colour in painting. It follows that a little white or black is equivalent to much colour, and hence their use as colours requires judgment and caution. By due attention to the synthesis of black, it may be rendered a harmonizing medium to all colours, to all which it lends brilliancy by its sedative effect on the eye, and its powers of contrast: nevertheless, we repeat, it must be introduced with caution when _hue_ is of greater importance than shade. Even when employed as a shadow, without much judgment in its use, black is apt to appear as local colour rather than as privation of light; and black pigments obtained by charring have a tendency to rise and predominate over other hues, subduing the more delicate tints by their chemical bleaching power upon other colours, and their own disposition to turn brown or dusky. For these reasons deep and transparent colours, which have darkness in their constitution, are better adapted as a rule for producing the true natural and permanent effects of shade. Many pictures of the early masters, and especially of the Roman and Florentine schools, evince the truth of our remarks; and it is to be feared the high reputation of these works has betrayed their admirers into this defective employment of black. Black substances reflect a small quantity of white light, which receives the complementary of the colour contiguous to the black. By 'complementary' is meant that colour which is required with another colour to form white light; thus, green is the complementary of red, blue of orange, and yellow of violet, or vice versâ; because green and red, blue and orange, and yellow and violet, each make up the full complement of rays necessary to form white light. Briefly digressing, we give the following mode of observing complementary colours:--Place a sheet of white paper on a table opposite to one of two windows admitting diffused daylight[C] into a room; take a piece of coloured glass and so place it that the coloured light transmitted through it falls over the surface of the paper; then put an opaque object on the paper close to the coloured glass. The shadow of this object will not appear black or of the colour of the glass, as might be supposed, but of its complementary colour; thus if the glass is red, the colour of the shadow will be green, although the whole of the paper surrounding it appears red. Similarly, if the glass is blue, the shadow will appear orange; if it is green, the shadow will appear red; and so with other colours. It is absolutely essential, however, to the success of this experiment, that the paper be also illuminated with the white light admitted from the other window.