323. From this principle it results that in many cases where grey is near to a pure colour in the model, the painter, if he wishes to imitate this grey which appears to him tinted with the complementary of the pure colour, need not use a coloured grey, as the effect will be produced in the imitation by the juxtaposition of the colour with the grey contiguous to it. Besides, the importance of this principle cannot be doubted, when we consider that all the modifications which a monochromous object presents (excepting those which result from the reflections of coloured lights emanating from neighbouring objects,) arise from the different relations of position between the parts of the object and the eye of the spectator; so that it is strictly true to say that, to reproduce by painting all these modifications, it suffices to have a colour exactly identical to that of the model, with black and white. In fact, with white we can reproduce all the modifications due to the weakening of the colour by light, and with black, those which are due to the height of its tone. If the colour of the model in certain parts gives rise to the manifestation of its complementary, because these parts do not return to the eye enough colour and white light to neutralize this manifestation, the modification may be imitated by the employment of a normal grey tone, properly surrounded with the colour of the object. It is necessary, in many cases, to employ with the colour of the object the colours which are near it; that is to say, the hues of the colour. For example; in imitating a rose, we can employ red shaded with a little yellow, and a little blue, or, in other terms, shaded with orange and violet; but the green shadows which we perceive in certain parts arise from the juxtaposition of red and normal grey. 5. To put a dark colour near a different, but lighter colour, is to heighten the tone of the first, and to lower that of the second, independently of the modification resulting from the mixture of the complementaries. An important consequence of this principle is, that the first effect may neutralize the second, or even oppose it. For example; a light blue placed beside a yellow tinges it orange, and consequently heightens its tone; while there are some blues, so dark relatively to the yellow, that they weaken it so much as not only to hide the orange tint, but even to cause sensitive eyes to feel that the yellow is rather green than orange. A very natural result, if we consider that the paler the yellow, the greener it appears. 6. Put beside each other two flat tints of different tones of the same colour, chiaro-’scuro is produced, because, in setting out from the line of juxtaposition, the tint of the band of the highest tone is insensibly enfeebled, while, setting out from the same line, the tint of the band of the lowest tone becomes heightened; thus there is a true gradation of light.