...he (a photographer) forgets that unless he has learnt when the tones of a picture are right or not, he will not know whether his work is good or b… - Alfred Horsley Hinton

The louder a sound is, the more we recognize it as being near, so the louder the "tone" of objects that is, the blacker or whiter the nearer they seem; and so if in our picture we wish to give a sense of distance, we must see that the darkest shadows and highest lights are in the foreground : and because we may not be able to materially alter things as the undiscriminating process gives them to us, we must seek for and select those scenes, those subjects, in which this arrangement of highest and deepest tones do come in the foreground, and then take care that our process renders them with fidelity, so that we may not lose the sense of their nearness or the feeling of greater distance of other planes which it is intended they shall give.

There is a difference in printing greater depth to any portion with the negative and shading down without the negative. In the former case we get a deeper and stronger image, still preserving to a great extent the relative contrasts between the lights and shades in that portion. This is not always what we require. In order to concentrate attention upon that is, to emphasize, some particular spot, it may be desirable to shade down and flatten some portion.

The different degree of light interference between blue and red also affords a power which we may be glad to avail ourselves, in some cases using the red where a very marked degree of lightening is desired, or blue where only a trifling difference is needed.