A Word About Half-Tones. If we consider that light travels in beams, it is impossible to conceive logically of a plane that is not facing either toward or away from those rays. Although some parts of an object face more and some less directly into the light, I cannot conceive of an object that is turned neither away nor toward the source. I cannot imagine a mysterious angle or plane that lies somehow between light and shadow. Probably what is meant by "half-tones" is what I call the darker lights, that is, those surfaces still receiving some light but not turned very directly into its path. The semantic distinction is important because the concept behind the idea of a half-tint tends to produce excessively soft and indecisive work. [Emphasis his.]And this:
Imagine, for example, that we are painting an interior scene where the light enters through a window on the left. Now, imagine that we draw one chair near that window and place another much farther away from the light. If we paint the same intensity of light on both chairs, it will be as if they both occupied the same position or were at the same distance from the window. There would be an anomaly, or contradiction, in our painted room that would produce an unconvincing suggestion of space. The drawing would suggest that our chairs were in different parts of the room, while the amount of light, or value, would suggest that they were both in the same place. Our painted room would not seem "real" because it would not be consistent with what we are accustomed to seeing. Our painted space would seem visually distorted. It is crucial for the value to be in perfect alignment with the spacial placement. Value and drawing must be in a logical relation. At every point, the light's value represents a spatial value. Like a symphony conductor, we must orchestrate our notes, or values, harmoniously in relation to the position of the light source. Our pictorial space will then sing true.As of this writing, Alibris has a copy that they want $127.45 for. If you can't afford it at that price, then look other places and keep checking. It's worth your effort.