In many, otherwise, excellent pictures of Claude's, the sun is placed at, or near the point of sight: so that all the shadows, running from that point, almost mechanically carry the eye into the picture. Whatever of good may proceed from this arrangement, its purpose is too easily detected; and it has an artificial effect.
Da Vinci says, 'The appearance of motion is lessened, according to the distance, in the same proportion as objects diminish in size.'
Open the side of a book against the light, and observe the gradations of shadow on the leaf.
If you turn half a sheet of paper up against the light (in the manner of the book), it will explain, by its shadows on the parallel part, the phenomena of half or demi-tint.
In any body that has many indentures, there will be many shadows and their grades: that body will have a greenish hue over its superfice, where the light falls on it. To keep the colour of that light pure, in this instance, requires great management; as the markings of the masses of foliage, &c., receiving the light. And yet, without these markings, or as it were carrying the shadow into the light, it would look bald. As this is done cleverly, so it will have the effect of subduing the harshness of the lights; which not being in compact masses, lose their force.
I often rumple a piece of paper, to observe the infinite variety of its shadows. And place a ball against the light, on a white surface, and observe its gradations. So, if you roll up a sheet of white paper, and lay it on a white surface, against the light, or make it stand up, it will describe the gradations of a column.
It is a very excellent method to keep a solid square, a solid sphere, a cylinder or tube, a cone (make a paper one), a cup, &c., by you, and place them in various directions in the light, making various memoranda of their lights, shadows, and reflexes, in one colour. By this means, light and shade will soon become familiar, and the task get easier at every trial.
A piece of white paper folded several ways, and laid on a table against the light, will reveal all the different degrees of shade. Then, observe the highest light and the deepest shade, with their gradations.
Observe, in a room with one window, having chairs, tables, sofas, &c. in it, where and how their shadows fall. This will assuredly lead the mind into the mysteries of light and shade, which must end in knowledge. At the very least, the power to see things as they are!
To render bodies in sunshine, the shadows must be dark, and marked strongly and distinctly, and the lights extended and broad. So, in-door objects have equally strong shadows, with the lights and shades distinctly divided and precise. All should, as a peremptory rule, receive the light from above. The light should come in from a sufficient height to give a shadow on the ground the same length as the object is high.