There are exceptions to this rule, which will be readily understood by following out the illustrations in the order given below.
Perspectives.—The utility of the heavy lines will be more apparent when drawing square, rectangular, or triangular objects.
Let us take [Fig. 101], which appears to be the perspective of a cube. Notice that all lines are of the same thickness. When the sketch was first brought to me I thought it was a cube; but the explanation which followed, showed that the man who[p. 98] made the sketch had an entirely different meaning.
He had intended to convey to my mind the idea of three pieces, A, B, C, of metal, of equal size, joined together so as to form a triangularly shaped pocket as shown in [Fig. 101]. The addition of the inner lines, like D, quickly dispelled the suggestion of the cube.
"But," he remarked, "I want to use the thinnest metal, like sheets of tin; and you show them thick by adding the inner lines."
Such being the case, if we did not want to show[p. 99] thickness as its structural form, we had to do it by making the lines themselves and the shading give that structural idea. This was done by using the single lines, as in [Fig. 103], and by a slight shading of the pieces A, B, C.
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| Fig. 105. | Fig. 106. |
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The Most Pronounced Lines.—If it had been a cube, or a solid block, the corners nearest the eye would have been most pronounced, as in [Fig. 104], and the side next to the observer would have been darkest.