Three highlights, to be exact, the first by James Montgomery Flagg, the other two by Charles Dana Gibson:

[CLICK IMAGES TO ENLARGE]

In Drawing with Pen and Ink, Arthur Guptill writes that Flagg “draws his lines very rapidly, as may be ascertained by a glance at his illustrations, yet in spite of this rapidity these lines are skilfully placed. Many of his blacks are added with a brush[…]. If one of these spots seems over-black or solid to Mr. Flagg, he scratches through the ink to the surface of the paper, thus making white lines[…]. He also employs cross-hatch freely where he feels the need of it” (p. 426).

And here’s Guptill on Charles Dana Gibson:

Mr. Gibson, it will be seen, has at his command almost every sort of line and dot which the pen is capable of making. And he uses them all. Though his work as a whole is extremely free and direct, being done with a dash and daring for which, among other things, he is famous, it is by no means carelessly done in the sense that the student sometimes seems to think such work to be. Mr. Gibson is undoubtedly primarily interested in the message that his drawing is supposed to convey. In its making he almost instinctively chooses for every detail of the whole the sort of stroke which will lend itself best to the expression of his purpose, whether it be a delicate, hair-like line or a stroke a quarter of an inch wide. [p. 426]