The Folger blog, The Collation, brings a nice little study of how shading has been introduced into line art over the centuries.

Detail from page 1 of C. Walter Hodges, The Globe Restored: A Study of the Elizabethan Theatre. Second edition. London: Oxford University Press, 1968. Folger PR2920 .H6 1968.

They use as their example this drawing of the Globe by C. Walter Hodges for an OUP book. Not sure I don’t prefer it without the tint as shown below.

C. Walter Hodges (1909-2004). The Second Globe Under Snow. Pen and ink drawing, circa 1968. Folger ART Box H688 no.3.5.

Still it does unquestionably make for a greater contrast between snow and non-snow areas.

The Folger, inveterate collectors, not only have the book, they have the artwork prepared for the book. Here’s a detail of the tint overlay.

We used to make these sorts of things all the time, using an Xacto knife to cut away the bits of a Letraset sheet of tint dots in order to create highlight and shadow, or often different shades of flat colors. You can see the feint cut marks in the backing sheet which remained after Mr Hodges had tweezered off the little bits of tint he wanted to remove.

If like me you start getting crazy trying to figure out exactly where on the printed version these cut-out highlights appear, you’ll finally figure out that The Collation have photographed the overlay from the back. In other words the tint image is flopped with regard to the line drawing.