Why do Birds:
Dudley Watkins did regularly use shading although it is sometimes hard to see.
To be truthful, so did Hergé. It's easy now to say that Hergé drew in a certain way, but he actually evolved it as he went, and refined things, and changed things, in the way that he drew throughout his life-time.
The "tenets" of which you speak, presumably Swart's definition of the clear-line
style, were not something to which Hergé adhered, as he would not have known them, and never enumerated them himself, and even when he spelled out elements of his technique, he didn't confine himself to them, or say that he wouldn't try something different if he felt that the situation warranted it.
Swart's definition is highly reductive, ignores things which don't meet his needs within Hergé's work, and is more of a "Platonic ideal" of his own than something which Hergé practised.
For example, look at the method Hergé used for drawing the Detectives and the Captain: in earlier books he clearly delineates the sleeves of their suits, and thus the characters' arms, by means of white hatching on black, and black hatching on white, using this to add shade and form. In later books he simplifies this, so that the entire body of the Captain or detective is basically a single amorphous black shape. If the arm is against the side, you don't have any shading to distinguish it.
As for light throwing shadows, he gives characters shadows from the desert sun in Crab
, and (possibly even more noticeably) there is the exquisite rendering of Tintin's night time walk through the wood in the light from the gipsy campfire in Emerald
graded if needed - so the reflector of Calculus's prototype sound device have been air-brushed to give them a metallic sheen, and the underwater sequences in Red Rackham's Treasure
likewise have a watery gloss provided by the colour, not the line art.
Line weights do
vary: Snowy is consistently drawn in a lighter weight line than Tintin, perhaps to emphasize his furry, fuzzy coat: it's also used on the bear cubs in Destination Moon
, to similar effect.
Even as late as Picaros
hatches under cars to show them speeding over the ground - it doesn't stand out, as you say about Watkins work, but it still is there. He also models the Henry Moore-esque statue in colour, not line work, so even in the last of his complete books he wasn't the purist Swart purports him to be.
I'd propose that there were in fact numerous cartoonists and illustrators working in what I have called elsewhere in these forums a "proto clear line" style: I'd include Hergé and Watkins, and add amongst others Rabier (of whom Hergé was a great admirer, and indeed he owned a signed and dedicated page of Zig and Puce
), Winsor McCay, Heath-Robinson, Joseph Pinchon (Bécassine
), and the various artists who worked on Rupert the Bear
Each of these developed a purity of line, without great
reliance on shading, and a mastery of form - making a character's volume appear accurate and consistent in the picture space, no matter the angle of view, which (to me at least) makes me think that they were each sharing a similar æsthetic.
I'd have to add that I think that there might be an element of necessity about this - that it was a style of work which was well served by mechanical reproduction, but also may have been defined by the limitations of the reproduction processes available at the time; however, that may be something to look into later.