Originally Posted by
LordJulius
AFAIK, Herge invented what is known as 'ligne claire', which translates as 'clear line'. What it means is obvious if you look at his art and that of his assistants or others influenced by him (E.P. Jacobs who did "Blake and Mortimer", Bob de Moor, Jacques Martin.). This used to be the prevalent style in Tintin, the Franco-Belgian bi-monthly magazine named after Herge's eponymous hero.
However, in the early 1950s a different art style became popular which was mainly found in the magazine "Spirou". It is much more dynamic and cartoonish than ligne claire and its most famous proponent was Andre Franquin (just compare a page from his Gaston or Spirou with one of Herge's and the differences will immediately become clear). This style is known as the "Ecole de Marcinelle" ("Marcinelle school") after the place where Spirou had its offices at the time. Other famous artists of that school are Morris (Lucky Luke), Maurice Tillieux (Jeff Jordan), Jije (who was a major influence on Moebius/Giraud) or Pierre Seron.
I actually read in the introduction to the Jeff Jordan book above that this style was so popular (because of Franquin) that the publisher of Spirou magazine at the time more or less forced all of his artists to adapt their art to Franquin's style; apparently Tillieux used to be more of a Herge follower first.