Why do Tintin's drawings look so clean, and what is the clear line?

Flip through a Tintin album and every object, from a rocket to a coffee cup, is drawn with the same clean outline. That look has a name: ligne claire, or clear line. It is a style created and pioneered by Hergé, the Belgian cartoonist behind Tintin, using strong clear lines, no hatching and downplayed contrast, often with cartoonish characters set against a realistic background. The name came late: it was coined by the Dutch artist Joost Swarte in 1977, long after Hergé had made it famous.

Hergé did not start out that way. He began with a looser, rougher style, likely influenced by American strip artists. Tintin debuted on 10 January 1929 in Le Petit Vingtième, a youth supplement of a Belgian newspaper, and he was fascinated by techniques such as the systematic use of speech bubbles that he found in American comics. His early albums, such as Tintin in the Land of the Soviets and Tintin in the Congo, were designed as conservative propaganda for children.

The turning point was a friendship. For The Blue Lotus, set in China, Hergé got lessons in Chinese art and calligraphy from Zhang Chongren, a Chinese student at the Brussels art academy, and devoted far more attention to accuracy. Hergé later said his research began with The Blue Lotus, out of a sense of responsibility to his readers. He also drew on Japanese influence: ligne claire was influenced by shin-hanga prints.

The style peaked in the 1950s, looked old-fashioned to a new generation in the 1960s and came back in the late 1970s, just as Swarte gave it a name. By 2007, Tintin had been published in more than 70 languages with more than 200 million copies sold, so that clean outline has reached readers in dozens of languages.