Jannon's career took place during a politically tense period. Jannon was a Protestant in mostly Catholic France. After apparently working with the Estienne family in Paris he set up an independent career as printer in Sedan in what is now north-eastern France, becoming printer for the Protestant Academy. By his report he took up punchcutting seriously in his thirties, although according to Williamson he would have cut decorative material and engravings at least before this. Sedan the time enjoyed an unstable independence as a principality at a time when the French government had conceded through the Edict of Nantes to allowing a complicated system of restricted liberties for Protestants. While acknowledging his talent and commissioning equipment from him, as documented by the surviving purchase order, it is known that authorities in 1644 raided an office in Caen where he had been commissioned to do printing. Warde initially assumed that this was the source of the Jannon materials in the Imprimerie Nationale before the government's purchase order came to light. Jannon's types and their descendants are recognizable by the triangular serifs on the top left of such characters as 'm', 'n' and 'r', which have a very steep slant in Jannon's design compared to Garamond's. The italics are also very different to Garamond's own or Granjon's, being much more ornate and with considerable variation in angle of the capitals. Opinions of Jannon's engraving quality have varied; Warde found them "of slight value as a book face" (the surviving Jannon sizes were intended as display faces, cut at 18pt or larger) and Vervliet described them as "famous not so much for the quality of the design but as for the long-term confusion it created", although many reproductions of his work were successful in printing in the twentieth century. Jannon cut far more types than those surviving in the Imprimerie collection: before the misattribution to Garamond, he was particularly respected for his engraving of an extremely small size of type, known for his workplace as "sédanoise", which was popular.