The majority of the posters created during the Great War were produced by means of chromolithography, a process that produces rich colors and expressive line work. These posters are very different from the war posters of later eras that were mass produced using faster and cheaper offset printing techniques.  

Lithography itself is a form of planographic printing, meaning that the surface is flat. It is very different from relief printing (printing from a raised surface) or intaglio printing (printing from an incised surface) because the creation of the image is dependent on chemical reactions as well as pressure from a press. An image is applied to a stone or zinc plate with a grease-based crayon. The plate is then coated with a gum and weak acid solution. The solution helps the grease drawing adhere to and penetrate the plate while causing the blank areas to repel the printing ink. The plate is dampened, inked, and then passed through the press along with the paper receiving the impression.  

Chromolithography is the addition of color into the actual printing process as opposed to adding color by hand to a black and white lithograph. It is a labor intensive process often involving a master printer in addition to the artist or designer of the image to be printed. For each color in the final print, a different plate will be prepared; this means that each sheet of paper will pass through the press as many times as there are colors in the final print. In order for the prints in progress to avoid being covered over by the next color being applied, each print in progress must be precisely "registered," or lined up, on the next colored plate. Today, due to the complexity and expense, chromolithography is a process associated more with fine art prints than with advertising and propaganda.  



References:  

The Complete Printmaker (1972). John Ross and Clare Romano. The Free Press: NY  

Printmaking History and Process (1978). Donald Saff and Deli Sacilotto. Holt, Rinehart, and Winston: NY